Sensory learning and memory formation Flashcards

Question

Adult neurogenesis in both vertebrate and invertebrate brains (Barker et al., 2011)

Answer 1

• Fish, amphibia: neurogenic cells in many brain areas • Reptiles, birds mammals (more concentrated than fish and amphibia): neurogenesis largely in lateral ventricles and hippocampus (mammals) - cells migrate throughout telencephalon (olfactory bulb, HVC) • CB - cerebellum • OB - olfactory bulb • V - lateral ventricles • HVC (RA only in songbirds) - cerebral nuclei - Hp - hippocampus see notes

Answer 2

Galed (1984) Gross (2000)

Answer 3

○ "Field observations can point to areas in which organisms express special competences, suggesting the existence either of refinements of known learning processes or previously unsuspected learning mechanisms ○ Lab investigations of plasticity can expand (/limit) the range of acceptable proximal explanations of changes in behav observed in field Field studies direct lab research on animal learning toward fruitful areas of investigation, while lab research can provide assistance to field workers in understanding the behav and neurobiological mechanisms that might be responsible for acquisition or development of adaptive responses"

Answer 4

For over 100 years a central assumption in the field of neuroscience has been that new neurons are not added to the adult mammalian brain. This perspective examines the origins of this dogma, its perseverance in the face of contradictory evidence, and its final collapse. The acceptance of adult neurogenesis may be part of a contemporary paradigm shift in our view of the plasticity and stability of the adult brain.

Answer 5

• Mole rats live in subterranean tunnel system - Amongst surface-dwelling rodents, SA rodents live in challenging habitat see notes

Answer 6

Burger et al. (2014)

Answer 7

Sex and reproductive status affect hippocampal neurogenesis and dentate gyrus (DG) size in rodents. Relatively few studies, however, address these two effects simultaneously and even fewer studies address this issue in wild populations. Here, we examined seasonal and sex differences in neurogenesis and DG size in a wild, polygynous and social rodent, Richardson’s ground squirrel (Uriocitellus richardsonii). Based on the behavioral ecology of this species, we predicted that both neurogenesis and DG size would be sexually dimorphic and the degree of dimorphism would be greatest in the breeding season. Using unbiased stereology and doublecortin (DCX) immunohistochemistry, we found that brain volume, DG size and number of DCX cells varied significantly between breeding and non-breeding seasons, but only brain volume and the number of DCX labeled cells differed between the sexes. Both sex and seasonal differences likely reflect circulating hormone levels, but the extent to which these differences relate to space use in this species is unclear. Based on the degree of seasonal differences in neurogenesis and the DG, we suggest that ground squirrels could be considered model species in which to examine hippocampal plasticity in an ecologically valid context.

Answer 8

• Learning changes properties of synaptic transmission • "When an axon of cell A is near enough to excite a cell B and repeatedly/persistently takes part in firing it, some growth processes/metabolic change takes place in one/both cell such that A's efficiency, as one of the cells firing B, is increased" • Neurons connected to indv units • Hebbian synapse - Still central idea in neuroscience

Answer 9

• Cajal (1893) first proposed the idea that the site of contact between neurons could play a role in memory formation - retain info • Foster and Sherrington (1897) termed these sites 'synapses' - Change behav - change something in neuron see notes • Hebb emphasised that there are likely to be many Hebb synapses in distributed networks • Particular association formed - Form memory - change way neurons paired see notes

Answer 10

Hinton (2003)

Answer 11

Modelers have come up with many different learning rules for neural networks. When a teacher specifies the correct output, error-driven rules work better than pure Hebb rules in which the changes in synapse strength depend on the correlation between pre and postsynaptic activities. But for unsupervised learning, Hebb rules can be very effective if they are combined with suitable normalization or "unlearning" terms to prevent the synapses growing without bound. Hebb rules that use rates of change of activity instead of activity itself are useful for discovering perceptual invariants and may also provide a way of implementing error-driven learning.

Answer 12

• Marine snail, sea hare • Ca 20,000 neurons - identify indv neurons • Body plan not segmented • Sensory neurons innervate mantle, gill and siphon • Gill can retract to protect it - imp response - controlled by ab ganglion • Gill has fine tissue - sensitive to damage - external lining - filters water - fac transfer of O2 • Siphon - lots of muscles - contract - regulate breathing • Neurons originate from ganglia • Flap mantle shelf to swim - Ganglia = 'brain' see notes

Answer 13

Alexandrescu and Carew (2020)

Answer 14

The formation of appropriate neural connections during development is critical for the proper wiring and functioning of the brain. Although considerable research suggests that the specificity of synapse formation is supported by complex intercellular signaling between potential presynaptic and postsynaptic partners, the extracellular factors and the intracellular signal transduction pathways engaged in this process remain largely unknown. Using the sensory-motor neural circuit that contributes to learning in defensive withdrawal reflexes in Aplysia californica, we investigated the molecular processes governing the interactions between sensory neurons and both target and non-target motor neurons during synapse formation in culture. We found that evolutionarily-conserved intercellular and intracellular signaling mechanisms critical for learning-related plasticity are also engaged during synaptogenesis in this in vitro model system. Our results reveal a surprising bidirectional regulation of molecular signaling between sensory neurons and non-target motor neurons. This regulation is mediated by signaling via both paracrine and autocrine diffusible factors that induce differential effects on transcription and on protein expression/activation in sensory neurons and in target and non-target motor neurons. Collectively, our data reveal novel molecular mechanisms that could underlie the repression of inappropriate synapse formation, and suggest mechanistic similarities between developmental and learning-related plasticity.

Answer 15

• A - presynaptic neuron • B - postsynaptic neuron • C - modulatory interneuron • Homosynaptic = Hebbian synapse - change by augmenting signal ○ Changes in B - changes in A can lead to changes in B ○ Depression test = habituation ○ Fac test = potentiation • Heterosynaptic - Aplysia - Change in B without post-synaptic changes see notes

Answer 16

Arami et al. (2013)

Answer 17

Most neurons in layer VI of the visual cortex project to the dorsal lateral geniculate nucleus (dLGN). These corticogeniculate projection neurons (CG cells) receive top-down synaptic inputs from upper layers (ULs) and bottom-up inputs from the underlying white matter (WM). Use-dependent plasticity of these synapses in layer VI of the cortex has received less attention than in other layers. In the present study, we used a retrograde tracer injected into dLGN to identify CG cells, and, by analyzing EPSPs evoked by electrical stimulation of the UL or WM site, examined whether these synapses show long-term synaptic plasticity. Theta-burst stimulation induced long-term potentiation (LTP) of activated synapses (hom-LTP) and long-term depression (LTD) of nonactivated synapses (het-LTD) in either pathway. The paired-pulse stimulation protocol and the analysis of coefficient variation of EPSPs suggested postsynaptic induction of these changes except UL-induced het-LTD, which may be presynaptic in origin. Intracellular injection of a Ca2+-chelator suggested an involvement of postsynaptic Ca2+ rise in all types of long-term plasticity. Pharmacological analysis indicated that NMDA receptors and type-5 metabotropic glutamate receptors are involved in WM-induced and UL-induced plasticity, respectively. Analysis with inhibitors and/or in transgenic mice suggested an involvement of cannabinoid type 1 receptors and calcineurin in UL-induced and WM-induced het-LTD, respectively. These results suggest that hom-LTP and het-LTD may play a role in switching the top-down or bottom-up regulation of CG cell function and/or in maintaining stability of synaptic transmission efficacy through different molecular mechanisms.

Answer 18

• Non-associative learning - response diminished with repeated presentation • Sensitisation - tail shock precedes the siphon touch (e.g. prior to habituation training) - initial response higher than in group that doesn’t experience sensitising stim - no temporal association between stim, therefore non-associative learning - Spaced trials more effective than massed trials in training (resulted in better LTM) - shown in diff systems and learning paradigms see notes • Adaptive - decrease energy expen - Dishabituation (tail shock) - restore level of response

Answer 19

Esdin et al. (2010)

Answer 20

Although habituation is possibly the simplest form of learning, we still do not fully understand the neurobiological basis of habituation in any organism. To advance the goal of a comprehensive understanding of habituation, we have studied long-term habituation (LTH) of the gill-withdrawal reflex (GWR) in the marine snail Aplysia californica. Previously, we showed that habituation of the GWR in a reduced preparation lasts for up to 12 h, and depends on protein synthesis, as well as activation of protein phosphatases 1 and 2A and postsynaptic glutamate receptors. Here, we have used the reduced preparation to further analyze the mechanisms of LTH in Aplysia. We found that LTH of the GWR depends on RNA synthesis because it was blocked by both the irreversible transcriptional inhibitor actinomycin-D and the reversible transcriptional inhibitor, 5,6-dichlorobenzimidazole riboside (DRB). In addition, LTH requires activation of protein phosphatase 2B (calcineurin), because it was disrupted by ascomycin. Finally, LTH was blocked by nitrendipine, which indicates that activation of L-type voltage-gated Ca2+ channels is required for this form of learning. Together with our previous results, the present results indicate that exclusively presynaptic mechanisms, although possibly sufficient for short-term habituation, are insufficient for LTH. Rather, LTH must involve postsynaptic, as well as presynaptic, mechanisms.

Answer 21

• A spike arrives at the axonal terminal of the presynaptic neuron • Ca2+ channels are opened and calcium enters axonal terminal triggering release of ntm into synaptic cleft • Ntm binds to receptors (ion channels, receptor proteins) which opens/closes ion channel at postsynaptic membrane creating neuronal signal in postsynaptic cell • Depolarises membrane - Post membrane - strong enough post potential --> AP see notes

Answer 22

Hickie et al. (1997)

Answer 23

The monosynaptic connection between the mechano-sensory neurons in the LE cluster and gill motoneurons has been extensively studied and used as a model for the gill-withdrawal reflex and its behavioural plasticity, In an attempt to evaluate the contribution of this synapse to the behaviour, we used voltage-sensitive dye recording to determine the number of activated LE neurons and the number of spikes made by each neuron in response to a light touch. In five preparations, light touch activated a median of five sensory cells with a median of 1.6 spikes per cell. From a comparison of the sizes of the motoneuron synaptic potentials elicited by LE spikes and elicited by a light siphon touch, we estimate that the LE sensory neurons contribute similar to 5% of the motoneuron synaptic potential in response to this touch. This result casts doubt on the validity of using this synaptic connection as a model for gill-withdrawal behaviour. Siphon nerve recordings reveal the existence of short-latency, low-threshold neurons that may provide much of the sensory input in response to a light touch

Answer 24

• Axoaxonal synapse between sensory and facilitatory interneuron • Heterosynaptic plasticity in ST sensitisation - Strengthened as a result of learning see notes • Biochem cascade • The facilitatory interneuron releases serotonin 1. Which increases cAMP level 2. And leads to 3. PKA activation (cAMP-dependent protein kinase) which promoted phosphorylation 4. Of proteins (de-/increasing function), here several ion channels (shown is one of K+ channel - delays closing of Ca2+ channels open which results in longer release of ntm to motor neuron - Substitution of tail shock with serotonin/cAMP injections induces synaptic fac (Brunelli et al., 1979)

Answer 25

Glanzman (2010)

Answer 26

Until recently, the literature on learning-related synaptic plasticity in invertebrates has been dominated by models assuming plasticity is mediated by presynaptic changes, whereas the vertebrate literature has been dominated by models assuming it is mediated by postsynaptic changes. Here I will argue that this situation does not reflect a biological reality and that, in fact, invertebrate and vertebrate nervous systems share a common set of mechanisms of synaptic plasticity.

Answer 27

• Pretraining: habituation training (siphon touch) • Training: 4 tail shocks per day over 4 days • R: retention trials (siphon touch) • Sensitisation lasted 3 weeks • Repeat exp • Test for recall - LT sensitisation see notes

Answer 28

Patel et al. (2018)

Answer 29

Most long-term memories are forgotten, becoming progressively less likely to be recalled. Still, some memory fragments may persist, as savings memory (easier relearning) can be detected long after recall has become impossible. What happens to a memory trace during forgetting that makes it inaccessible for recall and yet still effective to spark easier re-learning? We are addressing this question by tracking the transcriptional changes that accompany learning and then forgetting of a long-term sensitization memory in the tail-elicited siphon withdrawal reflex of Aplysia californica. First, we tracked savings memory. We found that even though recall of sensitization fades completely within 1 week of training, savings memory is still detectable at 2 weeks post training. Next, we tracked the time-course of regulation of 11 transcripts we previously identified as potentially being regulated after recall has become impossible. Remarkably, 3 transcripts still show strong regulation 2 weeks after training and an additional 4 are regulated for at least 1 week. These long-lasting changes in gene expression always begin early in the memory process, within 1 day of training. We present a synthesis of our results tracking gene expression changes accompanying sensitization and provide a testable model of how sensitization memory is forgotten.

Answer 30

• T1-T4 training days • R1 - retention at day 1 • R2 - 1 week - R3 - 3 weeks - for memory to decay see notes

Answer 31

Sanderson and Bannerman (2011)

Answer 32

Exposure to a spatial location leads to habituation of exploration such that, in a novelty preference test, rodents subsequently prefer exploring a novel location to the familiar location. According to Wagner's (1981) theory of memory, short-term and long-term habituation are caused by separate and sometimes opponent processes. In the present study, this dual-process account of memory was tested. Mice received a series of exposure training trials to a location before receiving a novelty preference test. The novelty preference was greater when tested after a short, rather than a long, interval. In contrast, the novelty preference was weaker when exposure training trials were separated by a short, rather than a long interval. Furthermore, it was found that long-term habituation was determined by the independent effects of the amount of exposure training and the number of exposure training trials when factors such as the intertrial interval and the cumulative intertrial interval were controlled. A final experiment demonstrated that a long-term reduction of exploration could be caused by a negative priming effect due to associations formed during exploration. These results provide evidence against a single-process account of habituation and suggest that spatial habituation is determined by both short-term, recency-based memory and long-term, incrementally strengthened memory.

Answer 33

• LTM formation requires protein synthesis/degradation • Transient changes in activity of intracellular signalling cascades - Increased no. sites for synaptic contact see notes

Answer 34

Hawkins et al. (2006)

Answer 35

Cellular studies of implicit and explicit memory suggest that experience-dependent modulation of synaptic strength and structure is a fundamental mechanism by which these memories are encoded, processed, and stored within the brain. In this review, we focus on recent advances in our understanding of the molecular mechanisms that underlie short-term, intermediate-term, and long-term forms of implicit memory in the marine invertebrate Aplysia californica, and consider how the conservation of common elements in each form may contribute to the different temporal phases of memory storage.

Answer 36

• LTM requires protein synthesis (transcription of DNA into mRNA + translation of mRNA into proteins) • CREB (CAMP-response element binding protein) transiently activated (phosphorylated) by biochem cascades involving cAMP and PKA • CREB initiates gene transcription and is central gene in regulatory gene network for LTM in both vertebrates and invertebrates • c/EBP is immediate early gene (IEG) • P: phosphoryl group added to CREB-1 (phosphorylation) • Late: 'late-response' genes that are activated by IEG proteins • Structural change = large no. neurons needed - Nucleus - reg gene see notes

Answer 37

Kandel (2012)

Answer 38

The analysis of the contributions to synaptic plasticity and memory of cAMP, PKA, CRE, CREB-1, CREB-2, and CPEB has recruited the efforts of many laboratories all over the world. These are six key steps in the molecular biological delineation of short-term memory and its conversion to long-term memory for both implicit (procedural) and explicit (declarative) memory. I here first trace the background for the clinical and behavioral studies of implicit memory that made a molecular biology of memory storage possible, and then detail the discovery and early history of these six molecular steps and their roles in explicit memory.

Answer 39

• Associative learning • Neural mechanisms underlying classical conditioning (associative learning) are mostly studied in Aplysia, rats, rabbits and Apis mellifera (honeybees) as well as genetically tractable organisms (mice, zebrafish, Drosophila (oldest)) • Conditioning exps: e.g. appetitive, eyeblink, taste, fear • Forward pairing effective in reinforcing CS control groups in classical conditioning exps: • Backward pairing - v. difficult • Unpaired presentation of CS and US • Only CS • Only US • Temporal contiguity is imp - Closer CS and US --> conditioning effect stronger see notes

Answer 40

Brandt et al. (2005) Santos et al. (2007)

Answer 41

○ Medulla, lobula: visual processing - lamina and photoreceptors ○ Antennal lobes: olfactory processing ○ Mushroom bodies: multimodal sensory integration, learning and memory ○ Proto-, duetero-, tritocerebrum: central processing, executive functions - fused to form insect brain ○ Started end of 19th century - Sucrose solutions to train bees - supplemented with study of brain see notes

Answer 42

The learning phenomenon can be analysed at various levels, but in this paper we treat a specific paradigm of artificial intelligence, i.e. artificial neural networks (ANNs), whose main virtue is their capacity to seek unified and mutually satisfactory solutions which are relevant to biological and psychological models. Many of the procedures and methods proposed previously have used biological and/or psychological principles, models, and data; here, we focus on models which look for a greater degree of coherence. Therefore we analyse and compare all aspects of the Gluck-Thompson and Hawkins ANN models. A multi-thread computer model is developed for analysis of these models in order to study simple learning phenomena in a marine invertebrate (Ap ysia calijbi-nica) and to check their applicability to research in psychology and neurobiology. The predictive capacities of the models differs significantly: the Hawkins model provides a better analysis of the behavioural repertory of Aplysia on both the associative and the non-associative learning level. The scope of the ANN modelling technique is broadened by integration with neurobiological and behavioural models of associative learning, allowing enhancement of some architectures and procedures that are currently being used.

Answer 43

``` • Nectar = suc, glu, fru • Motivated to feed • Study brain and do behav exps • CS+ ○ Just one pairing ○ 3x ITI of 10min - LTM for rest of life • CS- ○ May respond to some degree - generalisation ○ Some pairings but not others - Differential conditioning ```

Answer 44

Menzel and Müller (1996) Müller (2002) Menzel (1999) Debelle and Heisenberg (1994)

Answer 45

Learning and memory in honeybees is analyzed on five levels, using a topdown approach. (a) Observatory learning is applied during navigation and dance communication. (6) Local cues at the feeding site are learned associatively. (c) Classical conditioning of the proboscis extension response to olfactory stimuli provides insight into behavioral, neural, and neuropharmacological mechanisms of associative learning. (d) At the neural level, the pathways coding the conditioned and the unconditioned stimulus are identified. The reinforcing function of the unconditioned stimulus is traced to a particular neuron. (e) At the cellular level, the CAMP pathway is found to be critically involved. Nitric oxide is an essential mediator for the transfer from short- to long-term memory. see notes

Answer 46

Studies in a variety of organisms as diverse as molluscs, insects, birds and mammals have shown that memories can exist in a variety of temporal domains ranging from short-term memories in the range of minutes to long-term memories lasting a lifetime. While transient covalent modifications of proteins underlie short-term memory, the formation of long-term memory requires gene expression and protein synthesis. Different intracellular signalling cascades have been implicated in distinct aspects of learning and memory formation. Little is known however, about how learning in intact animals is related to the modulation of these signalling cascades and how this contributes to distinct neuronal and behavioural changes in vivo. Associative learning in the honeybee provides the opportunity to study processes of memory formation by analysing its progression through different phases, across levels of behaviour, neural circuits, and cellular signalling pathways. The findings reveal evidence that various cellular signalling pathways in the neuronal circuit of distinct brain areas play a role in different processes during learning and memory formation

Answer 47

Reward learning in honeybees initiates a sequence of events which leads to long-lasting memory passing through multiple phases of transient memories. The study of memory dynamics is performed at the behavioral (both natural foraging behavior and appetitive conditioning), neural circuit and molecular levels. The results of these combined eorts lead to a model which assumes ®ve kinds of sequential memories, each characterized by a set of behavioral and mechanistic properties. It is argued that these properties, although re¯ecting general characteristics of step-wise memory formation, are adapted to the species-speci®c adaptations in natural behavior, here to foraging at scattered and unreliable food sources

Answer 48

The corpora pedunculata, or mushroom bodies (MBs), in the brain of Drosophila melanogaster adults consist of approximately 2500 parallel Kenyon cell fibers derived from four MB neuroblasts. Hydroxyurea fed to newly hatched larvae selectively deletes these cells, resulting in complete, precise MB ablation. Adult flies developing without MBs behave normally in most respects, but are unable to perform in a classical conditioning paradigm that tests associative learning of odor cues and electric shock. This deficit cannot be attributed to reductions in olfactory sensitivity, shock reactivity, or locomotor behavior. The results demonstrate that MBs mediate associative odor learning in flies

Answer 49

• Red - long axons • PN - projection neurons • LIN - interneurons • GLO - glomerular - similar to vertebrate olfactory lobe • Antenna - imp touch organ - Sensory sensilla - diff types of receptors see notes

Answer 50

The anatomical substrates of neural nets are usually composed from reconstructions of neurons that were stained in different preparations. Realistic models of the structural relationships between neurons require a common framework. Here we present 3‐D reconstructions of single projection neurons (PN) connecting the antennal lobe (AL) with the mushroom body (MB) and lateral horn, groups of intrinsic mushroom body neurons (type 5 Kenyon cells), and a single mushroom body extrinsic neuron (PE1), aiming to compose components of the olfactory pathway in the honeybee. To do so, we constructed a digital standard atlas of the bee brain. The standard atlas was created as an average‐shape atlas of 22 neuropils, calculated from 20 individual immunostained whole‐mount bee brains. After correction for global size and positioning differences by repeatedly applying an intensity‐based nonrigid registration algorithm, a sequence of average label images was created. The results were qualitatively evaluated by generating average gray‐value images corresponding to the average label images and judging the level of detail within the labeled regions. We found that the first affine registration step in the sequence results in a blurred image because of considerable local shape differences. However, already the first nonrigid iteration in the sequence corrected for most of the shape differences among individuals, resulting in images rich in internal detail. A second iteration improved on that somewhat and was selected as the standard. Registering neurons from different preparations into the standard atlas reveals 1) that the m‐ACT neuron occupies the entire glomerulus (cortex and core) and overlaps with a local interneuron in the cortical layer; 2) that, in the MB calyces and the lateral horn of the protocerebral lobe, the axon terminals of two identified m‐ACT neurons arborize in separate but close areas of the neuropil; and 3) that MB‐intrinsic clawed Kenyon cells (type 5), with somata outside the calycal cups, project to the peduncle and lobe output system of the MB and contact (proximate) the dendritic tree of the PE1 neuron at the base of the vertical lobe. Thus the standard atlas and the procedures applied for registration serve the function of creating realistic neuroanatomical models of parts of a neural net. The Honeybee Standard Brain is accessible at www.neurobiologie.fu‐berlin.de/beebrain.

Answer 51

• VUMmx1 is unpaired neuron that branches widely in bee brain • Cell body lays in suboesophagal ganglion - into bottom of cell body • VUMmx1 is octopaminergic (containing or releasing octopamine) • Sucrose application leads to VUMmx1 excitation • Arborisations (a fine branching structure at the end of a nerve fibre) in antennal lobe and mushroom bodies • Soma in middle of brain - Sucrose sensations arrive at bottom of cell body see notes VUMmx1 - prime candidate neuron - r'ship with olfactory learning of animal - influences synapses related to olfactory learning

Answer 52

Pratavieira et al. (2019)

Answer 53

The proboscis extension response (PER) reflex may be used to condition the pairing of an odor with sucrose, which is applied to the antennae, in experiments to induce learning, where the odor represents a conditioned stimulus, while sucrose represents an unconditioned stimulus. A series of studies have been conducted on honeybees, relating learning and memory acquisition/retrieval using the PER as a strategy for accessing their ability to exhibit an unconditioned stimulus; however, the major metabolic processes involved in the PER are not well known. Thus, the aim of this investigation is profiling the metabolome of the honeybee brain involved in the PER. In this study, a semiquantitative approach of matrix-assisted laser desorption ionization (MALDI) mass spectral imaging (MSI) was used to profile the most abundant metabolites of the honeybee brain that support the PER. It was reported that execution of the PER requires the metabolic transformations of arginine, ornithine, and lysine as substrates for the production of putrescine, cadaverine, spermine, spermidine, 1,3-diaminopropane, and γ-aminobutyric acid (GABA). Considering the global metabolome of the brain of honeybee workers, the PER requires the consumption of large amounts of cadaverine and 1,3-diaminopropane, in parallel with the biosynthesis of high amounts of spermine, spermidine, and ornithine. To exhibit the PER, the brain of honeybee workers processes the conversion of l-arginine and l-lysine through the polyamine pathway, with different regional metabolomic profiles at the individual neuropil level. The outcomes of this study using this metabolic route as a reference are indicating that the antennal lobes and the calices (medial and lateral) were the most active brain regions for supporting the PER

Answer 54

• If odour (CS) paired with depolarisation of VUMmx1 neuron instead of sucrose, bees acquire association between odour and reward • VUMmx1 represents US • Cannot move mouth - Sucrose - move muscle instead and record from here see notes Can manip genes - turn neurons on and off see notes

Answer 55

Hammer (1993) Hammer (1997) heisenberg (2003)

Answer 56

DURING classical conditioning, animals learn to associate a neutral stimulus with a meaningful, or unconditioned, stimulus. The unconditioned stimulus is essential for forming associations, and modifications in the processing of the unconditioned stimulus are thought to underlie more complex learning forms1–4. Information on the neuronal representation of the unconditioned stimulus is therefore required for understanding both basic and higher-order features of conditioning. In honeybees, conditioning of the proboscis extension reflex occurs after a single pairing of an odour (conditioned stimulus) with food (unconditioned stimulus)5,6 and shows several higher-order features of conditioning6–8. I report here the identification of an interneuron that mediates the unconditioned stimulus in this associative learning. Its physiology is also compatible with a function in complex forms of associative learning. This neuron provides the first direct access to the cellular mechanisms underlying the reinforcing properties of the unconditioned stimulus pathway.

Answer 57

Appetitive learning of food-predicting stimuli, an essential part of foraging behavior in honeybees, follows the rules of associative learning. In the learning of odors as reward-predicting stimuli, an individual neuron, one of a small group of large ascending neurons that serve principal brain neuropiles, mediates the reward and has experience-dependent response properties. This implies that this neuron functions as an integral part of associative memory, might underlie more complex features of learning, and could participate in the implementation of learning rules. Moreover, its structural properties suggest that it organizes the interaction of functionally different neural nets during learning and experience-dependent behavior.

Answer 58

○ Since their discovery, the mushroom bodies of the insect brain have been assumed to be involved in cognitive processing. Genetic intervention in the fly Drosophila melanogaster has provided strong evidence that they are the seat of a memory trace for odours. ○ This localization of the 'engram' to a single layer of synapses allows us to design a simple circuit model of odour memory based on the functional anatomy of the olfactory system. In the model, complex odour mixtures are assumed to be represented by neuronal activity in sets of intrinsic mushroom body neurons (Kenyon cells). Conditioning renders an extrinsic mushroom-body output neuron (CR neuron) specifically responsive to such a set (and hence to the respective odour). ○ The localization of the memory trace for odours is based on the assumption that associative olfactory learning is mediated by synpatic plasticity. Evidence that the memory trace is represented by the output synapses of Kenyon cells relies on three findings. First, the mushroom bodies are necessary for olfactory learning. Second, in many animals (molluscs, mammals), cyclic AMP signalling is crucial for synaptic plasticity. In the fly, this has been confirmed for the larval neuromuscular junction. Third, in Drosophila several genes involved in cAMP regulation are required for olfactory learning and memory. They are all preferentially expressed in the mushroom bodies, some of them specifically in the mushroom body lobes (output region). One of them, rutabaga, has been shown to be required for olfactory learning exclusively in a set of about 700 Kenyon cells. Another one, amnesiac, reveals that cAMP regulation is required for olfactory learning only during the learning experiment (rather than during development of the mushroom bodies). The output of the Kenyon cell synapses can be blocked while they are modulated, and the memory can still be retrieved later. Mushroom bodies have other functions that are less understood. They seem to be involved in 'decision making', they regulate the perseverence of behaviour and they protect visual memories against context changes. A future circuit model that also addresses these functions might throw light on the basic operating principles of the brain.

Answer 59

• Naturally occurring allelic variations and mutations (rare - became more specific and common) - artificial selection of lines • Induced mutations (more targeted): transgenic inbred lines (mouse, Drosophila) ○ Knock-in/knock-out of genes: permanent loss/gain of function ○ Knock-down: reduced expression of gene ○ Permanent knock-down: modification of DNA - requires transgenic lines ○ Transient knock-downs (possible in species without transgenic lines) - lower/raise temp - only Drosophila - RNA interference (RNAi) with double-stranded RNA segments (microRNA and small interfering RNA), CRISPR/Cas9

Answer 60

Joo et al. (2020)

Answer 61

Topoisomerase 3 beta (Top3 beta) is the only dual-activity topoisomerase in animals that can change topology for both DNA and RNA, and facilitate transcription on DNA and translation on mRNAs. Top3 beta mutations have been linked to schizophrenia, autism, epilepsy, and cognitive impairment. Here we show that Top3 beta knockout mice exhibit behavioural phenotypes related to psychiatric disorders and cognitive impairment. The mice also display impairments in hippocampal neurogenesis and synaptic plasticity. Notably, the brains of the mutant mice exhibit impaired global neuronal activity-dependent transcription in response to fear conditioning stress, and the affected genes include many with known neuronal functions. Our data suggest that Top3 beta is essential for normal brain function, and that defective neuronal activity-dependent transcription may be a mechanism by which Top3 beta deletion causes cognitive impairment and psychiatric disorders. Topoisomerase 3 beta (Top3 beta) solves topological stress in DNA or RNA metabolism and its mutations are linked to mental disorders. Here, the authors describe transcriptional and behavioural impairments in Top3 beta-knockout mice and show that these are linked to impaired neurogenesis and synaptic plasticity.

Answer 62

• Groups of 40 flies placed in start tube and sequentially induced to new tubes by switching them away from light and inducing phototactic response • Electric shock in tubes with odour A, no shock in tubes with odour B, rest tube no odour no shock • Test rest tube v tubes with odour • 1 - single training trial • 3 - few training trials • 10 massed - 10 training trials with v. brief separation in time - 10 spaced - 10 training trials well separated in time - better results see notes • Classical conditioning in Drosophila? • Cellular mechanisms? • Flies demo many forms of simple learning? • Flies have proboscis extension reflex to sucrose which can be non-associatively (habituated and sensitised) conditioned • Flies can learn discriminative conditioning tasks (pos and neg cues must be identified) in which visual, olfactory and tactile cues are paired with pos (sucrose) or neg (shock) reinforcement • Fruit flies can be conditioned to avoid odours which have been paired with electrical shock - procedure involved t-maze (2-arm choice apparatus) - separate odours )3-octanol (OCT) or 4-methylcyclohexanol (MCH)) could be delivered to each arm - flies drawn into training tube containing one of odours, and electrically shocked with brief voltage pulses (10V-150V) - flies then placed at intersection of T-maze containing both odours - fraction of flies avoiding previously shock-paired odour was indicator of learning • Diff memory time course dependent on training schedule - after single training sessions, memory retention lasts about 1 day - multiple massed training sessions (10 sessions in immediate succession) gives 4 day retention (anesthesia-resistant intermediate term memory) - multiple spaced sessions (10 sessions with 15min inter-session intervals) gives greater than 7 day retention (long-term memory). (So now that we have trained flies, what can we do with them?) • Look at Drosophila mutants with abnormalities in the Gs coupled adenylyl cyclase - cAMP System - rutabaga - mutation in the gene encoding Ca++/Calmodulin-dependent adenylate cyclase leading to lower cAMP levels. Moderate mpairment of learning - acquisition affected - dunce - blocked cAMP phosphodiesterase which leads to high levels of cAMP. Moderate impairment of learning - acquisition affected. • Amnesiac - normal acquisition but deficient intermediate-term memory, affects a gene en a neuropeptide which acts through adenylate cyclase to increase cAMP. Suggests a role o neuropeptides in modulating or extending the effects of second messenger systems. ? radish - normal long-term memory, disrupted anesthesia-resistant memory (intermediate te - cellular mechanism is unknown. ? dCREB2-b - blocks long-term memory, but • Memory stages can be dissected using pharmacological manipulations such as the protein synthesis inhibitor cycloheximide (CXM) - Intermediate term, anesthesia-resistant component is CXM-insensitive, not dependent on protein synthesis or regulation of gene transcription - a longer term component is dependent on gene transcription and protein synthesis and is affected by CXM. Flies given CXM receiving spaced training show no seven-day retention. • Consolidated memory has multiple components - acquisition - dependent on intact neurotransmitter and second messenger systems - short/Intermediate term memory - dependent on direct, transient effects of second messenger activation such as protein phosphorylation or protein synthesis - long term memory - dependent on gene transcription regulated by second messenger activation. - Directions for molecular genetics - control time and duration of expression - the use of heat shock promoters in the dCREB2 mutant avoids developmental complications - control tissue specificity of expression - mushroom bodies are implicated in insect learning and memory - find similar vertebrate mutations. CREB mutant mice show long term memory deficits. Change as science develops see notes

Answer 63

Malik and Hodge (2014) Plomin (2000) Dubnau and Tully (1998)

Answer 64

○ Drosophila have been used in classical conditioning experiments for over 40 years, thus greatly facilitating our understanding of memory, including the elucidation of the molecular mechanisms involved in cognitive diseases1-7. Learning and memory can be assayed in larvae to study the effect of neurodevelopmental genes8-10 and in flies to measure the contribution of adult plasticity genes1-7. Furthermore, the short lifespan of Drosophila facilitates the analysis of genes mediating age-related memory impairment5,11-13. The availability of many inducible promoters that subdivide the Drosophila nervous system makes it possible to determine when and where a gene of interest is required for normal memory as well as relay of different aspects of the reinforcement signal3,4,14,16. ○ Studying memory in adult Drosophila allows for a detailed analysis of the behavior and circuitry involved and a measurement of long-term memory15-17. The length of the adult stage accommodates longer-term genetic, behavioral, dietary and pharmacological manipulations of memory, in addition to determining the effect of aging and neurodegenerative disease on memory3-6,11-13,15-21. - Classical conditioning is induced by the simultaneous presentation of a neutral odor cue (conditioned stimulus, CS+) and a reinforcement stimulus, e.g., an electric shock or sucrose, (unconditioned stimulus, US), that become associated with one another by the animal1,16. A second conditioned stimulus (CS-) is subsequently presented without the US. During the testing phase, Drosophila are simultaneously presented with CS+ and CS- odors. After the Drosophila are provided time to choose between the odors, the distribution of the animals is recorded. This procedure allows associative aversive or appetitive conditioning to be reliably measured without a bias introduced by the innate preference for either of the conditioned stimuli. Various control experiments are also performed to test whether all genotypes respond normally to odor and reinforcement alone

Answer 65

○ At cellular level molecules that act as coincidence detection are active in the pre- and post-synaptic side of the synapse - presynaptic adenylyl cyclase (dependent on calmodulin; amplifies cAMP); postsynaptic - AMPA and NMDA receptors - 2 conditions to be activated When CS and IS at same time

Answer 66

Genetic approaches have been used to investigate increasingly complex biological systems. Here we review the current state of genetic analysis of learning and memory in the fruitfly, Drosophila melanogaster. Emerging findings support two main themes. First, discovery and manipulation of genes involved with behavioral plasticity in genetically accessible systems such as D. melanogaster enables dissection of the biochemical, cellular, anatomical, and behavioral pathways of learning and memory. Second, because core cellular mechanisms of simple forms of learning are evolutionarily conserved, biological pathways discovered in invertebrates are likely to be conserved in vertebrate systems as well.

Answer 67

• Mutations affecting: ○ Second-messenger cascade in cell ▪ Rutabaga - affects Ca++/Calmodulin-dependent adenylate cyclase leading to lower cAMP levels ▪ Amnesiac - affects neuropeptides in modulating or extending the effects of second-messenger cascades ▪ Dunce - blocks cAMP phosphodiesterase which leads to v. high levels of cAMP ○ Protein synthesis (activation of transcription factors): ▪ dCREB2-b - blocks protein synthesis dependent LTM (control: CXM - protein synthesis inhibitor) - Radish - affects enzymes involved in cytoskeletal rearrangement and influences neuronal and synaptic morphology see notes

Answer 68

Khan et al. (2020)

Answer 69

Background In fly brains, the Drosophila Adar (adenosine deaminase acting on RNA) enzyme edits hundreds of transcripts to generate edited isoforms of encoded proteins. Nearly all editing events are absent or less efficient in larvae but increase at metamorphosis; the larger number and higher levels of editing suggest editing is most required when the brain is most complex. This idea is consistent with the fact that Adar mutations affect the adult brain most dramatically. However, it is unknown whether Drosophila Adar RNA editing events mediate some coherent physiological effect. To address this question, we performed a genetic screen for suppressors of Adar mutant defects. Adar(5G1) null mutant flies are partially viable, severely locomotion defective, aberrantly accumulate axonal neurotransmitter pre-synaptic vesicles and associated proteins, and develop an age-dependent vacuolar brain neurodegeneration. Results A genetic screen revealed suppression of all Adar(5G1) mutant phenotypes tested by reduced dosage of the Tor gene, which encodes a pro-growth kinase that increases translation and reduces autophagy in well-fed conditions. Suppression of Adar(5G1) phenotypes by reduced Tor is due to increased autophagy; overexpression of Atg5, which increases canonical autophagy initiation, reduces aberrant accumulation of synaptic vesicle proteins and suppresses all Adar mutant phenotypes tested. Endosomal microautophagy (eMI) is another Tor-inhibited autophagy pathway involved in synaptic homeostasis in Drosophila. Increased expression of the key eMI protein Hsc70-4 also reduces aberrant accumulation of synaptic vesicle proteins and suppresses all Adar(5G1) mutant phenotypes tested. Conclusions These findings link Drosophila Adar mutant synaptic and neurotransmission defects to more general cellular defects in autophagy; presumably, edited isoforms of CNS proteins are required for optimum synaptic response capabilities in the brain during the behaviorally complex adult life stage.

Answer 70

• Huge amount of genetic screens and reverse genetic approaches over more than 30 years revealed >80 genes involved in olfactory memory • Mushroom body (MB) neurons form key neural circuits for olfactory memories • Parallel and sequential use of diff mushroom body neurons to dynamically process memory, similar to mammalian brain - Kenyon cells densely packed see notes • Top line - US pathway ○ STM test - synapse strengthened • KC - Kenyon cells • PN - projection neurons • DPM - dorsal paired medial neurons in dorsal protocerebrum and widely innervate MB lobes - DA - dopaminergic neurons activated by US (shock)

Answer 71

Papanikolopoulou et al. (2019)

Answer 72

Although the involvement of pathological tau in neurodegenerative dementias is indisputable, its physiological roles have remained elusive in part because its abrogation has been reported without overt phenotypes in mice and Drosophila. This was addressed using the recently described Drosophila tau(KO) and Mi{MIC} mutants and focused on molecular and behavioral analyses. Initially, we show that Drosophila tau (dTau) loss precipitates dynamic cytoskeletal changes in the adult Drosophila CNS and translation upregulation. Significantly, we demonstrate for the first time distinct roles for dTau in adult mushroom body (MB)-dependent neuroplasticity as its down-regulation within alpha' beta' neurons impairs habituation. In accord with its negative regulation of translation, dTau loss specifically enhances protein synthesis-dependent long-term memory (PSD-LTM), but not anesthesia-resistant memory. In contrast, elevation of the protein in the MBs yielded premature habituation and depressed PSD-LTM. Therefore, tau loss in Drosophila dynamically alters brain cytoskeletal dynamics and profoundly affects neuronal proteostasis and plasticity.

Answer 73

• Conspecific as stim • Males kept in isolation before and during training trials - in food chambers with (training) or without (control) premated female - in test with new premated female males less likely to initiate courtship behav - Knock-out of orb2 learn and form STM but not LTM suggesting specific role of CBEP proteins in protein synthesis dependent changes at synapse see notes • Differences in response • +/+ = wild type • Q/+ = wild/mutated Other 2 = mutated

Answer 74

Dankert et al. (2009)

Answer 75

We introduce a method based on machine vision for automatically measuring aggression and courtship in Drosophila melanogaster. The genetic and neural circuit bases of these innate social behaviors are poorly understood. High-throughput behavioral screening in this genetically tractable model organism is a potentially powerful approach, but it is currently very laborious. Our system monitors interacting pairs of flies and computes their location, orientation and wing posture. These features are used for detecting behaviors exhibited during aggression and courtship. Among these, wing threat, lunging and tussling are specific to aggression; circling, wing extension (courtship 'song') and copulation are specific to courtship; locomotion and chasing are common to both. Ethograms may be constructed automatically from these measurements, saving considerable time and effort. This technology should enable large-scale screens for genes and neural circuits controlling courtship and aggression

Answer 76

• Animals learn r'ships of stim, actions and outcomes based on coincidence, temporal contiguity and order • Diff types of learning • Memories encoded as changes in synaptic strengths and connectivity's between neurons • Memory formation is multi-step process Morphology of neurons and brain areas changes as result of synaptic plasticity and memory formation