I1 - key papers Flashcards
(15 cards)
describe Somayaji’s use of FSCV to understand synchronous release
- recording electrode placed in dorsal striatum, stimulating electrode in ventral midbrain
- evoked DA release from SNc projections
- 30 pulses at 20Hz, 50Hz and 90Hz
- also 20, 30 and 60 pulses at constant 50Hz
- evoked DA release measured: correlated with stimulus frequency or pulse number
- demonstrates synchronous release
describe Liu et al 2022’s expt? [non-AIS release]
evidence for AP generation and release occurring at sites distinct from soma/AIS:
* midbrain DANs have extensive arbors in striatum, receive ACh inputs as DA axons express nAChRs
* synchronous activation of nAChRs can trigger APs directly in distal DA axons: ‘ectopic firing’
* using FSCV/amperometry in brain slices + patch-clamp records from DA axons
* dual colour fiber photometry to measure neural signals
* GRABDA + GRABACh: genetically encoded fluoro sensors for rapid detection of NT
* blocking nAChRs or Na channels w TTX abolishes axonally-driven release + field potentials: NT release not commanded from soma
local axonal computation allows striatal cholinergic system to broadcast DA release
what are the shortfalls of Liu et al 2022?
- electrical stimulation is not necessarily limited to one cell and can activate multiple cell types, complicting interpretation of circuit effects.
- Not behaviourally relevant, animals not awake, so not so physiological conditions, want to examine implications for plasticity
- Could pair naturalistic stimuli pr behaviours that activate striatal cholinergic INs and then use pharmacological interventions/genetic manipulation of nAChRs (conditional KOs) to assess functional impact own behaviour
- use more refined genetic tools in the future to target specific channels/receptors in distal axons and perform expts in awake animals
describe Tritsch 2012’s study on DANs and cotransmission
DANs in VTA + SNc inhibit spiny projection neurons in striatum through GABAaR agonist release
* these neurons don’t contain GABA packaging mRNA/protein (GAD65, GAD67 and VGAT)
* reexpression of VMAT2 in VGAT KO neurons restores GABA release
* GABA + DA are copackaged in VTA + SNc axons?
* additional studies needed to confirm presence of cofactor for loading + GABA-VMAT2 affinity
describe Rossi et al 1998 expt re extrasyn transmission?
studied inhib transmission at golgi cell - granule cell synapse in cerebellar cortex
* GABA release from golgi cells can spillover and activate granule cell receptors that are not directly post-syn to release site
* promoted by specific glomerular anatomy + presence of high-affinity a6 subunit GABAaRs in granule cells (order of mag higher affinity)
* spillover manifests are slow-rising, slow-decaying, small-amplitude IPSCs
* blocking GABA reuptake prolongs decay of IPSC
* i.e. GABA transporters limit extent of cross-talk
* also, strategic location of GABAR subtypes translates same chemical signal in qualitatively different inhibitory effects: fast, time locked synaptic + phasic vs slower, more diffuse extrasynaptic tonic/spillover mediated
what are the limitations of Rossi et al 1998?
- high affinity a6 properties and glomerular specialisationa re key to spillover, suggests might not be universal
- reliance on diffusional models in this paper is too much, difficult to extrapolate onto complex extarcellular spaces w glial processes + transporters (limit NT spread)
- alternatively: genetically mod transporter expression or use targeted NT sensors in vivo to directly measure extra-syn concs
describe Palmer 2014’s expt re coincidence detection of NMDARs
- in vivo whole cell patch-clamp recordings from layer2/3 pyramidal cells in mouse cortex
- combined with 2p micrscopy to measure Ca2+ transients in dendrites: spatially restricted technique w uncagable NMDA antagonsit tc-MK801 to locally block NMDARs on single dendrtiic branches and also global block with MK801
- recorded somatic AP firing in response to sensory stimuli
- global NMDAR block: reduces evoked + spontaneous somatic AP firing
- local NMDAR block: single tuft dendritic branch abolished Ca2+ transients, with little effect on somatic AP output
computational modelling: simultanoues NMDAR activation across multipl branches needed to influence somatic firing
* NMDAR-dependent electrogenesis across multiple sites vital for PN output due to coincidence-detector property
* enables sophisticated computation due to distributed activation requirements
describe Stuart + Sakmann’s 1997 expt
- simultaneous patch-pipette recordings from different locations on the same neuron (soma + dendrite)
- somatic depol precedes dendritic depol in AP, indicates initiation elsewhere followed by subseq backpropagation
- though is in vitro + extent of bAPs in vivo can be influenced by network, modualtors, dendritic morphology
what are the shortfalls of Palmer 2014’s NMDAR expt?
- global block affects all NMDARs, difficult to isolate specific contributions
- difficult to distinguish blockade of regen spikes from absence of sufficient synaptic input to drive them
could use optogenetic stimulation of specific inputs to target specific dendrites more physiologically
describe Losonczy 2006’s NMDAR coincidence detection expt
- Multisite, 2p glut uncaging, deliver spatiotemporal input patterns to single branches
- simultaneous recording uncaging-evoked EPSPs and local Ca signals
- Asynch input patterns sum linearly despite spatial clustering and have Ca signals mediated by NMDARs. ~20 inputs within 6ms produces supralinear summation due to dendritic spike initiation
- Synch input mediated by VGCCs and NMDARs, and Ca influx signals were larger
- Suggests individual branches function as singular integrative compartments
Shortfalls: seems to be well thought out expt, local 2p uncaging allows selective differences of input to single branches, without global disruption: targeted manipulation used powerfully
describe Favier 2021’s VGLUT expt
VGLUTs are crucial for packaging NTs into SVs. VGLUT3 typically expressed in non-glut populations, so its expression allows neurons to cosignal using glut as well as their 1ry NT
Loss of VGLUT3 attenuates nicotinic signalling ACh and glut may be stored in the same vesicles within cholinergic varicosities and then released
what are generic downsides of optogenetic studies? and cotransmission studies specifically?
- Nonspecific opsin expression in even a few off target cells can greatly skew eventual results: can misconstrue as corelease
- Need to be able to track vesicle populations from different locations differentially
pretty much all cotransmission evidence is derived from ex vivo studies, so full extent of functional significance in vivo is incompletely understood
* Determining precise mechs and synaptic loading of e.g. separate vesicles is challenging
describe Buzsaki et al 1996 [re bAPs and dendritic computation]
found AP firing rate affects integration of synaptic inputs:
found extent of axonal bAP during train of APs is dependent on frequency of somatic AP firing
- intracell and extracell in anaesthetised, and just extracell in behaving rat pyramidal cells
- indicates vg Ca influx into dendrites is under control of INs
- temporal coincidence of synaptic depol occurs due to reduction in dendritic Na following Na channel inactivation
ALSO - inhibitory INs can functionally KO a whole dendrite by selective Ca deactivation: innervating identical cells with different INs is functionall the same as using a whole different PN
- offers dramatic expansion in computational possibilities, across segments of the cell, multiplying PN functions
describe Gidon 2021 re dendritic computation
human L2/3 pyramidal neurons: showed dCaAPs had sharply tuned activation function
* coincident activation of 2 synaptic input pathways diminishes dCaAP amplitude: ANTICOINCIDANT FUNCTION (can compute XOR, thought to require whole networks)
* XOR returns true when exactly one of inputs is true
* though used reconstructed human neurons and simulations informed by patch clamp
* an in vivo demonstration to mimic Fromherz 1993 in computationally designed single arborised neuron is needed
descrive Pissadaki 2013 re clinical implications
biology-based computational model of energy budget + signal propagation in DANs, since they are so huge
* proposed synaptic stimulation might be necessary for APs to reliably invade entire arbor, impacting basal DA release
* increase follows a power law
* impairment in integration at somatodendritic level could affect firing patterns, though more likely energy metabolism and propagation reliability are the source
