What are the 4 main types of NT’s for the CNS?
- AA transmitters
- Small molecule transmitters
- Peptides
- Endocannabinoids
What are the amino acid transmitters?
Which are excitatory?
Inhibitory?
- Excitatory
- Glutamate
- Aspartate
- Inhibitory
- GABA (gamma amino butyric acid)
- Glycine
What are the small molecule transmitters?
- Acetylcholine
- Monoamines
- Histamine
So, monoamines are small molecule transmitters eh? What are the monamines we need to know?
- Catecholamines
- Dopamine
- Norepinephrine
- Serotonin (5-hydroxytryptamine, 5-HT)
What are the peptide NT’s?
- Opioids
- Tachykinins
- Many others
What are the endogenous opiod NT’s?
- Enkephalins
- Endorphins
- Dynorphins
What is the tachykinin we need to know?
Substance P
What are the ten sites of drug action that allow alteration of synaptic transmission?
- Action potential in presynaptic fiber
- synthesis of transmitter
- storage
- metabolism
- release
- reuptake into the nerve ending or uptake into a glial cell
- degradation
- receptor for the neurotransmitter
- receptor-induced increase or decrease in ionic conductance
- retrograde signaling.
What are teh three basic criteria that define classical NT’s?
- Localization - NT must be localized to the presynaptic terminal
- Release - The transmitter must be released from the presynaptic terminal in a calcium-dependent manner, concomitantly with presynaptic nerve activity
- Synaptic mimicry -
- Exogenous application of the transmitter should mimic the action of presynaptic nerve stimulation
- Pharmacological agonists and antagonists should mimic and block the transmitter action, respectively
What NT’s are not synthesized or stored in the presynaptic terminal?
Retrograde messengers - e.g. endocannabinoids
What are five examples of NT’s that activate ionotropic receptors from this DSA?
- Glutamate
- GABA
- Acetylcholine
- Glycine
- Serotonin
Metabotropic receptors indirectly modulate ion channels. What type of receptor are they?
GPCRs
What is the major functional effect of metabotropic receptors?
signal amplification, which can be excitatory or inhibitory depending on the G protein activated and the downstream effector protein
What are some of the key second messengers and signaling effectors mediated by metabotropic receptors?
- Adenylate cyclase and cyclic adenosine monophosphate (cAMP)
- Polyphosphoinositide products:
- Diacylglycerol (DAG)
- Inositol-triphosphate (IP3)
- Ion conductance (Ca++, K+, Na+, or Cl-)
What are some examples of NT’s that activate metabotropic receptors?
- Glutamate
- GABA
- Acetylcholine
- Dopamine
- Norepinephrine
- Serotonin
- Histamine
- Neuropeptides
- Endocannabinoids
Glutamate receptors include ionotropic and metabotropic. What are the types of ionotropic receptors?
- Non-NMDA
- NMDA
What are the non-NMDA receptors glutamate hits?
AMPA, Kainate
What do AMPA receptors do?
Mediate the vast majority of excitatory synaptic transmission in the brain via ligand gated sodium/potassium channels. (some are also permeable to calcium)
NMDA receptors are ligand gated sodium/calcium channels that are also highly calcium permeable. Overstimulation of these receptors is especially important in what conditions?
Ischemia and hypoxia d/t stroke mostly, where calcium influx via these receptors triggers apoptosis
What are two non-competative agonists for the NMDA receptor that are used recreationally/illegally?
What do they do at low doses?
High doses?
PCP and ketamine
Low = hallucinations and delusions
high = dissociative anesthesia
what do postsynaptic metabotropic glutamate receptors do?
Decreases K+ conductance; Increases IP3, DAG
What do presynaptic metabotropic receptors for glutamate do?
- Decreases Ca++ conductance (INHIBITORY); Decreases cAMP
how does glutamate contribute to migraines?
excessive glutamate release contributes to the cortical spreading depression implicated in the aura of migraine headache
Excessively rapid or sustained firing of a relatively small group of glutamatergic neurons in one region of the brain may rapidly lead to successive excitation of ever larger numbers of glutamatergic neurons until a major region of the brain is evoked into a paroxysmal discharge.
This can cause what potential outcomes?
- Seizure
- prolonged seizures and stroke can lead to apoptosis
What degerative disease may glutamate have a hand in?
What does this allow for as far as tx options go?
AD - NMDA receptor antagonist memantine is used to treat moderate to severe dementia of the AD type.
How is the NMDA receptor a “coincidence receptor”?
A single synaptic input results in the generation of a short-lasting excitatory postsynaptic potential (EPSP) that is mediated entirely by AMPA receptors. (B) When multiple inputs occur simultaneously, nerve depolarization removes the Mg++ block in NMDA receptor channels and the same single synaptic input generates a longer-lasting EPSP that is mediated by both AMPA and NMDA receptors. Thus, the NMDA receptor can “sense” the activity in adjacent inputs.
How is GABA inactivated?
- terminated by rapid reuptake by several types of plasma membrane transporters; GABA is also taken up by glial cells
What type of receptors are GABAA?
Ionotropic
What type of receptors are GABAB?
Metabotropic
What are some drugs that bind to GABAA Receptors?
Benzodiazepines
barbituates
ETOH
Benzodiazepines (e.g., alprazolam (Xanax), diazepam (Valium), midazolam (Versed), Clonazepam (Klonopin)) are used to treat what disorders?
4
- generalized anxiety disorder,
- panic disorders,
- sedation
- sleep disorders
What are barbiturates used for? 2
Sedative-hypotics
antiepileptics
Glycine works via ligand gated Cl- channels. What is a toxin that inhibits its release?
Tetanus toxin
What is an antagonist of glycin?
strychnine
At what receptors does glycine act as a co-agonist with glutamate?
NMDA
Parkinsons involves degeneration of dopaminogenic neurons in what structure primarily?
The striatum
What is a disease state that involves increased DA activity?
Psychosis (schizophrenia), thus D2 receptor antagonists are the classic therapy.
Cocaine abuse has what impact on DA?
Blocks DA uptake
What do amphetamines do to DA?
Increase release
Ventral tegmental DA pathways mediate the subjective effects of drugs of abuse in what pathway?
the reward pathway
What are the receptor types for NE?
All metabotropic
What does substance P do?
NT for sensory afferent neurons that mediate pain
