3. Neurotransmitters Flashcards
Neurotransmitters
chemical substances that move messages across the synapse. More than 100 substances.
What are the functions of neurotransmitters?
excitatory or inhibitory depending on their receptor (there are many subtypes that may have very different responses)
what are small-molecule neurotransmitters?
amino acids
monoamines
acetylcholine
Unconventional neurotrasmitters
neuropeptides
pituitary peptdes hypothalamic peptides brain-gut peptides opioid peptides miscellaneous peptides
what are the most common amino acids?
amino acids
excitatory neurotransmitters that are amino acids
glutamate and asparate
inhibitory neurotransmitters that are amino acids
Gamma-aminoburytic acid (GABA) and glycine
how are amino acids distributed
widely through the CNS
Glutamate involved in…
especially involved in learning through a particular receptor-type (NMDA receptors). Involved in excitoticity - prolonged depolarisation of postsynaptic cell -> neuron death
two classes of monoamines
catecholamines and indolamines (based on structure)
Most of them diffusely released into extracellular fluid
catecholamines
dopamine, epinephrine, norepinephrine;
All derived from one amino acid - tyrosine
indolamines
Serotonin or 5-HT (melatonin)
derived from tryptophan
two pathways of dopamine
two pathways are mesostriatal and mesolimbocortical
functions of dopamine
reward (motivation) pleasure, euphoria motor function (fine tuning) compulsion Perservation
Mesostriatal pathway
Dopamine from the substantia nigra to the striatum
mesolimbocortical
from the VTA to the hippocampus, nucleus accumbens and frontal cortex
behavioural effects of serotonin
mood perception memory anger aggression fear stress responses appetite addiction sexuality sleep cognition
seratonin pathway
Raphe nucleus to the striatum, nucleus accumbens, frontal cortex, hippocampus,
what was the first neurotransmitter to be detected?
acetylcholine (ACh)
What is acetylcholine usually referred to as?
the cholinergic system (i.e. acetylcholine-containing)
what are ACh receptors usually?
either nicotinic or muscarinic
nicotinic
ionotropic; excitatory
muscarinic
metabolic; both excitatory and inhibitory
what is Acetylcholine implied in?
Alzheimer’s disease; learning and memory
what is the cholinergic system?
projections of cholinergic neurons from the chollinergic nuclei of the pons and midbrain to the hippocampus, thalamus and amygdala
and also from the basal forebrain to the cerebral cortex
two kinds of unconventional neurotransmitters
nitric oxide, carbon monoxide
Endocannabinoids
Nitric Oxide, carbon monoxide
soluble gaseous neurotransmitter
easily penetrate the cell membrane and active second messengers
involved in retrogade transmission
endocannabinoids
includes anandamide - which was the first endocannabinoid to be discovered with similar properties to the main psychoactive properties of marijuana
The major effect on presynaptic neurons inhibiting synaptic transmission
how many neuroptides are identified?
about 100
what do the neuropeptides functions depend on?
their amino acid sequence
5 categories of neuroptides
pituitary peptides hypothalamic peptides brain-gut peptides opiate peptides miscellaneous hormones
pituitary peptides
those released from the pituitary gland (e.g. oxytocin; “love” hormone
hypothalamic peptides
those released from the hypothalamus (e.g. CRH; corticotropin releasing hormone; anxiety)
brain-gut peptides
those first identified in the gut (e.g. ghrelin; hunger hormone also thought to be involved in stress, anxiety, depression; learning etc.)
opiate peptides
those that resemble the structure of active ingredient of opium (endogenously produced; (e.g. endorphins; happy hormones)
miscellaneous hormones
those that dont fit any other category
how do drugs influence synaptic transmission
drugs either facilitate (agonists) or inhibit (antagonist) effects of neurotransmitters. Drugs can act on various steps of neurotransmitter action either pre or post synaptically
what are the 7 steps to neurotransmitter action
- neurotransmitter molecules are synthesised from precursors under the influence of enzymes
- neurotransmitter molecules are stored in vesicles
- neurotransmitter molecules that leak from their vesicles are destroyed by enzymes
- action potentials cause vesicles to fuse with the presynaptic membrane and release their neurotransmitter molecules into the synapse
- Released neurotransmitter molecules bind with autoreceptors and inhibit subsequent neurotransmitter release
- Released neurotransmitter molecules bind to postsynaptic receptors
- Released neurotransmitter molecules are deactivated by either reuptake or enzymatic degradation
