Monoamines Flashcards
what are the 3 CNS systems that control behaviour?
Autonomic nervous system
Hypothalamic-pituitary neurohormones
Diffuse monoamine system
what is the diffuse monoamine system?
Four systems, which have common principles:
- Small set of neurons at core
- Arise from brain stem
- One neuron influences many others
- Synapses release transmitter molecules into extracellular fluid
name the 4 systems that make up the diffuse monoamine system:
- Noradrenergic Locus Coeruleus
- Serotonergic Raphe Nuclei
- Dopaminergic Substantia Nigra and Ventral tegmental Area
- Cholinergic Basal Forebrain and Brain Stem Complexes
name the 4 neurotransmitters that make up the diffuse monoamine system:
NA, released from noradrenergic neurons
Serotonin, released from serotonergic neurons
Dopamine, released from dopaminergic neurons
Ach, released from cholinergic neurons
where do the neurotransmitters project from and where do they project to?
the 4 neurotransmitters project from the central core (where the cell bodies are) to different brain regions
eg. noradrenergic neurons project from the central core, the Locus Coeruleus - this projects to the cortex, hypothalamus, spinal cord, where noradrenaline is released
what is neurotransmission in the brain like?
- Fast point-to-point signalling
Neurotransmitters producing excitatory or inhibitory potentials
Ligand-gated ion channels
Glutamate, GABA, ACh - Slow transmission
Neurotransmitters and neuromodulators
G-protein coupled receptors
Monoamines, peptides, ACh
where do neurotransmitters act?
when the neurotransmitters are released, they act on receptors
eg. dopamine will act on D1 and D2 receptors
All of these receptors are g-protein coupled receptors – some inhibit AC, some stimulate AC (Gi/Gs coupled), some are Gq coupled, stimulating Phospholipase C
They are NOT ion channels. Given they are not ion channel receptors, transmission is slow.
-dopamine, serotonin, NA
Noradrenergic monoamine system
noradrenergic monoamine system
- consists of noradrenergic neurons (neurons which release NA)
- they project from the Locus coeruleus to the cortex, amygdala, hypothalamus and cerebellum – NA released in these places
NA post synaptic and pre synaptic receptors
NA in vesicles and released into synapse, binds to:
Post-synaptic receptors
-carry on the message
Pre-synaptic receptors
- autoreceptors
- inhibit NA release, negative feedback mechanism
- alpha-2
autoreceptors of the monoamine diffuse system
5-HT1A
D2/D3
alpha-2
names of reuptake transporters of the monoamine diffuse system
EAAT - glutamate
DAT - dopamine
SERT - serotonin
NET - noradrenaline
structure of reuptake transporters of the monoamine diffuse system
12 TMDs (TMD pore in neurone membrane)
Both ends intracellular
Pump monamines in neuron
DA, NA, 5HT transporters
actions of Reserpine and
Cocaine on noradrenaline release
Reserpine - depletes NA stores by inhibiting vesicular uptake
Cocaine - blocks NA re-uptake
different actions of adrenoceptors
Alpha 1 = Gq coupled, Phospholipase C, SM contraction
Alpha 2 = Gi coupled. These are autoreceptors. Decreased AC
Beta = Gi coupled AC, cAMP, contraction of cardiac muscle, SM relaxation
name an alpha 2 agonist
clonidine
actions of NA?
- NAergic neurons active when ‘awake’
- Arousal, wakefullness, mood (low NA in depressed patients)
- Blood pressure regulation - play role in reward system
- Addiction/gambling
too much NA
too little NA
: hyper arousal, high BP (cardiovascular problems), gambling problems
too low: depression-like behaviour (opposite of excitement)
actions of amphetamine on noradrenaline release and effects in the body?
amphetamine enters vesicles displacing NA into cytoplasm, increase NA leakage out of neurone
- increases alertness and exploratory behaviour
when is there an NA surge?
big impulsive-like excitement before you start gambling
Dopaminergic monoamine system
Dopamine is released from dopaminergic neurones
4 main pathways
1. Nigrostriatal pathway
-neurons project from the Nigro to the Striatum, where dopamine gets released and acts on dopamine receptors to induce movement (Parkinson’s)
- Mesolimbic pathway
- neurons which project from VTA to amygdala (emotions), hippocampus (learning and memory) and nucleus ocumbus (important region involved in pleasure/reward). This pathway has important role in rewards eg. foods, sex, pleasurable behaviours – the rewards activate the mesolimbic system and induce release of dopamine (schizophrenia) - Mesocortical pathway
- neurons project from the VTA region to the cortex - Tubero-hypophyseal pathway
- dopamine released from neurons to activate neighbouring neurons, but can also act as a neurohormone
- dopamine can be released from the hypothalamus directly to the blood circulation (portal system). Dopamine will go from the hypothalamus to the pituitary, and inhibit the release of prolactin