3 - CNS Transmission Flashcards
Requirements for chemical neurotransmission 1 2 3 4
• Synthesis/storage – Vesicular content • Release – Na & K ion channels – Calcium influx • Inactivation – Uptake – Metabolism • Receptors – Postjunctional – Prejunctional
Prejunctional noradrenergic receptors
Prejunctional alpha receptors
Example of a drug that acts centrally on presynaptic alpha adrenoceptors
Clonidine
CLearance of noradrenaline
Reuptaken pre- and postjunctionally (95% is neuronal, extraneuronal is low-affinity).
Degraded by MAO and COMT.
Effect of cocaine
1) Blocks noradrenaline, dopamine, serotonin reuptake.
2) Blocks Na+ channels (lead for local anaesthetic drugs)
Number of neurotransmitters in the CNS
Over 40
Catecholamine biosynthesis 1 2 3 4 5
1) Extracellular tyrosine taken up into neuron
2) Tyrosine hydroxylase converts tyrosine to L-DOPA
3) DOPA decarboxylase converts L-DOPA to dopamine
4) Dopamine is transported into a vesicle
5) In vesicle, dopamine-beta-hydroxylase converts dopamine to noradrenaline
How do adrenal glands produce adrenaline? 1 2 3 4 5 6
1) Extracellular tyrosine taken up into neuron
2) Tyrosine hydroxylase converts tyrosine to L-DOPA
3) DOPA decarboxylase converts L-DOPA to dopamine
4) Dopamine is transported into a vesicle
5) In vesicle, dopamine-beta-hydroxylase converts dopamine to noradrenaline
6) Phenyl-ethanolamine-N-methyl transferase converts noradrenaline to adrenaline
Why don’t sympathetic nerves produce adrenaline?
Lack phenyl-ethanolamine-N-methyl transferase
Why don’t CNS dopaminergic neurons deplete dopamine by making noradrenaline?
Lack dopamine beta-hydroxylase
Parts of brain affected by noradrenaline
Cortical, brainstem (caudal raphae nuclei)
Parts of brain affected by dopamine
Central brain (basal ganglia) and frontal cortex
Pathways involving dopamine that don't involve noradrenaline 1 2 3 4
1) Movement (Parkinson’s involves depletion of dopamine in basal ganglia)
2) Behaviour (schizophrenia involves changes in dopamine-rich areas, eg frontal cortex, basal ganglia, temporal lobe)
3) Dependence (dopamine in nucleus accumbens, ventral tegmental areas involved)
4) Pituitary function (prolactin secretion)
Can synapses be both excitatory and inhibitory?
No. Must be one or the other.
Examples of neurotransmitters that can be excitatory or inhibitory depending on receptors present
Dopamine, serotonin
