dopamine Flashcards
catecholamines
epinepherine, norepinepherine, dopamine
epinepherine operates in the
PNS
Catecholamine
neurotransmitters have common structure (with individual variations)
dopamine synthesis
L-tyrosine – Tyrosine hydroxylase -> L-DOPA – DOPA decarboxylase -> dopamine
when AMPT attaches to TH what does it do
inhibits the synthesis of dopamine, norepinepherine, epineperine
VMAT
is the transporter that loads dopamine into synaptic vesicles
Reserpine
Reserpine inhibits VMAT and depletes DA and NE as cytosolic catecholamines are rapidly degraded
Reserpine treatment causes
sedation in animals and induces depression in humans
intracellular pathway of dopamine
dopamine —MAO–> DOPAC — COMPT –> HVA
Extracellular pathway of dopamine
dopamine —COMPT–> 3MT — MAO –> HVA
Cocaine and amphetamine affect
DAT functions
Cocaine & amphetamines inhibits
DAT preventing dopamine reuptake
preventing dopamine uptake causes what ?
Increases dopamine in the synapse
Prolongs dopamine signalling
Hyperactivity of dopaminergic circuits
Presynaptic cell rich in
anabolic enzymes (TH, DOPA decarboxylase)
VMAT expressed on vesicles for
loading dopamine
Dopamine receptors in
postsynaptic membrane
Autoreceptors in
presynaptic membrane for feedback inhibition
Dopamine transporter (DAT) responsible for
reuptake
D1
family [D1, D5] – G-protein coupled receptors signalling through Gsα to ↑cAMP (Excitatory)
D2
family [D2, D3, D4] – G-protein coupled receptors signalling through Giα to ↓ cAMP (Inhibitory)
Unlike classical synapses, dopamine can often synapse onto the
neck of dendritic spines
synapsing onto the neck of dendritic spines
allows dopamine to modulate the activity of the synapse
Dopamine can gate the signals at dendritic spines –
– increasing or decreasing signal transmission
Dopamine accounts for 90% of
catecholamine neurotransmission in the CNS
Nigrostriatal system
projects from substantia nigra and ventral tegmental area to striatum (caudate and putamen)
Tuberoinfundibular system
projects from the hypothalamus to the medial eminence to stimulate the pituitary
prolactin secretion
Mesolimbic/mesocortical system
Projects from the ventral tegmental area to the limbic system, nucleus accumbens, mesial frontal, anterior cingulate, and entorhinal cortex
Dopaminergic lesions Bilateral nigrostriatal lesion
sensory neglect, motivational deficits, motor impairment.
Unilateral lesion of nigrostriatal pathway results in
postural asymmetry and turning
6-hydroxydopamine (6-OHDA) is a
selective neurotoxin.
Nigrostriatal system
Projects to the striatum
Involved in motor control
D1 and D2 family receptors
Degradation in Parkinson’s leads to motor symptoms