dopamine receptors

introduction

dopamine is a sympathomimetic amine which is an important endogenous neurotransmitter and sympathetic hormone
dopamine is removed from the synapse by dopamine transporter (DAT)
- DAT is inhibited by many recreational drugs such as amphetamines and related psychostimulant substances, cocaine which results in high levels of dopamine in the synapses and triggering the reward system
- subsequent falls in dopamine levels combined with down-regulation of receptor numbers results in anhedonia, shortened attention span, depression and drug-seeking behaviour
dopamine D2 receptors in the brain and autonomic ganglia are vital for a wide range of neurologic functions and are involved in the extrapyramidal movement control system, pleasure reward and motivation systems, cognition, learning, modulation of autonomic system and prolactin secretion
- upregulation of receptor numbers due to dopamine receptor blockers use may result in extrapyramidal reactions such as oculogyric crisis, dystonic reactions, akathisia and tardive dyskinesia
- cocaine appears to upregulate D3 receptors in nucleus accumbens, possibly contributing to drug seeking behavior
dopamine D1 receptors have an important role in increasing blood flow to the GIT and kidneys as well as an important role in working memory tasks and the reward system

D1 receptor - most blood vessels; genetic polymorphisms may have a aetiologic role in hypertension; nucleus accumbens involved in the reward system
D5 receptor
agonist: dopamine;
antagonist: phenothiazines, haloperidol;
G protein Gsα
post-synaptic ⇒ increased adenylyl cyclase ⇒ increased [cAMP]:
- ⇒ vasodilatation (esp. renal & mesenteric)-⇒ increased GFR; increased RBF; increased Na excretion