- D1 receptor raises cAMP and promotes direct-pathway action selection, movement, and reinforcement.
- D2 receptor lowers cAMP, suppresses the indirect pathway, and acts as an autoreceptor limiting dopamine release.
- D3 receptor is a high-affinity D2-like receptor in limbic circuits that shapes motivation and reward seeking.
- D4 receptor is a D2-like receptor in frontal circuits that modulates attention and cognitive flexibility.
- D5 receptor is a high-affinity D1-like receptor that supports hippocampal and prefrontal plasticity.
Other Important Relations
- Substantia Nigra dopamine biases the Basal Ganglia toward action; its loss produces the motor features of Parkinson’s disease.
- Ventral Tegmental Area dopamine carries reward-prediction errors to the Nucleus Accumbens and Prefrontal Cortex, linking motivation to Reinforcement Learning.
- Prefrontal Cortex dopamine follows an inverted-U: too little or too much impairs working memory and executive control.
- Tyrosine becomes L-DOPA through tyrosine hydroxylase, then dopamine through aromatic L-amino acid decarboxylase.
- Dopamine becomes norepinephrine through dopamine beta-hydroxylase, connecting the catecholamine synthesis pathway.
- MAO and COMT convert dopamine into DOPAC and homovanillic acid, commonly measured indices of dopamine turnover.
- Hypothalamic dopamine tonically inhibits prolactin release from the anterior pituitary.