Dopamine receptor signaling

Category: receptor_pharmacology

Overview

Dopamine GPCRs split D1-family (D1, D5 — Gs-coupled, increase cAMP) and D2-family (D2, D3, D4 — Gi-coupled, decrease cAMP). D1 → cortical-striatal motor planning. D2 → nigrostriatal motor control + tuberoinfundibular prolactin inhibition + mesocortical/mesolimbic mood + reward. Antipsychotics (typical: high D2 affinity, EPS-prone; atypical: D2 antagonism + 5-HT2A inverse agonism, lower EPS, broader receptor profile). Partial-agonist atypicals (aripiprazole, brexpiprazole, cariprazine) self-titrate dopamine tone — partial agonism stabilizes both hypo- and hyperdopaminergic states. L-DOPA + carbidopa supplies precursor for striatal dopamine in Parkinson's (cross-link: catecholamine_synthesis upstream). Stimulants (methylphenidate, amphetamine) raise synaptic DA via DAT blockade + release. Antiemetics (metoclopramide, prochlorperazine) act at D2 in the area postrema — EPS + tardive dyskinesia tail when used chronically.

Organ Systems

• nervous
• endocrine
• digestive

Pathway Steps

1. dopamine → dopamine-receptor-activation — via binding to D1/D5 (Gs) or D2/D3/D4 (Gi); cross-link: catecholamine_synthesis supplies dopamine. Dopamine acts on five GPCR subtypes in two families: D1-like (D1, D5; Gs, raise cAMP) and D2-like (D2, D3, D4; Gi, lower cAMP). This D1/D2 dichotomy underlies CNS pharmacology — antipsychotics are D2 antagonists while Parkinson’s therapy boosts D1/D2 signaling — shaping motor, reward, and endocrine effects.
2. dopamine-receptor-activation → cAMP second-messenger shift (D1-like ↑ / D2-like ↓) — via DAT reuptake (stimulant target) terminates synaptic signal. Dopamine receptors signal through cAMP: the D1-like family (D1, D5; Gs) raises it and the D2-like family (D2, D3, D4; Gi) lowers it. This opposing coupling means a dopaminergic drug’s net effect depends on which family it engages — the basis of antipsychotic (D2-blocking) versus Parkinson’s (D1/D2-boosting) pharmacology.
3. dopamine → homovanillic-acid — via MAO-B + COMT inactivation (cross-link: monoamine_oxidase_metabolism). Dopamine is cleared by reuptake (DAT) and degraded by MAO and COMT to homovanillic acid (HVA), its major metabolite. DAT is the target of cocaine and amphetamines, and MAO-B/COMT inhibitors are used in Parkinson’s to prolong dopamine action — the metabolic side of dopaminergic pharmacology.

Known Modulators

• levodopa (substrate) — dopamine precursor (peripheral AADC + cross-BBB then central AADC). always co-administered with carbidopa (peripheral AADC inhibitor) to prevent peripheral conversion + GI side effects
• aripiprazole (activator) — D2 partial agonist (also 5-HT1A partial, 5-HT2A inverse). dopamine stabilizer — partial agonist activity rescues mesocortical hypoactivity while damping mesolimbic hyperactivity
• brexpiprazole (activator) — D2 partial agonist. aripiprazole successor; slightly different receptor profile (more 5-HT1A); akathisia less prominent
• cariprazine (activator) — D3-preferring partial agonist (also D2 partial). unique D3-preference; depression + schizophrenia indications; longer half-life than aripiprazole
• olanzapine (inhibitor) — D2 antagonist (also 5-HT2A, H1, M1). atypical AP; H1 + 5-HT2C drive weight + metabolic side effects
• quetiapine (inhibitor) — D2 antagonist (transient — high koff). fast D2 dissociation distinguishes from clozapine; sedation-dominant at low doses (H1)
• risperidone (inhibitor) — D2 antagonist (also 5-HT2A). high D2 occupancy → EPS at therapeutic doses despite "atypical" label; hyperprolactinemia signature
• haloperidol (inhibitor) — D2 antagonist (high-potency typical). classic typical AP; acute IV use for delirium; tardive dyskinesia risk
• clozapine (inhibitor) — D2 antagonist (low affinity) + multi-receptor. low D2 occupancy paradox — minimal EPS; treatment-resistant schizophrenia gold standard; agranulocytosis monitoring
• metoclopramide (inhibitor) — D2 (area postrema + GI). antiemetic + gastric prokinetic; boxed warning for tardive dyskinesia with chronic use (>12 weeks)
• prochlorperazine (inhibitor) — D2 (phenothiazine). antiemetic + migraine; EPS + akathisia common acute side effects
• methylphenidate (inhibitor) — DAT + NET (transporter blocker). raises synaptic DA without releasing intracellular stores (unlike amphetamine); first-line ADHD
• amphetamine (inhibitor) — DAT + NET (also TAAR1 + VMAT reversal → release). mixed reuptake-blocker + releaser; greater abuse liability vs methylphenidate from the release component
• dextroamphetamine (inhibitor) — DAT + NET (same mechanism as amphetamine). D-enantiomer of amphetamine; component of Adderall (D:L 3:1)
• lisdexamfetamine (inhibitor) — DAT + NET (prodrug → dextroamphetamine in RBCs). lysine-conjugated d-amphetamine; cleaved by RBC peptidases at near-constant rate → smoother PK + lower abuse liability
• dexmethylphenidate (inhibitor) — DAT + NET. D-threo-methylphenidate (the active enantiomer of racemic methylphenidate); half the dose for same effect
• tesofensine (inhibitor) — DAT + NET + SERT (triple monoamine reuptake). tesofensine; obesity research compound; failed phase 3 cardiovascular signal
• 5 amino 1mq (inhibitor) — NNMT (nicotinamide N-methyltransferase). research compound; preserves intracellular NMN/NAD pool; weight + insulin sensitivity claims

References

• PMID 21303898