Table 1.

Pharmacological properties of dopamine receptors (Ki values in nanomolar)

Receptor/ligand	D1	D5	D2	D3	D4
Dopamine	~2,500 [163]	~225 [163]	~500 [164, 165]	~20–100 [164–166]	Canine brain ~28; D4.2 receptor ~180–400 [175]; D4.4 receptor ~43 [176]
Norepinephrine	~50,000 [163]	~12,000 [163]	>10,000 [165]	n.d.	Canine striatum ~1,750 [17]
Quinpirole	>10,000 [167]	>10,000 [167]	~600–1200 [164, 165]	~15–45 [164, 165, 167]	~30–45 [17, 167, 168]
Haloperidol	~25–350 [127, 128, 163]	~50–175 [128, 163]	~0.4–2.5 [127, 169–171]	~2–10 [127, 128, 164, 166, 172]	~0.8–20 [128, 169, 170]
Raclopride	n.d.	n.d.	~0.5–2.5 [169, 170]	~1–2 [169, 170]	~600 [170, 173]
Clozapine	~150–500 [127, 128, 163]	~250 [128, 163]	~40–400 [127, 164, 169–171, 174]	~100–500 [17, 127, 164, 167, 168]	~1.6–55 [17, 167, 168]

n.d. no data found.