Table 2. Competitive inhibition experiments of [³H]SCH 23390, [³H]YM-09151-2 or [³H]RX821002 versus DA and NE in sheep brain striatum.

RECEPTOR	BINDING PARAMETERS
	DA	NE
	KDB1: 8 ± 3	KDB1: 53 ± 90##
D1-like	KDB2: 8000 ±1000***	KDB2: 50000 ± 10000#
	Dc: -2.4	Dc: -2.4
	KDB1: 3.5 ± 0.6	KDB1: 60 ± 40##
D2-like	KDB2: 700 ± 200	KDB2: 3400 ± 100
	Dc: -1.7	Dc: -1.2
	KDB1: 6 ± 1	KDB1: 0.8 ± 0.1
α2	KDB2: 1000 ± 200	KDB2: 5000 ± 3000
	Dc: -1.6	Dc: -3.2

Binding parameters from competitive-inhibition experiments of [³H]SCH 23390 (D₁-like receptor antagonist), [³H]YM-09151-2 (D₂-like receptor antagonist) or [³H]RX821002 (α₂ receptor antagonist), versus NE and DA in sheep brain striatum. K_DB1, K_DB2 and D_c values were obtained according to the two-state dimer model (see Materials and Methods and ref. 22). Values for α_2- adrenoceptors are from Table 1. K_DB1 and K_DB2 (in nM) are expressed as means ± S.E.M. of 3-5 experiments performed in triplicate. Statistical differences between affinity parameters obtained were calculated by one-way ANOVA followed by Dunnett's post hoc test; for DA,

^***p<0.001 vs. D₂-like receptors; for NE,

^#p<0.05 and

^##p<0.01 vs. α₂ receptors.