Table 1. Competitive inhibition experiments of [³H]RX821002 versus NE, DA, clonidine and D₂-like receptor ligands in sheep brain cortex and striatum.

LIGAND	BINDING PARAMETERS
	CORTEX	STRIATUM
	KDB1: 0.3 ± 0.2 *	KDB1: 0.8 ± 0,1
NE	KDB2: 250 ± 100	KDB2: 5000 ± 3000
	DCB: -2.3	DCB: -3.2
	KDB1: 6.9 ± 0.2	KDB1: 6 ± 1
DA	KDB2: 350 ± 10 *	KDB2: 1000 ± 200
	DCB: -1.1	DCB: -1.6
	KDB1: 0.014 ± 0.003 *	KDB1: 0.036 ± 0.005
Clonidine	KDB2: 40 ± 20	KDB2: 20 ± 10
	DCB: -2.8	DCB: -2.1
	KDB1: 9 ± 2 **	KDB1: 51 ± 6
7-OH-PIPAT	KDB2: 430 ± 80
	DCB: -1.1	DCB: 0
	KDB1: 530 ± 50 **	KDB1: 110 ± 10
Quinpirole		KDB2: 2700 ± 400
	DCB: 0	DCB: -0.8
	KDB1: 0.055 ± 0.003 ***	KDB1: 0.42 ± 0.03
RO-105824	KDB2: 4000 ± 2000
	DCB: -4.3	DCB: 0

Binding parameters from competitive-inhibition experiments of [³H]RX821002 versus NE, DA, clonidine and D₂-like receptor ligands in membrane preparations from sheep brain cortex and striatum (Fig. 2). K_DB1, K_DB2 and D_CB values were obtained according to the two-state dimer model (see Materials and Methods and ref. 22). K_DB1 and K_DB2 (in nM) are expressed as means ± S.E.M. of 3 experiments performed in triplicate. Statistical differences between affinity parameters of cortical versus striatal adrenoceptors were calculated by non-paired, two-tailed Student's t test;

^*p<0.05,

^**p<0.01 and

^***p<0.001.