Effects of adrenalectomy on responses mediated by dopamine D-1 and D-2 receptors

The effects of surgical adrenalectomy were investigated on behavioural responses produced by the selective D-1 agonist, SK&F 38393, alone, and in combination with the D-2 agonist, quinpirole (LY171555). Further, stereotyped responses to apomorphine and LY171555 were assessed following treatment with either the D-1 or the D-2 antagonists, SCH 23390 and raclopride, respectively. There was no difference between sham-adrenalectomized (sham) and adrenalectomized (ADX) groups in responses to SK&F 38393. Although concomitant stimulation of both receptor subtypes increased the incidence of stereotyped sniffing behaviour, there was no difference in the magnitude of this effect between the sham and ADX groups. Raclopride reduced LY171555-induced sniffing and hypothermia less in ADX rats than in sham controls, which was consistent with the hypothesis that adrenocortical hormones affect D-2 receptor responsiveness. SCH 23390 had a greater inhibitory effect on LY171555 responses, but a smaller effect on apomorphine responses in the ADX group compared with their sham controls. It is concluded that the amplified D-2-stimulated response observed in ADX rats may be more dependent on tonic D-1 receptor activation than the control D-2 response of shams.