Independent roles of dopamine D1 and D2/3 receptors in rat thermoregulation

The present study was designed to examine a possible interaction between dopamine D-1 and D-2/3 receptors involved in thermoregulation in rats. The dose-dependent hypothermia produced by the dopamine D-1 receptor agonist A 68930 (0.9-15.0 mu mol kg(-1), s.c.), was augmented in an additive manner by pretreatment with the dopamine D-2/3 receptor agonist 7-OH-DPAT (0.06 mu mol kg(-1), s.c.). The dose-dependent hypothermia produced by 7-OH-DPAT (0.06-1.00 mu mol kg(-1) s.c.) was also augmented in an additive manner by pretreatment with A 68930 (0.9 mu mol kg(-1) s.c.). In contrast to these observations, locomotor activity measurements disclosed a marked interaction between the dopamine D-1 and D-2/3 receptor agonists. Thus, A 68930 (0.9-15.0 mu mol kg(-1), s.c.) produced a dose-dependent suppression of open-field locomotor activity. The addition of 7-OH-DPAT (1.00 mu mol kg(-1), s.c.), which by itself produced a weak suppression of locomotor activity, resulted in a gradual reversal of the A 68930-induced suppression of the locomotor activity. Thus, the present results provides strong support for an independent role of dopamine D, receptors in rat thermoregulatory mechanisms, distinct from effects mediated via the dopamine D-2 receptor family. (C) 1998 Elsevier Science B.V.