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

The present study was designed to examine a possible interaction between dopamine D1 and D2/3 receptors involved in thermoregulation in rats. The dose-dependent hypothermia produced by the dopamine D1 receptor agonist A 68930 (0.9-15.0 micromol kg-1, s.c.), was augmented in an additive manner by pretreatment with the dopamine D2/3 receptor agonist 7-OH-DPAT (0.06 micromol kg-1, s.c.). The dose-dependent hypothermia produced by 7-OH-DPAT (0.06-1.00 micromol kg-1 s.c.) was also augmented in an additive manner by pretreatment with A 68930 (0.9 micromol kg-1 s.c.). In contrast to these observations, locomotor activity measurements disclosed a marked interaction between the dopamine D1 and D2/3 receptor agonists. Thus, A 68930 (0.9-15.0 micromol kg-1, s.c.) produced a dose-dependent suppression of open-field locomotor activity. The addition of 7-OH-DPAT (1.00 micromol 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 D1 receptors in rat thermoregulatory mechanisms, distinct from effects mediated via the dopamine D2 receptor family.