A different balance in the sensitivity of D1 and D2 dopamine receptors accounts for differences in apomorphine-induced hypothermic effects in Swiss and C3H mice.

In several strains of mice: Swiss CD1, BALB, DBA2, C57, the mixed D1/D2 direct dopamine receptor agonist, apomorphine, elicited a marked and virtually similar hypothermic effect. By contrast, in C3H mice, this effect was obviously less and shorter. Similarly, the hypothermic effects of two direct D2 dopamine agonists RU 24926 and piribedil were respectively lesser or absent in C3H, compared to Swiss CD1 mice. On the contrary, the hyperthermic effect of the D1 dopamine agonist SKF 38393 was greater in C3H than in Swiss CD1 mice. This unbalanced sensitivity of D1 and D2 dopamine receptors, involved in thermoregulation, likely accounts for the low responsiveness of C3H to the apomorphine-induced hypothermic effect.