Is acetylcholine involved in a dopamine receptor mediated hypothermia in mice and rats?

1 Apomorphine and oxotremorine caused a dose-related fall in core temperature in the mouse and a fall in core temperature preceded by an increase in tail-skin temperature in the rat.2 In both species the slope of the dose-response curve was greater for oxotremorine (8.2 +/- 0.6 mice, 0.9 +/- 0.1 rats) than it was for apomorphine (1.7 +/- 0.3 mice, 0.5 +/- 0.07 rats).3 The mouse was more sensitive than the rat to the effects of both agonists.4 Atropine (0.625 to 5 mg/kg) and hyoscine (0.5 and 1 mg/kg) caused a dose-related rightward shift of the dose-response curve to oxotremorine in mice, but pimozide (0.25 to 1 mg/kg) was ineffective. Similar results were obtained in the rat.5 Pimozide (0.125 to 1 mg/kg) caused a dose-related rightward shift of the dose-response curve to apomorphine in mice, but atropine (1.25 to 1 mg/kg) and hyoscine (0.5 and 1 mg/kg) were ineffective. Similar results were obtained in the rat.6 Intrahypothalamic injection of apomorphine (10 mug) and oxotremorine (1.25 mug) caused a fall in core temperature in rats. Pimozide (0.5 mg/kg i.p.) caused reversal of the effect of apomorphine but did not significantly change the response to oxotremorine. Atropine (2.5 mg/kg i.p.) blocked the effect of oxotremorine, but not that of apomorphine.7 These results suggest that there are both central dopamine and central muscarinic acetylcholine receptors which mediate a fall in core temperature in rodents, but do not support the hypothesis that any connection exists between these two receptor populations.