Implications of dopamine agonist-induced hypothermia following increased density of dopamine receptors in the mouse.

An investigation was made of hypothermia induced by dopamine (DA) agonists as a model of the effect of various treatments or conditions on the sensitivity of central postsynaptic DA receptors. Selective supersensitivity of these receptors (defined as an increase in Bmax) was induced by means of intraventricular injections of 6-hydroxydopamine (6-OHDA) in animals pretreated with desmethylimipramine (DMI). Supersensitivity was also produced by the chronic administration of haloperidol. The supersensitivity of DA receptors induced by 6-OHDA was found to be associated with a reduced hypothermic response to apomorphine. Supersensitivity elicited by the chronic administration of haloperidol, which very probably did not produce a specific effect on the density of DA receptors but also affected serotonergic receptors, did not elicit any change in hypothermia induced by apomorphine. The results of the present study are not consistent with the view that DA receptors mediate hypothermia per se, but rather suggest that hypothermia induced by DA agonists is more complex, probably involving serotonergic receptors primarily, though other factors may also be contributory. Furthermore, the results of the present study suggest that the functional significance of supersensitivity of DA receptors induced by 6-OHDA versus chronic treatment with haloperidol may be quite different, depending upon the effector system examined.