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

Involvement of dopamine receptor subtypes in mouse thermoregulation

The effects of dopamine agonists on core body temperature (BT) were tested in mice. Apomorphine (APO) reduced BT of the mice dose dependently. The response was inhibited by the D-2 antagonist sulpiride, but not by the D-1 antagonist SCH 23390. The D-2 agonist quinpirole also decreased BT and this was prevented by sulpiride pretreatment. Administration of the D-1 agonist SKF 38393 increased BT. This hyperthermia was decreased by SCH 23390 pretreatment. In reserpinized animals, APO caused a dose-related increase in BT. The hyperthermic response of the drug was abolished in animals pretreated with a combination of sulpiride with SCH 23390, but not by single administration of sulpiride or SCH 23390. Quinpirole and SKF 38393 caused hyperthermia in reserpinized mice. The response was decreased in animals pretreated with sulpiride or SCH 23390, respectively. BT of the intact mice was decreased, while that of reserpinized animals was increased by SCH 23390 but not by sulpiride pretreatment. It is concluded that the presynaptic dopamine neurons are involved in hypothermia, while both postsynaptic D-1 and D-2 dopamine receptors may mediated the hyperthermia induced by dopaminergic agents.

Supersensitivity of d-amphetamine-induced hyperthermia in rats following continuous treatment with neuroleptics

Following short term treatments with the neuroleptic drugs haloperidol, chlorpromazine and oxypertine, there was an increase in the sensitivity of rats to the hyperthermic effects of d-amphetamine. There was no significant difference in the body temperature of control and neuroleptic-treated rats prior to challenge with d-amphetamine. No change in the maximal hyperthermic response was observed. It is possible that these responses may be related to the neuroleptic malignant syndrome occasionally observed in human patients following short term neuroleptic treatments.

Neuroleptic-induced hypothermia in mice: lack of evidence for a central mechanism

The present study investigated the ability of neuroleptic drugs to induce hypothermia in mice when they were administered intraperitoneally (i.p.) or intracerebroventricularly (i.c.v.). Twelve neuroleptics belonging to five chemical classes including phenothiazines, butyrophenones, benzamides, thioxanthenes and diphenylbutylpiperidines were injected i.p. All of them, except benzamides, induced a dose-dependent decrease in rectal temperature. Neuroleptics were administered i.c.v. via cannulae previously implanted in mice to determine whether this response might have a central origin. None of the drugs tested induced hypothermia at doses which did not produce toxic effects. These negative results suggest that neuroleptics act to elicit hypothermia via a peripheral, rather than a central mechanism. Since some neuroleptics possess alpha-adrenolytic properties which could induce hypothermia by promoting vasodilatation, we attempted to antagonize the hypothermia produced by peripheral administration of two neuroleptics with phenylephrine, an alpha-adrenoceptor agonist that does not cross the blood-brain barrier. The hypothermia induced by both chlorpromazine and haloperidol was attenuated by phenylephrine, supporting the view that peripheral alpha-adrenoceptors may mediate neuroleptic-induced hypothermia.