The functional role of the noradrenergic neurons in the thermoregulatory circuits in mice.

Abstract

Intracerebroventricular (i.c.v.) treatment of mice with 6-hydroxydopamine (6-OHDA; 20--50 micrograms per mouse), which depletes brain noradrenaline (NA) and DA, completely prevents or significantly diminishes the hypothermic effect of various classes of drugs: dopaminomimetics--apomorphine (0.5--10 mg/kg), piribedil (40--100 mg/kg), bromocriptine (3 to 10 mg/kg), CM 29-712 (2--10 mg/kg), d, l-amphetamine (1--2 mg/kg), and L-DOPA (10--100 mg/kg) in combination with Ro 4-4602 (5--40 mg/kg); cholinomimetics--oxotremorine (0.04--0.05 mg/kg), arecoline (5--10 mg/kg) and pilocarpine (2--3 mg/kg); neuroleptics--chlorpromazine, promazine, perphenazine, chlorprothixene, haloperidol, fluanisone (5--10 mg/kg); central alpha-adrenoblocker aceperone (20--40 mg/kg); inhibitor of tyrosine-hydroxylase alpha-methyltyrosine (200--300 mg/kg); inhibitor of dopamine-beta-hydroxylase--disulfiram (150--250 mg/kg) and FLA-63 (15--25 mg/kg). This antihypothermic effect was demonstrated up to 3 months after administration of 6-OHDA for DA-mimetics and neuroleptics and up to 3 weeks for cholinomimetics. The hypothermic effect of presumable GABA-mimetics Phenybut (100--150 mg/kg) and Lioresal (10--25 mg/kg) was enhanced by a prior 6-OHDA treatment. Pretreatment of mice with desipramine (25 to 30 mg/kg i.p.), protriptyline (20 mg/kg) or AW 15(1)1129 (15--20 mg/kg) 20--45 min before 6-OHDA administration protects the central NA-ergic neurons from a destructive effect of 6-OHDA and partially or completely counteracts the antihypothermic as well as prohypothermic (in the case of GABA-mimetics) effect of 6-OHDA. In rats desipramine counteracted antihypothermic effect of 6-OHDA in the case of piribedil, but not of apomorphine. Intracerebroventricular treatment of mice with a low (15 microgram) dose of 5, 6-dihydroxytryptamine (5, 6-DHT) enhanced the hypothermic effects of DA-mimetics; higher doses of 5, 6-DHT (26 and 30 micrograms) and 5, 7-DHT (40 and 46 micrograms) diminished the hypothermic effects; the antihypothermic effect of 6-OHDA was stronger than that of equimolar doses of 5, 6- or 5,7-DHT; desipramine pretreatment counteracted antihypothermic effects of 5, 6-DHT and 5, 7-DHT as well as depletion of brain NA they produce. The data presented reveal the key position for NA-ergic neurons in a temperature regulation and, particularly, in effects of various drugs on body temperature in mice. The tentative fragment of the neuronal thermoregulatory circuit is proposed in attempt to account for the presented an other known data concerning drug action (and interactions) on core temperature in mice.