RESUMEN
In chloral anaesthetized rats, apomorphine, bromocriptine, lergotrile, piribedil and its presumed active metabolite S 584, induced a hypothermia antagonized, except for S 584, by stereotactically controlled microinjections of haloperidol into the preopticus medialis nucleus. Hypothermia was also produced by these dopamine agonists when they were injected directly into the preopticus medialis nucleus. Furthermore, apomorphine-induced hypothermia was antagonized by an infusion of sulpiride into the preopticus medialis nucleus. These data suggest that the dopamine receptors located in the preopticus medialis nucleus which are involved in dopamine agonists-induced hypothermia do not possess the same pharmacological characteristics as the D1 subtype.
Asunto(s)
Apomorfina/farmacología , Hipotermia Inducida , Receptores Dopaminérgicos/fisiología , Anestesia General , Animales , Apomorfina/antagonistas & inhibidores , Hidrato de Cloral , Antagonistas de Dopamina , Relación Dosis-Respuesta a Droga , Haloperidol/farmacología , Hipotálamo/metabolismo , Masculino , RatasRESUMEN
Intracerebroventricular (i.c.v.) administration of histamine in chloral anaesthetized rats exposed to an ambient temperature of 22 C elicited a rise in their colonic temperature associated with a shivering. This effect was shared by the H2 receptor agonists dimaprit and impromidine. Impromidine is, in this respect, a partial agonist with an ED50 much lower than histamine. The histamine-induced rise in core temperature was antagonized by cimetidine administered either centrally (in doses of 25-40 micrograms, i.c.v.) or peripherally (large doses greater than or equal to 50 mg/kg i.p.) This constitutes an indication for the crossing of the blood-brain barrier by cimetidine. The H2 histamine receptors involved in this effect seem to be located mainly in the preopticus medialis nucleus (p.o.m.n.) of the hypothalamus since bilateral microinjections of histamine (5 ng) into this nucleus induced the effect, whereas cimetidine injected into the p.o.m.n., antagonised the relative hyperthermia elicited by an intracerebroventricular administration of histamine.
Asunto(s)
Temperatura Corporal/efectos de los fármacos , Histamina/farmacología , Hipotálamo/efectos de los fármacos , Área Preóptica/efectos de los fármacos , Receptores Histamínicos H2/efectos de los fármacos , Receptores Histamínicos/efectos de los fármacos , Animales , Hidrato de Cloral/análogos & derivados , Hidrato de Cloral/farmacología , Dimaprit , Guanidinas/farmacología , Antagonistas de los Receptores Histamínicos H1/farmacología , Antagonistas de los Receptores H2 de la Histamina/farmacología , Imidazoles/farmacología , Impromidina , Masculino , Área Preóptica/fisiología , Ratas , Ratas Endogámicas , Tiourea/farmacologíaRESUMEN
Systemic administration of apomorphine induces hypothermia in anaesthetized rats as well as in conscious rats exposed to an ambient temperature of 22 degrees C. The central nature of this effect is confirmed by the antagonism exerted by haloperidol and the lack of antagonism with domperidone. Dopamine receptors involved in the hypothermic effect of apomorphine seem to be located in the preopticus medialis nucleus (p.o.m.n.) of the hypothalamus since: (i) injections of apomorphine (5 ng), dopamine (100 ng) or (+)-amphetamine (50 ng) into this nucleus induce hpothermia, (ii) haloperidol injected into the p.o.m.n. antagonizes the hypothermic effect of a systemic administration of apomorphine, (iii) heat lesions of the p.o.m.n. strongly reduce the hypothermic effect of a systemic injection of apomorphine.