Serotonergic mechanisms in the hypothalamus mediate thermoregulatory responses in rats

Central side effects of pentamethylmelamine: biochemical and behavioural studies

The central side effects of pentamethylmelamine (PMM), an antitumoral agent, were studied on brain neurotransmitters from the biochemical and behavioural points of view. PMM causes a dose-related reduction in the body temperature and motility of mice. 100 mg/kg of PMM lowers the levels of noradrenaline (NA) and raises 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) in the telencephalon. A similar dose increased striatal levels of dopamine (DA) metabolites, homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC), at earlier times (30 min), reducing their levels at 2 hr. These effects disappear at longer times (4 hr). No changes were observed in the levels of 3-methoxytyramine (3-MT), the extraneuronal metabolite of DA. The serotonin metabolite 5-hydroxyindolacetic acid (5HIAA) was almost not affected. PMM and its metabolites do not displace [3H]-spiroperidol from mouse striatal binding sites. These data show that some of the neurological effects induced by PMM are associated with changes in the metabolism and/or release of brain catecholamines but are not mediated by direct action on DA receptors.

Clonidine-induced hypothermia: possible involvement of cholinergic and serotonergic mechanisms

The thermoregulatory effects (including metabolic, vasomotor and respiratory activities) produced by an injection of clonidine (1-3 micrograms in 0.5 microliter) into the preoptic anterior hypothalamus were assessed in conscious rats at ambient temperatures (Ta) of 8, 22 and 30 degrees C. Intrahypothalamic administration of clonidine caused a dose-dependent fall in rectal temperature at Ta 8 degrees C and 22 degrees C. The hypothermia in response to clonidine was due to decreased metabolic heat production and/or cutaneous vasodilation. There was no change in respiratory evaporative heat loss. The clonidine-induced hypothermic response was attenuated by pretreatment of the rats with either 5,7-dihydroxytryptamine (10 micrograms, administered intrahypothalamicly, 14 days before clonidine injection), yohimbine (0.2 microgram, administered intrahypothalamicly, 10 min before clonidine injection), cyproheptadine (1 microgram, administered intrahypothalamicly, 10 min before clonidine injection), or atropine (0.1 microgram, administered intrahypothalamicly, 10 min before clonidine injection). The data indicate that clonidine may act on alpha-adrenoceptors located on a serotonin-acetylcholine pathway within the preoptic anterior hypothalamus to induce hypothermia by promoting a reduction in metabolic heat production and/or an enhancement in dry heat loss in rats.

Effects of hypothalamic noradrenaline depletion with 6-hydroxydopamine on the body temperature regulation of the rat

Rats which had been pretreated with 3 intrahypothalamic doses of 10 micrograms of 6-hydroxydopamine (6-OHDA) to cause a selective depletion of hypothalamic noradrenaline to 26.7% of control hypothalamic noradrenaline maintained rectal temperature within the normal limits displayed by the control group. However, noradrenaline-depleted rats displayed a decrease in both cutaneous temperature and metabolic heat production in the cold (8 degrees C). Intrahypothalamic injections of 6-OHDA in normal rats at room temperature (22 degrees C) caused an acute hyperthermia of up to 1.1 degree C which lasted for about 6 h. The acute hyperthermia in response to 6-OHDA was due to both cutaneous vasoconstriction and increased metabolism in the rat. Selective depletion of hypothalamic noradrenaline without affecting hypothalamic dopamine by prior treatment with 6-OHDA markedly reduced the hyperthermic responses to a subsequent dose of 6-OHDA. Therefore, the acute hyperthermic responses to 6-OHDA may be related to a release of noradrenaline in the hypothalamus. The data indicate that activation of noradrenergic pathways in the hypothalamus facilities heat production and inhibits heat loss mechanisms in the rat.

Stress-induced anorexia: implications for anorexia nervosa

Recent studies have suggested that stress may be a precipitating factor in the etiology of anorexia nervosa. The present paper examines the possible mechanisms involved in stress-induced anorexia and suggests how stress-induced changes in opiate systems, the hypothalamic-pituitary-adrenal axis and serotonergic systems may provide an explanation of many of the physiological and behavioral responses observed in anorexia nervosa. The present paper suggests that certain psychosocial and endocrinological factors may interact to provide the setting conditions for the syndrome. Finally, it is suggested that a dual therapeutic approach is required in that the syndrome needs to be treated both physiologically and psychologically to prevent relapse.