Intracerebroventricular injection of sympathomimetic drugs inhibits both heat production and heat loss mechanisms in the rat

Validation of the hypothermic action of preoptic norepinephrine in guinea pigs

Conscious guinea pigs were either microinjected intrapreoptically (iPO) with various doses of norepinephrine (NE) bilaterally or microdialyzed with pyrogen-free saline (PFS) or 10 micrograms/microliters NE unilaterally immediately and unilaterally or bilaterally 2 days after probe insertion. Core temperature (Tco), skin temperature (Tsk), and rate of oxygen consumption (VO2) were monitored continuously. The microinjection of low doses of NE induced Tco rises, whereas that of the highest dose (10 micrograms/microliters) caused an initial Tco fall followed by a rise. The microdialysis of PFS or NE immediately after probe insertion caused Tco rises; the former was abolished and the latter was converted into a fall by indomethacin (Indo, a prostaglandin synthase inhibitor) pretreatment. Two days later, PFS evoked no thermal response whereas NE induced a Tco fall; neither response was affected by Indo pretreatment. The falls in Tco produced by NE microdialyzed uni- or bilaterally were similar. The microdialysis of NE induced a 15% reduction in metabolic rate but no change in Tsk. These results indicate that the Tco rise induced by NE microinjected iPO is a methodological artifact mediated by PGE2, whereas the Tco fall observed in its microdialysis appears to represent the authentic physiological action of this transmitter effected by a reduction in metabolic rate.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

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.

Rapid identification of correctly located intracerebroventricular cannula in the rat

We describe a radiographic technique to identify a correctly located cannula in the ventricular system of the rat brain during life. A suspension of thorium dioxide was infused into the left lateral ventricle through a cannula placed in the brain under stereotaxic guidance. Correctly located injections were identified by the presence of a distinct thorium shadow on lateral X-ray of the in situ brain. When 6-hydroxydopamine was co-injected with thorium the resultant depletion of striatal dopamine and the changes in a conditioned avoidance responses were correlated with the degree of spreading of thorium through the ventricular system.

A prostaglandin-adrenergic link occurs in the hypothalamic pathways which mediate the fever induced by vasopressin in the rat

The effects of direct administration of vasopressin into the preoptic anterior hypothalamus on thermoregulatory functions were assessed in conscious rats at various ambient temperatures. Intrahypothalamic administration of vasopressin caused fever, increased metabolic heat production and decreased heat loss (cutaneous vasoconstriction) in rats. There was no changes in respiratory evaporative heat loss in response to administration of these drugs. Furthermore, it was found that the fever reactions induced by intrahypothalamic vasopressin was antagonized by pretreatment of animals with an intrahypothalamic dose of either yohimbine (an alpha-adrenergic receptor antagonist), propranolol (a beta-adrenergic receptor antagonist), or sodium acetylsalicylate (a prostaglandin synthetase inhibitor). The data indicate that a prostaglandin-adrenergic link occurs in the hypothalamic pathways which mediate the vasopressin-induced fever in rats.

An adrenergic link in the hypothalamic pathways which mediates morphine- and beta-endorphin-induced hyperthermia in the rat

The mechanism underlying the hyperthermia induced by intrahypothalamic administration of either morphine or beta-endorphin has been investigated in conscious rats. Direct administration of morphine (1--8 micrograms in 1 microliter) or beta-endorphin (1--3 micrograms in 1 microliter) into the anterior hypothalamus caused hyperthermia in rats at the ambient temperature (8, 22 and 30 degrees C) studied. The hyperthermia in response to opiods was brought about by both increased metabolism and cutaneous vasoconstriction. This hyperthermia, unlike the hypothermia induced by intraventricular administration of opiods was not blocked by naloxone nor did tolerance develop to the response. However, the hypothermia induced by intrahypothalamic administration of opioids was greatly reduced by pretreatment with intrahypothalamic administration of either yohimbine (a blocking agent of alpha-adrenergic receptors) or DL-propranolol (a blocking agent of beta-adrenergic receptors) in the rat. These observations suggest that an adrenergic link occurs in the hypothalamic pathways which mediate morphine- and beta-endorphin-induced hyperthermia in the rat.

Effects of angiotensin II on metabolic, respiratory and vasomotor activities as well as body temperatures in the rabbit

The effects of intraventricular administration of angiotensin II (10 to 50 micrograms, third cerebral ventricle) on thermoregulatory responses of conscious rabbits to different ambient temperatures (Ta) of 2, 22 and 32 degrees C were assessed. Angiotensin II administration produced dose-dependent hypothermia in rabbits at both 2 and 22 degrees C Ta. The hypothermia in response to angiotensin II was due to decreased metabolic heat production and increased heat losses. The increase in heat loss was shown by an increase in both skin blood flow and respiratory evaporative heat loss. However, at 32 degrees C Ta, angiotensin II produced no change in rectal temperature or other thermoregulatory responses. The data indicate that angiotensin II decreases heat production and increases heat loss mechanisms in the rabbit brain which leads to hypothermia.