Alterations in body temperature elicited by intrahypothalamic administration of tetrodotoxin, ouabain and A23187 ionophore in the conscious cat.
Ouabain, tetrodotoxin, and calcium selective ionophore (A23187) were administered bilaterally into the hypothalamus of the unrestrained, fully conscious cat, while body temperature and other indicators of thermoregulatory responses were monitored continuously. Posterior hypothalamic microinjection of 2.0 to 10.0 ng or tissue perfusion with 1.1 X 10(-7) to 1.1 X 10(-8) M ouabain elicited dose dependent increases in body temperature accompanied by pinnae vasoconstriction, shivering and postural changes consistent with heat conservation. Tetrodotoxin, microinjected in doses of 0.5 and 5.0 ng or tissue perfusions with 7.8 X 10(-9) to 7.8 X 10(-7) M in the posterior hypothalamus elicited dose dependent falls in body temperature. However, tetrodotoxin microinjected into the anterior hypothalamic region elicited only increases in temperature. The calcium selective ionophore, A23187, at least at the concentrations used in this study, did not appear to produce any consistent effects on thermoregulation. These data support the hypothesis that the ionic milieu of the posterior hypothalamic region is essential in the maintenance of body temperature. Further, they suggest that increasing the [Ca++]/[Na+] acts in a manner similar to a depression in the firing frequency of a distinct population of cells, which may in turn determine in some way the "set-point" for body temperature. There is no evidence to support the concept that increasing the [Ca++]/[Na+] causes an increased release of the synaptic contents of the region.