REDUCED, FEBRILE RESPONSES TO PYROGENS AFTER LESIONS OF THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS

The hypothalamic paraventricular nucleus (PVN) is recognized as a majo r site of autonomic control, but the role of this nucleus in thermoreg ulation is unclear. Therefore the role of the PVN in the febrile respo nse and in the maintenance of normal body temperature was investigated . Conscious, unrestrained rats with chronic lesions of the PVN receive d intracerebroventricular injections of several doses of prostaglandin (PG) E(2) or intraperitoneal applications of Escherichia coli lipopol ysaccaride. The body temperatures of both lesioned and sham-operated a nimals, monitored via radio telemetry, were compared. Intracerebrovent ricular PGE(2) at doses of 10, 25, and 50 ng caused dose-dependent fev ers in both PVN-lesioned and sham-operated animals, which at lower dos es were smaller in the lesioned animals than in the sham-operated anim als. Intraperitoneal lipopolysaccharide application, 50 mu g/kg body w t, evoked a significantly lower febrile response in PVN-lesioned anima ls than in controls. The body temperature of PVN-lesioned animals and controls showed no difference during 300 min of exposure to heat (32 d egrees C) or cold (7 degrees C). These results suggest that the PVN co ntributes to the complex regulation of temperature during the febrile response but not during the maintenance of normal body temperature.