Sympathetic activity following paraventricular or ventromedial hypothalamic lesions in rats

The present experiment was designed to measure the sympathetic firing rate of nerve filaments to interscapular brown adipose tissue in rats with acute and chronic lesions in the ventromedial hypothalamus or paraventricular nucleus. Female rats received injections of kainic acid into either the paraventricular nucleus or the ventromedial hypothalamus. The sympathetic activity was measured by recording the firing rate of nerve filaments to interscapular brown adipose tissue after mounting the filaments on silver wire electrodes connected to an amplifier and rate meter. In acute experiments performed 30 minutes after the lesion, the basal firing rate was reduced in both groups and was significantly lower in the VMH-lesioned rats than in those with PVN lesions. In the chronic experiment kainic acid was injected into the VMH or PVN and the sympathetic firing rate was measured 7 to 9 days later. Both lesioned groups gained more weight than controls, but the VMH-lesioned rats gained more weight than the PVN-lesioned rats. The basal firing rate of sympathetic nerve filaments in the VMH-lesioned rats was lower than in the other groups. There was no significant difference in the sympathetic activity between PVN-lesioned and control rats. These experiments support the hypothesis that lesions of the ventromedial hypothalamus reduce the sympathetic activity but that lesions in the paraventricular nucleus do not.