Acoustic modulation of neural activity in the hypothalamus of the leopard frog

Horseradish applications in the ventral hypothalamus of the northern leopard frog, Rana pipiens, demonstrated inputs from three auditory nuclei, the anterior and central thalamic nuclei and the secondary isthmal nucleus, in a pattern identical to that seen in Rana catesbeiana. Single-unit recordings from the area receiving these inputs revealed neurons with high spontaneous firing rates. In approximately half of the isolated neurons, the firing rate could be increased or, less often, decreased, by more than 20% by the presentation of a repetitive noise burst or conspecific mating call. Treatment with human chorionic gonadotropin prior to recording resulted in no significant differences in the number or response properties of the acoustically sensitive hypothalamic cells. These results suggest that acoustic signals such as those used for intraspecific communication can modulate neural activity in a part of the basal forebrain involved in endocrine regulation.