Thalamic and Midbrain Auditory Projections to the Preoptic Area and Ventral Hypothalamus in the Green Treefrog (Hyla Cinerea)

Iontophoretic injections of horseradish peroxidase (HRP) into either the preoptic area or ventral hypothalamus of the green treefrog, (Hyla cinerea), demonstrated inputs from thalamic and midbrain auditory nuclei. In a pattern similar to that seen in Rana catesbeiana and Rana pipiens, the central thalamic and secondary isthmal nuclei were found to provide heavy input to the ventral hypothalamus. Additionally, a lighter input from the anterior thalamic nucleus was seen. In contrast, the preoptic area receives a major input from the anterior thalamic and secondary isthmal nuclei, and possibly a sparse input from the central thalamic nucleus. These results suggest that in treefrogs multimodal and auditory information may reach the preoptic area and ventral hypothalamus, two regions involved in endocrine regulation and the control of reproductive behavior, via largely separate major pathways from the thalamus combined with a common midbrain input. Furthermore, the ventral hypothalamus receives heavy input from the preoptic area, lateral amygdala, suprachiasmatic nucleus, anterior entopeduncular nucleus, and a lighter input from the striatum. Nonauditory afferents to the preoptic area originate in the medial and lateral septal nuclei, medial pallium, and the dorsal-, lateral-, and ventral hypothalamus. The preoptic area and ventral hypothalamus are reciprocally connected.