DOUD, Andrea*; BOYD, Sunny K.; Univ. of Notre Dame; Univ. of Notre Dame: Location of AVT Target Neurons in the Amphibian Hindbrain

Arginine vasotocin (AVT), a behaviorally-active neuropeptide in the bullfrog (Rana catesbeiana), is found widespread across the central nervous system. This peptide specifically alters vocal behaviors in many frog species, and also in representatives from other vertebrate classes. Vocal behavior in frogs is controlled by central pattern generators and laryngeal motor nuclei in the brainstem. Although AVT-immunoreactive cells and fibers are found in these brain regions, whether the pattern generator or motor nuclei possess AVT receptors is not clear. We used a novel ligand, AVT conjugated to the fluorescent molecule Oregon Green (AVT-OG), to locate putative AVT target cells in the brainstem. Male bullfrogs were anesthetized in ice water and the brain was removed to artificial CSF. AVT-OG (80 ng) in 4 uL CSF was administered to the surface of the medulla for 30 minutes. The brain was then fixed, sectioned and examined for the appearance of fluorescent endosomes � indicating internalization of the ligand. AVT-OG fluorescence was observed throughout the rostro-caudal extent of the medulla. Neurons in caudal regions of the medulla, corresponding to the region of cranial nerves IX and X, were labeled with most consistency. Such neurons tended to be larger in size and grouped with several other similar labeled neurons. Double-label experiments are underway to determine if these cells are laryngeal motor neurons. AVT-OG internalization in the bullfrog medulla supports the hypothesis that hindbrain pattern generator and motor nuclei possess functional AVT receptors.