Fluorescent Vasotocin Conjugate for Identification of the Target Cells for Brain Actions of Vasotocin

The effects of neuropeptides on the brain are a major focus of neuroendocrine research, and little progress has been made in the identification of the target neurons for many neuropeptides. Arginine8-vasotocin (AVT) is a neurohypophyseal peptide present in nonmammalian vertebrates that controls many neural and behavioral functions. Here we describe synthesis and functional characterization of an AVT-Oregon green conjugate 1 (AVT−OG 1) that can be used in vivo to identify AVT target neurons. Application of AVT−OG 1 to the brainstem of an amphibian produces rapid, endosome-like internalization together with typical AVT-like neurophysiological effects. Thus, preparation of AVT−OG 1, which preserves the peptide's neurophysiological effects, is useful as a fluorescent marker for AVT target neurons. Consequently, AVT−OG 1 conjugate will have considerable utility for analyzing the neural actions of AVT in the intact brain.