Immunocytochemical localization of vasoactive intestinal polypeptide (VIP) in the brain of the little brown bat (Myotis lucifugus).

Vasoactive intestinal polypeptide (VIP)-like immunoreactivity has been examined in the brain of the little brown bat, Myotis lucifugus, using light microscopic immunocytochemistry and the indirect antibody enzyme method of Sternberger. Animals were sacrificed at three different and discrete levels of physiological activity: euthermic, hypothermic and hibernating. The density and distribution of immunoreactive neurons and fibres was compared in the three animal groups with the aid of a computerized image analysis system. Our results were compared with those of previous studies in laboratory species such as the rat and cat. Our study has demonstrated marked changes in the density of VIP-immunoreactive fibres and plexuses in the anterior hypothalamic area which correspond to the physiological state of the animal. In addition we have demonstrated the presence of VIP immunoreactive perikarya in a number of previously unreported locations. These include the paraventricular and periventricular hypothalamic nuclei, the linear raphe nucleus, nucleus interfascicularis, and in neurons embedded in the fibres of the dorsal tegmental decussation.