NPY up-regulation in the tadpole brain of Euphlyctis cyanophlyctis during osmotic stress

Most of the amphibians breed in temporary ponds vulnerable to occasional desiccation, thus, leaving their larvae exposed to stressful fluctuations in various environmental parameters including salinity. These animals possess a well suited central adaptive mechanism to adapt to these alterations. Neuropeptide Y (NPY), a 36 amino acid neurotransmitter, has been reported to antagonize various neuropsychological consequences of stress within the mammalian brain. Osmotic regulation of NPY in the hypothalamo-neurohypophysial pathway of mammalian brain is also known. Although the molecule possesses an extensive distribution in the brain of amphibians, its functional association is not well understood. We have investigated the endogenous response of NPY-ergic system to osmotically stressful conditions in the brain of Indian skipper frog-Euphlyctis cyanophlyctis tadpoles. Using Immunohistochemistry, we observed an up-regulation of NPY immunoreactivity (NPY-ir) in the brain of tadpoles exposed to stressful salt concentrations. A significant increase of NPY-ir occurred in the pallium and septum regions of telencephalon; preoptic area, epithalamic, thalamic and hypothalamic parts of diencephalon. Most of the regions are implicated in the modulation of stress and anxiety related brain functions and have also been shown to respond to the salinity stress in mammals. In addition, NPY producing neurons in pre-optic and hypothalamic parts show a close co-existence with the vasopressin-ergic neurons. Thus, our study suggests a possible role of NPY in stabilizing the neuro-endocrinological consequences of osmotic stress in an amphibian brain.