Distribution and characterization of endozepine-like immunoreactivity in the central nervous system of the frog Rana ridibunda.

The localization of endozepine-like immunoreactivity in the brain of the frog Rana ridibunda was investigated by indirect immunofluorescence, using an antiserum against synthetic rat octadecaneuropeptide (ODN). A specific immunoreaction was detected in ependymal cells lining the ventricular system of the brain and in circumventricular organs. Numerous immunoreactive cells were found covering the walls of the lateral ventricles in the telencephalon, as well as in the diencephalic and mesencephalic ventricles. In the hypothalamus, both the preoptic nucleus and the infundibular region showed numerous immunopositive cells. Ependymal cells lining the rhomboencephalic fourth ventricle and the central canal of the spinal cord were also immunoreactive. The concentration of endozepine-like immunoreactivity was measured in various regions of the brain using a sensitive and specific radioimmunoassay for rat ODN. The highest levels of ODN-like immunoreactivity were found in the infundibulum, cerebellum and preoptic area. Reverse phase high performance liquid chromatography and radioimmunoassay quantification were used to characterize endozepines in the frog brain. The elution profiles of the different brain regions revealed four major immunoreactive peaks. The present results demonstrate the presence of peptides immunologically related to the endozepine family in the central nervous system of the frog. The localization of immunoreactive endozepines in ependymal cells suggests that these peptides play important neuromodulatory functions in the amphibian brain.