Seasonal ovarian immunolocalization of neuropeptide Y and its role in steriodogenesis in Asian catfish, Clarias batrachus

The present study was undertaken to examine the cellular localization and potential steroidogenic role of neuropeptide Y (NPY) in the ovary of the freshwater catfish, Clarias batrachus. NPY-immunoreaction was observed in the follicular cells (granulosa and thecal cells) in the growing ovarian follicles, and the intensity of staining increased steadily from the initiation of follicular development until follicles were fully grown. Thereafter as follicles matured the stain intensity decreased. Positive correlations were found between NPY expression and the ovarian levels of 17β-estradiol, testosterone, and activities of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) in the ovary. In vitro NPY treatment stimulated the production of the two steroids and the activities of two enzymes. This is the first report of NPY immunoreactivity at the cellular level in the fish ovary and implicates this orexigenic peptide in the modulation of ovarian steroidogenesis.