Effect of photoperiod and melatonin administration on folliculostellate cells of viscacha pituitary pars distalis.

ACOSTA, MARIANO; MOHAMED, FABIAN

Ciudad de Mendoza, Mendoza, Argentina.

Congreso; XXVIII Reunión Anual de la Sociedad de Biología de Cuyo; 2010

Sociedad de Biología de Cuyo

Numerous reports have shown the effect of photoperiod and melatonin administration on the different hormone secreting cell types in the pituitary pars distalis. The viscacha (Lagostomus maximus maximus) is a rodent with photoperiod-dependent seasonal reproduction. The aim of this study was to examine the effect of photoperiod seasonal variations and melatonin administration on the folliculostellate cells (FSC) in pituitary pars distalis of adult male viscacha. Immunohistochemistry and image analysis were used to measure the percentage of S-100-positive area (total, cellular and colloidal) and the number of FSC. The S-100 protein was immunolocalized at intracellular (FSC) and extracellular (follicular colloid) levels. The morphometric parameters analyzed exhibited seasonal variations with highest values in the summer (long photoperiod) and lowest values in the winter (short photoperiod). The administration of melatonin provoked a significant decrease of immunostaining. Results suggest that the natural photoperiod, through melatonin, might be the most important environmental signal causing the decrease in FSC immunostaining observed in the winter. These findings agree with seasonal changes previously reported in endocrine cells and suggest that FSC may be involved in the paracrine regulation of the secretory activity of pituitary pars distalis through S-100 protein production.