Cytochemical identification of endocrine thymus of chicken in relation to aging

Age related cytochemical changes of thymic endocrine cells were studied in 78 day old chicks at five day interval to age of day 60 employing a panel of cytochemical stains. Methenamine silver revealed cell morphology including cell processes distinctly while diamine silver revealed a stronger argentaffinity in these cells. The cells had greater affinity for diamine silver compared to methenamine silver (Argentaffin), followed by formaldehyde induced auto-fluorescence, argyrophilia, lead hematoxylin and HCl-toluidine. The chromaffin reaction was the weakest. Cytochemically, three different endocrine cell populations i.e. argentaffin cells, argyrophilic cells and amine precursor uptake and decarboxylation series (APUD)/chromaffin cells, formed the resident population of thymic endocrine cells. Occurrence of numerous serotonin storing cells, moderately frequent APUD cells, and fewer chromaffin as well as mast cells suggests for a conspicuous reservoir of amine storing cells in thymus. Morphologically argentaffin cells were of four types i.e. the peripherally granulated spherical cells (Type-I), densely granulated oval cells (Type-II), pyramidal argentaffin cells (Type-III) and diffusely granulated elongated cells (Type-IV). The type-II argentaffin cells were most frequent in the medulla followed by the type-I cells and the type-III cells. The type-IV cells were least in frequency. The age related changes in frequency of these cells are also discussed.