Light and electron microscopic studies on the pars intermedia of the chameleon

The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200-600 nm; (2) light cells, far fewer in number, containing granules 150-300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.