Distribution of PRL, GH, TSH and ACTH cells in the pituitary distal lobe of pre‐ and prometamorphic Bufo viridis larvae

Abstract

The differentiation and topographical localization of prolactin (PRL), growth hormone (GH), thyrotropin (TSH), and adrenocorti‐cotropic hormone (ACTH) cells were studied, using immunohisto‐chemical techniques, in Bufo viridis larval pituitary at different developmental stages, i.e., the beginning of premetamorphosis, the beginning of prometamorphosis, and mid‐prometamorphosis. The four cell types are distributed in different areas of the distal lobe. PRL cells mainly occur in the anterior half, while GH cells are mostly localized in the posterior half, ACTH cells in the dorsoros‐tral area, and TSH cells in the ventrorostral one. This distribution is maintained, without significant changes, during development. All the different cell types undergo a relevant increase in their cell number during premetamorphosis; in particular, TSH cells are very few at the beginning of premetamorphosis, being the least abundant cell population, but become well represented at the end of it. On the other hand, GH cells are the most numerous cell population, both during pre‐ and prometamorphosis. Finally, our observations indicate that the pituitary intermediate lobe is already well differentiated and distinct from the pars distalis at the beginning of premetamorphosis.