Identification and localization of hormone‐producing cells in the pituitary of male Padogobius martensi(Pisces, Gobiidae): a histochemical and immunocytochemical study

Abstract

The adenohypophysial cell types of the adult male freshwater goby Padogobius martensi were identified and localized using histochemical and immunocytochemical techniques. Lactotropes were arranged in an irregular mass which occupied a major portion of the rostral pars distalis(RPD). Lead haematoxylin (PbH) stained the corticotropes selectively. These cells formed large clusters or islets between the neurohypophysial branches penetrating the RPD and the lactotropes. In addition, few isolated or clustered corticotropes were observed in the proximal pars distalis(PPD). Corticotropes showed a moderate immunoreactivity to synthetic anti‐human adrenocorticotropic hormone 1–24 but a strong immunoreactivity with antiserum to human α‐melanocyte‐stimulating hormone, which so far has not been observed in any other teleosts. Of the two mouse monoclonal antibodies to the human thyrotropin β subunit used, one failed to bind the thyrotropes, while the other stained selectively but very weakly cells in the dorsal‐anterior part of the proximal pars distalis(PPD) indicating that thyrotropes were probably located in this region. Somatotropes were arranged mainly in a multicellular layer bordering the neurohypophysial processes penetrating the PPD, but some were isolated throughout the PPD. The antiserum to rainbow trout Oncorhynchus mykiss gonadotropin I β subunit bound to gonadotropes located in the central and ventral part of the PPD, and along the external periphery of the pars intermedia(PI). The cells reacting to the antiserum to rainbow trout gonadotropin II β subunit largely showed the same distribution as gonadotropes I, but some were also found isolated or in small clusters between somatolactotropes and melanotropes at the interface PI/neurohypophysis (NH) and throughout the PI, as well as intermingled with thyrotropes in the dorsal‐anterior part of the PPD, and with lactotropes and corticotropes in the RPD. These results indicate the presence of two types of both gonadotropins and gonadotropes in P. martensi, but do not exclude some degree of gonadotropin I and gonadotropin II colocalization in the same cells. A distribution of gonadotropes II throughout the adenohypophysis similar to that found in P. martensi has not yet been observed in other teleosts; it suggests the possibility of local interactions between these cells and all the other adenohypophysial cell types. The PI contained somatolactotropes, which were distributed along the neurohypophysial border, and melanotropes which were arranged in clusters mostly located further away from the neural tissue. Melanotropes did not react to PbH and showed positive immunostaining to both anti‐human ACTH 1–24 and anti‐human α‐MSH.