Seasonal plasticity of the pituitary pars intermedia of the one-humped camel (Camelus dromedarius).

The pituitary pars intermedia of Camelus dromedarius is well developed and completely surrounds the pars nervosa. Two major groups of cells are present: endocrine (ec) and glial-like cells (glc). The ec group is composed of three morphologically distinct cell types. Type I, or polyhedral light cells (LC-I) and type II, or polyhedral dark cells (DC-II), have secretory granules of heterogeneous electron density whose size ranges from 170 to 300nm. Type III cells are elongated with homogeneous electron-dense secretory granules of 80-200nm. The glc make up an organized network, form follicles in the centrolobular zones and are positive for vimentin and S-100ß immunolabelling. The nerve fibres penetrating the lobe are numerous, and can be classified into two types according to the membrane bound vesicles found in their endings (ne). Ultrastructural quantitative analysis revealed significant variations in PI elements between winter and summer seasons (F=8.014, p=0.006). DC-II cells characterized by developed biosynthetic machinery and a large pool of secretory granules storage are increased with the ne in winter. However, LC-I cells showing frequent cytoplasmic degranulation are predominant with glc in summer. Thus, important cellular remodelling occurs in the dromedary PI that may depend upon, or perhaps anticipate, external living conditions.

Components of the basal lamina and dystrophin-dystroglycan complex in the neurointermediate lobe of rat pituitary gland: different localizations of beta-dystroglycan, dystrobrevins, alpha1-syntrophin, and aquaporin-4.

The so-called neurointermediate lobe is composed of the intermediate and neural lobes of the pituitary. The present immunohistochemical study investigated components of the basal lamina (laminin, agrin, and perlecan), the dystrophin-dystroglycan complex (dystrophin, beta-dystroglycan, alpha1-dystrobrevin, beta-dystrobrevin, utrophin, and alpha1-syntrophin), and the aquaporins (aquaporin-4 and -9). Glia markers (GFAP, S100, and glutamine synthetase) and components of connective tissue (collagen type I and fibronectin) were also labeled. In the neurohypophysis, immunostaining of basal lamina delineated meningeal invaginations. In these invaginations, vessels were seen to penetrate the organ without submerging into its parenchyma. On the parenchymal side of the invaginations, beta-dystroglycan was detected, whereas utrophin was detected in the walls of vessels. Immunostaining of alpha1-dystrobrevin and alpha1-syntrophin did not delineate the vessels. The cells of the intermediate lobe were fully immunoreactive to alpha1-dystrobrevin and alpha1-syntrophin, whereas components of the basal lamina delineated the contours of the cells. GFAP-immunoreactive processes surrounded them. Aquaporin-4 localized at the periphery of the neurohypophysis, mainly adjacent to the intermediate lobe but not along the vessels. It colocalized only partially with GFAP and not at all with alpha1-syntrophin. Aquaporin-9 was not detected. These results emphasize the possibility that the components of the dystrophin-dystroglycan complex localize differently and raise the question about the roles of dystrobrevins, alpha1-syntrophin, and aquaporin-4 in the functions of the intermediate and neural lobes, respectively.

Transgene expression of prion protein induces crinophagy in intermediate pituitary cells.

The cellular form of the prion protein (PrP(C)) is a plasma membrane-anchored glycoprotein whose physiological function is poorly understood. Here we report the effect of transgene expression of Xenopus PrP(C) fused to the C-terminus of the green fluorescent protein (GFP-PrP(C)) specifically in the neuroendocrine intermediate pituitary melanotrope cells of Xenopus laevis. In the transgenic melanotrope cells, the level of the prohormone proopiomelanocortin (POMC) in the secretory pathway was reduced when the cells were (i) exposed for a relatively long time to the transgene product (by physiologically inducing transgene expression), (ii) metabolically stressed, or (iii) forced to produce unfolded POMC. Intriguingly, although the overall ultrastructure was normal, electron microscopy revealed the induction of lysosomes taking up POMC secretory granules (crinophagy) in the transgenic melanotrope cells, likely causing the reduced POMC levels. Together, our results indicate that in neuroendocrine cells transgene expression of PrP(C) affects the functioning of the secretory pathway and induces crinophagy.

Possible involvement of brain-derived neurotrophic factor (BDNF) in the innervation of dopaminergic neurons from the rat periventricular nucleus to the pars intermedia.

Developing neurons are guided to their appropriate targets by specific guidance substances that have neurotrophic actions. The aim of the present study was to elucidate the mechanism by which hypothalamic neurons reach the pars intermedia (PI) by correlating the development of dopaminergic (DA) neurons arising in the periventricular nucleus (PeV) of fetal rats with the expression of brain-derived neurotrophic factor (BDNF) in the rat pituitary. The differentiation of DA neurons was observed by immunohistochemistry using an antibody against tyrosine hydroxylase (TH), whereas the ontogenesis of BDNF mRNA in the PI was examined by in situ hybridization and RT-PCR. Immunoreactive TH-neurons were first observed in the PeV at embryonic day (E) 16.5, following which time their axons elongated toward the pituitary. TH-positive reactions were observed in the connective tissue between the PI and the pars nervosa at E20.5. Innervation of the PI by TH-positive neurons was determined at postnatal day (P) 1.5; however, BDNF mRNA was first detected in the PI cells at E17.5, with an increase in its expression clearly visible at E21.5 and continuing high expression levels in the PI thereafter. These results suggest that BDNF is a specific guidance cue for DA neurons elongating from the PeV to the PI.