Intercellular Communication Within the Rat Anterior Pituitary: XIV Electron Microscopic and Immunohistochemical Study on the Relationship Between the Agranular Cells and GnRH Neurons in the Dorsal Pars Tuberalis of the Pituitary Gland

Abstract

Although numerous investigators in 1970s to 1980s have reported the distribution of LH-RH nerve fibers in the median eminence, a few LH-RH fibers have been shown to be present in the pars tuberalis. The significance of the finding remains to be elucidated, and there are few studies on the distribution of LH-RH neurons in the pars tuberalis, especially in the dorsal pars tuberalis (DPT). Adult male Wistar-Imamichi rats were separated into two groups: one for electron microscopy and the other for immunohistochemistry to observe LH-RH and neurofilaments. Pituitary glands attached to the brain were fixed by perfusion, and the sections were prepared parallel to the sagittal plane. The typical glandular structure of the pars tuberalis was evident beneath the bottom floor of the third ventricle, and the thick glandular structure was present in the foremost region. Closer to the anterior lobe, the glandular structure changed to be a thin layer, and it was again observed at the posterior portion. Then the pituitary stalk was surrounded with the dorsal, lateral, and ventral pars tuberalis. LH-RH and neurofilaments fibers were noted in the bottom floor, and some of them vertically descended to the gland. Adjacent to the glandular folliculostellate cells in the pars tuberalis, Herring bodies with numerous dense granules invading into the gland were present between the pituitary stalk and DPT. It was postulated that the ''message'' carried by LH-RH might have been transmitted to the cells in the DPT to aid in the modulation of LH release.

Immunohistochemistry of connexin 43 throughout anterior pituitary gland in a transgenic rat with green fluorescent protein-expressing folliculo-stellate cells

“…2), suggesting that FS cells were interconnected by GJ throughout the anterior pituitary gland. This histological observation is consistent with the hypothesis of Soji's group that the network system of interconnected FS cells through GJ modulates hormone release in the anterior pituitary gland, as summarized in their recent report (Shirasawa et al ., 2007). Furthermore, we detected two patterns of immunoreactive connexin 43 in the anterior pituitary gland, mainly on cell bodies in the pars tuberalis and transitional zone, and on cytoplasmic processes in the pars distalis (Fig.…”

“…Finally, the present in vivo and in vitro findings support the Soji hypothesis, which proposed a novel signal transmission mechanism via networked FS cells in the anterior pituitary gland (Shirasawa et al ., 2007). Utilizing the primary culture of anterior pituitary cells from S100b‐GFP rat, we are now conducting further studies on the FS cell network and the actions of FS cells on hormone‐producing cells.…”

“…(1975) first reported the presence of gap junctions (GJ) in the anterior pituitary gland, and Soji and Herbert (1989) determined that these junctions exist specifically between FS cells. Furthermore, based on recent morphological and electrophysiological studies, Soji's group has proposed a new theory on the function of FS cells by which FS cells interconnected via GJ form a network from the pars tuberalis through the pars distalis, to transmit signals regulating hormone release from hormone‐producing cells in addition to the established hypophyseal–portal vein system (Shirasawa et al ., 2007). But the network of FS cells with GJ throughout the anterior pituitary gland has not been confirmed.…”

Histological characterization of gonadotropin-releasing hormone (GnRH) in the hypothalamus of the South American plains vizcacha (Lagostomus maximus)

“…However, it is worth to note that the forebrain cortex of L. maximus shows more pronounced gyrus or folds than the brains of the above mentioned rodents including the hystricognatha long-tailed chinchilla, its closest evolutionary relative (Jackson et al 1996;Weir 1970). GnRH localization has been described in the hypothalamus of mouse, rat, guinea pig, lamb and other mammals, by light and electron microscopy (Silverman et al 1985(Silverman et al , 1987(Silverman et al , 1990Shirasawa et al 2007;Yin et al 2007). Here we observed GnRH expression at both hypothalamus and placenta-to-term in the vizcacha.…”

Involvement of the adrenal glands and testis in gap junction formation via testosterone within the male rat anterior pituitary gland

“…Folliculo‐stellate cells are coupled by gap junctions in normal mature rats and extend slender, cytoplasmic processes among the hormone‐producing granular cells to form a cell network throughout the anterior pituitary gland (Horiguchi et al,2011; Inoue et al,1999; Sakuma et al,2001; Shirasawa et al,2004, 2007; Soji and Herbert,1990; Yamamoto et al,1993). These junctions are composed of transmembrane channels allowing the free transcellular exchange of small cytoplasmic molecules such as ions, amino acids, sugars, and several second messengers including inositol 1,4,5‐triphosphate (Kumar and Gilula,1996; Loewenstein,1981; Spray,1994; Wolburg and Rohlmann,1995).…”