Intercellular Communication within the Rat Anterior Pituitary: Immunohistochemical Study on the Relationship between the Hypothalamus, Agranular Cells and GnRH Neurons in the Pars Tuberalis and Anterior Pituitary Gland

Abstract

The pars tuberalis has been generally understood as a simple forward elongation of the glandular pituitary that develops into an architecturally similar structure. In rats, it is also believed that the pars tuberalis completely encircles the infundibular stalk at the ventral portion of hypothalamus. Intact Wistar-Imamichi rats were used in the present study, and frontal and sagittal serial sections of the pituitary gland/brain complex were prepared. Serial sections were stained with hematoxylin-eosin and with antibodies to LH-RH, S-100 protein or LH-RH receptor. Electron microscopic analyses were also conducted. The anatomical end of the epithelial structure of the pars tuberalis was observed at approximately 1 mm behind the optic chiasm. At this point, both the capillaries and the pars tuberalis spread and interdigitated over the median eminence. The pars tuberalis did not, however, completely encircle the pituitary stalk. Electron microscopic observations revealed some profiles of neuroendocrine nerve elements that were also present between the agranular cells of the pars tuberalis. A few LH-RHpositive nerve fibers were initially found just behind the optic chiasm, while the number of LH-RH-positive reactions increased around the capillary vessels. These reactions then decreased significantly and were sparsely distributed both in the diencephalon and in the area near the pituitary stalk where the two separated. LH-RH receptors were observed on S-100 protein-positive cells in the pars tuberalis. The present observations show the significance of the pars tuberalis and its relationship between the anterior pituitary gland and the hypothalamus as organs that possibly form another collaborating mechanism for the regulation of hormone secretion of the anterior pituitary gland.

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

“…There are numerous reports describing localization, morphological characteristics, gene expression, and/or regulation to the gonadal–pituitary axis of LH‐RH and LH‐RH neurons (Barry and Carette, 1975; Naik, 1975a, b; Setalo et al, 1975; Siverman and Krey, 1978; Ibata et al, 1979; Rethelyi et al, 1981; Kelly et al, 1985; Foster and Youngai, 1991; Nakazawa et al, 1991; Oka and Ichikawa, 1992; D'Este et al, 2000; Yanagisono et al, 2001; Mabuchi et al, 2004; Kurita et al, 2004). Oka and Ichikawa (1992) reported the nonsynaptic release of LH‐RH in fresh fish brain.…”

“…Oka and Ichikawa (1992) reported the nonsynaptic release of LH‐RH in fresh fish brain. Only few reports, however, referred to the existence of LH‐RH–positive nerves in the pars tuberalis (Naik, 1975a; Yanagisono et al, 2001; Mabuchi et al, 2004; Kurita et al, 2004). Of these, only Kurita et al (2004) and Mabuchi et al (2004) found by electron microscopy direct entry of the neuroendocrine fiber into the pars tuberalis of pituitary gland.…”

“…Only few reports, however, referred to the existence of LH‐RH–positive nerves in the pars tuberalis (Naik, 1975a; Yanagisono et al, 2001; Mabuchi et al, 2004; Kurita et al, 2004). Of these, only Kurita et al (2004) and Mabuchi et al (2004) found by electron microscopy direct entry of the neuroendocrine fiber into the pars tuberalis of pituitary gland. Although almost all authors pointed to a relationship between LH‐RH fibers and ependymal cell layers or the tanycytes of the third ventricle, only Naik (1975a), Yanagisono et al (2001), and Kurita et al (2004) referred to LH‐RH immunoreactivity in the pars tuberalis.…”

“…For convenience of explanation, the hypothalamotuberal region was tentatively named as follows. The pars tuberalis incompletely encircled the pituitary stalk (Kurita et al, 2004). And therefore, it consisted of the following three parts: a basal part, both lateral parts, and two dorsal parts as shown in Figure 1.…”

An In Vivo and In Vitro Immunohistochemical Study of Integrin Alpha Subunit Localization in the Rat Anterior Pituitary

“…The cells construct unique topography caused by homologous and heterologous interactions between cell types and between cells and extracellular matrix [7,11,12]. Junctional complexes have been identified among folliculo-stellate cells [10,18]. On the other hand, observations of the intercellular space among hormone-producing cells have very rarely indicated the presence of desmosomes among prolactin-producing cells [17].…”