Ultrastructural immunocytochemical localization of luteinizing hormone-releasing hormone (LH-RH) in the median eminence of the guinea pig

Abstract

LH-RH was localized at the ultrastructural level in axons and nerve terminals of the median eminence of the male guinea pig. LH-RH positive neuronal profiles were most concentrated in the medial-dorsal aspect of the infundibular stalk and in the post-infundibular median eminence at the level immediately following separation of the stalk from the base of the brain. LH-RH containing axon profiles were most abundant in the palisade zone; nerve terminals in contact with the hypophysial portal vasculature were relatively rare. The hormone was present within granules that measured 900-1,200 A in axons of the palisade zone and 400-800 A in nerve terminals abutting on the portal plexus. The differently sized granules represent heterogeneous populations.

Light and Electron Microscopic Immunocytochemical Evidence that Delta Sleep-Inducing Peptide and Gonadotropin-Releasing Hormone Are Coexpressed in the Same Nerve Structures in the Guinea Pig Median Eminence

“…The distributing feature of DSIP-positive axons in apposi tion to tanycyte was very similar to serotonin-containing and GnRH-containing axons and terminals in the median eminence [29][30][31]. It has recently been noted that the median eminence is not only the site of the release of the hypophysiotropic factors into the portal capillary, it can also play an important role in modifying the hypothalamic regulation of pituitary hormones [32], Furthennore, it has been shown that besides its effect on LH release, in the rat DSIP may also influence secretion of so matostatin [10] and sleep-related growth hormone [II] at the level of median eminence possible via dopaminergic receptors.…”

Effect of Castration and Steroid Replacement on Immunoreactive Gonadotropin-Releasing Hormone in the Hypothalamus and Preoptic Area*

“…The present immunocytochemical study suggests that both the number of detectable GnRH-containing axons and nerve endings as well as the amount of GnRH in the remaining immunoreactive processes are reduced after removal of the negative feedback action of gonadal steroids. Based on the ultrastructural localization of GnRH in neurosecretory granules within axons and nerve endings (28,29), this decreased immunoreactivity could be due to a depletion of such intraneuronal granules after castration. It is important to note that the effect of castration on immunoreactive GnRH was most obvious at the level of the postinfundibular median eminence, especially in the mouse.…”

Ultrastructure of gonadotropin-releasing hormone neuronal structures derived from normal fetal preoptic area and transplanted into hypogonadal mutant (hpg) mice

“…However, if grafts are placed within the lateral ventricle, then GnRH fibers that exit into the host find other appropriate pathways (i.e., stria terminalis and fomix), though arrival at other targets (i.e., medial amygdala ) has not yet been demonstrated (Kokoris et al, 1984). As in normal animals (Goldsmith and Ganong, 1975;Silverman and Desnoyers, 1976), few neurosecretory terminals abut directly on the capillaries but rather are separated from them by glial processes of varying width. Whether movement of glial processes during times of increased release occurs in this system as it does in the posterior pituitary (Hatton et al, 1984) has not yet been studied.…”