Electron microscopic observation of substance P-like immunoreactive nerve fibres and innervation in the anterior pituitary of macaques

Evidence for nodose ganglion as the source of innervation to the anterior lobe of the pituitary gland

Recent studies have provided convincing evidence for the presence of peptidergic nerve fibers in the pituitary anterior lobe in several animal species. This study was aimed at elucidating the origin of this innervation by neuroanatomical tracing, denervation experiments, and immunohistochemistry. Immunohistochemistry against substance P and growth-associated protein 43 revealed a dense fiber plexus within the anterior lobe, and these markers were mostly colocalized. Retrograde tracing with Fluorogold from the pituitary gland stained neurons in the hypothalamus, superior cervical ganglia and the nodose ganglia. None of the Fluorogold-labelled neurons in the hypothalamus or superior cervical ganglion were substance P-immunoreactive, while many of the neuronal cell bodies in the nodose ganglion exhibited substance P immunoreactivity. There were no Fluorogold-labelled neurons in the trigeminal, otic or cervical dorsal root ganglia. Surgical transection of the pituitary stalk or bilateral removal of the superior cervical ganglion did not abolish the anterior lobe nerve fibers, and anterograde tracing with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate from the pituitary stalk failed to stain any nerve fibers within the anterior lobe. Our findings suggest that the nodose ganglion neurons likely innervate the pituitary anterior lobe, while neither hypothalamus nor sympathetic superior cervical ganglion may be a source of this innervation. By showing a distinct neuronal system in the pituitary anterior lobe our findings (i) support the previous functional studies demonstrating a distinct regulation of the morphology of the anterior lobe innervation by hormonal changes, and (ii) suggest that the innervation of the pituitary anterior lobe is a part of the visceral innervation by the vagus nerve rather than a part of the other intracranial innervation. These findings provide a neuroanatomic basis for the reported observations about the neural regulation of the pituitary anterior lobe.

Galanin immunoreactive innervations of the anterior pituitary in the monkey and the dog

As we know, the anterior pituitary is regulated by hypothalamic hormones via the portal system. However, our recent studies have demonstrated the presence of a substantial amount of substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing nerve fibers in the anterior pituitary. In the present paper, the existence of a considerable amount of galanin (GAL)like immunoreactive (ir) nerve fibers with numerous of varicosities in the anterior pituitaries of the Macaca mulatta monkey and the dog were reported. In the monkey, GAL-ir nerve fibers with a large amount of varicosities were mainly located in the medial part of the gland, dominantly in its dorso-posterior regions. A great majority of varicosities were found to be closely related to the glandular tissue although some were located along the walls of blood sinus. GAL-ir nerve fibers were traced to enter the pars distalis of the anterior pituitary from the stalk as well as from the meningeal sheath covering the upper part of the anterior pituitary. Numerous GAL-ir cells presented in the pars distalis and the pars intermedia of the adenohypophysis. In the dog pituitary, GAL-ir nerve fibers were mainly located in the tail part and some in oral region. A majority of GAL-ir nerve fibers were at the periphery of the gland, especially in the medial planes, although some could be found deep in the gland. They appeared in individual fibers or in patches. Many GAL-ir nerve fibers and fiber fascicles existed in the median eminence and the sheath covering the tail and the oral part of the pituitary.

The relationship of galanin immunoreactive nerve fibers to glandular cells in the anterior pituitary in the monkey

The anterior pituitary is known to be regulated by hypothalamic hormones via the portal system. However, our recent studies have demonstrated the presence of a substantial amount of substance P (SP)-, calcitonin gene-related peptide (CGRP)- and galanin (GAL)- immunoreactive (ir) nerve fibers with numerous varicosities in the anterior pituitaries of the Macaca mulatta monkey. The present study investigated the relationship of the GAL-ir nerve fibers to the glandular cells. The M. mulatta monkeys were used and sections of the anterior pituitary were double immunostained. GAL-ir nerve fibers and/or varicosities were found in proximity to contact directly with corticotropes, somatotropes, lactotropes, gonadotropes and thyrotropes without any exception. These findings indicate that a direct neural factor may be involved in the regulation of adenohypophyseal secretion.