Response of Calcitonin-Gene-Related Peptide-Like Immunoreactive Nerve Fibers of the Anterior Pituitary to Adrenalectomy in the Rat

Abstract

The mammalian anterior pituitary is known to be regulated by humoral factors only, no direct neural influence having ever been discovered. Our recent studies have shown in several species that there are substantial amounts of substance P and calcitonin-gene-related peptide-like immunoreactive (CGRP-LI) nerve fibers in the anterior pituitary and that they can make synaptic contacts with secretory cells, among which corticotropes. In the present study, we investigated changes in CGRP-LI nerve fibers of the anterior pituitary after bilateral adrenalectomy in the rat. The results show that the number of CGRP-LI nerve fibers increases significantly. In parallel, they cover a wider area of the gland after the operation, suggesting a direct neural influence.

Evidence for axonal sprouting in the anterior pituitary following adrenalectomy in the rat

“…The increase in GAP-43-LI is much more prominent than the increase in CGRP-like immunoreactivity demonstrated pre¬ viously. In the case of the CGRP-LI study (Ju et al 1994) there was a 1-7-fold increase in the average area density of the nerve fibers following adrenalectomy, -whereas in the present case the increase was 37-fold. But CGRP-LI nerve fibers are not the only kind of nerve fibers present in the anterior pituitary.…”

“…(also known as B-50, F-l, pp.46 and neuromodulin) is a 24 kDa, nervous system-specific, membrane phospho¬ protein which has been implicated in axonal growth and synaptic remolding of the nervous system (Benowitz & Routtenberg 1987, Benowitz et al 1988, Skene 1989, Woolf eí al. 1990, Gispen et al 1991, Curtís et al 1992, Kruger et al 1993, Meberg et al 1993 (Ju et al 1994). The present study has demonstrated a very large increase in GAP-43-LI under the same conditions.…”

“…This has been further confirmed by the response of the nerve fibers to hormone manipulations. Following adrenalectomy, the number of the CGRP-LI nerve fibers in the anterior pituitary was found to increase significantly (Ju et al 1994). The increase in immunoreactive nerve fibers could be the result of an increase in the peptide content of the nerve fibers or may be due to an actual increase in the number of nerve fibers.…”

“…They have been found to be in close contact with the gland cells (Ju & Liu 19896,c), even to make synaptic contacts with them (Ju & Zhang 1990. Furthermore, Ju et al (1994) found that 4 days after adrenalectomy an increase in the number of calcitonin gene-related peptide (CGRP)-like immuno¬ reactive (LI) nerve fibers in the anterior pituitary was induced. A hypothesis of neural-humoral dual regulation of the anterior pituitary has thus been formulated (Ju et al 1991(Ju et al , 1994.…”

“…The aforementioned increase of CGRP-LI nerve fibers in the anterior pituitary following adrenalectomy (Ju et al 1994) could be the result of an increase in the peptide content in the unstained pre-existing nerve fibers so as to render them detectable immunohistochemically, or it could be due to axonal sprouting which resulted in an actual increase in the number of the nerve fibers. To examine the latter possibility we studied the change in expression of the neuronal growth-associated protein GAP-43 in the anterior pituitary following adrenalectomy in the rat immunohistochemically.…”