Substance P and Luteinizing Hormone-Releasing Hormone Levels in the Brain of the Male Golden Hamster Are Both Altered by Castration and Testosterone Replacement

Publisher Website
Google Scholar
Abstract
The effects of castration and testosterone (T) replacement on levels of substance P (SP) and luteinizing hormone-releasing hormone (LHRH) were assessed in discrete areas of the male hamster brain. The animals were either castrated, castrated and given a chronically low or high dose of T by Silastic implant, or sham-operated. Brain tissues and trunk blood were collected 3 weeks after surgery. Plasma T levels were maintained within the normal range by the implants but at significantly lower or higher levels than the mean for sham-operated males. Levels of SP and LHRH were quantified in the olfactory bulbs, rostral basal forebrain, anterior hypothalamic and preoptic area, medial basal hypothalamic area and median eminence, and brain stem. In general, castration and T replacement effected opposite changes in levels of SP and LHRH. In the medial basal hypothalamic area and median eminence SP levels were found to be inversely related to the chronic T levels, whereas the LHRH levels were directly correlated. In the anterior hypothalamic and preoptic area, castration reduced levels of SP. Conversely, castration elevated levels of LHRH in this area. This inverse dynamic relationship between changing peptide levels was also observed in the rostral basal forebrain but not in the olfactory bulbs. In most of these forebrain regions, the dose-response curves for the experimental groups could not incorporate the peptide levels in the sham-operated control group. SP levels in the brain stem showed a monotonic inverse relationship to circulating T levels which did include the control group values. The results are consistent with hypotheses that LHRH expression and release in the basal forebrain and diencephalon may be partially regulated by SP-containing neuronal systems, and that variations in circulating T levels associated with episodic gonadotropin secretion are important for maintaining normal LHRH and SP levels in the forebrain.