Somatostatin in the rat periventricular nucleus: sex differences and effect of gonadal steroids

Abstract

In the rat, the sexual dimorphism in growth hormone release is driven by sex steroids, and is suggested to result mainly from differences in somatostatin (SOM) release patterns from the median eminence. We studied the effect of gonadal steroids on SOM peptide-containing cells in the periventricular nucleus (PeVN) of ovariectomized (OVX) female rats, and compared these data with data from intact male rats. Adult female rats were treated with estradiol (E2) and/or progesterone (P), 3 months (long-term) or 2 weeks (short-term) after ovariectomy (OVX). Perfusion-fixed brains were sliced and stained, and the number of SOM-immunoreactive (-ir) cells and total SOM-ir area (in μm2) were determined using computer assisted analysis. SOM-ir cells in the PeVN showed a very characteristic rostro-caudal distribution and localization in relation to the third ventricle. Both the number of SOM-ir cells and total SOM-ir area in the PeVN were higher in male compared to OVX female rats. Neither the number of SOM-ir cells, nor the total SOM-ir area in the PeVN was affected by E2 or P treatment alone. Treatment with both gonadal steroids, however, did increase total SOM-immunoreactivity. This study is the first to describe SOM cell distribution within the rat PeVN in great detail. A clear sex difference exists in SOM peptide content in the rat PeVN. In addition, E2 and P may act synergistically to affect SOM cells in the female PeVN, suggesting that both gonadal steroids may be involved in the generation of the typical feminine SOM release pattern.

Somatostatin in the Periventricular Nucleus of the Female Rat: Age Specific Effects of Estrogen and Onset of Reproductive Aging

“…Estrogen did not affect total numbers of SOM-ir cells in the PeVN of young female rats in line with our previous studies (Van Vugt et al, 2008) and those of others (Estupina et al, 1996). Other studies reported a decrease in SOM mRNA content in the PeVN following OVX which was reversed by E 2 treatment Zorilla et al, 1991).…”

“…at ZT5 and ZT 11. Brains sections were stained for SOM peptide as described previously (Van Vugt et al, 2008).…”

“…The brains were processed for SOM immunocytochemistry as described in detail previously (Van der Beek et al, 1991;Van Vugt et al, 2008). Staining was performed in two separate runs (4.5 and 9 mo) and intra-assay variation was controlled for by including a group of young animals at 2 and 32 h after E 2 treatment in the second run.…”

“…For staining, primary polyclonal rabbit antibody raised against SOM peptide (Somaar 080289, NIN, Amsterdam, NL) (Buijs et al, 1989) was used followed by detection with biotinylated goat anti-rabbit IgG and Avidin-Biotin Complexelite (ABC; Vector Laboratories). SOM-immunoreactive (-ir) neurons in the PeVN of the left side of the brain were counted using computer assisted analysis as described previously (Van Vugt et al, 2008). In addition to counting SOM-ir cells, also the amount/quantity of SOM-ir fibers (expressed in µm 2 ) was measured in these images in the young females only.…”

“…Recent studies demonstrated a clear sex difference in the number and distribution of SOM peptide containing cells in the PEVN. In the female numbers were affected by ovariectomy and gonadal steroid treatment (Van Vugt et al, 2008). During the early phase of reproductive aging, normal (or even elevated) levels of plasma estradiol (E 2 ), are correlated with a decline in somatotropic axis activity (Chandrashekar and Bartke, 1993;Vom Saal et al, 1994;Wilshire et al, 1995).…”