Sexual dimorphism of growth hormone in the hypothalamus: regulation by estradiol

Abstract

GH is best known as an anterior pituitary hormone fundamental in regulating growth, differentiation, and metabolism. GH peptide and mRNA are also present in brain, in which their functions are less well known. Here we describe the distribution of GH neurons and fibers and sex differences in Gh mRNA in adult mouse brain. Cell bodies exhibiting GH immunoreactivity are distributed in many brain regions, particularly in the hypothalamus in which retrograde labeling suggests that some of these cells project to the median eminence. To determine whether Gh mRNA is sexual dimorphic, we carried out quantitative RT-PCR on microdissected brain nuclei. Ovary-intact mice had elevated Gh mRNA in the arcuate nucleus and medial preoptic area (MPOA) compared with gonad-intact males. In males, castration increased Gh mRNA in the MPOA, whereas ovariectomy decreased Gh mRNA in both regions. When gonadectomized adults of both sexes were treated with estradiol Gh mRNA increased in females but had no effect in castrated males. Tamoxifen was able to blunt the rise in Gh mRNA in response to estradiol in females. In addition, we found that estrogen receptor-α is coexpressed in GH neurons in the MPOA and arcuate nucleus. In summary, the findings reveal sexual dimorphisms in Gh gene expression in areas of the brain associated with reproduction and behavior. Interestingly, estradiol enhances Gh mRNA in females only, suggesting that multiple factors orchestrate this sexual dimorphism.

Fig. 1.

Representative photomicrographs of GH-IR staining in VP (A), ARC (B), ME (C), and MPOA (D). Scale bar (A, C, and D), 50 μm, scale bar (B), 100 μm and in box insert, scale bar, 20 μm. ac, Anterior commissure; opt, optic chiasm; 3v, third ventricle.

Fig. 2.

Confocal image of GH neurons in the VP. GH-IR was labeled green, and DAPI, a neuronal nucleus marker, was labeled blue, whereas DiI fluoresces red. Filled arrows indicate colocalization of GH, DAPI, and DiI, whereas open arrows indicate colocalization of DiI and DAPI only. A, GH, DAPI, and DiI colocalization in neurons within the VP (scale bar, 20 μm). B, High-magnification image of the white box in A showing a ±15 μm diameter GH neuron exhibiting DiI and DAPI colocalization (scale bar, 10 μm).

Fig. 3.

Sections dual labeled for ERα and GH. A, ARC showing GH cytoplasmic label (brown) and ERα in the nucleus (black) (scale bar, 50 μm). B, Magnified version of the area within the black box in A: closed arrows indicate colocalization between GH and ERα, whereas open arrows indicate cells labeled for ERα only, and arrowheads indicate cell labeled for GH only (scale bar, 20 μm). C, MPOA showing GH and ERα labeling (scale bar, 50 μm). D, Magnified version of the area within the black box in C showing colocalization between ERα and GH cells of the MPOA (scale bar, 10 μm). opt, Optic chiasm.

Fig. 4.

Influence of sex and gonadal hormones on Gh mRNA expression (mean ± sem) in the MPOA and ARC. Gh mRNA expression MPOA (A, C, and E) and ARC (B, D, and F). In A and B, GDX and gonad males and females were compared. In C and D, GDX males and females implanted with EB (21) or empty implants for 7 d were examined. In E and F, we examined the combined effects of the ER antagonist tamoxifen (38) and EB on Gh mRNA in females only. *, Significantly different from ovary-intact females (A and B), GDX + EB females (C and D), and OVX + EB (E) P < 0.05, #, Significantly different from GDX males (P < 0.05).