J. Kamegai et al., Estrogen receptor (ER)alpha, but not ER beta, gene is expressed in growth hormone-releasing hormone neurons of the male rat hypothalamus, ENDOCRINOL, 142(2), 2001, pp. 538-543
GH synthesis and release from pituitary somatotropes is controlled by the o
pposing actions of the hypothalamic neuropeptides, GH-releasing hormone (GH
RH), and somatostatin (SS). There is a striking sex difference in the patte
rn of GH secretion in rats. Early reports indicate that gonadal steroids ha
ve important imprinting effects during the neonatal period. Recently, our l
aboratory and others have reported that the GH secretory pattern is altered
by short-term gonadal steroid treatment in adult rat, suggesting that gona
dal steroids are also important determinants of the pattern of GH secretion
during adult life. However, the site of action of gonadal steroids in the
adult rat hypothalamus is still unknown. In this study, we used in, situ hy
bridization in the adult male rat brain to determine whether GHRH neurons a
nd/or SS neurons coexpress estrogen receptor alpha (ER alpha) and ER beta g
enes. In the medial basal hypothalamus of adult male rat, the ER alpha mess
enger RNA (mRNA) was located in medial preoptic area (MPA) and arcuate nucl
eus (ARC), whereas ER beta mRNA was detected in MPA, supraoptic nucleus, an
d paraventricular nucleus. From studies using adjacent sections, the distri
bution of ER alpha mRNA-containing cells appeared to overlap in part with t
hose of GHRH and SS expressing cells only in the ARC. On the other hand, th
e distribution of ER beta mRNA-containing cells does not appear to overlap
with GHRH cells or SS cells. The double label in situ hybridization studies
showed that in the ARC, 70% of GHRH neurons contain ERa mRNA, whereas less
than 5% of SS neurons expressed the ER alpha gene. These results indicated
that GHRH neurons are direct target cells for estrogens, and estrogens may
act directly on GHRH neurons through ER alpha during adult life to modify
GH secretory patterns.