Leptin, a newly-discovered hormonal product of the obese (ob) gene, is expressed by adipocytes and thought to play a role in the regulation of food intake and metabolism. We tested the hypothesis that leptin signals metabolic information to the reproductive system by examining its effects on the reproductive system of ob/ob mice, which have a congenital deficiency in leptin and are infertile. We treated pair-fed males and females with leptin (50 microg twice daily, ip) or vehicle (n=10/group) for 14 days, after which the animals were bled and killed. Leptin-treated females had significantly elevated serum levels of LH, increased ovarian and uterine weights, and stimulated aspects of ovarian and uterine histology compared to controls. Leptin-treated males had significantly elevated serum levels of FSH, increased testicular and seminal vesicle weights, greater seminal vesicle epithelial cell height, and elevated sperm counts compared to controls. These results demonstrate that leptin stimulates the reproductive endocrine system in both sexes of ob/ob mice and suggest that leptin may serve as a permissive signal to the reproductive system of normal animals.

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Using probes for rat neural nitric oxide synthase (NOS) mRNA and GnRH mRNA, we performed in situ hybridization to survey NOS mRNA distribution within the hypothalamus of the male and female rat and sought evidence for its expression in GnRH neurons. The NOS cRNA probe was radiolabelled with 35S, and a digoxigenin-labeled rat GnRH cRNA probe was used for double-label studies. NOS mRNA was localized in discrete hypothalamic areas, in grain clusters suggestive of individual neurons. NOS mRNA-positive cells were located mainly in the supraoptic and paraventricular nucleus, particularly overlying the magnocellular division. Rostrally, cells expressing NOS mRNA were especially prominent in the diagonal band of Broca, in a distribution very similar to GnRH neurons. Nevertheless, only one of 370 cells labeled for GnRH mRNA appeared to be positive for NOS mRNA. We conclude that NOS mRNA is located prominently in regions where CRH, AVP and oxytocin cells are located. NOS mRNA-positive cells are located in close proximity to GnRH neurons, but rarely do such neurons express NOS mRNA.

Growth hormone (GH) participates in the regulation of its own secretion by acting through a short-loop feedback mechanism to regulate the synthesis and secretion of somatostatin (SS) and growth hormone-releasing hormone (GHRH). The mechanism of GH's action in certain peripheral targets involves the induction of c-fos. Similarly, we hypothesized that GH induces the expression of c-fos mRNA in SS and GHRH neurons in the hypothalamus. Using in situ hybridization, we observed a significant induction of c-fos mRNA in the arcuate nucleus of human GH-treated compared with control animals. Contrary to our hypothesis, only 11% of GHRH mRNA-containing and 5% of SS mRNA-containing neurons colabeled for c-fos mRNA. These findings indicate that GH feedback on the hypothalamus includes the induction of c-fos mRNA primarily in neurons other than GHRH and SS in the arcuate nucleus and suggest that these unidentified neurons located in the arcuate nucleus are directly involved in transducing the effects of GH in the brain.

We tested the hypotheses that in the male rat, expression of proopiomelanocortin (POMC) mRNA in cells of the arcuate nucleus displays a diurnal fluctuation and that expression of this rhythm is dependent upon the secretory products of the testis. To accomplish this, we sacrificed groups of testes-intact and castrated adult male rats throughout the day and compared levels of POMC mRNA in individual cells of the arcuate nucleus across time and between groups. Adult male rats were housed on a 12-12 L D cycle with lights on a 0600 h and were divided into groups that were either castrated or left intact. Four days later, pairs from these groups were sacrificed at 0600 h, 1200 h, 1800 h, 2400 h, and again at 0600 h (n = 4 per group at each time point). We used in situ hybridization and a computerized image analysis system to measure cellular levels of POMC mRNA, as reflected by the number of autoradiographic grains over individual cells in the rostral quarter of the arcuate nucleus (counting approximately 30 cells per animal). Using cosinor analysis, we observed that in intact male rats, POMC mRNA levels varied significantly over the 24 h day with a nadir value at 1800 h. In contrast, there was no significant diurnal variation in POMC mRNA levels in castrated animals. POMC mRNA levels were significantly greater in the intact compared with castrated animals at every time point (P < 0.01), except at 1800 h, when the groups did not differ significantly from one another.(ABSTRACT TRUNCATED AT 250 WORDS)