Abstract
To examine the hypothesis that whether nitric oxide (NO) in the brain is involved in actions of estrogen on reproduction and ingestion in ruminant species, three experiments were conducted using ovariectomized (ovx) or ovx plus estradiol (E) treated goats. In experiment 1, distributions of cells containing estrogen receptor (ER) or NO synthase (NOS) in the hypothalamus were determined immunohistochemically, which revealed that both ER and NOS positive cells were localized abundantly in the ventromedial nucleus of the hypothalamus (VMH). In experiment 2, several doses of sodium nitroprusside (SNP), an NO donor, was administered into the unilateral VMH of ovx goats immediately before the presentation of food. Injection of 1.5 μg SNP resulted in an abrupt decrease in food intake during the first 60-min of a 240-min feeding period. However, higher doses of SNP had no effect on food intake. In experiment 3, on the other hand, NG-monomethyl-L-arginine (L-NMMA), a NOS inhibitor, was injected into the bilateral VMH of animals which had been treated with E. Although following the vehicle injection food intake was significantly suppressed by E as was seen in the VMH intact animal, this E-induced decrease in food intake was prevented by administering L-NMMA. This NOS inhibitor, on the other hand, altered neither the timing of the luteinizing hormone surge nor estrous behavior. These data suggest that NO in the VMH is involved in mediation of suppressive effect of E on ingestive behavior in the goat.unctions in the goat.
