DATA ON LOCATION OF NEURAL STRUCTURES INDISPENSABLE FOR OCCURRENCE OF OVARIAN COMPENSATORY HYPERTROPHY

Ovarian compensatory hypertrophy following the removal of one ovary, and the postcastration changes in the pituitary were studied in female rats with two kinds of intra-hypothalamic deafferentation. In one group of animals, the medial basal part of the anterior hypothalamus commencing at the level of the posterior border of the suprachias-matic nucleus was cut around from both sides, from the anterior and from above, leaving only the posterior connections of this area intact. In other rats, a frontal cut of half-dome shape was made behind the anterior hypothalamus. Dcaffercntations were performed by means of a small, double-edged, bayonet-shaped knife fixed in the holder of a stereotaxic instrument. Ovarian compensatory hypertrophy occurred in rats with interruption of the neural connections of the medial basal part of the anterior hypothalamus, but this effect was not observed in animals in which frontal cut was made behind the anterior hypothalamus; the ovaries were polyfollicular in both groups. One month after the removal of the second ovary, castration cells were found in the piruitarics of both groups of deafferented animals, even when ovarian compensatory hypertrophy did not occur. The assumption that estrogen-sensitive neurons are located in the anterior hypothalamus, and that these are primarily involved in the mediation of the negative feedback action of estrogens on the pituitary, is supported by these data, which indicate that these structures are able to exert their influence on the pituitary in the absence of the majority of their neural afferents. In addition, the findings are consistent with the view that the arcuate region-pituitary complex is sensitive to estrogens. But it seems very likely that these latter structures are less sensitive to a decrease in blood-cstrogcn levels than are those in the anterior hypothalamus. © 1969 S. Karger AG, Basel.