Effects of hypothalamic differentiation on LH secretion and the estrous cycle in the hamster.

Abstract

A study was made of the effects of partial and total deafferentation of the medial basal hypothalamus (MBH) on the estrous cycle, endocrine organ wt, and pituitary and serum LH values in the golden hamster. Complete deafferentation (CC) as well as extended anterior frontal deafferentation (EFC) blocked cyclic ovulation immediately and permanently. Smaller anterior cuts (FC) blocked ovulation for 8–12 days, but this effect was transient, and by 3 weeks following deafferentation the hamsters were showing normal 4–day cycles. Posterior—lateral deafferentation (PL) had no effect, either acute or chronic, on ovulation. Ovarian and uterine wt was drastically reduced in CC animals, indicating a lack of gonadotropin release, and this was confirmed by low serum LH levels and very high pituitary LH concentrations, determined by radioimmunoassay. In EFC animals uterine wt was increased over diestrous and metestrous controls, and their ovaries contained large cystic follicles. Furthermore, serum LH values were elevated in the EFC group, a finding which may indicate that this cut severs a neural pathway inhibitory to release of LH. In FC animals both serum and pituitary LH levels were raised. Since FC hamsters ovulate while EFC animals do not, the results suggest that neurons entering the MBH from an antero—lateral direction are essential for the activation of ovulation, and that fibers entering anteriorly along the midline exert an inhibitory influence on the tonic secretion and release of pituitary LH. (Endocrinology91: 95, 1972)