Effects of Electrical Stimulation of the Medial Basal Hypothalamus on thein VivoRelease of Luteinizing Hormone-Releasing Hormone in the Prepubertal and Peripubertal Female Monkey*

Abstract

In this study the hypothesis that the LHRH neurosecretory system of the prepubertal female monkey has the capacity to function in a manner comparable to that of monkeys in more mature stages of development was tested. Using push-pull perfusion in the stalk-median eminence, effects of electrical stimulation of the medial basal hypothalamus on in vivo LHRH release were determined in conscious prepubertal, early pubertal, and midpubertal monkeys. After a 180-min period of baseline sample collection, electrical stimulation was applied six times at 90-min intervals via a monopolar electrode, the tip of which was 1-2 mm rostro-dorsal to the perfusion site. Control experiments were performed in the same manner, but without electrical stimulation. During control perfusions, the mean LHRH level remained stable. Mean (+/- SEM) LHRH release for the entire perfusion period in control experiments was 0.5 +/- 0.2, 2.4 +/- 0.4, and 2.2 +/- 0.7 pg/ml.10 min for the prepubertal (n = 6), early pubertal (n = 4), and midpubertal (n = 6) groups, respectively. Mean LHRH release in the prepubertal group was significantly lower than that in either of the older groups (P less than 0.05). In contrast, in all three age groups, repeated electrical stimulation of the medial basal hypothalamus resulted in 1) a short latency increase in LHRH release occurring within 20 min after each stimulation, and/or 2) a gradual increase in mean LHRH release over several hours. In the prepubertal group (n = 4), mean LHRH levels were 0.8 +/- 0.5 pg/ml.10 min during the 90 min before the first electrical stimulation and increased to 6.1 +/- 2.9 pg/ml.10 min during the 90 min after the sixth stimulation. This degree of responsiveness was similar to that of the older age groups. Mean LHRH levels before stimulation were 1.3 +/- 0.6 and 2.4 +/- 1.1 pg/ml.10 min in the early pubertal (n = 5) and midpubertal (n = 5) groups, respectively, and increased to 7.8 +/- 3.5 and 6.0 +/- 1.8 pg/ml.10 min, respectively, after the sixth stimulation. These increases in LHRH concentration with electrical stimulation were significant for all three age groups (P less than 0.03-0.001), while there were no significant differences between age groups. The temporal patterns of these responses suggest that electrical stimulation elicits LHRH release with a similar magnitude in all three age groups by 1) depolarizing LHRH neurons directly, and/or 2) stimulating multineuronal systems that synapse with LHRH neurons.(ABSTRACT TRUNCATED AT 400 WORDS)