Puberty-related increase in episodic LHRH release from rat hypothalamus in vitro

The retrochiasmatic hypothalamus (RCH) was removed from brains of male rats between 12 and 50 days of age, and immediately studied in vitro. The release of LHRH from the RCH was evaluated by periodic (7.5-min) collections of culture medium and subsequent RIA. With synthetic LHRH in the experimental system, the mean (+/- 1 SD) recovery was 94 +/- 7% with a variation coefficient of 14 +/- 3%. An increase in LHRH release was considered to be significant when it exceeded 6 pg/7.5 min. Biological viability of RCH in vitro was assessed by an increased release of LHRH in response to the depolarizing effect of veratridine. As age increased, from 12 to 50 days, the hypothalamic LHRH content steadily increased. However, a significant increase in veratridine - induced release of LHRH occurred only at 23 days and thereafter. At various ages, single hypothalami were studied during a mean 112-min period to evaluate the spontaneous release of LHRH. In all age groups, the in vitro LHRH release occurred in pulses. However, mean pulse frequency increased significantly with age: in 12- and 17-day-old rats, 0.3 pulse/112 min was observed; at 23, 25 and 27 days, this frequency varied between 1.8 and 3.0 pulses/112 min. At 50 days of age, the observed frequency was within the same range. We conclude that the RCH obtained from rats of various ages may retain in vitro its capacity to release LHRH episodically and that the frequency of these episodic pulses markedly increases with age to the time of the onset of puberty in male rats.