NOREPINEPHRINE UTILIZATION IN THE HYPOTHALAMUS OF THE MALE-RAT DURINGADOLESCENT DEVELOPMENT

This study examined the influence of adolescent development and pubert al changes in gonadal function on the development of norepinephrine (N E) turnover in the hypothalamus and cerebral cortex of rats from late juvenile to young adult ages. In one study, NE utilization was estimat ed in intact male rats and in male rats castrated at 14 days of age. N E levels were measured 15, 30, 45, 60, 120, and 240 min after inhibiti on of catecholamine synthesis at 28, 42, and 70 days of age. In a seco nd study, male rats were made precocious by chronic testosterone expos ure over days 14-28 and on the 28th day NE utilization was measured in both the hypothalamus and cerebral cortex. Turnover rates were calcul ated based on steady-state kinetics. The results indicate that in vivo NE levels and turnover rates in both the hypothalamus and cortex sign ificantly increase from a late juvenile age to adulthood. However, whe n NE levels measured after synthesis inhibition were expressed as a pe rcentage of the mean basal values, there was a significant effect of a ge only in the hypothalamus. Hence, the age-related increases in hypot halamic NE turnover appear to reflect age-related changes in NE utiliz ation, whereas not age-related changes in NE utilization. During mid-p uberty (42 days), NE utilization in the hypothalamus was markedly diff erent from that observed in this region at either 28 or 70 days. At 28 and 70 days, NE levels decreased to 50% of basal levels by 4 h follow ing synthesis inhibition. At 42 days, NE levels decreased slightly ove r the first 45 min to 11% of basal levels but by 60 min reached 50% of basal levels. Juvenile gonadectomy had no significant effect on turno ver rates at any of the ages. Chronic exposure to testosterone propion ate accelerated gonadal development and increased plasma testosterone levels but did not affect NE turnover rates in either the hypothalamus or the cortex. These results indicate that function within the hypoth alamic noradrenergic system, therefore, changes over adolescent develo pment, but the change is not influenced by gonadal hormones. The diffe rences seen in NE utilization over adolescence may reflect changing ph ysiologic function within the NE cells or changes in synaptic input on to the NE terminals in the hypothalamus.