S. Choi et Ck. Kellogg, NOREPINEPHRINE UTILIZATION IN THE HYPOTHALAMUS OF THE MALE-RAT DURINGADOLESCENT DEVELOPMENT, Developmental neuroscience, 14(5-6), 1992, pp. 369-376
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.