Sj. Choi et al., CONTROL OF ENDOGENOUS NOREPINEPHRINE RELEASE IN THE HYPOTHALAMUS OF MALE-RATS CHANGES OVER ADOLESCENT DEVELOPMENT, Developmental brain research, 98(1), 1997, pp. 134-141
In order to evaluate mechanisms that could contribute to the effect of
adolescent development on the in vivo utilization of norepinephrine (
NE) in the hypothalamus, the depolarized release of endogenous norepin
ephrine (using 50 mM potassium) was measured in vitro in hypothalamic
explants from male rats over late juvenile (28 days) to young adult (7
0 days) ages. Depolarized release, expressed as a percent of the total
endogenous pool, was significantly greater in juveniles than in eithe
r adolescents (42 days) or young adults, Incubation in the presence of
idazoxan, an alpha(2)-adrenoceptor antagonist, increased the depolari
zed fractional NE release in adolescent and young adult rats; however,
the same drug decreased depolarized release in juveniles. Inhibition
of norepinephrine reuptake by incubation in the presence of nisoxetine
(1 mu M) significantly increased depolarized release (fractional and
absolute) in young adults only. A higher concentration of nisoxetine (
5 mu M) significantly increased depolarized release in juveniles, but
significantly reduced release in adults. Nisoxetine did not influence
release in adolescents at either concentration. The possibilities that
adolescent development brings about a change in alpha(2)-adrenorecept
or subtype and that juveniles may have a greater NE reuptake capacity
than adults are discussed. Hypothalamic NE projections are important t
o several regulatory functions, and changes that take place in this sy
stem over adolescence may be important for the emergence of adult-typi
cal responses as well as render adolescents vulnerable to specific dys
functions.