Sj. Choi et Ck. Kellogg, ADOLESCENT DEVELOPMENT INFLUENCES FUNCTIONAL RESPONSIVENESS OF NORADRENERGIC PROJECTIONS TO THE HYPOTHALAMUS IN MALE-RATS, Developmental brain research, 94(2), 1996, pp. 144-151
Hypothalamic noradrenergic utilization In vivo and the in vitro depola
rized release of norepinephrine (NE) were measured at 28, 42, and 70 d
ays of age in male rats to determine the Impact of adolescent developm
ent on the functional responsiveness of this transmitter system. At ea
ch age, function was determined in control rats and rats challenged by
restraint. NE utilization in vivo was estimated by measuring the decr
ease in NE levels following administration of a synthesis inhibitor, a
lpha-methyl-p-tyrosine methyl ester (alpha-MT, 250 mg/kg). The half-li
fe of approach to a new steady-state was determined. To measure depola
rized release of NE. the hypothalamus was incubated in vitro in a high
potassium (50 mM) medium and the percent of endogenous NE released in
to the medium was determined. The in vivo results indicated that hypot
halamic NE utilization in control animals decreases as animals mature.
Additionally, the in vitro results indicated that the percent NE rele
ased upon depolarization also decreased with maturation in control ani
mals. Restraint shifted the NE decay curve measured in vivo to the rig
ht at all ages. Overall, however, restraint tended to increase NE util
ization at 70 days, have little effect at 42 days, and retard utilizat
ion at 28 days, Furthermore, restraint markedly reduced the depolarize
d release of NE at 28 days, had no effect at 42 days and slightly, but
significantly, increased release at 70 days. Restraint significantly
increased plasma corticosterone al all ages. Hypothalamic NE projectio
ns are important to an organism's regulatory responses, and changes th
at take place over adolescence in this system may be important for the
emergence of adult-typical responses as well as render adolescents vu
lnerable to specific dysfunctions.