Mv. Milanes et al., SIMULTANEOUS CHANGES IN HYPOTHALAMIC CATECHOLAMINE LEVELS AND PLASMA-CORTICOSTERONE CONCENTRATION IN THE RAT AFTER ACUTE MORPHINE AND DURING TOLERANCE, Neuropeptides, 24(5), 1993, pp. 279-284
The effects of morphine on plasma corticosterone and hypothalamic nora
drenaline (NA) and dopamine (DA) content were studied in naive and in
morphine-tolerant rats. Acutely administered morphine (30 mg/kg i.p.)
significantly increased the plasma levels of corticosterone and signif
icantly reduced the hypothalamic NA and DA content. In chronically mor
phine-treated rats (subcutaneously implanted with pellets for 7 days),
a challenge dose of morphine (30 mg/kg intraperitoneally (i.p.)) did
not modify the plasma corticosterone levels and inhibited the morphine
-induced decreases in hypothalamic NA and DA content. These results su
ggest that: (1) In naive rats, the morphine-induced activation of hypo
thalamus- pituitary- adrenocortical (HPA) axis is mediated by catechol
aminergic neurons in the hypothalamus; (2) In tolerant rats morphine d
id not modify the plasma corticosterone concentrations, presumably by
attenuating hypothalamic noradrenergic and dopaminergic activity. (3)
Hypothalamic catecholamines have a role in regulating the HPA axis dur
ing morphine tolerance.