EFFECTS OF ADRENAL-STEROIDS ON BASAL GANGLIA NEUROPEPTIDE MESSENGER-RNA AND TYROSINE-HYDROXYLASE RADIOIMMUNOREACTIVE LEVELS IN THE ADRENALECTOMIZED RAT

To investigate the effects of type I (mineralocorticoid) and type II ( glucocorticoid) receptor activation on striatal neuropeptide [preproen kephalin (PPE), preprotachykinin (PPT), and preprodynorphin (DYN)] mRN A and midbrain cholecystokinin (CCK) mRNA as well as striatal tyrosine hydroxylase radioimmunoreactivity (TH-RIC) levels, we administered ei ther replacement levels of corticosterone (CORT; 0.5 mg/kg/day, s,c,) or pharmacological levels of deoxycorticosterone acetate (DOCA; a mine ralocorticoid steroid with ability to bind to type I and type II recep tors; 5 mg/kg, s.c.) to adrenalectomized adult male rats. After 1 week of recovery from adrenalectomy surgery, animals were injected daily w ith sesame oil or CORT for 1, 3, or 7 days or DOCA for 3 or 7 days and killed 16 h after the last injection. Adrenalectomy resulted in a dec rease in all three striatal neuropeptide mRNA levels, compared with sh am-operated rats. CORT replacement resulted in recovered PPE and PPT m RNA levels after 1 day and elevated PPE mRNA levels over those in sham -operated controls after 3 days. In contrast, DYN mRNA levels showed r ecovery after 7 days of CORT replacement. Results after DOCA treatment largely paralleled those after CORT replacement. There were no signif icant treatment effects on indirect markers of midbrain dopaminergic a ctivity, i.e., CCK mRNA and TH-RIC. From these results we conclude tha t compared with striatal tachykinin and dynorphinergic neurons, enkeph alinergic cells show greater sensitivity, whereas the dopaminergic sys tem, including mesencephalic CCK, demonstrates an insensitivity to phy siological CORT and to pharmacological DOCA treatment.