STEADY-STATE METHADONE IN RATS DOES NOT CHANGE MESSENGER-RNA LEVELS OF CORTICOTROPIN-RELEASING FACTOR, ITS PITUITARY RECEPTOR OR PROOPIOMELANOCORTIN

Male Fischer rats received either methadone (a long-acting opioid agon ist, 10 mg/kg/day) or saline (24 mu 1/day) subcutaneously by osmotic m inipumps for 7 days. Chronic steady-state methadone administration did not alter (a) corticotropin-releasing factor (CRF) mRNA in the hypoth alamus, (b) proopiomelanocortin (POMC) and CRF type receptor (CRF-R1) mRNAs in the anterior lobe and neurointermediate/posterior lobe of the pituitary, or (c) circulating levels of corticosterone. No change was found in levels of either POMC mRNA in the hypothalamus and amygdala, or CRF mRNA in the frontal cortex, olfactory bulb and amygdala. These results demonstrate that neither the activity of the hypothalamic-pit uitary-adrenal axis, nor the beta-endorphin and CRF systems in the bra in, are altered by steady-state occupancy of opioid receptors with the long-acting opioid agonist methadone.