Effects of prenatal morphine and adult estrogen administration on mu-opioid inhibition of norepinephrine release from hypothalamic slices.
The present study tested the hypotheses that exposure to morphine in utero (10 mg/kg twice a day on gestation days 11-18) and acute estrogen treatment in adulthood alter mu-opioid regulation of hypothalamic norepinephrine (NE) release in sexually mature rats. Both basal and KCl-stimulated NE releases were measured in superfused hypothalamic and preoptic area (POA) slices preloaded with 3H-NE. The mu-opioid receptor agonist D-Ala2, MePhe4-Gly-ol5-enkephalin (DAMGO; 10 or 100 nM) or the opioid antagonist naloxone (1 microM) was applied to some slices 15 min prior to KCl stimulation. Prenatal morphine had no effect on basal or KCl-stimulated release of preloaded 3H-NE from hypothalamic and POA slices from adult male progeny. Neither the mu-opioid agonist DAMGO nor the nonspecific antagonist naloxone significantly affected KCl-evoked overflow of 3H-NE in slices from either brain region of male rats. Adult female offspring were ovariectomized (OVX), and some were injected with a replacement dose of estrogen 48 h prior to sacrifice. Prenatal morphine had no effect on basal or KCl-stimulated release of 3H-NE from hypothalamic or POA slices or on the response of slices to opioid drugs. Estrogen treatment modestly increased KCl-evoked release of 3H-NE from POA slices from females. Moreover, there was a significant interaction between opioid drugs and estrogen treatment on KCl-evoked overflow of 3H-NE. In hypothalamic and POA slices from OVX females, DAMGO reduced KCl-evoked efflux of 3H-NE. This inhibitory effect of DAMGO was not apparent in slices from estrogen-treated females. In addition, naloxone increased KCl-stimulated NE release in slices from both hypothalamus and POA of estrogen-treated female rats but not control OVX females. Thus, prenatal exposure to morphine does not alter basal, KCl-evoked or mu-opioid modulation of NE efflux from hypothalamic or POA slices in adult progeny of either sex. However, treatment of adult, OVX females with estrogen attenuates mu-opioid inhibition and promotes the appearance of naloxone facilitation of KCl-evoked 3H-NE release from hypothalamic and POA slices.
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Department of Psychiatry, Albert Einstein College of Medicine, Bronx, N.Y., USA.
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D000595:Amino Acid Sequence; D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D010052:Ovariectomy; D011189:Potassium Chloride / Q000494:pharmacology; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000502:physiology*
D004745:Enkephalins; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D004958:Estradiol; D011189:Potassium Chloride; D009020:Morphine; D009638:Norepinephrine