Changes in hypothalamic oxytocin levels during morphine tolerance.
The role of hypothalamic oxytocin neurons in the hypothalamus-pituitary-adrenal (HPA) axis adaptation during opioid tolerance has not been explored. In this study the modification of oxytocin levels in different hypothalamic nuclei was determined after acute or chronic morphine exposure. Male rats were implanted with placebo (naïve) or morphine (tolerant) pellets for 7 days. On day 8, groups of rats received an acute injection of either saline i.p. or morphine (30 mg/kg i.p.) and were sacrificed 30 min later. In morphine-tolerant rats, there was a decrease in the oxytocin content in the median eminence (ME) and in the supraoptic nucleus (SO) after acute injection of saline or morphine. No modifications were seen in the paraventricular nucleus (PVN). The present study demonstrates that chronic morphine administration alters the brain oxytocin system, which suggests that this peptide might contribute to the behavioural, emotional and neuroendocrine responses to opioids.
Laorden
M L
ML
Department of Physiology and Pharmacology, University School of Medicine, Murcia, Spain.
Milanés
M V
MV
Chapleur-Château
M
M
Burlet
A
A
D000818:Animals; D004361:Drug Tolerance / Q000502:physiology*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008473:Median Eminence / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology*; D010121:Oxytocin / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013495:Supraoptic Nucleus / Q000378:metabolism; D013997:Time Factors
D010121:Oxytocin; D009020:Morphine