[Increased release of orphanin FQ (OFQ) in brain of chronic morphine tolerant rats].
The changes in OFQ-immunoreactivity (OFQ-ir) content and release of cerebroventricular perfusate, periaqueductal gray (PAG) and amygadala of chronic morphine tolerant rats were measured with radioimmunoassay (RIA). The results indicate: (1) chronic morphine tolerance was achieved in rats by injecting increasing doses of morphine (10, 20, 40, 50, 60 mg/kg, s.c., tid). The content of OFQ-ir in cerebroventricular perfusate in the rats of normal saline (NS) group remained at a steady level during the injections from d 1 to d 5, while in the morphine-treated group of rats the content of OFQ-ir showed 25% increase (P < 0.05 vs NS) and 52% increase (P < 0.01 vs NS) after 3 and 5 days' morphine injection respectively. (2) The content of OFQ-ir in PAG of rats receiving morphine injection for 1, 3 and 5 days showed respectively increases of 17% (P < 0.05), 48% (P < 0.05) and 80% (P < 0.01) against the NS group. (3) The content of OFQ-ir in rat amygdala receiving 1 day injection of morphine showed a 8% decrease, which was not significantly different from NS group. However, there was a 36% and 55% (P < 0.05) increase respectively after injection for 3 and 5 days. It is suggested that in the later stage of chronic morphine treatment, large amount of OFQ was released from rat brain to antagonize the effect of opioids, which may play an important role in the development of morphine tolerance.
Yuan
L
L
Neuroscience Research Institute, Beijing Medical University, Beijing 100083.
Han
Z
Z
Zhang
Z K
ZK
Han
J S
JS
D000679:Amygdala / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D004361:Drug Tolerance; D005260:Female; D009021:Morphine Dependence / Q000378:metabolism*; D018847:Opioid Peptides / Q000378:metabolism*; D010487:Periaqueductal Gray / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000819:agonists*; D000097629:Nociceptin
D018847:Opioid Peptides; D011957:Receptors, Opioid; D000097629:Nociceptin