PubMed · 4701606
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R G Black, J J Bonica. 1973. Analgesic blocks.. https://doi.org/10.1080/00325481.1973.11713460
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The present study was designed to observe the effect of orphanin FQ (OFQ, also known as 'nociceptin'), a newly-discovered neuropeptide, on pain behavior and morphine analgesia evaluated by formalin test in rats. It was found that intracerebroventricular (i.c.v.) injection of 0.1 microg OFQ had no effect on formalin-induced pain behavior; but 1, 5, 10 or 20 microg OFQ produced prolonged lifting, licking, biting or shaking of the affected paw with higher pain scoring in dose dependent manner. Repeated i.c.v. injection of antisense olignucleotide (ASO) complementary to OFQ receptor but not mismatch olignucleotide (MSO) resulted in the decrease of pain behavior; in such circumstances, OFQ showed no enhancing effect on formalin nociception. OFQ (0.1 or 1 microg, i.c.v.) significantly attenuated morphine analgesia and ASO could validly antagonize the effect of it. Pretreatment with MSO had no such effect. The present results suggest that OFQ enhances the pain behavior of rat and antagonizes morphine analgesia in formalin test.
We recently demonstrated an olfactorily induced tail skin temperature drop in saline-injected rats exposed to an oxytocin-injected cagemate, an effect abolished by olfactory impairment. Treatment with oxytocin may induce both nociceptive and anti-nociceptive effects. The contrasting effects likely depend on the model and dosage used. Here we report an increased hindpaw withdrawal latency in response to nociceptive heat following the subcutaneous administration of oxytocin (1 mg/kg). An increased withdrawal response latency was also found in the untreated cagemates of an oxytocin-treated rat. The anti-nociceptive effect was abolished in oxytocin-antagonist-injected cagemates. Our results suggests that an olfactorily induced oxytocinergic mechanism is activated in the cagemates of an oxytocin-injected rat promoting anti-nociception.