Study of interaction between opioid and ?-2 adrenergic systems in analgesic effect of oxytocin in locus coeruleus nucleus

Introduction: Oxytocin is a active neuropeptide of central nervous system. In this study the effects of naloxone (opioid receptor antagonist) and yohimbine (α-2 adrenergic receptor antagonist) on analgesic effect of oxytocin applied into the locus coeruleus (LC) nucleus were investigated. Methods: Adult male Wistar rats were used. Animals divided into different groups receiving saline, oxytocin (3 nmol / 2μl), naloxone (3 nmol / 2μl) + oxytocin, yohimbine (3 nmol / 2μl) + oxytocin, and naloxone + yohimbine + oxytocin. Hot-plate and tail-flick tests were used to evaluate pain threshold. Results: Data showed that the injection of oxytocin into the LC nucleus increases the response time to thermal stimulations in both tail flick and hot plate tests. Injection of naloxone and yohimbine either separately and or in combination inhibite the antinociception effect of oxytocin. Conclusion: It seems that oxytocin induces its inhibitory effect on acute pain via LC nucleus. This effect is probably mediated by the combination of opioid and α-2 adrenergic systems.