Objective: Orexin neuropeptides are implicated in physical dependence on opioids and expression of withdrawal symptoms in drug abuse. The paraventricular nucleus of the midline thalamus (PVT) has a high expression of orexin receptors. The current research studied the effect of orexin-A in the PVT area on the development of behavioral indices produced by morphine withdrawal in rats.
Methods: Male Wistar rats weighing 250-300 gr were utilised. To produce drug dependence, morphine (6, 16, 26, 36, 46, 56, and 66 mg/kg, 2 ml/kg) was injected at an interval of 24 hrs for 7 days. To assess the involvement of the orexin in withdrawal syndrome, we injected orexin-A (100 μM, 200 nl) into the PVT for 7 days before each morphine injection. On the day after the last injection of morphine, naloxone (2.5 mg/kg, i.p.) was injected to elicit the morphine withdrawal symptoms which were observed and checked for 25 min.
Results: The results of the current research showed that the orexin-A in PVT enhances the severity of behavioral symptoms prompted by the injection of naloxone in drug-dependent rats.
Conclusions: These observations imply that targeting the orexin receptors in PVT might exhibit a new therapeutic strategy for the future treatment of dependence.
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