Effects of CA1 α2-adrenergic receptors on morphine-induced exploratory behaviors.

Introduction: The adrenergic and opioidergic systems play a crucial role in regulating cognitive and non-cognitive behaviors. The aim of this study was to evaluate the effects of CA1 α2-adrenoceptors on the exploratory behaviors induced by morphine. Methods: This assessment was conducted in rats using the elevated plus-maze test based on a test-retest paradigm. Bilateral guide cannulas were stereotaxically implanted in the CA1 regions of rats to allow intra-CA1 α2-adrenoceptors agonist (clonidine) or antagonist (yohimbine) microinjections. Results: Pre-test administration of morphine (6 mg/kg) showed an anxiolytic-like response. The extension of this effect during the retest session, 24h later, indicated impairment of aversive memory. Pre-test microinjection of clonidine (4 µg/rat) induced anxiolytic-like behavior on the test day in the absence or presence of a subthreshold dose of morphine (4 mg/kg) and increased avoidance to the open-arms during the retest session, but it was not significant compared with control group. Pre-test microinjection of yohimbine (4 µg/rat) induced an anxiogenic-like behavior on test day in the absence or presence of an effective dose of morphine (6mg/kg) and increased avoidance to the open-arms during the retest session. Concurrent microinjection of a subthreshold dose of yohimbine (1 μg/rat) with an effective dose of clonidine or with an effective dose of clonidine plus a subthreshold dose of morphine blocked anxiolytic-like behaviors, but did not change avoidance to the open-arms. Conclusion: According to our findings, it appears that CA1 α2-adrenoceptors affect anxiolytic-like effects of morphine, but they do not appear to play a significant role in the morphine-induced memory impairment. [ABSTRACT FROM AUTHOR]