Background: The nucleus accumbens (NAc) is a part of the rewarding cortico-mesolimbic dopamine (DA) pathway. This is a heterogeneous structure divided in two sub regions termed core and shell. DA function in the NAc is critical for goal-oriented behaviors, including those motivated by drug and brain stimulation reward. In the conditioned-place preference (CPP) paradigm, a test assessing animal’s ability to associate drug-induced effects with environmental cause to quantify drug reward for example morphine.
Methods: In the present study, we investigated the influence of electrical stimulation with different current intensities on (25 and 100 m A) with and without an effective dose of morphine (0.5 and 5 mg/kg) on CPP. Results: Subcutaneous administration of morphine 5 mg/kg produced significant CPP in comparison with saline group. Our findings also showed that electrical stimulation of NAc (100 m A) significantly (P < 0.01) suppressed morphine-induced CPP that reveals impaired learning and memory formation in the process of conditioning. We found that morphine-induced CPP can be successfully suppressed by current intensity (100 m A). It was probably due to decreasing of dopamine contents and its metabolites in the NAc. Current intensity (100 m A) in combination with ineffective dose of morphine (0.5 mg/kg) increased morphine-induced CPP probability via the prove reward system.
Conclusions: Since stimulation of dopaminergic neurons increases tendency to dependence to morphine, therefore in the present study, the stimulation of the NAc suppressed morphine-induced CPP that this shows impairment of learning and memory formation.