Different current intensities electrical stimulation of prelimbic cortex of mPFC produces different effects on morphine-induced conditioned place preference in rats

The medial prefrontal cortex (mPFC) is a part of brain reward system involved in higher cognitive functions such as learning and memory. The mPFC receives strong dopaminergic innervations from ventral tegmental area (VTA) that comprises a portion of the mesolimbic dopaminergic system (MLDS), and in turn sends glutamate projection to both the VTA and nucleus accumbens (NAc). In the present study, we investigated the influence of electrical stimulation with different current intensities on prelimbic cortex (PL, subdivision of mPFC) (25, 50, 100, and 150 μA) with and without an effective dose of morphine (0.5 and 5 mg/kg) on CPP during conditioning and post-conditioning phases. Subcutaneous administration of morphine 5 mg/kg produced significant CPP in comparison with saline group. Our findings also showed that electrical stimulation of PL (100 μA) suppressed morphine-induced CPP that reveals impaired learning and memory formation in the process of conditioning through the blocking connection from the hippocampus to the prelimbic cortex of mPFC. A lowest current intensity (25 μA) in combination with ineffective dose of morphine (0.5 mg/kg) increased morphine-induced CPP probability via the prove reward system.

► Morphine at 2.5 and 5 mg/kg (SC) produced CPP.
► High electrical stimulation (100 μA) of prelimbic cortex suppressed morphine-induced CPP.
► A lowest current intensity (25 μA) in combination with ineffective dose of morphine (0.5 mg/kg) increased morphine-induced CPP.