Sensitivity change of dopamine receptors in hippocampus (CA1) and its effect on morphine-induced condition place preference

In the present study, the effects of intra-cerebral hippocampus (CA1) injections of apomorphine D1, D2-like receptors agonists on morphine-induced place preference in male Wistar rats have been investigated. Subcutaneous administration of different dose of morphine sulphate (1, 3, 6 and 9 mg/kg) produced a dose-dependent conditioned place preference (CPP). Intra-cerebral hippocampus (CA1) administration of apomorphine (0.25, 0.5 and 1 ?g/rat) 5 days before measuring CPP (using a 3-day schedule at the specific time) with an ineffective dose of morphine (1 and 3 mg/kg) decreased a significant CPP. In other words, apomorphine (0.25, 0.5, and 1 ?g/rat) injection into hippocampus decreased CPP in combination with morphine (1 and 3 mg/kg). Since apomorphine is D1, D2-like receptors agonist of dopamine and has sensitized both receptors, the study of which of these receptors causes the significant CPP reduction is going on.