Fig. 7

Graphical scheme to show behavioral protocol. a Acquisition and expression phases of Morphine-induced conditioned place preference (CPP) by injection of morphine (5 mg/kg; sc) during 3 days. b To investigate the role of mGlu8 in the nucleus accumbens (NAc) in the acquisition of morphine-induced CPP, the animals in the separate groups received S-3,4-DCPG, (0.03, 0.3, and 3 μg/0.5 μL saline) or saline into the NAc 5 min before the rats received morphine during acquisition phase. c To find out the role of mGlu8 in the expression of morphine -induced CPP, the animals received highest dose of S-3,4-DCPG (3 μg/0.5 μL saline) or Saline 5 min prior to CPP test