Effects of unilateral microinjection of different doses of SCH23390, a D1-like receptor antagonist, into the dorsal hippocampus (CA1) on intra-VTA orexin-induced CPP (A) conditioning score and (B) locomotor activity induced by microinjection of Orexin into the VTA during 10-min period on post-test day. In this set of experiments, animals received different doses of SCH23390 (0.25, 1 and 4 µg/0.5 µL saline) or Saline (0.5 μL/side) as a vehicle in the CA1, 5 min prior to intra-VTA injection of orexin A (100 ng/0.3 µL saline) during the 3-day conditioning period. The anatomical control group (n = 6) received the highest dose of SCH23390 (4 µg/0.5 µL saline), 5 min prior to intra-VTA orexin-induced conditioned place preference. Each bar shows the mean ± SEM for 6 rats. *P < 0.05, **P < 0.01, ***P < 0.001 different from the vehicle-control group (white bar). ††P < 0.01, †††P < 0.001 different from the control group (black bar)