**p<0 01 & ***p<0 001 show differences between dose groups vs respective control group in each class

Figure 4: Effects of L-arginine (3μg/rat, intra-CA1) plus L-NAME (0.3-3μg/rat, intra-CA1) on expression of morphine response in lesioned categories using conditioning task At first the animals were injected colchicine (2 or 8μg/rat, intra-CA1).They were then tested for place conditioning induced of morphine (after recovery). Before testing the animals were microinjected L-NAME (0.3- 3μg/rat, intra-CA1) prior to L-arginine (3μg/rat, intra-CA1). Control groups of these classes legend 0 in Figure only received saline throughout the procedure (both intra-CA1 and peripherally).