Figure 5. Acute effects of cocaine in NAc slices. Voltammetric traces of DA signals taken prior to (black) and following bath application of 500 nM cocaine (gray). Cocaine significantly increased both the amplitude and the decay time constant (tau) in slices from both WT (10 slices from 3 subjects) and NR1DATCre (7 slices from 4 subjects) mice. **p,0.001; ***p,0.0001, paired t-test. doi:10.1371/journal.pone.0012141.g005 p = 0.130). In the animals that received AP5 infusion into the VTA, there is no difference in total distance traveled between days 1 and 4 of cocaine injection (Two way ANOVA, F1,22 = 0.510, p = 0.484). In summary, behavioral sensitization to cocaine was blocked by intra-VTA infusion of the NMDAR antagonist AP5 in both the WT and the NR1DATCre animals, suggesting that NMDARs localized on non-DA neurons in the VTA are responsible for cocaine sensitization. NMDA, Sensitization, and VTA NMDARs in DA neurons are not required for the development of conditioned place preference (CPP) to cocaine in NR1DATCre animals To evaluate the rewarding properties of cocaine in NR1DATCre mice, we employed a CPP paradigm (Fig. 9). In addition, to assess the persistence and relapse of cocaine-seeking behavior in NR1DATCre animals, we studied the extinction and reinstatement of the CPP response. There was no difference between time spent in each of the conditioning compartments during pre-test (genotype x compartment interaction: F(1,31) = 1.3; p = 0.26), ensuring an unbiased baseline (Fig. 9A). Two-factor repeated measures ANOVA (genotype: WT vs. NR1DATCre animals; drug: saline vs. cocaine pairing; conditioning: pre-test vs. post-test) revealed a significant main effect of the drug (F(1,28) = 32.8; p, 0. 001) as well as significant drug x conditioning (F(1,23) = 78.5; p,0.0001) and genotype x drug x conditioning (F(1,23) = 15.7; p,0.0001) interactions. Analysis of the interaction revealed a significant conditioning effect for the cocaine-paired compartment in both WT (F(1,7) = 6.2; p = 0.041) an NR1DATCre (F(1,7) = 39.7; p,0.0001) mice, indicating that animals from both genotypes demonstrated significant preference for the cocaine paired- compartment (Fig. 9B). CPP was then extinguished by repeated saline injections (8 days) in both the previously cocaine-paired floor and the saline-paired floor (Fig. 9C). There was no significant preference for cocaine-paired compartment in NR1DATCre animals (F(1,7) = 0.02; p = 0. 889) and WT (F(1,7) = 0.14; p = 0. 71), indicating that both genotypes showed robust extinction after 8 sessions. As relapse to cocaine-seeking behavior can be triggered by drug exposure, we tested for reinstatement of CPP. Following the extinction phase, the reinstatement of CPP was investigated with a challenge cocaine injection (10 mg/kg). Following this priming dose of cocaine there was no significant effect of conditioning in WT (F(1,7) = 1.56; p = 0. 27) and NR1DATCre (F(1,7) = 0.82; p = 0. 39) animals (Fig. 9D), indicating that there was Figure 6. Basal locomotor activity in NR1DATCre mice. (A) Locomotor response to novel environment. Total distance traveled in the first hour in the locomotor chamber in WT (n = 8) and NR1DATCre KO (n = 8) animals. KO animals were significantly less active during the first hour presented to the activity chambers, p,0.05, two-tailed t-test. (B) Total distance traveled in 24 hours in the locomotor chamber. There were not significant differences between the genotypes, p = 0.519, two-tailed t-test. (C) Day-night locomotion in a 24 hr circadian cycle at 1 hr intervals in WT and NR1DATCre animals. doi:10.1371/journal.pone.0012141.g006 PLoS ONE | www.plosone.org 9 August 2010 | Volume 5 | Issue 8 | e12141