NMDA, Sensitization, and VTA Figure 4. Summary of DA release in the NAc following deletion of NR1 in DA neurons. DA release was elicited by local, single pulse (1 ms) electrical stimulation in brain slices, and the DA signal was monitored using fast scan cyclic voltammetry (FSCV). (A) Input-output relationship (current intensity versus peak DA signal) from slices obtained from WT (black circles) and NR1DATCre (grey circles) mice. Number of slices and number of mice are noted in parentheses. A significantly greater release was observed in NR1DATCre mice (Two way repeated measures ANOVA; genotype x stimulus intensity, F440,10 = 1.91, p = 0.04). Acute blockade of NMDA receptors does not alter DA release in the NAc. (B) Representative DA signals elicited by single pulse stimulation in a WT mouse prior to (control) and 15 minutes following AP5 application (40 mM). Inset of the control response shows the cyclic voltammogram obtained during the peak of the signal, confirming the identity of the DA signal. Summary of AP5 effects on DA signals elicited by single pulse stimulation (n = 10). Signals were obtained every 2 min. AP5 was applied during the time indicated by the gray bar. (C) Summary of frequency-response curves obtained in WT (black circles) and NR1DATCre mice (grey circles). A significant reduction in DA release was observed in the NR1DATCre mice (two way RM-ANOVA; genotype x frequency, F160,4 = 3.57, p = 0.008). Summary of frequency-response curves obtained in the absence (control, filled circles) and presence (AP5, open circles) of AP5 (n = 10). No significant effect of NMDA antagonism was seen (two way RM-ANOVA; treatment x frequency, F72, 4 = 1.46, p = 0.2239). doi:10.1371/journal.pone.0012141.g004 To explore the development of sensitization initiated in the home cage environment (Fig. 7B), we exposed WT and NR1DATCre mice to 6 daily treatments of 1) saline, or 2) cocaine (15 mg/kg for one day, followed by 20 mg/kg for 5 days) in the home cage. Locomotor activity was measured in activity chambers on day 7 after a cocaine injection (15 mg/kg, i.p.) given to both the saline and cocaine pretreated groups. Compared to the mice pretreated with daily saline, both WT and NR1DATCre mice given daily cocaine demonstrated a significant increase in cocaine-induced motor activity in both WT and NR1DATCre mice (Two way ANOVA, treatment, F1,25 = 15.330, p,0.001). Although there was a trend toward less sensitization for the NR1DATCre animals, compared to WTs, this was not statistically significant (Two way ANOVA, F1,25 = 0.295, p = 0.592). Intra-VTA administration of the NMDAR antagonist AP5 prevents the initiation of behavioral sensitization to cocaine in NR1DATCre mice It has been previously reported that NMDAR antagonist infusion into VTA blocks sensitization to cocaine [1,4,5]. To determine whether AP5 blocks sensitization in the absence of NR1 expression in DA neurons, we infused AP5 into the VTA (Fig. 8A) of both WT and NR1DATCre animals prior to receiving the daily i.p. injections of cocaine in a novel environment. Figure 8B summarizes the total distance traveled by animals pretreated with intra-VTA infusion of saline or AP5. The results show a significant difference between days 1 and 4 for the saline-infused animals (p,0.001) for both WT and KO animals (Two way ANOVA, F1,21 = 18.533, p,0.001) and there is no significant difference between the genotypes (Two way ANOVA, F1,21 = 2.522, PLoS ONE | www.plosone.org 8 August 2010 | Volume 5 | Issue 8 | e12141