NMDA Receptors on Non-Dopaminergic Neurons in the VTA Support Cocaine Sensitization Yu Luo1., Cameron H. Good1., Oscar Diaz-Ruiz1, YaJun Zhang 1 , Alexander F. Hoffman1, Lufei Shan 1 , Serena Y. Kuang 1 , Nasir Malik1, Vladimir I. Chefer2, Andreas C. Tomac1¤, Carl R. Lupica1, Cristina M. 1 Ba¨ ckman * 1 Cellular Neurobiology Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland, United States of America, 2 Behavioral Neuroscience Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland, United States of America Abstract Background: The initiation of behavioral sensitization to cocaine and other psychomotor stimulants is thought to reflect N- methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity in the mesolimbic dopamine (DA) circuitry. The importance of drug induced NMDAR mediated adaptations in ventral tegmental area (VTA) DA neurons, and its association with drug seeking behaviors, has recently been evaluated in Cre-loxp mice lacking functional NMDARs in DA neurons expressing Cre recombinase under the control of the endogenous dopamine transporter gene (NR1DATCre mice). Methodology and Principal Findings: Using an additional NR1DATCre mouse transgenic model, we demonstrate that while the selective inactivation of NMDARs in DA neurons eliminates the induction of molecular changes leading to synaptic strengthening, behavioral measures such as cocaine induced locomotor sensitization and conditioned place preference remain intact in NR1DATCre mice. Since VTA DA neurons projecting to the prefrontal cortex and amygdala express little or no detectable levels of the dopamine transporter, it has been speculated that NMDA receptors in DA neurons projecting to these brain areas may have been spared in NR1DATCre mice. Here we demonstrate that the NMDA receptor gene is ablated in the majority of VTA DA neurons, including those exhibiting undetectable DAT expression levels in our NR1DATCre transgenic model, and that application of an NMDAR antagonist within the VTA of NR1DATCre animals still blocks sensitization to cocaine. Conclusions/Significance: These results eliminate the possibility of NMDAR mediated neuroplasticity in the different DA neuronal subpopulations in our NR1DATCre mouse model and therefore suggest that NMDARs on non-DA neurons within the VTA must play a major role in cocaine-related addictive behavior. Citation: Luo Y, Good CH, Diaz-Ruiz O, Zhang Y, Hoffman AF, et al. (2010) NMDA Receptors on Non-Dopaminergic Neurons in the VTA Support Cocaine Sensitization. PLoS ONE 5(8): e12141. doi:10.1371/journal.pone.0012141 Editor: Georges Chapouthier, L’universite´ Pierre et Marie Curie, France Received July 6, 2010; Accepted July 19, 2010; Published August 16, 2010 Copyright: 2010 Luo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was supported by the Intramural Research Program of the National Institute on Drug Abuse, National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: cbackman@mail.nih.gov . These authors contributed equally to this work. ¤ Current address: Department of Neurological Surgery, Case Western Reserve University, Cleveland, Ohio, United States of America Introduction Midbrain dopamine (DA) neurons in the ventral tegmental area (VTA) represent a common substrate for drugs of abuse and mediate the engagement of addictive behaviors. Glutamatergic transmission within the VTA has been shown to be particularly important since local injection of glutamate antagonists during repeated drug administration blocks behavioral sensitization and conditional place preference (CPP) [1,2,3,4,5,6]. Previous work has also shown that abused drugs evoke N-methyl-D-aspartate receptor (NMDAR)-dependent, long-term potentiation (LTP) of glutamatergic transmission in DA neurons [7,8,9]. Therefore, NMDAR-dependent LTP might represent an essential component of the neural basis of sensitization, and the development of compulsive drug-seeking behavior. The role of VTA NMDARs in addictive behavior was recently investigated using DA cell-specific ablation of the gene coding for subunit 1 of the NMDA receptor (NR1), by expressing Cre recombinase using the DAT promoter [10,11]. This causes a selective absence of functional NMDARs on DA neurons expressing DAT, and represents a significant advance because it permits an evaluation of NMDAR function in these cells, compared to the non-selective effects of antagonists on multiple neuron subtypes. Surprisingly, these prior studies demonstrated that despite the elimination of NMDAR-dependent LTP in DA neurons in these NR1 knockout (KO) mice, cocaine sensitization developed normally [10,11], suggesting that locomo- tor sensitization does not require NMDAR-dependent neuronal plasticity. The role of NR1 on VTA DA neurons in the reinforcing effects of cocaine also remains uncertain since previous studies reported conflicting results of this KO on CPP. Zweifel et al., [11] reported that the loss of NR1 in DA neurons blocked cocaine CPP, whereas PLoS ONE | www.plosone.org 1 August 2010 | Volume 5 | Issue 8 | e12141