Both ionotropic and metabotropic glutamate receptors (mGluRs) are involved in the behavioral effects of pyschostimulants; however, the specific contributions of individual mGluR subtypes remain unknown. Here we show that mice lacking the mGluR5 gene do not self-administer cocaine, and show no increased locomotor activity following cocaine treatment, despite showing cocaine-induced increases in nucleus accumbens (NAcc) dopamine (DA) levels similar to wild-type (WT) mice. These results demonstrate a significant contribution of mGlu5 receptors to the behavioral effects of cocaine, and suggest that they may be involved in cocaine addiction.

Despite great advances in basic neuroscience knowledge, the improved understanding of brain functioning has not yet led to the introduction of truly novel pharmacological approaches to the treatment of central nervous system disorders. This situation has been partly attributed to the difficulty of predicting efficacy in patients based on results from preclinical studies. To address these issues, this review critically discusses the traditional role of animal models in drug discovery, the difficulties encountered, and the reasons why this approach has led to suboptimal utilization of the information animal models provide. The discussion focuses on how animal models can contribute most effectively to translational medicine and drug discovery and the changes needed to increase the probability of achieving clinical benefit. Emphasis is placed on the need to improve the flow of information from the clinical/human domain to the preclinical domain and the benefits of using truly translational measures in both preclinical and clinical testing. Few would dispute the need to move away from the concept of modeling CNS diseases in their entirety using animals. However, the current emphasis on specific dimensions of psychopathology that can be objectively assessed in both clinical populations and animal models has not yet provided concrete examples of successful preclinical-clinical translation in CNS drug discovery. The purpose of this review is to strongly encourage ever more intensive clinical and preclinical interactions to ensure that basic science knowledge gained from improved animal models with good predictive and construct validity readily becomes available to the pharmaceutical industry and clinical researchers to benefit patients as quickly as possible.

␣6* nicotinic acetylcholine receptors (nAChRs) are highly and selectively expressed by mesostriatal dopamine (DA) neurons. These neurons are thought to mediate several behavioral effects of nicotine, including locomotion, habit learning, and reinforcement. Yet the functional role of ␣6* nAChRs in midbrain DA neurons is mostly unknown. The aim of this study was to determine the composition and in vivo functional role of ␣6* nAChR in mesolimbic DA neurons of male rats. Immunoprecipitation and immunopurification techniques coupled with cell-specific lesions showed that the composition of ␣6* nAChR in the mesostriatal system is heterogeneous, with (non-␣4)␣6␤2* being predominant in the mesolimbic pathway and ␣4␣6␤2* in the nigrostriatal pathway. We verified whether ␣6* receptors mediate the systemic effects of nicotine on the mesolimbic DA pathway by perfusing the selective antagonists ␣-conotoxin MII (CntxMII) (␣3/␣6␤2* selective) or ␣-conotoxin PIA (CntxPIA) (␣6␤2* selective) into ventral tegmental area (VTA). The intra-VTA perfusion of CntxMII or CntxPIA markedly decreased systemic nicotine-elicited DA release in the nucleus accumbens and habituated locomotion; the intra-VTA perfusion of CntxMII also decreased the rate of nicotine infusion in the maintenance phase of nicotine, but not of food, self-administration. Overall, the results of these experiments show that the ␣6␤2* nAChRs expressed in the VTA are necessary for the effects of systemic nicotine on DA neuron activity and DA-dependent behaviors such as locomotion and reinforcement, and suggest that ␣6␤2*-selective compounds capable of crossing the blood-brain barrier may affect the addictive properties of nicotine and therefore be useful in the treatment of tobacco dependence.

Summary Despite decades of research on neurobiological mechanisms of psychostimulant addiction, the only effective treatment for many addicts is contingency management, a behavioral treatment that uses alternative non-drug rewards to maintain abstinence. However, when contingency management is discontinued, most addicts relapse to drug use. The brain mechanisms underlying relapse after cessation of contingency management are largely unknown, and until recently, an animal model of this human condition did not exist. Here we used a novel rat model in which the availability of a mutually exclusive palatable food maintains prolonged voluntary abstinence from intravenous methamphetamine self-administration to demonstrate that activation of monosynaptic glutamatergic projections from anterior insular cortex to central amygdala is critical to relapse after cessation of contingency management. We identified the anterior insular cortex-to-central amygdala projection as a new addiction- and motivation-related projection and a potential target for relapse prevention.

Memories that are emotionally arousing generally promote the survival of species; however, the systems that modulate emotional learning can go awry, resulting in pathological conditions such as post-traumatic stress disorders, phobias, and addiction. Understanding the conditions under which emotional memories can be targeted is a major research focus as the potential to translate these methods into clinical populations carries important implications. It has been demonstrated that both fear and drug-related memories can be destabilised at their retrieval and require reconsolidation to be maintained. Therefore, memory reconsolidation offers a potential target period during which the aberrant memories underlying psychiatric disorders can be disrupted. Monfils et al. in 2009 have shown for the first time that safe information provided through an extinction session after retrieval (during the reconsolidation window) may update the original memory trace and prevent the return of fear in rats. In recent years several authors have then tested the effect of post-retrieval extinction on reconsolidation of either fear or drug related memories in both laboratory animals and humans. In this article we review the literature on post-reactivation extinction, discuss the differences across studies on the methodological ground, and review the potential boundary conditions that may explain existing discrepancies and limit the potential application of post-reactivation extinction approaches.