Activation of Prefrontal Cortical Parvalbumin Interneurons Facilitates Extinction of Reward-Seeking Behavior

Forming and breaking associations between emotionally salient environmental stimuli and rewarding or aversive outcomes is an essential component of learned adaptive behavior. Importantly, when cue-reward contingencies degrade, animals must exhibit behavioral flexibility to extinguish prior learned associations. Understanding the specific neural circuit mechanisms that operate during the formation and extinction of conditioned behaviors is critical because dysregulation of these neural processes is hypothesized to underlie many of the maladaptive and pathological behaviors observed in various neuropsychiatric disorders in humans. The medial prefrontal cortex (mPFC) participates in the behavioral adaptations seen in both appetitive and aversive-cue-mediated responding, but the precise cell types and circuit mechanisms sufficient for driving these complex behavioral states remain largely unspecified. Here, we recorded and manipulated the activity of parvalbumin-positive fast spiking interneurons (PV+ FSIs) in the prelimbic area (PrL) of the mPFC in mice. In vivo photostimulation of PV+ FSIs resulted in a net inhibition of PrL neurons, providing a circuit blueprint for behavioral manipulations. Photostimulation of mPFC PV+ cells did not alter anticipatory or consummatory licking behavior during reinforced training sessions. However, optical activation of these inhibitory interneurons to cues associated with reward significantly accelerated the extinction of behavior during non-reinforced test sessions. These data suggest that suppression of excitatory mPFC networks via increased activity of PV+ FSIs may enhance reward-related behavioral flexibility

Therapeutic Potential of Metabotropic Glutamate Receptor Modulators

Glutamate is the main excitatory neurotransmitter in the central nervous system (CNS) and is a major player in complex brain functions. Glutamatergic transmission is primarily mediated by ionotropic glutamate receptors, which include NMDA, AMPA and kainate receptors. However, glutamate exerts modulatory actions through a family of metabotropic G-protein-coupled glutamate receptors (mGluRs). Dysfunctions of glutamatergic neurotransmission have been implicated in the etiology of several diseases. Therefore, pharmacological modulation of ionotropic glutamate receptors has been widely investigated as a potential therapeutic strategy for the treatment of several disorders associated with glutamatergic dysfunction. However, blockade of ionotropic glutamate receptors might be accompanied by severe side effects due to their vital role in many important physiological functions. A different strategy aimed at pharmacologically interfering with mGluR function has recently gained interest. Many subtype selective agonists and antagonists have been identified and widely used in preclinical studies as an attempt to elucidate the role of specific mGluRs subtypes in glutamatergic transmission. These studies have allowed linkage between specific subtypes and various physiological functions and more importantly to pathological states. This article reviews the currently available knowledge regarding the therapeutic potential of targeting mGluRs in the treatment of several CNS disorders, including schizophrenia, addiction, major depressive disorder and anxiety, Fragile X Syndrome, Parkinson’s disease, Alzheimer’s disease and pain