175 Postmortem and genetic evidence suggest that α2/α3containing GABAA receptors are the most relevant targets for the treatment of cognitive dysfunction in schizophrenia. It is the α2-containing GABAA receptors that are up regulated on the postsynaptic axon initial segments of pyramidal neurons in schizophrenia.176 In mice, deletion of the α3 subunit results in mild hyperactivity and a pronounced deficit in PPI of the acoustic startle response,

Inhibitors,research,lifescience,medical suggesting a hyperdopaminergic phenotype.177 Targeting these specific receptor subtypes would circumvent the adverse cognitive and sedative effects associated with nonspecific agonists, like benzodiazepines, which are attributable to their affinity for α1 and/or α5containing GABAA receptors.178 α2-GABAA receptors A recent proof-of-concept trial was conducted with MK0777, a benzodiazepine-like compound selective Inhibitors,research,lifescience,medical for GABAA receptors containing α2 or α3 subunits, to determine whether selective enhancement of GABAergic transmission would improve cognitive functions and gamma oscillations in patients with schizophrenia.179 MK0777 improved the performance of patients in several working memory

tasks, and was associated with increased gamma band power in the frontal cortex during task performance. However, MK-0777 did not significantly alter scores on the Brief Psychiatric Rating Scale (BPRS) or Repeatable Battery Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical for the Assessment of Neuropsychological status, except for improvement in the delayed memory index in the latter test. α3-GABAA receptors Mouse genetics supports the hypothesis that a3GABAA receptors are involved in sensorimotor gating,177 a process that is disrupted in schizophrenia. Compounds that would selectively augment signaling through these receptors would be potentially beneficial in treating this schizophrenia endophenotype. As the a3containing GABAA receptor is the major subtype expressed on dopaminergic and other

monoaminergic neurons,180 agonists at this receptor might augment the inhibitory tone of these neurons and reverse their hyperfunctioning state Inhibitors,research,lifescience,medical in psychosis. Cholinergic therapeutic targets Levetiracetam Muscarinic receptors Muscarinic PD173074 mouse acetylcholine (mACh) receptors are widely distributed throughout the neocortex and are promising targets for numerous neurological and psychiatric disorders.181 Five isoforms (M1-M5) of these G-protein coupled metabotropic receptors have been identified and characterized.182 The therapeutic potential for muscarinic receptor activation in schizophrenia is fueled in large part by the efficacy of acetylcholine esterase inhibitors, which elevate synaptic acetylcholine levels, in reducing behavioral disturbances in Alzheimer’s disease patients that are reminiscent of symptoms of schizophrenia.183,184 These effects are in addition to the primary cognitive enhancement due to the therapy.