However, the persistence of cognitive impairments in individuals with schizophrenia suggests that these neuroplastic changes in GABA neurotransmission from chandelier neurons are insufficient as compensatory responses. Alternatively, it is possible that compensation at chandelier cell synapses is not effective because additional interneuron subclasses

are also functionally deficient in schizophrenia.65 Consistent with this interpretation, other findings indicate that alterations in PVcontaining GABA neurons cannot account for all of the observed findings in postmortem studies of schizophrenia. For example, the levels of GAD67 and GAT1 mRNAs are reduced to comparable Inhibitors,research,lifescience,medical degrees in layers 2-5 ,47,53 even though the density of PV neurons Inhibitors,research,lifescience,medical is much greater in layers 3 and 4 than in layers 2 and 5.66 In addition, PV mRNA expression was reduced in layers 3 and 4, but not in layers 2 and 5, in subjects with schizophrenia.57 Indeed,

other studies have found lower tissue concentrations of the mRNAs for the neuropeptides somatostatin (SST) and cholecystokinin (CCK) in the DLPFC of subjects with schizophrenia (Figure 3). 51 In the cortex, SST is expressed by GABA neurons located in layers 2 and 5 that do not express PV or CR.67 CCK is also heavily expressed in GABA neurons that do not contain either PV or SST located principally in layers Inhibitors,research,lifescience,medical 2-3 of the primate prefrontal cortex.68 Interestingly, the axon terminals of CCK-containing large basket neurons, which target selectively pyramidal neuron cell bodies, contain type I cannabinoid receptors (CB1R),69 and the mRNA and protein levels of CB1R are also lower in schizophrenia.70 Inhibitors,research,lifescience,medical Because activation of the CB1R suppresses GABA release from the terminals of CCK neurons, the downregulation of this receptor

may represent a compensatory GSK2656157 clinical trial response to reduce the ability of endogenous cannabinoids to decrease GABA Inhibitors,research,lifescience,medical release from CCK/CBlR-containing axon terminals.70 Altered GABA neurotransmission in PV-containing neurons impairs prefrontal network synchrony in schizophrenia Reduced GABA signaling from PV-containing GABA neurons to the perisomatic region of pyramidal out neurons in the DLPFC might contribute to the pathophysiology of working memory dysfunction via the following mechanisms. First, the activity of DLPFC GABA neurons is essential for normal working memory function in monkeys.71,72 Second, PV-positive GABA neurons and pyramidal neurons share common sources (eg, thalamic afferents) of excitatory input.55 The resulting feed-forward, disynaptic inhibition creates a time window during which the number of excitatory inputs required to evoke pyramidal neuron firing must occur.73 Third, both chandelier and basket neurons target multiple pyramidal neurons,74 enabling them to use this timing mechanism to synchronize the activity of local populations of pyramidal neurons.