The neurons release additional GABA, activating presynaptic GABAB receptors on the excitatory inputs to pyramidal neurons, which diminish the PF-06463922 cost release of glutamate onto the pyramidal neurons (Figure 2). The result is diminished pyramidal neuron response to repeated sensory stimuli. Thus, the brainstem can regulate hippocampal response in the presence of high sensory input. Although α7 nAChRs have both presynaptic and postsynaptic expression

(Frazier et al., 1998), their postsynaptic expression in humans is especially marked on inhibitory neurons of the hippocampus (Alkondon et al., 2000). Rodents have similar expression in the hippocampus, but primates have much more expression in the interneurons of the nucleus reticularis thalamis; the selective advantage of this higher expression may be greater see more inhibitory

control of sensory input to the cerebral cortex. Three lines of evidence support the possibility that the failure of sensory inhibition in schizophrenia results from decreased expression of α7 nAChRs. First, postmortem studies of the hippocampus and thalamus show diminished labeling of putative inhibitory neurons by α-bungarotoxin, an antagonist of α7 nAChRs (Court et al., 1999). Second, the defect in inhibition is linked to the chromosome 15q14 locus of CHRNA7, the gene for the α7 nAChR subunit. Polymorphisms in the α7 5′ promoter and in a nearby partial duplication of the gene, FAM7A, are associated with both schizophrenia and the defect in inhibition ( Leonard et al., 2002). It should, however, be noted that many genes have been associated with schizophrenia

and there is no definitive model of its genetic transmission. Yet some of the other genes identified, such as NRG1, are involved in the assembly of α7 nAChRs, further supporting a potential link over between α7 nAChRs and schizophrenia ( Mathew et al., 2007). Third, persons with schizophrenia have the greatest rate and intensity of cigarette smoking of any identifiable subgroup in the population. Over 80% smoke, most of them multiple packs per day. Per cigarette they extract more nicotine than other smokers with comparable cigarette consumption by inhaling more deeply and holding the smoke in their lungs. Cigarette smoking transiently improves their sensory inhibition. While it is not yet possible to know precisely how well α7 nAChRs are activated by smoked nicotine, one can reasonably hypothesize that the patients’ higher dose of nicotine activates α7 nAChRs ( Adler et al., 1993, Papke and Thinschmidt, 1998 and Royal College of Physicians, 2007). Inhibition of the evoked response to auditory stimuli is significantly increased after patients smoke, an effect that is blocked by antagonists of α7 nAChRs in animal models ( Luntz-Leybman et al., 1992).