Atypical antipsychotics fail to substantially improve cognitive impairment associated with schizophrenia (CIAS) and one strategy to improve it is to stimulate adult neurogenesis in hippocampus, because this structure is part of an altered circuitry that underlies aspects of CIAS. Deficits in hippocampal adult neurogenesis may disrupt cognitive processes that are dependent on newborn neurons, such as pattern separation (the formation of distinct representations of similar inputs). Mechanisms by which hippocampal adult neurogenesis can be increased are therefore of therapeutic interest and a promising molecular target is the activation of serotonin 5-HT(1A) receptors because agonists at this site increase adult neuronal proliferation in the dentate gyrus. We hypothesize that use of antipsychotics possessing 5-HT(1A) receptor agonist properties may protect against or attenuate CIAS by a dual mechanism: a favorable influence on adult neurogenesis that develops upon sustained drug treatment, and an increase in dopamine levels in the prefrontal cortex that starts upon acute treatment. This hypothesis is consistent with the beneficial properties of 5-HT(1A) activation reported from pilot clinical studies using 5-HT(1A) agonists as adjunct to antipsychotic treatments. Recent antipsychotics, including clozapine and aripiprazole, exhibit different levels of 5-HT(1A) receptor partial agonism and may, therefore, differentially elicit hippocampal adult neurogenesis and increases in prefrontal cortex dopamine. We suggest that comparative studies should elucidate correlations between effects of antipsychotics on adult neurogenesis and prefrontal cortex dopamine with effects on performance in translational cognitive tasks known to involve new born neurons, such as tasks involving pattern separation, and working memory tasks sensitive to prefrontal cortex dopamine levels.
Keywords: Atypical antipsychotics; CIAS; Declarative memory; Hippocampus; Pattern separation; Tri-synaptic pathway.
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