Severe Cross-Modal Object Recognition Deficits in Rats Treated Sub-Chronically with NMDA Receptor Antagonists are Reversed by Systemic Nicotine: Implications for Abnormal Multisensory Integration in Schizophrenia

Abstract

Schizophrenia is a complex and debilitating disorder, characterized by positive, negative, and cognitive symptoms. Among the cognitive deficits observed in patients with schizophrenia, recent work has indicated abnormalities in multisensory integration, a process that is important for the formation of comprehensive environmental percepts and for the appropriate guidance of behavior. Very little is known about the neural bases of such multisensory integration deficits, partly because of the lack of viable behavioral tasks to assess this process in animal models. In this study, we used our recently developed rodent cross-modal object recognition (CMOR) task to investigate multisensory integration functions in rats treated sub-chronically with one of two N-methyl-D-aspartate receptor (NMDAR) antagonists, MK-801, or ketamine; such treatment is known to produce schizophrenia-like symptoms. Rats treated with the NMDAR antagonists were impaired on the standard spontaneous object recognition (SOR) task, unimodal (tactile or visual only) versions of SOR, and the CMOR task with intermediate to long retention delays between acquisition and testing phases, but they displayed a selective CMOR task deficit when mnemonic demand was minimized. This selective impairment in multisensory information processing was dose-dependently reversed by acute systemic administration of nicotine. These findings suggest that persistent NMDAR hypofunction may contribute to the multisensory integration deficits observed in patients with schizophrenia and highlight the valuable potential of the CMOR task to facilitate further systematic investigation of the neural bases of, and potential treatments for, this hitherto overlooked aspect of cognitive dysfunction in schizophrenia.