Disruption of Prefrontal Cortex Large Scale Neuronal Activity by Different Classes of Psychotomimetic Drugs

Schizophrenia is thought to be a disorder of neural coordination, not cellular pathology. In rats, three different psychotomimetic drugs—MK801 (an NMDA receptor antagonist), DOI (a serotonergic hallucinogen), and amphetamine—all disrupted population activity and modulated gamma oscillations in the prefrontal cortex, but through different mechanisms. MK801 increased population activity, DOI decreased it, and amphetamine had little effect. All three drugs reduced correlations between spike-rate and local field potential power specifically in the gamma band, suggesting they disconnect spike-discharge from gamma oscillators. Gamma oscillations support cognitive functions affected in schizophrenia, offering insight into cortical processing deficits.

Study at a glance

Abstract

In the absence of overt cellular pathology but profound perceptual disorganization and cognitive deficits, schizophrenia is increasingly considered a disorder of neural coordination. Thus, different causal factors can similarly interrupt the dynamic function of neuronal ensembles and networks, in particular in the prefrontal cortex (PFC), leading to behavioral disorganization. The importance of establishing preclinical biomarkers for this aberrant function has prompted investigations into the nature of psychotomimetic drug effects on PFC neuronal activity. The drugs used in this context include serotonergic hallucinogens, amphetamine, and NMDA receptor antagonists. A prominent line of thinking is that these drugs create psychotomimetic states by similarly disinhibiting the activity of PFC pyramidal neurons. In the present study we did not find evidence in support of this mechanism in PFC subregions of freely moving rats. Whereas the NMDA receptor antagonist MK801 increased PFC population activity, the serotonergic hallucinogen DOI dose-dependently decreased population activity. Amphetamine did not strongly affect this measure. Despite different effects on the direction of change in activity, all three drugs caused similar net disruptions of population activity and modulated gamma oscillations. We also observed reduced correlations between spike-rate and local field potential power selectively in the gamma band suggesting that these drugs disconnect spike-discharge from PFC gamma oscillators. Gamma band oscillations support cognitive functions affected in schizophrenia. These findings provide insight into mechanisms that may lead to cortical processing deficits in schizophrenia and provide a novel electrophysiological approach for phenotypic characterization of animal models of this disease.