Cocaine- and Amphetamine-Regulated Transcript Peptide (CART) Alleviates MK-801-Induced Schizophrenic Dementia-Like Symptoms

Abstract

Exaggerated thoughts, diminished mood and impaired cognition are the hallmarks of the schizophrenia-like condition. These symptoms are attributed to the dysregulation of dopamine and glutamate signaling in the brain. Since cocaine- and amphetamine-regulated transcript peptide (CART) modulates actions of dopamine as well as glutamate, we tested the role of this peptide in MK-801-induced schizophrenic dementia-like condition. MK-801-treated rats were allowed to interact with conspecific juvenile and tested for short-term (30-min) and long-term (24-h) social memory acquisition and recall. While MK-801 impaired the social interaction with a juvenile, the behavior was restored in CART [intracerebroventricular (icv) or intra-ventral tegmental area (VTA)] pre-treated animals. This action of CART was blocked by SCH23390 (dopamine D1 receptor antagonist) administered directly into the prefrontal cortex (PFC). Application of neuronal tracer Di-I in the PFC retrogradely labeled dopamine cells of the VTA, which in turn seem to receive CARTergic innervation. A significant increase in CARTimmunoreactivity was evidenced in the VTA, PFC and accumbens of the animals allowed to interact with a juvenile. However, MK-801 treatment attenuated the peptide expression and induced social memory deficits. The schizophrenic dementia-like symptoms following antagonism of glutamatergic receptors may be attributed to the reduced dopamine activity in the mesocortical system. We suggest that CART may, positively modulate the dopamine system to alleviate cognitive deficits associated with schizophrenia.

Keywords: MK-801; cocaine- and amphetamine-regulated transcript peptide; immunohistochemistry; schizophrenia; social recognition test.