Cocaine-responsive gene expression changes in rat hippocampus

Chronic cocaine use is known to elicit changes in the pattern of gene expression within the brain. The hippocampus plays a critical role in learning and memory and may also play a role in mediating behaviors associated with cocaine abuse. To profile the gene expression response of the hippocampus to chronic cocaine treatment, cDNA hybridization arrays were used to illuminate cocaine-regulated genes in rats treated non-contingently with a binge model of cocaine (45 mg/kg/day, i.p.) for 14 days. Validation of mRNA changes illuminated by hybridization array analysis was accomplished by measuring immunoreactive protein (via specific immunoblots). The induction of protein kinase Calpha, potassium channel 1.1, and metabotropic glutamate receptor 5 seen by hybridization arrays was confirmed at the level of protein. Immunoblot screening of previously described cocaine-responsive genes demonstrated increased levels of protein tyrosine kinase 2, beta-catenin, and protein kinase Cepsilon. While some of these changes exist in previously described cocaine-responsive models, others are novel to any model of cocaine use. The inductions of potassium channel 1.1, protein tyrosine kinase 2 and metabotropic glutamate receptor 5 are novel findings to hippocampal cocaine-responsive gene expression. These proteins have been shown to subserve learning and memory and/or long-term potentiation functions within the hippocampus. Additionally, these genes are known to interact with one another, forming a more complex pattern of gene expression changes. The findings suggest altered expression of genes with a number of different functions in the rat hippocampus after a 'binge' style of non-contingent cocaine administration. These changes in gene expression may play roles in neuronal plasticity and the behavioral phenomena associated with cocaine abuse.