One of the more surprising results from the human genome project was the absence of a significantly greater number of genes in the human genome in comparison with ‘less complex’ species [63]. An explanation for this is emerging from our growing appreciation of epigenetic modulation, in which the gene DNA sequence is unchanged, but the expression of gene products is altered. A particularly important element of epigenetic modulation is the potential for influencing gene expression by environment and experience. The development of drug dependency and addiction is a function of both genetic predisposition and environmental factors [64]. Thus, epigenetic mechanisms provide particularly potent machinery for addictive processes. Indeed, the Nestler laboratory has invoked chromatin remodeling, an epigenetic phenomenon, as a key element of cocaine adaptation [65,66]. Alternative splicing is a powerful mechanism for regulating gene expression, contributing to the functional diversity of proteins [67], and enabling cells to adapt to various environmental cues. Particularly relevant to this review are recent studies on mRNAs encoding N-type calcium channels in PC12 cells [68] and in vivo rat glutamate receptor NMDAR1(N- methyl d-aspartic
