Repeated cocaine exposure induces neural plasticity as implied by the development of dependence and sensitization. An under explored but critical aspect of cocaine-dependent plasticity is the impact of cocaine on proteins involved in synaptic remodeling during drug-seeking behaviors. This proposal focuses on the proteins that regulate the extracellular matrix (ECM). These proteins are critical for dynamic processes involved in synaptic reorganization during learning. We envision that the ECM acts as a scaffold to optimally align pre- and postsynaptic elements, which must be transiently degraded during synaptic remodeling. Since drug abuse is believed to involve a learning process, molecules involved in remodeling should be altered in brain areas implicated in drug abuse. This notion is supported by recent studies reporting morphological changes in brain regions critical for drug-taking behavior. We hypothesize that these morphological changes require shifts in the expression of ECM proteins, which are dependent on the regulators, matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Recent work in our laboratories has demonstrated that activity of the enzyme MMP-9 in the hippocampus is correlated with active learning of a water maze spatial learning task. In addition, acute cocaine treatment increases MMP-9 activity in the nucleus accumbens and medial prefrontal cortex, with a concomitant decrease in the ventral tegmental area. In contrast, only small changes were found in the substantia nigra and striatum, suggesting a specificity of cocaine's effects on plasticity of mesocorticolimbic pathways. The proposed studies will assess the level of expression of MMPs and TIMPs critical for remodeling processes believed to occur during learning and extinction of a cocaine conditioned place preference (CPP) task. These studies will determine which brain regions exhibit plastic changes associated with the pairing of contextual information with cocaine, whether or not the same brain sites are involved in the extinction of cocaine CPP behavior, and if these molecules can be further altered once initial learning of the CPP task has taken place. We postulate that repeated cocaine initially produces synaptic rearrangement in specific brain regions linked to drug craving and addiction, and that changes in MMPs/TIMPs are indicators of this rearrangement. Moreover, subsequent to repeated cocaine treatment, there may be an attenuation or loss of neural plasticity in these brain sites that contributes to the long-lasting nature of addiction.
| Brown, Travis E; Forquer, Melissa R; Cocking, Davelle L et al. (2007) Role of matrix metalloproteinases in the acquisition and reconsolidation of cocaine-induced conditioned place preference. Learn Mem 14:214-23 |
