ration produced locomotor sensitization in EC, IC, and SC rats, when the nicotine-mediated activity was expressed as a percent change from the respective saline controls EC rats displayed greater sensitization to nicotine than IC and SC rats. In addition, the magnitude of change from saline control in nicotine-induced enhancement of pDARPP-32 Thr34 and pCREB in PFC was strikingly increased in EC rats relative to IC and SC rats, indicating a potential mechanism through which environmental enrichment could reduce locomotor effects of nicotine. Together, the findings demonstrate a novel role of PFC pDARPP-32 Thr34 in enriched environment-induced neuroplasticity and behavioral changes associated with repeated nicotine administration. Relative to the 
IC condition, the complexity of an enriched environment paradigm comprises multiple components: a large space, physical exercise, novel objects, and social cohorts. We acknowledge that one limitation of the current study is that the results do not address which of these components, or combination of components, is specifically responsible for the PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22212322 environmentalinduced behavioral and neurochemical changes. To examine this issue completely, several variations of ��control��conditions would be needed, including manipulations to study the effects of cages size, numbers of social partners, presence of novel objects, amount of exercise, and so on, which is beyond the scope of the current study. In this study, we chose a social control condition with only one other animal in a small cage because this represents the NIH standard housing condition, which is the most typical housing condition used across various laboratories and allows for crosscomparisons with results published in the literature. However, some studies have used other controls, such as single-housed animals with novel objects or social caged animals without novel objects. For example, in a recent study, an SC condition, and a novelty condition were used as control conditions for the EC group. When the escalation of cocaine was examined in a self-administration paradigm, only NC and IC rats showed escalation, suggesting that social cohorts may be a primary factor in the behavioral effects of an enriched environment. In addition, the effect of exercise has been shown to have dramatic effects on reducing drug-taking behavior as well as influencing neurochemical changes. AGI-6780 Moreover, when only novelty was used to distinguish between enriched and standard environments, enrichment in mice eliminated both behavioral sensitization and conditioned place 9 Enriched Environment Regulates Signaling Proteins preference to cocaine, suggesting novelty acts as the main neuroprotective factor. The findings from our current study, as well as the reported above, suggest that the effects of each enrichment component on behavioral and neurochemical changes is an interesting topic for future study. The most important finding from the study is that EC rats show diminished basal levels of pDARPP-32 Thr34 in PFC and NAc relative to IC and SC rats under saline control conditions, indicating that PKA-mediated Thr34 pathway is quite sensitive to enrichment-induced plasticity. The Thr34 phosphorylation levels are regulated by both dopaminergic and glutamatergic receptor stimulation signaling. D1 receptor stimulation results in phosphorylation at Thr34, whereas activation of D2 receptor of DA and N-methyl-D-aspartate glutamate receptor results in the dephosphorylation of Th
