Environmental enrichment decreases cell surface expression of the dopamine transporter in rat medial prefrontal cortex Jun Zhu,* Subbu Apparsundaram, Michael T. Bardoà and Linda P. Dwoskin* *College of Pharmacy,  Department of Anatomy and Neurobiology, and àDepartment of Psychology, University of Kentucky, Lexington, Kentucky, USA Abstract Rats raised in an enriched environmental condition (EC) exhibit a decreased (35%) maximal velocity (V max ) of [ 3 H]dopamine (DA) uptake in medial prefrontal cortex (mPFC) compared with rats raised in an impoverished con- dition (IC); however, no differences between EC and IC groups in V max for [ 3 H]DA uptake were found in nucleus accumbens and striatum. Using biotinylation and immuno- blotting techniques, the present study examined whether the brain region-specific decrease in DA transporter (DAT) function is the result of a reduction in DAT cell surface expression. In mPFC, nucleus accumbens and striatum, total DAT immunoreactivity was not different between EC and IC groups. Whereas no differences in cell surface expression of DAT were found in nucleus accumbens and striatum, DAT immunoreactivity in the biotinylated cell surface fraction of mPFC was decreased (39%) in EC compared with IC rats, consistent with the magnitude of the previously observed decrease in V max for [ 3 H]DA uptake in mPFC in EC rats. These results suggest that the decrease in DAT cell surface expression in the mPFC may be responsible for decreased DAT function in the mPFC of EC compared with IC rats, and that there is plasticity in the regulatory mechanisms medi- ating DAT trafficking and function. Keywords: dopamine transporter, environmental enrich- ment, medial prefrontal cortex, nucleus accumbens, striatum, trafficking. J. Neurochem. (2005) 93, 1434–1443. Environmental enrichment during development contributes to individual differences in behavior and vulnerability to drug abuse (Bowling et al. 1993; Bowling and Bardo 1994). Rats reared in an enriched environmental condition (EC), consisting of social housing and novel objects, display less locomotor activity in an inescapable novel environment than those raised in an impoverished condition (IC) (Jones et al. 1990; Bowling et al. 1993; Smith et al. 1997). EC rats enter a novel compartment, manipulate novel objects and habituate to novel stimuli more rapidly than IC rats (Renner and Rosenzweig 1986; Zimmermann et al. 2001). Such differ- ences in response to novelty may contribute to differences in drug abuse vulnerability, as EC rats also exhibit a reduced propensity to acquire amphetamine self-administration than IC rats (Bowling et al. 1993; Bowling and Bardo 1994; Bardo et al. 1999, 2001). Environment-induced alterations in the response to psy- chostimulants are thought to result from underlying changes in mesolimbic dopamine (DA) function (Blanc et al. 1980; Bowling et al. 1993; Rilke et al. 1995; Hall et al. 1998). Extracellular DA concentrations are regulated by the DA transporter (DAT), which transports extracellular DA into the presynaptic terminal. The DAT is a major target for psychostimulants, which inhibit DAT function and increase extracellular DA concentrations (Horn 1990). The DAT is regulated by activation of protein kinase C, which decreases the maximal velocity (V max ) of DA uptake and decreases DAT cell surface expression in cell expression systems and in brain (Copeland et al. 1996; Huff et al. 1997; Vaughan et al. 1997; Zhang et al. 1997; Pristupa et al. 1998; Daniels and Amara 1999; Melikian and Buckley 1999; Chi and Reith Received January 5, 2005; revised manuscript received February 4, 2005; accepted February 7, 2004. Address correspondence and reprint requests to Linda P. Dwoskin, PhD, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, KY 40536–0082, USA. E-mail: ldwoskin@email.uky.edu Abbreviations used: DA, dopamine; DAT, DA transporter; EC, enriched environment condition; IC, impoverished condition; mPFC, medial prefrontal cortex; NET, norepinephrine transporter; PAGE, polyacrylamide gel electrophoresis; PBS, phosphate-buffered saline; PP2A, protein phosphatase 2A; PMA, b-phorbol-12-myristate-13-acet- ate; SERT, serotonin transporter; SDS, sodium dodecyl sulfate; sulfo- NHS-biotin, sulfosuccinimidobiotin; V max , maximal velocity; 6-OHDA, 6-hydroxydopamine hydrochloride. Journal of Neurochemistry , 2005, 93, 1434–1443 doi:10.1111/j.1471-4159.2005.03130.x 1434 Ó 2005 International Society for Neurochemistry, J. Neurochem. (2005) 93, 1434–1443