Environmental enrichment increases the in vivo extracellular concentration of dopamine in the nucleus accumbens: a microdialysis study

The present study was designed to elucidate the effects of environmental enrichment in adulthood (EE) on the in vivo basal and stimulated extracellular concentration of dopamine in the nucleus accumbens of awake rats. The effects of EE on novelty-induced motor activity in an open field and on the levels of brain-derived neurotrophic factor (BDNF) in the nucleus accumbens and striatum were also analysed. Male Wistar rats (3 months of age) were housed in enriched or control conditions during 12 months. After behavioural testing, animals were subdivided in two groups. In one of the groups, BDNF protein levels were determined. In the second group of rats, microdialysis experiments were performed to monitor dialysate concentrations of dopamine in the nucleus accumbens after the perfusion of the glutamatergic agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA; 100 mu M) or potassium (100 mM). Both basal and potassium stimulated dialysate concentrations of dopamine were higher in EE than in control rats (basal: 80%; potassium: 210%). EE did not significantly change the increases of dialysate concentrations of dopamine induced by AMPA although there was a trend towards an enhancement of the effects of AMPA. EE decreased novelty-induced locomotor activity but did not modify the levels of BDNF in the nucleus accumbens or in the striatum. These results suggest that the in vivo activity of the mesolimbic dopamine system is enhanced by housing rats in an enriched environment and that this effect is not mediated by BDNF. These findings may be relevant for the understanding of the effects of EE on motor behaviour.