Effects of Environmental Enrichment on Nicotine Sensitization in Rats Neonatally Treated with Quinpirole: Analyses of Glial Cell Line-Derived Neurotrophic Factor and Implications towards Schizophrenia

Abstract

The current study analyzed the effects of environmental enrichment versus isolation housing on the behavioral sensitization to nicotine in the neonatal quinpirole (NQ; dopamine D2-like agonist) model of dopamine D2 receptor supersensitivity, a rodent model of schizophrenia. NQ treatment in rats increases dopamine D2 receptor sensitivity throughout the animal’s lifetime, consistent with schizophrenia. Animals were administered NQ (1 mg/kg) or saline (NS) from postnatal day (P)1 to P21, weaned, and immediately placed into enriched housing or isolated in wire cages throughout the experiment. Rats were behaviorally sensitized to nicotine (0.5 mg/kg base) or saline every consecutive day from P38 to P45, and brain tissue was harvested at P46. Results revealed that neither housing condition reduced nicotine sensitization in NQ rats, whereas enrichment reduced sensitization to nicotine in NS-treated animals. The nucleus accumbens (NAcc) was analyzed for glial cell line-derived neurotrophic factor (GDNF), a neurotrophin important in dopamine plasticity. Results were complex, and revealed that NAcc GDNF was increased in animals given nicotine, regardless of housing condition. Further, enrichment increased GDNF in NQ rats regardless of adolescent drug treatment and in NS-treated rats given nicotine, but did not increase GDNF in NS-treated controls compared to the isolated housing condition. This study demonstrates that environmental experience has a prominent impact on the behavioral and the neural plasticity NAcc response to nicotine in adolescence.