Resumo

Objectives: Exposure to environmental enrichment during adolescence decreases consumption and the reinforcing properties of ethanol (EtOH) in spontaneously hypertensive rats (SHR) (Behav Brain Res,208:231,2010). Sensitivity to acute EtOH effects predict high consumption in rodents (Life Sci,77:693,2005) and tolerance contribute to vulnerability to abuse and addiction (Psychopharmacol,125:285,1996). The aim of this study was to investigate whether exposure of SHR to environmental enrichment alter the anxiolytic/stimulant effects of EtOH in the open field test (OF) and the development of tolerance to motor impairment induced by acute administration of EtOH on the tilting plane (TP). Methods: Female SHR were maintained (24h/day) in a standard environment (SE) or enriched environment (EE) from post-weaning to adulthood, when were tested. The EE consisted of two interconnected cages containing a variety of stimuli sensory. SE and EE animals (n=10/group) received i.p. injections of EtOH (0.5, 1.2 or 2.0 g/kg) or saline (Sal) 5 min before the OF, where locomotor activity and anxiety-like behavior were evaluated for 5 min. Independent groups of animals reared in SE and EE (n=7-8/group) were used to assess motor coordination induced by EtOH i.p. injections in the TP test. The animal was placed in the apparatus and then the platform was manually tilted 0-90° in a range of 5 seconds and the angle of fall of the animal was converted to percentage of motor impairment (Psychopharmacol, 170:343,2003). Acute tolerance was assessed 24 h later by re-exposing the rats on the TP at 15, 30, 45 and 60 min intervals after EtOH (2.7 g/kg) or Sal. Following each session on the TP, blood samples were collected by caudal puncture for subsequent dosages of EtOH levels. Results: EtOH 1.2 g/kg significantly increased the total locomotor activity in the OF arena of both groups SE and EE, compared to respective control (141.2±7.0 vs 179.4±2.7; 73.2±2.8 vs 96.7±2.2; Sal vs EtOH, respectively). This effect also was accompanied by an increase in the percentage of central crossings (SE and EE: 29.8±1.5 vs 42.4±1.5; 39.5±2.9 vs 52.5±2.0, Sal vs EtOH, respectively) and in the time spent (sec) in central area (SE and EE: 66.3±9.2 vs 107.6±2.6; 106.2±4.0 vs 137.8±3.4; Sal vs EtOH, respectively). In contrast to SE, the animals reared in EE and injected with EtOH (2.0 g/kg) showed a significant decreased locomotor activity in OF test (165.5±5.9 vs 57.4±2.3*), and increased the % of central crossings (47.5±2.8 vs 59.4±2.3*) and in the time spent in central area (123.4±4.3 vs 184.7±4.3*). Both groups, SE and EE developed acute tolerance to EtOH (2.7g/kg) [% motor impairment: 00.0 vs 39.7±4.8; 00.0 vs 24.6±5.1, Sal vs EtOH, respectively)] compared with their respective control. Additionally, EE animals had a lower percent of motor impairment induced by EtOH than SE animals, in the first session of TP (56.4±4.2 vs 26.4±4.5*) and also, they showed reduced blood levels of EtOH in the first 30 min interval after treatment (279.2±6.5 vs 208.6±18.6* mg/dl).*(P<0.05) SE vs EE. Conclusions: These results show that exposure to EE reduces stimulant effects induced by moderate doses of EtOH and did not prevent the development to acute tolerance to EtOH- induced motor impairment. These findings suggest that the rearing environment may cause changes in neuroadaptive and pharmacokinetic processes implicated in the central effects of EtOH in female SHR. Financial support: CAPES and CNPq