Unconditioned sensitization and conditioned tolerance to the stimulating effect of ethanol in the infant rat

CASTELLO, S.; MUGNAINI, M.; REVILLO, D.A.; ARIAS, C. ; MOLINA, J.C.

Congreso; Congreso Anual de la Sociedad Argentina de Neurociencias.; 2013

Relatively high ethanol doses (between 1.25 and 2.5 g/kg) induce acute locomotor stimulating effects in preweanling rats, an effect associated with its rewarding properties. The locomotor stimulating effect of ethanol is rapidly attenuated after repeated ethanol administration (tolerance) in preweanling or adult rats. The goal of the present work was to analyze whether tolerance-induced by ethanol is context-dependent (conditioned tolerance) in Wistar infant rats. In experiment 1, subjects (PD 8 to 12) were administered with ethanol (0 or 2.5g/kg) before being placed in an open field containing an odor cue. On PD 15, pups were tested for locomotor activation after ethanol administration in an open field containing or not the odor cue. In experiment 2, one group of subjects (PD 8 to 12) received 0 or 2.5 g/kg ethanol before being placed in an open field containing an odor cue, while another group of pups remained in pairs in a holding cage after ethanol administration. On PD 15 all pups were tested in an open field after being injected with ethanol (0 or 2.5 g/kg) in presence of the odor. Results showed ethanol induced locomotor activating effects in infant rats (PDs 8 to PD15). Repeated exposure to the drug did not induce tolerance when pups were tested in absence of the odor cue (Experiment 1), but when the odor was present in training and testing, there were conditioned tolerance to the stimulating effect induced by ethanol (Experiment 2). Besides, an unconditioned sensitization effect was observed on PD 15 in pups trained in absence of the odor cue. These results were the first evidence of conditioned tolerance and unconditioned sensitization to the locomotor activating effect induced by ethanol in this ontogenetic period.