Ethanol-mediated aversive learning as a function of locomotor activity in a novel environment in infant Sprague-Dawley rats

Abstract

Unlike adult heterogeneous rats, infant rats are sensitive to ethanol's locomotor stimulating effects. Susceptibility to this ethanol effect varies as a function of baseline locomotor activity levels. Infant rats with higher baseline activity levels are more sensitive to ethanol's stimulating effects than those with lower baseline activity levels. The present study was designed to analyze susceptibility to ethanol-induced motivational learning in subpopulations of infant heterogeneous rats that differ in baseline activity in a novel environment. On postnatal day 11 (PD 11) baseline locomotor activity was registered and infants were divided into high and low responders (HR, LR). In Experiment 1, pups were trained in a procedure of conditioned taste aversion employing ethanol (0.0, 0.5 or 2.5 g/kg) as unconditioned stimulus (US) and saccharin as conditioned stimulus. In Experiment 2 the same procedure was employed with LiCl (0.0, 0.25 or 0.5% of body weight of a 0.3 M LiCl solution) as US. HR were more resistant to the aversive effects of ethanol than LR while magnitude of LiCl-induced conditioned taste aversion was similar in HR and LR. These results suggest the possibility of early detection of subpopulations of rats with differential sensitivity to ethanol's effects.

Figure 1

Baseline locomotor activity (operationalized through the number of beams broken) registered on PD 11. Subjects are separated as a function of: a) Ethanol treatment (0, 0.5 or 2.5 g/kg) administered during conditioning; and b) locomotor activity level during baseline (high responders, HR, and low responders, LR). Vertical lines illustrate standard errors of the means. Group HR-0 (n = 11), Group HR-0.5 (n = 12), Group HR-2.5 (n = 9), Group LR-0 (n = 11), Gropu LR-0.5 (n = 9), Group LR-2.5 (n = 13).

Figure 2

Intake of saccharin (operationalized through the percentage of body weight gained) as a function of ethanol treatment (0.0, 0.5 and 2.5 g/kg ethanol) and baseline activity level (high responders Vs low responders) during conditioning (postnatal days 12 and 13) or testing (PD14). Vertical lines illustrate standard errors of the means. Group HR-0 (n = 11), Group HR-0.5 (n = 12), Group HR-2.5 (n = 9), Group LR-0 (n = 11), Gropu LR-0.5 (n = 9), Group LR-2.5 (n = 13).

Figure 3

Locomotor activity scores on PD11 (operationalized through the number of beams broken) as a function of LiCl dose (0, 0.25 or 0.50 % % of body weight of 0.3 M LiCl). Subjects were divided as a function of baseline activity level in high or low responders (HR or LR). Vertical lines illustrate standard errors of the means. Group HR-0 (n = 11), Group HR-0.25 (n = 9), Group HR-0.5 (n = 12), Group LR-0 (n = 11), Gropu LR-0.25 (n = 13), Group LR-0.5 (n = 10).

Figure 4

Intake of saccharin (operationalized through the percentage of body weight gained) as a function of ethanol treatment (0.0, 0.5 and 2.5 g/kg ethanol) and baseline activity level (high responders Vs low responders) during conditioning (postnatal days 12 and 13) or testing (PD14). Vertical lines illustrate standard errors of the means. Group HR-0 (n = 11), Group HR-0.25 (n = 9), Group HR-0.5 (n = 12), Group LR-0 (n = 11), Gropu LR-0.25 (n = 13), Group LR-0.5 (n = 10).