Tolerance to the effects of ethanol on the speed and success of reaction time responding in the rat: effects of age and intoxicated practice

An animal model of human reaction time (RT) was used to investigate the effects of age and intoxicated practice on the development of tolerance to the motor impairing effects of ethanol (EtOH). Young (8–9 month) and old (24–26 month) Fischer 344 rats were trained to release a lever in response to an auditory and visual stimulus in order to avoid mild footshock. The animals were divided into groups to receive either intoxicated (EtOH-before) or unintoxicated (EtOH-after) RT testing. Successful avoidance and response latencies were impaired in young and old rats after the initial exposure to EtOH (EtOH-before group). Tolerance developed to EtOH's effects on successful avoidance and on response latencies whether or not the rats received intoxicated RT practice; however, intoxicated practice facilitated tolerance development to EtOH's effects on successful avoidance but not on response latencies. While the initial sensitivity and the level of tolerance that developed to EtOH's effects were similar in young and old rats, the old rats were generally more sensitive to EtOH and developed tolerance at a slower rate. These results suggest that tolerance develops to the effects of EtOH on RT and that intoxicated practice can have different effects on the parameters of the behavioral response.