Effects of route of administration of ethanol on high-speed reaction time in young and old rats

The blood ethanol concentrations (BECs) and reactive capacity of young (8 months) and old (24 months) male Fischer 344 rats were compared at 5, 10, 20, 45, 65, and 90 min following the administration of ethanol (EtOH). The time-dependent effects of intragastric intubation (IG; 3 g/kg) and intraperitoneal injection (IP; 1.5 g/kg) of EtOH (20% w/v) were determined. Subsequent to IG delivery, BECs rose most rapidly within the first 20 min, but did not reach peak levels until 90 min for both young (240 mg/dl) and old rats (250 mg/dl). Following IP injections, BECs escalated within 5 min to 250 mg/dl in the young, to 175 mg/dl in the old, and declined gradually to a stabilized value of 150 mg/dl (young) and 130 mg/dl (old). The old rats never achieved the high BECs seen in the young. Reactive capacity, a measure of auditory/visual reaction time, was inversely related to BECs. As BECs (IP) declined, performance improved at a similar rate in both age groups, although the old rats' performance was more impaired than that of the young. However, BEC per se was not an adequate predictor of reactive capacity. When EtOH was delivered by IG so that BECs remained high for long periods of time, reactive capacity was far less impaired compared with IP delivery in which comparable BECs were present for only a few minutes. The possibility was noted that behavioral tolerance may have developed during the 90-min post-EtOH period, and that the IP delivery method may disrupt behavior in ways independent of brain ethanol levels.