SPATIAL-LEARNING ABILITY OF RATS FOLLOWING DIFFERING LEVELS OF EXPOSURE TO ALCOHOL DURING EARLY POSTNATAL LIFE

Rats exposed to a relatively high dose (7.5 g/kg body weight) of alcoh ol on either the fifth or tenth postnatal day of age have been reporte d to have long-lasting deficits in spatial learning ability as tested on the Morris water maze task. The question arises concerning the leve l of alcohol required to achieve this effect. Wistar rats were exposed to either 2, 4 or 6 g/kg body weight of ethanol administered as a 10% solution. This ethanol was given over an 8-h period on the fifth post natal day of age by means of an intragastric cannula. Gastrostomy cont rols received a 5% sucrose solution substituted isocalorically for the ethanol. Another set of pups raised by their mother were used as suck le controls. All surgical procedures were carried out under halothane vapour anaesthesia. After the artificial feeding regimes all pups were returned to lactating dams and weaned at 21 days of age. The spatial learning ability of these rats was tested in the Morris water maze whe n they were between 61-64 days of age. This task requires the rats to swim in a pool containing water made opaque and locate and climb onto a submerged platform. The time taken to accomplish this is known as th e escape latency. Each rat was subjected to 24 trials over 3 days of t he test period. Statistical analysis of the escape latency data reveal ed that the rats given 6 g/kg body weight of ethanol had significant d eficits in their spatial learning ability compared with their control groups. However, there was no significant difference in spatial learni ng ability for the rats given either 2 or 4 g/kg body weight of ethano l compared with their respective gastrostomy or suckle control animals . We concluded that ethanol exposure greater than 4 g/kg over an 8-h p eriod to 5-day-old rats is required for them to develop long-term defi cits in spatial learning behaviour. (C) 1998 Elsevier Science Inc.