Acute ethanol administration and acute allopregnanolone administration impair spatial memory in the Morris water task

Acute ethanol administration degrades performance on many learning and memory tasks, including tasks that are dependent on spatial information. One common test of spatial learning and memory is the Morris water task, a task that requires subjects to learn the spatial location of a submerged escape platform located in a pool of cloudy water. However, although some studies report that acute ethanol administration degrades spatial memory performance in the Morris task, other studies report no significant performance impairment. Acute ethanol administration also produces a dose- and time-dependent increase in the concentration of the endogenous neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in rat brain. Given that ethanol and allopregnanolone are both gamma-aminobutyric acid type A receptor modulators, both drugs should produce similar degradations in spatial learning and memory.

Adult male rats were trained with either the spatial version or the nonspatial version of the Morris water task. After 4 days of training, the spatial or nonspatial memory performance of subjects was assessed after either an ethanol (1.0, 1.5, or 2.0 g/kg) or allopregnanolone (12.5, 17.0, or 20.0 mg/kg) challenge.

Acute ethanol administration and acute allopregnanolone administration impaired spatial memory performance in a dose-dependent manner in the Morris water task. In addition, the impairment was selective in that neither acute ethanol nor acute allopregnanolone administration impaired nonspatial memory performance in the Morris water task.

Acute ethanol administration and acute allopregnanolone administration impaired spatial memory performance but did not impair nonspatial memory performance in the Morris water task. These results demonstrate that both ethanol and allopregnanolone produce selective cognitive deficits that are not due to general sensory or motor deficits.