Repeated unpredictable stress blunts alcohol-induced memory deficit in adolescent rat

There exists a complex interaction between alcohol and stress on brain and behavior. Alcohol and stress are both known to affect memory. Whether stress and alcohol together can modulate memory functions in adolescent rats is not known. In the present study, effects of repeated unpredictable stress (RUPS) on contextual fear conditioning, a hippocampus-related memory function, were investigated in alcohol-treated adolescent rats.

Rats were divided into four experimental groups: group i - saline-treated non-stressed rats (sal no stress), group ii - alcohol-treated non-stressed rats (alc no stress), group iii - saline-treated rats subjected to stress (sal + RUPS), group iv - alcohol-treated rats subjected to stress (alc + RUPS). All rats were trained in the fear conditioning paradigm, and 24 h later were tested for contextual fear conditioning in the conditioning chamber, and nonspecific fear memory in a modified chamber.

Stress, in the presence or absence of alcohol, did not alter nonspecific fear. RUPS exposure did not affect contextual freezing in vehicle-treated adolescent rats. Compared to vehicle-treated non-stressed rats, alcohol-treated non-stressed rats showed significant impairments in contextual freezing. Alcohol-treated RUPS rats performed better in the contextual freezing task than alcohol-treated non-stressed rats.

RUPS exposure did not alter contextual fear conditioning in adolescent rats. Alcohol significantly reduced contextual fear memory in non-stressed rats. Alcohol-treated RUPS rats showed significantly better memory than alcohol-treated non-stressed rats. Together, these data suggest resiliency to stress-induced memory impairment in adolescent rats, and RUPS exposure causes blunting of alcohol's negative effects on contextual fear conditioning.