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Effects of ethanol exposure on spatial learning in mice during synaptogenesis.

BACKGROUND
The effects of exposure to ethanol (EtOH) on spatial learning in mice during synaptogenesis and changes after maturation are not well understood. In this study, we used a water maze test to evaluate the effects of EtOH exposure on spatial learning during synaptogenesis period.


METHODS
One-week-old pups from dams not exposed to EtOH during pregnancy were given 2 dorsal subcutaneous injections of 2.5 g/kg EtOH at a 2-h interval. At 8 h (n=6) and 24 h (n=5) after the first EtOH injection, the brains were perfused and fixed. The brain tissue sections were analyzed by TUNEL assay to detect DNA fragmentation and by immunohistochemistry to detect activated caspase-3. In addition, at 5 h (n=10), 8 h (n=5), and 24 h (n=7) after the first EtOH injection, blood and cerebral EtOH concentrations were measured by headspace gas chromatography. A water maze test was performed at age 7 weeks and 12 weeks.


RESULTS
In neonatal EtOH exposure group, mice had a prolonged time to reach the platform compared to a control group. This trend was similar both trials of age 7 weeks and age 12 weeks. At 24 h after EtOH injection in the neonatal EtOH exposure group, the incidence of TUNEL and activated caspase-3 positive cells was 6.1 +/- 1.8% and 6.4 +/- 1.0%, respectively, in the cerebral cortex, 1.6 +/- 0.9% and 1.2 +/- 0.9%, respectively, in the hippocampus, and 11.0 +/- 4.4% and 16.3 +/- 7.8%, respectively, in the thalamus. In blood and cerebral tissue from mice treated with EtOH, as in the neonatal EtOH exposure group, EtOH remained at 0.93 +/- 0.79 mg/g and 0.96 +/- 0.78 mg/g, respectively, after 24 h.


CONCLUSIONS
The impairment in spatial learning due to EtOH exposure during the neonatal periods did not tend to improve after reaching maturity. Impairment in spatial learning after maturity in mice exposed to EtOH during synaptogenesis is likely due to apoptosis of brain neurons caused by EtOH.