Postnatal anoxia from CO2 for one minute produces sex-specific changes in contextual fear conditioning in adult rats.

In a split-litter design, equal numbers of male and female rats were exposed either to carbon dioxide for 1 min, or to the control condition on either postnatal Days 9-10 or 17-18. At 120 days of age half the numbers of rats in each condition were given subclinical dosages of lithium (1.5 mEq/kg) and pilocarpine (15 mg/kg) or saline. 40 days later all rats were tested in a conditioned fear paradigm. A four-way analysis of variance as a function of the variables anoxia, age at the time of anoxia sex, and subclinical seizure induction indicated a significant interaction between sex and anoxic history. Post hoc analysis showed that performance of male rats exposed to the anoxic condition did not differ from normal or anoxic female rats. The results suggest that only 1 min. of preweaning anoxia may produce permanent changes in contextual fear conditioning for male but not female rats.