Effects of a long-interval retention on the hypoxia-induced impairment of performance in a fixed-interval schedule.

Retention of the fixed-interval (FI) responding was studied in rats after a chronic hypoxic treatment. The rats were trained over a 25-day period on a FI 60 s schedule. The rats were then given a normoxic or hypoxic (3.5 % O2 for 10 min) treatment once a day for 4 days after which they were maintained in the animal quarters for 6 supplementary days. A retention test consisting of 4 daily FI 60 session followed the 10-day interval. The results showed that the performance during the retention test was very similar for both groups of rats. These data contrast with the deficit of retention observed when the retention FI 60 session were undertaken 24 h after the same hypoxic treatment. It is suggested that the results are due to a recovery from hypoxia-induced retrieval deficits rather than to the progressive attenuation of non-specific effects of hypoxia, such as anhedonia, hypoactivity, motivational changes or structural brain damage.