Prenatal protein malnutrition and working memory performance in adult rats

The performance of prenatally protein malnourished rats was examined in 2 different tasks of learning and memory beginning at 90 or 160 days of age. In Experiment 1, a rewarded alternation task, run as a spatial working memory procedure on an elevated T-maze, revealed no differences between the formerly malnourished (6/25) and control (25/25) rats when either a minimal or a 20-s inter-trial delay was used. Neither was there a difference when an additional, and conflicting, 'information' run was given to provide a source of proactive interference. In extinction, the 6/25 rats required significantly more sessions to abolish their learned alternation response than the controls. In Experiment 2, an operant equivalent of the T-maze task was applied which allowed greater control over the delay interval and task difficulty. Each trial consisted of a forced information response, for which a randomly selected lever was presented, followed by a free-choice stage, when both levers were presented. The rats were rewarded for pressing the lever not presented at the information stage. The inter-trial interval was always 30 s. When the information response requirement was 10 presses no group differences were found in acquisition of the alternation response or in task performance at delays of 5, 10, 15 or 30 s between information and choice stages. As task difficulty was increased, the performance of the 6/25 rats improved more than that of the 25/25 rats, such that they performed significantly better at the longest delay when the information response requirement was 2 presses. This superior performance of the experimental animals is discussed. No differences in reversal were detected. It was concluded that there is no straight-forward 'hippocampal syndrome' in prenatally malnourished adult rats. Working memory appears largely unaffected, whereas susceptibility to interference and extinction may be modified, depending upon the test parameters employed.