Hyperactivity induced by prenatal administration of methylazoxymethanol: association with altered performance on conditioning tasks in rats.

Methylazoxymethanol (MAM), an alkylating agent which kills dividing cells, produces microcephaly when administered to rats at 15 days gestation. Rats treated prenatally with MAM were tested on a variety of behavioral tests. The MAM-treated animals performed better than controls in the acquisition of a food-reinforced operant response, but poorer than controls on a passive avoidance procedure. When required to reverse the passive avoidance procedure by actively avoiding the portion of a chamber that was associated with shock, MAM-treated rats performed better than controls. The MAM-treated rats were microcephalic and were also hyperactive compared to controls. It was postulated that the behavioral changes observed in the conditioning tasks may be attributable to hyperactivity. A possible neurochemical basis for this hyperactivity is discussed.