Behavioral characteristics of micrencephalic rats in high and low shuttlebox avoidance lines.

Rats of two lines, selectively bred for high and low shuttlebox avoidance response, and unselected line of the Sprague-Dawley (SD) rats were given an IP injection of methylnitrosourea (MNU) at 5 mg/kg on day 13 of gestation. Their offspring, all with micrencephaly, were subjected to the Biel maze, shuttlebox avoidance, and wheel cage activity tests during 6 to 9 weeks of age. Results from micrencephalic rats were compared with those obtained from untreated control offspring of the respective lines. The MNU-treated offspring in each line made more errors than controls in the Biel maze, and showed similar avoidance responses to controls in the shuttlebox test. Line differences in effects of MNU treatment were observed in elapsed time in the straight channel, extinction of shuttlebox avoidance responses, and activity in the wheel cage. These line differences in effects of MNU treatment may be related to control baseline levels of behavior in which the three lines differed widely, and suggest that the behavioral effects of prenatal MNU treatment vary in rats depending on the lines used.