Open‐field behavior and heart rate in prenatally X‐irradiated rats

Abstract

Abstract Albino rats were exposed to X irradiation in utero on day 16 of gestation. In two separate experiments, animals that received 200 r, but not those that received 100 r, showed increased locomotor activity in an open‐field on three successive daily 3‐minute test sessions. In contrast to this hyperactivity, exploration measured by the duration of sniffing at novel objects was lower in irradiated animals on the first test day, but reached the level of the controls on the second test day. Animals with previous testing experience did not show increased locomotor activity at the age of one year. Measures of defecation did not discriminate as reliably as did locomotor activity. Animals that received 200 r also had a higher heart rate than a control group, with the difference decreasing over a 60‐minute testing period. The data would indicate that prenatally X‐irradiated rats show fearfulness when exposed to novel situations but with increased exposure to the testing situation or experience the animals' responses tend to approximate those of unexposed animals.