The effect of magnocellular basal forebrain lesions on circadian locomotor activity in the rat

Locomotor activity (LMA) was assessed in rats given ibotenic acid lesions in the nucleus basalis magnocellularis (group NBM) or sham surgery (group OC). Two weeks after surgery, rats were monitored for 8 hours during the middle of either the 12 hr light (day) or 12 dark (night) period of the diurnal cycle. Six behavioral measures of LMA were examined: horizontal activity, vertical activity (rearing), distance travelled, movement time, movement velocity (distance/time) and revolutions (turning behavior). During the day, no statistically significant differences between the NBM and OC groups were observed in any of the measures. At night, both NBM and OC groups generally were more active than during the day, and the NBM group generally was more active than the OC group. Because the diurnal LMA of rats with NBM lesions was not significantly affected during the day, when laboratory animals are usually tested, hypotheses regarding lesion-induced locomotor abnormalities cannot be invoked to account entirely for the impaired performance observed in NBM rats on tasks designed to measure learning and memory.