Nocturnal rotation in normal rats: correlation with amphetamine-induced rotation and effects of nigrostriatal lesions.

Normal unoperated rats were observed to rotate (turn in circles) at night. For most (91.7%) rats, the preferred direction of rotation was consistent across hours and days and was the same as the direction of rotation elicited by D-amphetamine (1.0 mg/kg) during the day. The magnitudes of nocturnal and D-amphetamine-induced rotation were also highly correlated. After rats showed stable diurnal patterns of rotation, unilateral lesions were made in either the substantia nigra, the nigrostriatal bundle or the caudate nucleus. All lesions produced transient contralateral rotation within the first 24-48 h after surgery. The time-course of this contralateral rotation was more prolonged after nigral lesions than after nigrostriatal bundle lesions and least after caudate lesions, suggesting that the duration of a degeneration release of dopamine is proportional to the length of the degenerating axon. Lesion size was correlated with the intensity of contralateral rotation but not with the time-course. At each rostralcaudal level, the magnitude of contralateral rotation was greater if the lesion was in the side of the brain opposite to the preoperative direction of rotation than if in the same side. By three days after surgery, all rats returned to a mostly normal diurnal cycle with the direction of rotation now being ipsilateral to the lesion. D-Amphetamine potentiated the ipsilateral rotation, though rats with lesions in the same side of the brain as the preoperative direction of rotation had larger drug responses than rats with similar lesions in the opposite side of the brain. By one month after surgery, the direction of spontaneous rotation of most rats had returned to the preoperative direction. As at all other times, the magnitude of rotation was, in part, dependent on the side of the lesion with respect to the preoperative bias. It is suggested that, following a unilateral lesion, compensatory processes occur to a greater extent if the lesion is in the normally more active side of the brain.