Asymmetry of EEG arousal in rats with unilateral 6-hydroxydopamine lesions of substantia nigra: Quantification of neglect

Abstract

In an attempt to find an objective measure of the sensorimotor dysfunction elicited by unilateral 6-hydroxydopamine lesions of substantia nigra in rats, asymmetry revealed by neurological testing and drug-induced turning was compared with the arousing potency of lateralized nociceptive stimuli. Rats anesthetized with urethane reacted to pressure pulses applied to trunk skin contralateral to the lesion with shorter-lasting EEG arousal than to ipsilateral stimuli of the same intensity. Asymmetry expressed by the EEG arousal asymmetry index (arousal duration elicited by the contralateral stimulus ÷ sum of arousal durations elicited by contralateral and ipsilateral stimuli) was more pronounced in the upper part of the trunk than in the lower. Similarly, EEG arousal reactions elicited from the rostral and middle stimulation points on the intact side lasted longer than those from the caudal point. Significant correlations were found between the EEG arousal asymmetry index and the intensity of contralateral turning after apomorphine or the symmetry score of the tactile orienting reactions. On the other hand the deficit in contralateral visual placing was correlated with the asymmetry score of somesthetic placing and with the intensity of ipsilateral turning after amphetamine. The quantitative EEG arousal asymmetry index proved to be a more sensitive and reproducible measure of neglect than the rough scoring procedure used in neurological testing. It is concluded that the complex neglect syndrome is due to failure of sensorimotor integration and that a substantial part of this deficit consists of the impairment of the arousal supporting systems which can be accounted for by blockade of the nigrostriatal dopaminergic pathway.