Effects of both 6-hydroxydopamine-induced and electrolytic lesion of the substantia nigra on the rotational behavior and audiogenic seizures in the rat.

1. Twenty-eight male albino rats were evaluated for audiogenic seizure sensitivity by systematic observation and the recording of behavior by ethological methods. The animals were subjected to high-intensity acoustic stimulation and their behavior was evaluated by reference to an audiogenic severity index (SI). Animals were classified as susceptible (S) or resistant (R) depending on the SI value. R animals were: 1) subjected to chemical lesion of the substantia nigra compacta with 6-hydroxydopamine (6OHDA), followed by SI quantitation, contralateral electrolytic lesion of the substantia nigra reticulata and new SI evaluation (N = 6); 2) a group of control animals (N = 10) received 0.9% saline followed by SI evaluation, contralateral sham (mechanical) lesion and new SI calculation; 3) another group (N = 10) was subjected to unilateral electrolytical lesion of the substantia nigra reticulata and SI evaluation. 2. Effects of asymmetry were observed after chemical or electrolytic lesions, but these alterations correlated only with increased audiogenic sensitivity in rats with electrolytic lesions in the substantia nigra reticulata. No behavioral changes were observed in any of the controls. The amphetamine-induced rotational behavior presented a definite left pattern (ipsilateral to the 6OHDA lesion) for the animals with bilateral lesions, with an asymmetry index of 98%, whereas the sham-lesioned controls showed a 60% asymmetry index which was not significant. 3. The relationship between asymmetry and simultaneous audiogenic sensitivity may correspond to changes in the basal ganglia possibly in the hypersensitive postsynaptic portions of the substantia nigra reticulata efferents.