Induction of preconvulsive behavior and Fos expression by dopamine-induced nigral lesion in the rat

The substantia nigra pars reticulata (SNpr) has been proposed to play an important role in controlling the propagation and/or the generation of limbic seizures. Earlier work has shown that SN lesions have differential effects on seizure activity, suggesting that at least two discrete topographical regions mediate anticonvulsant or proconvulsant effects. The present investigation showed that exogenous dopamine (DA; 1.5-2.0 mumol) unilaterally injected into the anterior SNpr induced preconvulsive behavior (starting, immobilization, facial and mouth movements and wet-dog shakes). In addition, these rats showed Fos oncoprotein expression in the limbic system. These effects were observed in 90% of the rats with anterior SNpr DA injection. Rats with posterior SNpr injection did not show preconvulsive behavior nor Fos expression. These results show for the first time that unilateral DA lesion of the anterior portion of SNpr elicits Fos expression and preconvulsive behavior. In addition, the results suggest that lesion of the anterior and posterior regions of SNpr appear to exert different influences in the generation of preconvulsive behavior. The time course of behavior changes and Fos expression was also studied.