Effect of midbrain and pontine tegmental lesions on the maximal electroshock seizure pattern in rats.

A bilaterally induced mechanical lesion of the midbrain was highly effective in abolishing the hindlimb extensor (HLE) component of the maximal electroshock seizures (MES) in rats. Although these lesions produced damage to a variety of midbrain structures, correlations between different lesion placements and effects in the MES test provided evidence that damage to superior cerebellar peduncle (PCS) and/or reticular formation (RF) was responsible for inhibition of hindlimb extension. Moreover, discretely placed electrolytic lesions disrupting either the PCS or the RF were found to abolish the hindlimb extensor component of the MES test. These findings are consistent with the work of other investigators showing that total cerebellectomy abolishes the HLE component of MES and suggest that activity in the cerebellum and the midbrain reticular formation plays a major role in regulating the tonic phase of electroshock induced seizures.