Neuraminidase activity in different regions of the seizing epileptic and non-epileptic brain.

The sialic acid in the brain is split from sialoglucoconjugates by sialidases (neuraminidases, EC 3.2.1.18), and is postulated to act as an inhibitor of cellular adhesion and to play a role in various membrane functions. Since epilepsy alters cellular interactions and connectivity, it is reasonable to propose that sialidases can be affected by this pathological state or, alternately, by seizures. Therefore, we studied the activity of total, soluble, and membranal sialidases in various brain regions in normal, kindled epileptic and non-epileptic seizing rats. The results showed that in kindled rats, the total activity of the sialidases significantly decreased in cerebral cortex (11.38%) and cerebellum (28.58%), whereas it increased in brainstem (35.51%), hypothalamus (2.88%) and hippocampus (9.37%). The activity of the membranous sialidases in kindled rats followed the same pattern as the total activity, whereas the activity of soluble sialidase was significantly lower than membranous activity. Interestingly, the activity of total and membranal sialidases in non-epileptic seizing rats paralleled that observed in kindled rats. We suggest that the seizure-induced decrease of sialidasic activity may not modify the number of sialic acid molecules bound to gangliosides in cell membranes, as compared to areas of increased activity, that may decrease them. These changes in sialidases' activity may reflect functional disturbances of membrane polysialylated gangliosides related to the functional and anatomical plastic changes associated to seizures. Our data indicate that these changes are related to the presence of seizures rather than to an established epileptic state.