Physiological and behavioural consequences of seizures induced in the rat by intrahippocampal tetanus toxin

Injecting tetanus toxin into rat hippocampus induces a syndrome of intermittent generalized seizures which recurs for about one month. Following remission from their seizures, the rats exhibit very persistent impairments of learning and memory. Learning was impaired on a circular platform task and a spatial reference memory task, and evoked responses from the commissural-CA3 pyramidal cell system were depressed for up to 22 weeks after injection. There was no significant loss of pyramidal neurons because antidromic responses, evoked from other parts of the commissural fibre system, were not affected by the toxin treatment. The depression of these pyramidal neurons provides a reasonable physiological explanation for the learning impairment. These results suggest that impairments of neuronal function can be significant factors in the development of interictal behavioural abnormalities.