ABERRANT TIMM-STAINED FIBERS IN THE DENTATE GYRUS FOLLOWING TETANUS TOXIN-INDUCED SEIZURES IN THE RAT

The present study addresses whether seizures, which result from the ch ronic block of inhibition caused by an intrahippocampal injection of t etanus toxin, induce axonal sprouting of the hippocampal messy fibres. Timm stain was used to identify the messy fibre terminals. In nine of 15 animals killed at 1 month or later after an injection of tetanus t oxin, Timm-stained terminals were observed bilaterally in the inner mo lecular layer and in seven animals a meshwork of Timm-stained fibres/t erminals was also observed bilaterally in the outer molecular layer of the fascia dentata. None of these changes were observed in any of the 12 saline-injected controls, There was no obvious correlation between the number of motor fits an animal exhibited and the amount of Timm-s tained fibre sprouting present in either the inner or outer molecular layer, The Timm-stained axonal sprouting into the outer molecular laye r of the fascia dentata may simply reflect the reinnervation of sites on the granule cell dendrites, previously occupied by the terminals of the hilar somatostatin-containing cells, These hilar somatostatin-con taining cells which are believed to project to the outer molecular lay er are known to succumb to the seizure activity in this animal model o f epilepsy.