DENDRITIC SHRINKAGE AND DYE-COUPLING BETWEEN RAT HIPPOCAMPAL CA1 PYRAMIDAL CELLS IN THE TETANUS TOXIN MODEL OF EPILEPSY

A small dose of tetanus toxin injected into the rat hippocampus produc es a chronic model of temporal lobe epilepsy. We have examined whether morphological changes occur in hippocampal CAI pyramidal cells in thi s model by using intracellular injections of biocytin. Eight weeks aft er the injection of tetanus toxin, significantly more 'dye-coupled' ce lls were found in this group than in the buffer (control) injected gro up (63% compared with 7%). Half of these coupled cells appeared to be linked at the soma, and the other half by dendrodendritic contacts. An alysis of the dendritic trees revealed that the tetanus toxin group sh owed a decrease in complexity around the proximal to mid-apical dendri tic regions and around the mid- to distal basal dendritic regions. The dye-coupling indicates that electrotonic interaction is induced or st rengthened between hippocampal neurones, possibly as a result of the e pilepsy-induced dendritic damage.