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 produces a chronic model of temporal lobe epilepsy. We have examined whether morphological changes occur in hippocampal CA1 pyramidal cells in this model by using intracellular injections of biocytin. Eight weeks after the injection of tetanus toxin, significantly more "dye-coupled' cells were found in this group than in the buffer (control) injected group (63% compared with 7%). Half of these coupled cells appeared to be linked at the soma, and the other half by dendrodendritic contacts. Analysis of the dendritic trees revealed that the tetanus toxin group showed a decrease in complexity around the proximal to mid-apical dendritic regions and around the mid- to distal basal dendritic regions. The dye-coupling indicates that electrotonic interaction is induced or strengthened between hippocampal neurones, possibly as a result of the epilepsy-induced dendritic damage.