Preservation of dendrites with the presence of reorganized mossy fiber collaterals in hippocampal dentate granule cells in patients with temporal lobe epilepsy

Abstract

Dendritic morphology was studied in human hippocampal dentate granule cells (DGCs) by intracellularly-injecting biocytin in slice preparations that were obtained from temporal lobe epilepsy patients who underwent a surgical treatment for medically-intractable seizures. These DGCs had a fan-shaped dendritic domain of 54.1°± 4.1 S.E.M. with 13.8 ± 1.1 branch points and an estimated total dendritic length of 11535.6 µm ± 3045.4. Dendritic spines were counted, and spine density was calculated to be 0.25 spines/ µm ± 0.16 S.E.M., However, when the cells were categorized into two groups based on the presence or absence of the aberrant mossy fiber collaterals, the number of dendritic branches was significantly lower and spine density was significantly higher in DGCs that had aberrant collaterals. In particular, in the proximal dendrite, the spine density was 5 times higher in DGCs whose own mossy fibers were reorganized sending aberrant collaterals to this dendritic region (0.750 spines/ µm ± 0.203 S.E.M.: P < 0.01) than the DGCs without such collaterals (0.082 spines/ µm ± 0.021 S.E.M.). These results suggest that the axonal reorganization may have an effect on the morphology of DGC dendrites directly or indirectly in such a way that dendritic structure and spines could be protected from seizure-induced excitotoxic cell damage.