Synaptophysin immunoreactivity in temporal lobe epilepsy-associated hippocampal sclerosis

Abstract

We have previously devised a semiquantitative grading system for hippocampal sclerosis (HS) in specimens resected for intractable temporal lobe epilepsy. The grades range from zero to four based on the amount and distribution of neuronal loss and gliosis. In the present study hippocampal sections from 25 patients who had temporal lobe epilepsy and had previously been assigned a grade were examined with synaptophysin immunohistochemistry, and the synaptic content in specific hippocampal fields was correlated with the results of the HS grading system. There was evidence of both significant synaptic loss and increased synaptic density in different fields of the hippocampus with increasing HS. A marked decrement of synaptic immunostaining was present in fields CA1 and CA4 that were highly correlated with HS grade. Sector CA4 seemed to respond in a more graded or continuous way to the pathological insults occurring in temporal lobe epilepsy than did CA1, which appeared to exhibit an all or nothing response. Also, while the width of the outer part of the molecular layer of the dentate (mld) gyrus decreased with increasing HS grade, the inner part of the mld became wider and showed an increased synaptic density so that the overall width of the mld was increased in the high-grade group. We conclude that quantitative measurement of synaptic loss in CA1 and CA4 using synaptophysin immunohistochemistry is a sensitive method for detecting HS and correlates well with the empirically derived HS grading scale, with CA4 exhibiting a more graded response than CA1. In addition, a plasticity response in the inner part of the mld in patients with high-grade HS has been confirmed and quantitated.