Ca2+ and in vitro kainate damage to cortical and hippocampal SMI-32(+) neurons.

SMI-32 is a monoclonal antibody to non-phosphorylated neurofilament epitopes, which labels subsets of pyramidal neurons prone to degeneration in Alzheimer's disease. We found SMI-32 to identify a small minority of neurons in dissociated cultures of murine cortex and hippocampus (SMI-32(+) neurons). Labeled neurons, which were larger than average and were often immunoreactive for GABA, were preferentially destroyed by brief kainate exposures. This rapidly triggered kainate damage to SMI-32(+) neurons was dependent upon the presence of Ca2+ in the media during the toxic exposure. Furthermore, most SMI-32(+) neurons in both cortex and hippocampus were subject to kainate-activated cobalt uptake, a histochemical procedure that marks cells with Ca2+ permeable AMPA/kainate channels. The unusual vulnerability of cortical and hippocampal SMI-32(+) neurons to AMPA/kainate receptor-mediated injury may result from rapid Ca2+ entry through Ca2+ permeable AMPA/kainate receptor-gated channels.