As shown in Figure 1, ISEL-positive cells in the tissue sections were identified by the presence of a characteristic brown staining in the nuclei. The characteristic brown diaminobenzidine (DAB; Ventana Medical Systems Inc, Tucson, Ariz) reaction product appeared either as either (1) diffuse nuclear staining, (2) chromatin clumps, or (3) nuclear blebs. In most cases, the vast majority of nuclei showed no ISEL-positive staining. The slides were codified and analyzed under strictly blinded conditions using a Leitz Laborlux (LEICA Microsystems, Wetzlar, Germany) bright-field microscope equipped with a solid-state video camera interfaced to a Bioquant Image Analysis System. Initially, a column of cortex (width, 300 µm) was delineated using a 4× objective lens, and the sampling field extended across the 6 layers from the pial surface above layer I to the interface of layer VI with the underlying white matter. Using a 40× objective lens, the position of each ISEL-positive nucleus was marked using a X,Y,Z-encoder (Boeckler Instruments, Petershagen, Germany) interfaced with the BIOQUANT System (BIOQUANT Image Analysis Corp, Nashville, Tenn) (Figure 2). The number of nuclei showing staining that was diffuse or that appeared as chromatin clumps or nuclear blebbing was determined for each layer of each case (Figure 2). Although there was no specific way of distinguishing between neurons and glia in the ISEL preparation, most of the labeled nuclei were larger than those typically seen in glial cells, and this suggested that the data reported herein may have been derived from neuronal cells, particularly since few if any labeled cells were found in the subcortical white matter. The data were expressed as a numerical density (ie, the number of nuclei per square millimeter of sampling field) for each type of ISEL-positive nucleus. The latter data for the respective cases were averaged across the 3 groups and expressed as a mean (SE). Using a frequency histogram analysis, the data were found to be distributed in a nonnormal manner. Accordingly, the nonparametric Kruskal-Wallis test was used to assess the significance of differences in the means across the 3 groups. A 2 × 2 contingency table analysis was also used to evaluate differences in the distribution patterns.