Fig. 1.

A, Light micrograph of a semithin section through CA1 of an untreated (control) cultured hippocampal slice maintained in vitro for 16 d. Several pyramidal neurons (P) are shown with their contiguous apical (a) or basal (arrowheads) dendrites. A basophilic organelle (arrow) can be seen clearly in one CA1 neuron. Magnification, 1200×. B, Light micrograph of CA1 neurons from a semithin section obtained from a cultured slice exposed to ZPAD, an inhibitor of cathepsins B and L, from culture day 11–16. The pyramidal cells (P) show many of the same features as those in A, including centrally located nuclei, apical (a) dendrites, and basal (arrowheads) dendrites. Inspection of the cytoplasm of these neurons, however, reveals a dramatic increase in the number of basophilic punctate structures (arrows). Note that many neurons show an asymmetrical distribution of the darkly stained granules in that more are found in the basal portion of their cell bodies. Magnification, 1200×.