Fig. 5. The histologic appearance of activated caspase-3–positive neuronal profiles in the lateral septum (A) , anterodorsal thalamic nucleus (B) , caudate nucleus (C) , and cerebellum (D) of fetal brains harvested 3 h after a 5-h exposure to ketamine. Most of the affected neurons in the septum (A) and thalamus (B) are large multipolar neurons that are relatively resistant and thus are in a relatively early stage of degeneration. The affected neurons in the caudate nucleus (C) are morphologically heterogeneous. A small cell type degenerates rapidly and presents as a faintly stained, small, condensed, shrunken structure amid other larger cells that degenerate on a slightly later time schedule. The most sensitive cell population in the cerebellum (D) is one that is located in the inner portion of the inner granule cell layer (IGL). These cells degenerate rapidly after exposure of either infant rodents or fetal monkeys to alcohol or anesthetic drugs. As explained in previous publications,8,39it is not clear whether they are granule cells or other cell types that are migrating through the granule cell layer.