Histology and immunohistochemistry. A: Severe neuronal loss and astrogliosis of the mediodorsal thalamic nucleus in the present case. Neurons are indicated by arrows, reactive astrocytes by circles. B: For comparison, the same thalamic nucleus is shown in an age-matched subject without prion disease; neurons are indicated by arrows. C: Immunohistochemistry for glial fibrillary acidic protein (GFAP) reveals reactive astrocytic gliosis in the mediodorsal thalamic nucleus of the present case but not in a control subject of the same age without prion disease (D). E: Prominent astrogliosis in the frontal cortex. The inset (lower left corner) depicts three reactive astrocytes at higher magnification. F: Fine spongiform degeneration of the parietal cortex. G: Intense punctate or "synaptic" PrP immunostaining and sparse clusters of small granules in the cerebral cortex (parahippocampal gyrus; 3F4 antibody).