Thalamic retrograde degeneration in the congenitally hydrocephalic rat is attributable to apoptotic cell death

Congenitally hydrocephalic HTX rats develop ventricular dilatation with extensive damage of the cerebral white matter. Recently, we have reported that neuronal cell death also occurs in the thalamus of HTX rats. To investigate the mechanism underlying this thalamic degeneration in these animals, we carried out a histopathological study of the brain at different phases of postnatal development. Eosinophilic neurons with condensed chromatin or fragmented nuclei were observed in the thalamus from postnatal day 17 onward. The incidence of cell death in the thalamus increased with the progression of hydrocephalus. Ultrastructurally, thalamic neurons occasionally had apoptotic features including nuclear chromatin condensation and marginalization. Immunohistochemically, single-stranded DNA-positive neuronal nuclei were found in the thalamus. They were also positively stained with the TUNEL method. Marked loss of myelin and axons with many TUNEL-positive oligodendrocytes were found in the cerebral white matter. These findings suggest that the neuronal cell death observed in the thalamus in hydrocephalic HTX rats is retrograde degeneration due to extensive damage of axons in the cerebral white matter and that the thalamic retrograde degeneration is attributable to apoptotic cell death.