Loss of parvalbumin immunoreactivity defines selectively vulnerable thalamic reticular nucleus neurons following cardiac arrest in the rat

The thalamic reticular nucleus (NRT) is one of the most vulnerable structures to selective neuronal damage both in human cardiac arrest patients and in experimental rodent global cerebral ischemia models. The detailed distribution of neuronal injury within the NRT was examined following 10-min cardiac arrest in the rat with conventional Nissl staining, ⁴⁵Ca autoradiography and immunocytochemistry of the calcium binding proteins parvalbumin (PV) and calretinin (CR). While Nissl staining was almost unable to show the exact boundary of the nucleus and of the lesion, immunocytochemistry of PV proved to be the most useful index of the exact location and extent of neuronal loss in the NRT after ischemia. Calcium autoradiography was a sensitive method for detecting the lesion, and showed a similar distribution to the loss of PV staining, but did not give optimal spatial resolution. Quantitative analysis of PV staining at 7 days of recirculation demonstrated cell loss restricted to the lateral aspect of the middle segment of the NRT, identical with the distribution of large fusiform neurons in the somatosensory component of the nucleus. CR-positive neurons in the NRT were completely spared, although not all surviving neurons contained CR. These studies provide the first detailed characterization of the distribution of vulnerable neurons within the NRT after experimental ischemia and suggest that immunocytochemistry of PV is a useful tool for quantitative analysis of the lesion for use in further experiments to elucidate the mechanisms of selective vulnerability of the NRT.