Focal ischemia induces transient expression of IL-6 in the substantia nigra pars reticulata.

We examined the expression of IL-6 in the substantia nigra pars reticulata (SNr) at various time points after transient (3 h) middle cerebral artery occlusion (MCAO) in rats. The animals were killed at 1, 3, 7 or 14 days following operation. Coronal brain sections were processed for immunohistochemistry with antibodies against GFAP, OX-42 and IL-6 and for Nissl staining. Microglial activation was detected 3 and 7 days after ischemia. Reactive astrocytes have been found 7 and 14 days after ischemia. IL-6 expression was detected 3 and 7 days after ischemia. IL-6-positive cells beared the typical morphology of neurons. Distribution of IL-6-positive cells within the SNr was not homogenous. The lateral area of the SNr bears the highest number of IL-6-positive neurons while the central core bears the lowest. Quantification of intact neurons in the SNr 14 days after reperfusion shows that the highest amount of cell loss was found in the central core of the SNr and less neuronal cell loss was observed in the lateral area of the SNr. Thus, the SNr area with the highest IL-6 expression 3 and 7 days after ischemia bears the highest number of intact neurons 14 days after ischemia. This finding could be a clue for the neuroprotective role of IL-6 in the remote region SNr after focal cerebral ischemia.