Densitometric analysis of cytochrome oxidase in ischemic rat brain

Elevated brain lactate during incomplete ischemia is thought to contribute to the irreversibility of cell damage by interference with mitochondrial respiratory function, that should be evident in reduced cytochrome oxidase (CO) activity. In this study changes in the density of CO staining in a stroke model in the rat were assessed. Brains were analyzed subsequent to 30 min of ischemia followed by 30 min of reperfusion. The effects of postischemic treatment with sodium dichloroacetate (DCA)--a compound used to decrease lactate, were also evaluated. Examination of lateral cortex, hippocampus, and corpus striatum showed different intensities of CO in a distribution consistent with known regional variations in metabolic activity of the forebrain. Known laminar staining patterns in lateral cortex and areal patterns in the hippocampus were also confirmed. Comparable regions in ischemic forebrain were stained less densely for CO than controls. Image analysis demonstrated that the density of CO: (a) was greater in lateral cortex than hippocampus in control; (b) in ischemics was reduced by an equal degree in cortex and hippocampus; (c) lacked regional uniformity in ischemic rats; and (d) was not changed by DCA treatment in the majority of cases of ischemia. Our results suggest that lactate may not be the major determinant of 'selective vulnerability'. Despite elevated lactate levels in lateral cortex when compared to hippocampus in a previous study, the proportionate decrease in CO activity in lateral cortex and hippocampus was equal. However, there was a considerable decrease in CO activity subsequent to high brain lactate and some ischemic hemispheres appeared to respond to DCA treatment. Therefore, the role of excessive lactate in the exacerbation of 'selective vulnerability' warrants further evaluation. CO histochemistry can be used successfully to determine the distribution of pathology and the quality of fixation of ischemic forebrain. Densitometric measurements allowed comparative assessment of degrees of injury and the effects of treatment in discrete anatomical regions. This kind of analysis may allow localization of pathology within specific cellular circuits.