Application of silicon microphysiometry to tissue slices: detection of metabolic correlates of selective vulnerability.

The silicon microphysiometer is a recently developed instrument which measures rates of proton efflux in real time from small numbers of cultured cells. Since the main products of cellular metabolism are lactic acid and carbon dioxide, this instrument affords an indirect but sensitive measure of cellular metabolism. We previously described the use of the instrument with primary neuronal cultures (Raley-Susman, K.M., Miller, K.R., Owicki, J.C. and Sapolsky, R.M., Effects of excitotoxin exposure on metabolic rate of primary hippocampal cultures: application of silicon microphysiometer to neurobiology, J. Neurosci., 12 (1992) 773-780). In the present report, we adapt the instrument for the indirect measurement of metabolism in tissue slices. In initial studies, we demonstrate stable measures of metabolism with low background noise in hippocampal slices. In addition, measures were relatively insensitive to slice thickness, preparation time or the possible contribution of contaminating bacteria. We then demonstrate the ability to detect metabolic correlates of selective vulnerability in individual hippocampal cell fields. Specifically, we observe a metabolic response to kainic acid that was selective for CA3-derived tissue, and a response to cyanide that was selective for CA1-derived tissue. This corresponds to the well-known vulnerability of CA3 and CA1 to excitotoxic and ischemic insults, respectively. Finally, we show that glucocorticoids, stress-sensitive steroid hormones which are known to exacerbate the toxicity in kainic acid in CA3 neurons, exacerbate the metabolic effects of this excitotoxin as well; in this case, the steroid manipulation was carried out in rats prior to killing. Thus, this instrument represents a complement to more traditional approaches for assessing metabolism in specific brain regions and it can potentially be used for a broad variety of studies with animals of differing ages and pre-mortem manipulations.