Abstract
An accurately validated method was developed for quantitative determination of succinate dehydrogenase (EC 1.3.99.1; SDH) activity in individual sympathetic neuron perikarya by microdensitometric measurement of an SDH-nitroblue tetrazolium-derived formazan final reaction product. Optimal incubation medium and reaction conditions were determined for measurement of reaction product in cryostat sections of rat superior cervical and celiac-superior mesenteric ganglia. The Beer-Lambert laws were verified for the ganglion tissue, and microdensitometric measurements (expressed as mean cell density readings; MCDR/min-1), characteristic of the Michaelis-Menten equation, enabled the results to be used for enzyme kinetic determinations of SDH activity. Km and Vmax values were obtained following Hans linear transformation of the readings. Between the ages of 6-24 months no significant variations in Km values were recorded, indicating an unchanged structure for SDH (overall mean Km = 0.083 +/- 0.055 mM). However, in both ganglia there were significant decreases (ranging from 43-54%) in Vmax values for SDH at 24 months. The overall mean Vmax value at 6 months was 4.01 +/- 0.61 (MCDR) and at 24 months was 2.07 +/- 0.76 (MCDR). This suggests that an overall decrease in metabolic activity takes place with age in sympathetic neurons of the rat superior cervical and celiac-superior mesenteric ganglia.