Effect of AF64A on cerebral oxygen consumption in young and old rats

Regional brain O2 consumption was determined in conscious Fischer-344 rats 3- and 33-months of age after intrahippocampal injection of the selective presynaptic cholinergic neurotoxin AF64A to investigate the influence of acetylcholine on this parameter. Regional cerebral blood flow (rCBF) was determined with 14[C]-iodoantipyrine. Regional arterial and venous oxygen saturation was measured microspectrophotometrically. Regional cerebral oxygen consumption was calculated by multiplying rCBF and cerebral oxygen extraction. Systemic hemodynamic and blood gas parameters were not altered by aging or AF64A. Aging or sham injection per se did not have any significant effect on rCBF, oxygen extraction and cerebral oxygen consumption. In 3-month-old AF64A-treated rats, rCBF, oxygen extraction or cerebral oxygen consumption were significantly lower than in the control group of the same age. Old AF64A-treated animals demonstrated a significant decrease in rCBF and cerebral oxygen consumption but not in cerebral oxygen extraction when compared to the sham-lesioned group of the same age. Oxygen consumption was significantly decreased by AF64A in each examined region of both young and old groups of rats, although the decreases were less severe in the older rats. This may be related to the lesser influence of the cholinergic system on cerebral oxygen consumption in old animals or a decreased toxicity of AF64A in older animals.