The changes in density of M-cholinergic receptors in different areas of senile rats and the regulatoryaction of Huang Qi (黄芪 Radix Astragali,a drug for warming yang and replenishing qi) were observedby autoradiography.The results showed that the gray scale displayed in brain sections was clear andmainly distributed in the cortex,hippocampus and striate body,while that due to nonspecificcombination was negligible.The gray scale in the cortex,hippocampus and striate body of theexperimental group was markedly lower than that in the young control rats,decreased respectively by24.87%,14.12% and 12.76% (all P<0.05);but it was obviously higher than those in the senile controlrats,increased respectively by 24.15%,14.38% and 13.47% (P<0.05).The data indicate that Huang Qi(黄芪 Radix Astragali) may up-regulate the decreased density of M-cholinergic receptors in the brain ofsenile rats. The changes in density of M-cholinergic receptors in different areas of senile rats and the regulatoryaction of Huang Qi (黄芪 Radix Astragali,a drug for warming yang and replenishing qi) were observed by autoradiography.The results showed that the gray scale displayed in brain sections Was clear andmainly distributed in the cortex,hippocampus and striate body,while that due to nonspecificcombination was negligible.The gray scale in the cortex,hippocampus and striate body of the experimental group was markedly lower than that in the young control rats,decreased respectively by24. 87%,14.12% and 12.76% (all P<0.05); but it was obviously higher than those in the senile controlrats,increased respectively by 24.15%,14.38% and 13.47% (P<0.05).The data indicate that Huang Qi (黄芪 Radix Astragali) may up-regulate the declined density of M-cholinergic receptors in the brain ofsenile rats.