Comparison of cholinergic drug effects on regional brain glucose consumption in rats and humans by means of autoradiography and position emission tomography.

Cholinergic mechanisms have been extensively studied in animals and have been implicated in the pathogenesis of human disorders such as Alzheimer's disease. However, few investigations have directly evaluated the validity of extrapolating the results of animal studies to humans. As a component of a continuing examination of the contribution of cholinergic deficits to the alterations in brain metabolism that occur in Alzheimer's disease, we have compared the effects of scopolamine and physostigmine on regional brain energy metabolism in both rats and humans, using a common region of interest atlas. In Alzheimer's patients and in rodents, physostigmine increased glucose metabolism in several regions (e.g. thalamus) and decreased it in others. Overall, there was a significant positive correlation for the effects of physostigmine in the nineteen brain regions studied in both species (r = 0.51, P < 0.05). In normal humans, scopolamine induced a metabolic increase in most brain regions except in the thalamus. Outside this structure, the regional effects of scopolamine were significantly and negatively correlated (r = 0.58, P < 0.01) between rat and human. These results suggest that: (1) cholinergic mechanisms have a similar anatomic distribution in both species, (2) muscarinic receptor-mediated cholinergic effects could predominate outside the thalamus, (3) muscarinic mechanisms are inhibitory in humans but are more complex and possibly excitatory in rats, (4) nicotinic stimulatory effects are found in the thalamus of both species, and (5) physostigmine, but not scopolamine, alters glucose consumption similarly in both species.