Soman-induced brain lesions demonstrated by muscarinic receptor autoradiography.

Repeated exposure of rats to sublethal doses of soman resulted in moderate to severe symptoms of anticholinesterase intoxication and a pronounced weight loss within a small subgroup of these animals. A consistent pattern of cell loss and extensive neuronal necrosis appeared in specific brain areas within this subgroup. This neuropathology was not noted in rats unless they showed marked symptoms of poisoning including a precipitous weight loss. Neuropathology was most notable in the piriform cortex and thalamus. Quantitative receptor autoradiography indicated that these subjects had a significant decrease in muscarinic receptors in the piriform cortex and thalamus. The ratio of the muscarinic receptor densities in soman-treated rats with lesions to soman-treated rats without lesions was 57%, piriform cortex; 64%, ventrolateral thalamus; and 50%, mediodorsal thalamus. These decrements are distinguished from adaptive down-regulation because they are larger, there is no indication of recovery and there is a correspondence between histological lesions and the areas with decreases in muscarinic receptors. Thus, quantitative receptor autoradiography provides, in addition to kinetic information and topographical distribution, radiohistochemical evidence of neuronal damage.