Histochemical changes of central cholinesterases inhib-ited by soman

Histochemical localization of the central cholinesterases (ChE) was studied after inhibition by systematic in-toxication of soman (methyl pinacolyl phosphonofluoridate) in rodents (mainly in rats). There was a regional ChE inhibition figure in centr'al nervous tissues below the lethal dose of soman. Larger than a lethal dose usually yielded an extensive inhibi-tion. There was always a small artery at the center of each regional ChE-inhibited area, but the ChE activity of capillary walls still remained in the area. It was very likely that the infiltration of soman into surrounding tissues was easier through the wall of small arteries or arterioles than through that of capillaries. The reason for this phenomenon was discussed briefly.