Brain neuronal RNA metabolism during sustained low-level soman toxication

The Long Term Changes in Liver DNA and Total Protein Contents Following Low Level Sarin Exposure in Rats

1. The changes in contents of DNA and total protein in the liver of the rats exposed to low level sarin by inhalation at 3, 6 and 12 months following the exposure were studied. The influence of sarin on the DNA and protein metabolism in liver was determinated by the measurements of incorporation of tritiated thymidine into DNA, the concentration of DNA and total protein. 2. Our results show that not only symptomatic level 3 but also asymptomatic levels 1 and 2 of sarin are able to significantly decrease the incorporation of radiolabelled thymidine without changing total concentrations of DNA as well as protein at three months following sarin exposure. On the other hand, the significant decrease in total contents of DNA and protein in liver without the changes in the incorporation of tritiated thymidine was determined in liver six months following sarin exposure. Practically no significant changes in the metabolism of DNA and protein were observed at 12 months following sarin exposure. 3. Thus, not only clinically manifested intoxication but also low-level, asymptomatic exposure to nerve agents such as sarin is able to influence the metabolism of nucleic acids as well as proteins even several months following the exposure.

The Influence of Sarin on Various Physiological Functions in Rats Following Single or Repeated Low-Level Inhalation Exposure

Long-term effects of low doses of highly toxic organophosphorus agent sarin on various hematological and biochemical markers and physiological functions were studied in rats exposed to sarin by inhalation. The results indicate that low-level sarin-exposed rats show long-term increase in studied markers of stress and decrease in synthesis of DNA de novo without the disturbance of the functions of cholinergic nervous system. Moreover, sarin at low doses is able to induce some neurotoxic effects including an increase in the excitability of central nervous system in rats at 3 mo following inhalation exposure. Relatively long-term spatial discrimination impairments in rats exposed to low-level sarin was demonstrated too. Therefore, nerve agents such as sarin seem to be harmful not only at high, clinically symptomatic doses but also at low doses without acute clinical manifestation of overstimulation of cholinergic nervous system because of long-term manifestation of alteration of neurophysiological and neurobehavioral functions in sarin-exposed rats.

Differential sensitivity of CNS regions to acetylcholinesterase inhibition following chronic low-dose soman treatment in the rat

Several discrete brain regions were analyzed for regional brain sensitivity to acetylcholinesterase (AChE) inhibition following administration of repeated low-dose soman (39 micrograms/kg, SC; once daily for 5 days). The same brain regions were also assayed on days 3 through 7 after the last injection of soman, to examine possible recovery of AChE. The observed regional brain sensitivity to AChE inhibition can be described in the following order: frontal cortex = piriform cortex greater than hippocampus = cerebellum = thalamus greater than striatum = hypothalamus. Most brain areas showed only a small recovery from this inhibition through the seventh day following the last soman injection. The progressive nature of the AChE inhibition during the week of soman administration and the failure to find a significant interaction between injection and day indicates that tolerance to soman exposure did not develop in this paradigm. The protocol described here appears to provide a useful method to study prophylactic measures for low-dose repeated soman exposure and evaluation of differential CNS inhibition and recovery from AChE inhibition.

Effect of soman intoxication on the organization of rat brain ribosomes and the translational activity of mRNA in a cell-free system

The effect of soman on rat brain ribosomes organization and translational activity of mRNA in cell-free system was studied in rats exposed to 1.3 LD50 soman (120 micrograms/kg body weight) and in rats repeatedly injected with 0.4 LD50 soman (35 micrograms/kg). Fifteen minutes after the injection of 1.3 LD50 soman the heavy polyribosomal fraction from rat brain was found to be enriched and translational activity of mRNA was enhanced. In rats administered five injections of 0.4 LD50 soman at 24-h intervals, the low density ribosomes appeared as the predominant fraction whereas the activity of mRNA in all cell-free system was significantly impaired. It is concluded that soman intoxication expresses a stimulatory or inhibitory effect on the processes of protein synthesis in the rat brain, depending on the dose schedule of soman administration.

Soman intoxication-induced increase in the levels of mRNAs coding for acute phase reactants

The effect of lethal and repetitive sublethal soman intoxication on the composition of rat liver mRNA was examined by cell-free translation and hybridization. It was found that lethal as well as sustained sublethal soman poisoning of rats elicited a typical acute phase response as judged by a several-fold increase in levels of mRNAs coding for the major acute phase proteins and the vast number of systemic and metabolic changes creating the acute phase response should be taken into account when the metabolic events during the recovery from organophosphate intoxication are under consideration.