The effects of repeated low-dose sarin exposure

• Published in: Toxicology and applied pharmacology Vol. 215; no. 2; pp. 119 - 134
• Main Authors: Shih, T.-M., Hulet, S.W., McDonough, J.H.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-09-2006; Elsevier
• Subjects: Acetylcholine; Acetylcholinesterase; Acetylcholinesterase - blood; Animals; Behavior, Animal - drug effects; Biological and medical sciences; Body weight; Body Weight - drug effects; Chemical and industrial products toxicology. Toxic occupational diseases; Chemical Warfare Agents - toxicity; Choline; Cholinesterase inhibitors; Cholinesterase Inhibitors - toxicity; Dose-Response Relationship, Drug; Electroencephalogram; Electroencephalography - drug effects; Erythrocytes - drug effects; Erythrocytes - enzymology; Functional observational battery; Gait - drug effects; Gas, fumes; Guinea Pigs; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; In vivo microdialysis; Injections, Subcutaneous; Lethal Dose 50; Longevity - drug effects; Male; Medical sciences; Nerve agent; Nervous system (semeiology, syndromes); Nervous System - drug effects; Nervous System - physiopathology; Neurology; Neurotoxicity Syndromes - etiology; Neurotoxicity Syndromes - metabolism; Neurotoxicity Syndromes - physiopathology; Organophosphate; Pathology; Repeated exposure; Sarin; Sarin - toxicity; Seizures; Seizures - chemically induced; Seizures - physiopathology; Sleep Stages - drug effects; Toxicology; Electroencephalogram; ACh; NT; Body weight; Repeated exposure; Acetylcholinesterase; LD 50; DFP; RBC; Organophosphate; Sarin; FOB; HPLC; Seizures; AChE; OP; DOPAC; EEG; Functional observational battery; i.m; LC 50; s.c; i.p; Nerve agent; Cholinesterase inhibitors; Pathology; HVA; Choline; CWNA; Acetylcholine; MTD; In vivo microdialysis; Choleretic; Hepatoprotector; Epilepsy; Electrophysiology; Esterases; Electroencephalography; Multiple dose; Chemical warfare agent; Anticholinesterase agent; Neurological disorder; Nervous system diseases; Toxic gas; Enzyme; Low dose; Exposure; Cholinesterase; Carboxylic ester hydrolases; Cerebral disorder; Toxin; In vivo; Anatomic pathology; Microdialysis; Convulsion; Central nervous system disease; Neurotoxin; Neurotransmitter; Hydrolases; Inhibitor; Organophosphorus compounds
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1016/j.taap.2006.02.003

This project assessed the effects of repeated low-dose exposure of guinea pigs to the organophosphorus nerve agent sarin. Animals were injected once a day, 5 days per week (Monday–Friday), for 2 weeks with fractions (0.3×, 0.4×, 0.5×, or 0.6×) of the established LD
50 dose of sarin (42 μg/kg, s.c.). The animals were assessed for changes in body weight, red blood cell (RBC) acetylcholinesterase (AChE) levels, neurobehavioral reactions to a functional observational battery (FOB), cortical electroencephalographic (EEG) power spectrum, and intrinsic acetylcholine (ACh) neurotransmitter (NT) regulation over the 2 weeks of sarin exposure and for up to 12 days postinjection. No guinea pig receiving 0.3, 0.4 or 0.5 × LD
50 of sarin showed signs of cortical EEG seizures despite decreases in RBC AChE levels to as low as 10% of baseline, while seizures were evident in animals receiving 0.6 × LD
50 of sarin as early as the second day; subsequent injections led to incapacitation and death. Animals receiving 0.5 × LD
50 sarin showed obvious signs of cholinergic toxicity; overall, 2 of 13 animals receiving 0.5 × LD
50 sarin died before all 10 injections were given, and there was a significant increase in the angle of gait in the animals that lived. By the 10th day of injection, the animals receiving saline were significantly easier to remove from their cages and handle and significantly less responsive to an approaching pencil and touch on the rump in comparison with the first day of testing. In contrast, the animals receiving 0.4 × LD
50 sarin failed to show any significant reductions in their responses to an approaching pencil and a touch on the rump as compared with the first day. The 0.5 × LD
50 sarin animals also failed to show any significant changes to the approach and touch responses and did not adjust to handling or removal from the cage from the first day of injections to the last day of handling. Thus, the guinea pigs receiving the 0.4 and 0.5 × LD
50 doses of sarin failed to habituate to some aspects of neurobehavioral testing. Spectral analysis of EEG data suggested that repeated sarin exposure may disrupt normal sleeping patterns (i.e., lower frequency bandwidths). While these EEG changes returned to relative normalcy 6 days after the last injection in animals receiving 0.4 × LD
50 sarin, these changes were still observed in the animals that received 0.5 × LD
50 sarin. Ten to twelve days after the last sarin injection (in 0.4 × LD
50 group only), neurochemical data showed that striatal choline levels were reduced in comparison to the saline group. At this time, atropine sulfate (5 mg/kg, i.p.) challenge resulted in a transient elevation in striatal ACh levels in animals exposed to repeated 0.4 × LD
50 sarin as well as in control animals. No evidence of brain or heart pathology was found in any guinea pig that survived all 10 sarin injections.