title: Impaired auditory and contextual fear conditioning in soman-exposed rats.
abstract: Exposure to soman (GD) can result in prolonged seizures and subsequent neuropathology in a variety of brain regions including the amygdala and hippocampus. Both regions are believed to play important roles in the development and expression of fear conditioning. The purpose of this experiment was to test these conditioning tasks as a possible behavioral correlate of the observed neuropathology. Male rats were exposed to GD (1.0 or 1.2×LD50) or saline followed with injections of atropine sulfate, the oxime HI-6 and diazepam. Fear conditioning was conducted on post-exposure day (PED) 8 followed by measuring freezing to contextual and auditory conditioned stimuli on PED 9 and 10 respectively. Contextual and auditory fear conditioning was severely impaired in both the 1.0×LD50 and 1.2×LD50 GD groups. Both GD groups spent less time freezing than controls when returned to the context in which conditioning occurred. The 1.0×LD50 and 1.2×LD50 groups had very low levels of freezing following presentation of the auditory conditioned stimulus. Neuronal fiber degeneration was present in the piriform cortex, thalamus, and amygdala in GD-exposed animals regardless of dose. The present study suggests that contextual and auditory fear conditioning is impaired in GD-exposed rats possibly due to neuropathology observed in the hippocampus, amygdala and thalamus.
authors.affiliation: Analytical Toxicology Division, U.S. Army Medical Institute of Chemical Defense Aberdeen Proving Ground, MD 21010, United States. mark.moffett1@us.army.mil
authors.forename: Mark C
authors.initials: MC
authors.lastname: Moffett
authors.forename: Mark K
authors.initials: MK
authors.lastname: Schultz
authors.forename: Julia E
authors.initials: JE
authors.lastname: Schwartz
authors.forename: Michael F
authors.initials: MF
authors.lastname: Stone
authors.forename: Lucille A
authors.initials: LA
authors.lastname: Lumley
mesh_terms: D000161:Acoustic Stimulation; D000679:Amygdala / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000633:toxicity; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology; D005239:Fear / Q000187:drug effects* / Q000502:physiology; D046352:Freezing Reaction, Cataleptic / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D008297:Male; D009410:Nerve Degeneration / Q000139:chemically induced / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012999:Soman / Q000633:toxicity*; D013788:Thalamus / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology
chemical_list: D002800:Cholinesterase Inhibitors; D012999:Soman