Title page for ETD etd-12052009-020159


Type of Document Master's Thesis
Author Carboni, Deborah Ann
URN etd-12052009-020159
Title Comparative evolution of mipafox-induced delayed neuropathy in the rat and hen
Degree Master of Science
Department Veterinary Medical Sciences
Advisory Committee
Advisor Name Title
Jortner, Bernard S. Committee Chair
Dyer, Karen R. Committee Member
Ehrich, Marion F. Committee Member
Keywords
  • Organophosphorus compounds
Date of Defense 1993-08-09
Availability restricted
Abstract
The group of chemicals designated organophosphorus

compounds have had a significant impact on modern life, including use as pesticides, industrial plasticizers and chemical warfare agents. Exposure to certain organophosphates produces a delayed degeneration of the longest and largest

nerve fibers, including those of the ascending and descending tracts of the spinal cord, a condition termed organophosphorus ester-induced delayed neuropathy (OPIDN). Recorded incidents

of such an effect in humans have led to research regarding this neurological disease. Among the OPIDN-inducing agents is mipafox, an organophosphate insecticide, the compound we chose

to employ in our studies. Although the hen is the primary experimental model in the safety assessment of organophosphates, current research has suggested that the rat may have some validity as an experimental model. We examined the sequential neuropathic effects of a single dose of mipafox (30mg/kg) in rats and hens on a comparative basis to determine the better experimental model. Organophosphorus ester-induced

delayed neuropathy (OPIDN) has been reported in rats and hens, but sequential pathological studies exist only for the latter. We performed studies of the temporal development of bilateral

lesions elicited by 30 mg/kg of mipafox (ip) in the medulla and

cervical spinal cord of male Long-Evans rats (> 60 days of age) and White Leghorn hens (> 18 months of age). In two studies, this dosage inhibited brain neurotoxic esterase 4 hours after administration by more than 70% in both the brain and spinal cord of rats and hens. In rats, lesions were seen in distal levels of the fasciculus gracilis, and mainly consisted of numbers of swollen, vacuolated myelinated axons, restricted to

medullary levels of the tract. These varied in intensity

between animals and were seen in 5/5 on day 7, 3/3 on day 14, 4/4 on day 21, 6/8 on day 28 and 7/9 on day 35. Occasional similarly swollen fibers were seen in this region in some controls as well. Hens had extensive regions of myelinated fiber degeneration consisting of swollen, debris-laden axons progressing to allerian-like degeneration in distal (rostral) levels of spinocerebellar tracts and fasciculus gracilis.

These were seen in 1/4 on day 7, 4/4 on days 14 and 21, 3/3 on day 28 and 2/2 on day 35. The prominent central nervous system lesions of OPIDN in hens evolved in a stereotypical fashion, becoming most florid by day 21. In contrast, rats had a more erratic evolutionary course of lesion development, which did not approach the hen in severity. Resolution of these rodent neuropathic changes was seen by day 35.

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