Preliminary morphological and histochemical changes in rat spinal cord neurons following arsenic ingestion

Aqueous sodium arsenite was administered in closes of 1.0, 1.5 and 2.0 mg/kg body weight (bw)/day by intragastric route to adult Wistar rats, (groups II, III and IV respectively, n = 6 aninials/group)for a period of 12 weeks. Controls (group I) received distilled water without added arsenite. At the end of experimental period, four animals four each group were peifusion fixed with 4% paraformaldehyde and two animalsfroin each group were used for fresh tissue purposes (for SDH localization). Fixed tissue blocks from the cervical and lumbar spinal cords were processed for paraffin and cryostat sectioning. Measurements of nuclear area were carried out in cresyl violet (CV) stained paraffin sections by Image Analysis. Cryostat sections (20 mu m) of the cervical and lumbar spinal cords of fixed and fresh frozen tissue blocks (n = 21 croup) were stained for localization of cytochrome oxidase (CO) and succinic dehydrogenase (SDH) activities, respectively. Quantitative estimations of enzyme activities was determined from, mean grey values obtained by age Analysis. The results revealed a dose related reduction in the mean log nuclear area and in the two enzyme activities. The differences noted between the cervical and lumbar motor neurons, viz. (i) the decrease in mean log nuclear area were observed only in cervical motor neurons of animals receiving 2.0 mg/kg bw whereas for the lumbar motor neurons this was true of all closes of arsenite; (ii) in general, CO expression was higher in the cervical than in lumbar spinal cord and (iii) reduction in SDH activity was more pronounced in the cervical spinal cord with closes of 1.5 and 2.0 mg/kg bw as compared to lumbar spinal cord. These observations may throw some light on the earlier observations [Jenkins RB. Inorganic arsenic and the nervous system. Brain 1996;89:479-98] reporting differences in the affliction to arsenic ingestion between the fore limb and hind limb inusculature (in human subjects). Our observations ascertain that the 0 neurons, which innervate these musculature, also differ in some characteristics. (c) 2004 Elsevier Inc. All rights reserved.