The effects of thiamin on the neurophysiological alterations induced by lead.

The neurophysiological and histopathological alterations were evaluated in Sprague-Dawley rats exposed to 1,000 ppm lead in drinking water and treated with thiamin (25 mg/kg or 50 mg/kg bw), calcium ethylenediamine tetraacetic acid (CaEDTA) (50 mg/kg bw) or their combination for 8 weeks. Alterations in the brain-stem auditory evoked responses (BAERs) were observed during the treatment period. Latency periods associated with the BAERs were increased after 4 weeks of lead exposure. The neurophysiological alterations induced by lead exposure were prevented by thiamin or CaEDTA treatment. The latency periods in the lead exposed rats treated with thiamin, CaEDTA or the combined treatment did not increase in a similar fashion, but resembled more closely the latency periods observed in the rats which were not exposed to lead. The higher dose of thiamin (50 mg/kg) was more effective than the lower dose (25 mg/kg) in the comparable treatment groups. Histopathological examination of the animals did not reveal any pathological changes in the brain, although lesions often associated with lead toxicity were observed in the kidney. The severity of the lesions was not influenced by thiamin or CaEDta treatment. The absence of morphological damage in the CNS in the presence of neurophysiological alterations, indicates that functional deficits may be observed prior to histological evidence of pathological damage.