Recovery of brain dysfunction after methylmercury exposure in rats.
We studied the time course of central nervous system (CNS) involvement after the termination of methylmercury exposure to rats, in order to investigate whether or not the involvement still progresses even after the termination of exposure. Methylmercury chloride (MMC), at a dose of 2 mg/kg/day, was subcutaneously injected for 25 consecutive days in 12 adult male Sprague-Dawley rats. Six of them were sacrificed on the final day of exposure (group A) after completing the observations of behavioral changes and determining the local cerebral glucose utilization (LCGU) as an indicator of cerebral neuronal activities. Histological examinations of the brain and the sciatic nerve were done. The other six rats were further followed up for 90 days after the termination of exposure (group B). In addition, six rats that received physiological saline served as a control. Group A showed a significant reduction of LCGU without any accompanying cerebral histological alterations and a moderate loss of myelinated fibers in the sciatic nerve. Group B showed normal LCGU rates while severe axonal degeneration of the sciatic nerve was found on the final day of the 90-day follow-up period. The present results demonstrate that a transient involvement of the CNS can occur after MMC exposure. In addition, a complete recovery may occur when the process is mild enough not to cause histological alterations. In contrast, the involvement of the peripheral nerve is much more severe than that of the CNS and it was observed to progress even after the cessation of MMC exposure. Therefore, it seems unlikely, at least in rats, that a steadily progressive course occurs in the CNS but not in the peripheral nerves over a long period of time after MMC exposure.
Shigematsu
J
J
Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-Ku, 812-8582, Fukuoka, Japan. junya.shigematsu@mb6.seikyou.ne.jp
Yasuda
T
T
Goto
Y
Y
Tanaka
K
K
Tobimatsu
S
S
Kato
M
M
D000818:Animals; D001772:Blood Cell Count; D001774:Blood Chemical Analysis; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D008297:Male; D008767:Methylmercury Compounds / Q000494:pharmacology* / Q000506:poisoning; D051381:Rats; D017207:Rats, Sprague-Dawley; D020127:Recovery of Function / Q000187:drug effects* / Q000502:physiology; D012584:Sciatic Nerve / Q000187:drug effects*; D013997:Time Factors
D008767:Methylmercury Compounds; D005947:Glucose; C004925:methylmercuric chloride