STRUCTURAL PRESERVATION OF CEREBELLAR GRANULE CELLS FOLLOWING NEUROINTOXICATION WITH METHYL MERCURY - A STEREOLOGICAL STUDY OF THE RAT CEREBELLUM

Methyl mercury intoxication causes ataxia. Structural changes of cereb ellar and peripheral nerve tissues have been described. However, it is still unclear whether the ataxia is of cerebellar or peripheral origi n. To clarify this question further, the effects of methyl mercury int oxication on the numbers of granule and Purkinje cells and the volume of Purkinje cell perikarya have been evaluated with stereological meth ods. Rats were intoxicated with methyl mercury, at a dose of 2 mg/kg p er day for 19 successive days, and the analysis was carried out 2.5 or 4.5 weeks later. The total numbers of cerebellar granule cells and Pu rkinje cells were estimated using an optical fractionator and the mean volume of the Purkinje cells was estimated by the vertical rotator te chnique. The volumes of the granular cell layer, the molecular layer a nd the white matter were estimated using the Cavalieri principle. The intoxicated animals developed hindlimb incoordination when held by the tail. Although pronounced axonal degeneration occurred in the periphe ral nervous system, no changes were found in cerebellar cell numbers o r cell sizes in either of the test groups. The absence of detectable l ight microscopic changes in the cerebellum indicates that the peripher al nervous system is affected prior to the cerebellum in rats intoxica ted with organic mercury.