METALLOTHIONEIN INDUCTION IN RAT BRAIN AFTER INTRASTRIATAL INJECTION OF ZINC AND CADMIUM SALTS

Brain parenchyma is protected against excess metals by the barrier system in the brain. To evaluate the expression of metallothionein (MT), a protective protein against heavy metals, in the brain parenchyma, zinc sulfate (0.2 or 2μmol) or cadmium chloride (2 or 20nmol) was injected into the left striatum of rats. Seventy-two h later, the MT level in the ipsilateral striatum injected with 0.2μmol of zinc sulfate was not significantly higher than that after injection with vehicle. When the striatum was injected with 2μmol of zinc sulfate, on the other hand, the MT level in the ipsilateral striatum, showing apparent degeneration, was significantly higher than that after injection with vehicle : the former was approximately 1.5 times the latter. In the case of injection with cadmium chloride at doses of 2 and 20nmol, the MT levels in the ipsilateral striatum was approximately twice that after injection with vehicle. The MT level in the contralateral striatum and other brain regions were not affected by injection with either metal salt at any dose. When zinc sulfate of 100μmol/kg body weight, corresponding to the lower dose tested(0.1μmol/g brain), was subcutaneously injected, the hepatic MT level was approximately four times higher than the normal hepatic level. These results suggest that the changes of MT level in the brain were small compared to those observed in the liver.