To study MPTP-induced muscular rigidity, we try to detect the changes of both dopamine (DA) and GABA within rat striatums by immunohistochemical means. A high dose (30 mg/kg) of MPTP i. p. injected into rats produces behavioral abnormalities (tremor and ataxia), and higher doses (>60 mg/kg) develop an acutely muscular rigidity without producing a measurable histological change. GABA is induced in the striatum of 4 MPTP (30 mg/kg) i. p. treated-rats developed tremor and ataxia. But the animals recovered to an apparently normal state and are not showed GABAimmunoreactivity. Dense GABA-immunoreactivity is observed in the striatum developed muscular rigidity, when the animals are injected with 60 mg/kg MPTP i. p.. At this time, their striatums show slight decrease of DA-immunoreactivity in medium sized-spiny neurons. The results give some insight as to how DA and GABA function within the striatum with respect to the development of neuronal abnormalities. It is also suggested by our behavioral and immunohistochemical studies that effects induced by the depletion of DA within the striatum may be mediated through the inhibition of the striato-nigral GABAergic pathway, which in turn may lead to an activation of the nigrothalamic or nigro-collicular GABAergic pathway. This study indicates that the role of striatal GABAergic transmission is important in the development of muscular rigidity. The activity within the striatum can be followed with immunohistochemical technique for GABA morphologically.
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