Monoamine oxidase-B in motor cortex and spinal cord in amyotrophic lateral sclerosis studied by quantitative autoradiography.

The distribution of MAO-B was studied by using an in vitro quantitative autoradiographical method in the post-mortem spinal cord and motor cortex from control and ALS cases. 3H-L-deprenyl was used as a radiotracer. Sections stained with thionine were used to count glial cells. In both control and ALS spinal cords, high density of 3H-L deprenyl binding was observed around the central canal, in the substantia gelatinosa and other grey matter regions. In the ALS cases a pronounced and statistically significant increase of MAO-B was observed in the corticospinal tract, the motor neuron areas and in the ventral white matter. An increase in the number of glial cells in spinal cords from ALS cases was also evident. Moreover, the concentration of MAO-B was highly correlated with glial cell counts in thionine stained sections in various regions of the spinal cord, both in controls and ALS cases. An elevated level of 3H-L-deprenyl binding, in ALS cases, was observed in all the individual laminae of the pre- and post-central gyri of the cerebral cortex. There was no difference in MAO-B concentration between the two groups in the occipital cortex. A substantial increase in the concentration of MAO-B was observed in the white matter of ALS cases. Reactive gliosis has been shown to be associated with neurodegenerative disorders and experimental lesions in animals. The most likely explanation for the increase of MAO-B in ALS and in other neurodegenerative disorders seems to be that the increase is a consequence of the reactive gliosis associated with these disorders.