The corticofugal projections from the sensorimotor cortex to the spinal cord. A neuroanatomical and autoradiographical study in the cat with some methodological comments.

An autoradiographical analysis of the corticospinal projections from the sensorimotor cortex of the cat using several 3H-labelled protein precursors showed a distribution of radioactivity on the contralateral side of the spinal cord in fairly good agreement with the findings using silver impregnation techniques. The findings on the ipsilateral side were sparse and the radioactivity was located to the transitional area of lamina VII and VIII almost as intensely as over the contralateral lamina VII. This pattern was more in line with that of the monkey and indicates a more common corticospinal terminal pattern in higher vertebrates. The corticospinal tracts were difficult to demonstrate even in horizontal sections apart from the crossed lateral tract. This was interpreted as a sign of insufficiency of the labelling considering the number of strongly labelled cortical cells. The lumbosacrally projecting neurons were rather difficult to demonstrate and most of them were situated in the more superficial areas around the cruciform sulcus. The investigation was mainly based on labelling the cortex with 3H-fucose which provided the most intense, differential and reproducable labellings. This was considered due to a lesser tendency to encounter selective neuronal uptake phenomenas. The transported amounts of radioactivity were relatively poor and unsuitable for studies of the finer somatotopics or EM-autoradiography of the synaptology.