Neuronal chromatin changes in layer V pyramidal cells of somatomotor cortex after pyramidal tract lesions as demonstrated by [3H]actinomycin D binding.

Changes in chromatin structure of pyramidal tract neurons after medullary pyramidal tract lesions were examined autoradiographically utilizing [3H]actinomycin D (Act D) binding to nuclei in frozen sections of brain. After a right pyramidal tract lesion, the binding of Act D to nuclei of axotomized pyramidal neurons of somatomotor cortex layer V increased sharply at 1 and 5 days postoperation, compared with pyramidal cells of the left side or hippocampal control cells of the left hemisphere. At 3, 7, 9, and 11 days the axotomized cells showed significantly decreased binding compared with controls. The unoperated pyramidal cells showed a significantly decreased Act D binding at 2 h and 9 days postoperation compared with the ipsilateral hippocampal control cells. The data suggested that intrinsic neurons of the central nervous system had a response pattern of chromatin changes to axotomy that was basically similar to that of peripheral neurons (sensory ganglion cells). However, the response was compressed into the 1st week postoperation with only a brief reaction which might be correlated to axonal regeneration. This reaction was followed by a prolonged depression of Act D nuclear binding which may be associated with cellular atrophy.