Alterations of [3H]actinomycin D binding to axotomized dorsal root ganglion cell nuclei: an autoradiographic method to detect changes in chromatin structure and RNA synthesis.

An autoradiographic method was developed to quantify on a comparative basis the binding of [3H]actinomycin D (Act D) to the cell nuclei of frozen, unfixed sections of spinal sensory ganglia in rats. After a crush lesion of the sciatic nerve, alterations of [3H]Act D binding were found in L5 and L6 dorsal root ganglia which corresponded to changes in RNA synthesis observed in other studies. An increase in Act D binding was seen at 1 to 3 days postoperation, followed by a decrease at 5 to 7 days. By 9 to 11 days a second increase in binding occurred, followed by a decrease at 14 days. Contralateral ganglia exhibited an increase in Act D binding only at 5 days compared with unoperated controls. The timing of the response in axotomized ganglia differed with the distance of the lesion from the cell body. The observed patterns of Act D binding confirm that changes of chromatin structure are closely associated with the alterations of RNA and protein synthesis occurring after axon injury. The method may be useful as an indicator for alterations in RNA synthesis related to changes in chromatin structure in complex tissues.