Autoradiographic localisation of 3H-uridine in spinal ganglion neurones of the rat and the effects of methyl mercury poisoning.

The uptake of 3H-uridine into rat spinal ganglion neurones has been followed by autoradiography for up to 48 h after its intravenous injection. Labelling of nucleoli and of nuclei reached a peak within 1 h and then declined. Nuclear labelling returned to background levels by 24 h, but nucleolar labelling was still significant after 48 h. Animals dosed with methyl mercury chloride (7.5 mg/kg daily) showed no change in labelling rate in nucleolus or nucleus after 1, 2, or 4 doses. After 8 doses there was severe reduction in labelling in both nucleolus and nucleus; this amount causes extensive loss of axons, loss of some cell bodies and a marked reduction in amino acid incorporation into proteins. On recovery after a further 8 days, labelling levels returned to normal. It is concluded that at the time when loss of ribosomes occurs from the cytoplasm methyl mercury is more likely to be directly disturbing ribosomal structure than RNA synthesis, for methyl mercury causes marked changes in ribosomal organisation after 4 doses, but disturbances to RNA synthesis do not occur until the 8th dose.