Changes in axonally transported proteins in the mature and developing rat nervous system during early stages of methyl mercury exposure.

It was established by means of SDS polyacrylamide gel electrophoresis that direct injections of methyl mercury (10 micrograms Hg) into the mature rat vitreous body of the eye decrease protein synthesis in the retina and optic nerve at 4 hours after injection. Although the global spectrum of polypeptides did not change, a specific decrease in the volume of polypeptides of 20-23 K daltons molecular weight was evident. Conversely, systemic exposure to methyl mercury resulted in increased protein synthesis of polypeptides of 20-23 K molecular weight both in adult (8 mgHg/kg/day for 8 days) and neonatal rats (2 mgHg/kg/day for 10 days). In addition, specific changes in the volume of polypeptides 75-90 K molecular weight were noted in sciatic nerves of neonatal rats. These data are consistent with a bimodal response in protein synthesis following MeHg treatment. Local presence of MeHg following direct injection into the eye causes a reduction in protein synthesis, while chronic systemic exposure results in increased synthesis and transport of proteins in both mature and developing optic nerves and neonatal sciatic nerves. Thus, these systems possess the capacity to attempt regenerative processes through induction of a small subset of proteins known as GAPs (Growth-Associated Proteins) during the early stages of systemic methyl mercury exposure. These wide spread and system-specific changes are consistent with growth-specific functions during the early stages of methyl mercury exposure.