Radiolabeling motoneuron proteins in the isolated frog spinal cord preparation

An in vitro method for radiolabeling protein in adult frog spinal motoneurons is described, with per cell incorporations which are 2-3 orders of magnitude higher than previously reported for mammalian brain neurons. In the procedure, isolated lumbar spinal cord preparations from Rana pipiens are labeled with 3H-L-leucine, motoneuron cell bodies are recovered and TCA-precipitated protein is analyzed by scintillation counting. The higher levels of labeling (> 90 cpm/cell body) allow one to quantify newly synthesized protein within individual or small groups of identified nerve cell bodies. Motoneuronal labeling correlates directly with cell body size, and other sources of variation in labeling and their control are identified and discussed.