| Abstract: | We have developed a method to immunoprecipitate rat nerve growth factor (NGF) receptor proteins and have applied the method to detect NGF receptor molecules in the rat brain. Crosslinking 125I-labeled NGF to either PC12 cells or cultured rat sympathetic neurons yielded two radiolabeled molecules (90 kDa and 220 kDa) that were immunoprecipitated by monoclonal antibody 192-IgG. Further, 192-IgG precipitated two radiolabeled proteins, with the expected sizes (80 kDa and 210 kDa) of noncrosslinked NGF receptor components, from among numerous surface-iodinated PC12 cell proteins. These results demonstrate the specific immunoprecipitation of NGF receptor molecules by 192-IgG. We applied the 125I-NGF crosslinking and 192-IgG-mediated immunoprecipitation procedures to plasma membrane preparations of the following areas of rat brain: medial septum, cerebellum, brainstem, hippocampus, cerebral cortex, thalamus, and olfactory bulb. NGF receptor molecules of the same molecular masses as the peripheral receptor components were consistently detected in all of these regions and in preparations from whole brains. Removal of the peripheral sympathetic innervation of the brain did not eliminate these NGF receptor proteins, indicating that the receptor is endogenous to central nervous system tissues. We also observed retrograde transport of 125I-labeled 192-IgG from the parietal cortex to the nucleus basalis and from the hippocampus to the nucleus of the diagonal band of Broca and the medial septal nucleus. These findings demonstrate the presence in brain of NGF receptor molecules indistinguishable from those of the peripheral nervous system. |
