Liposome-entrapped [125I]anti-tetanus immunoglobulin G: evidence for entry into spinal cord neurons of the rat.

Intrathecally administered free anti-tetanus immunoglobulin G (IgG) diffuses through the spinal cord but does not enter nerve cells. In order to facilitate entry into neurons, 125I-labeled anti-tetanus IgG was entrapped in liposomes. After injection into the cerebrospinal fluid of rats, however, only a very low specific radioactivity of the spinal cord could be calculated from gross counts and no neuronal labeling was seen in autoradiographs. Therefore, it was assumed that the liposomes were unable to cross the basement membrane of the spinal cord surface. To circumvent this barrier the liposome-entrapped [125I]IgGs were injected directly into the grey matter. Histoautoradiographs then showed marked accumulations of radioactivity in neurons. Direct intraspinal injection of free [125I]IgG, on the other hand, failed to produce heavy neuronal labeling.