In vivo test for myelinotoxicity of cerebrospinal fluid

A quantitative double blind procedure is described to test the myelinotoxicity of cerebrospinal fluid (SSF) by using optic nerves of Xenopus tadpoles as an in vivo model of a myelinated CNS tract. Only 0.5 ml of unconcentrated CSF is needed for a test and the result is known in 5 days. Groups of 8-10 Xenopus tadpoles received a subcutaneous injection of 12-13 muL of a coded CSF sample or of a saline control solution around the right optic nerve. After 48 h, whole mounts of the right optic nerves were prepared and the slides were randomized before using a differential-interference contrast microscope to count the myelin lesions. The myelinotoxicity of a CSF sample was considered positive (+) when it produced significantly higher (P less than 0.01) counts than the saline control. When P was less than 0.05, the counts were recorded as borderline (+/-) and it was negative (-) when P was greater than 0.05.