Immunoblots of rat SCO at PN30 (panel A) and cisternal CSF at PN7 (panel B), using AFRU and anti-P15 as primary antibodies. The four AFRU-immunoreactive compounds with the largest molecular mass (630, 450,390, 320 kDa) are present in the SCO and missing from the CSF. Two other compounds (200, 63 kDa) are present in the SCO and CSF (processed forms?). The CSF has four bands (180, 164, 145, 120 kDa) not seen in the SCO. The SCO has only one large molecular mass compound reacting with anti-P15 (specific for SCO-spondin) and several bands of lower molecular masses. The CSF compounds of 200, 180, 145 and 63 kDa, reacting with both antibodies are most likely to be SCO-spondin derivatives.