The effects of human myelin basic protein (HMBP) on the bioelectrical activity of the frog spinal cord

The effects of human myelin basic protein (HMBP) and its individual microheterogeneous components on the electrical activity of the frog spinal cord are compared with those of bovine MBP (BMBP) and glutamate (Glu). HMBP causes a dose-dependent depolarization of the ventral (VR) and dorsal (DR) roots with a reduction of the evoked root potentials. The amplitude of the depolarization induced by 0.01 mM HMBP corresponds to that observed with application of 1 mM Glu. A weaker depolarization persists during blockade of synaptic transmission by MgSO4 or tetrodotoxin, suggesting a direct depolarizing effect on motoneurones and primary afferents. HMBP causes a long-lasting tachyphylaxis. The individual microheterogeneous components of HMBP (peaks 1, 2 and 3), and a mixture of smaller myelin basic proteins elicit similar responses, whereas BMBP and its microheterogeneous components are slightly less active.