Effects of exogenous neuraminidase on unit activity in frog spinal cord and fish optic tectum

The effect of exogenous neuraminidase on spontaneous and evoked synaptic activity was investigated following injection of the enzyme into frog spinal cord and into cord and into the carp optic tectum. 1. Injection of enzyme into spinal cord segments caused a significant increase of motoneuron activity in the corresponding spinal nerve, which lasted for 7--31 min. 2. The amplitude of postsynaptic evoked potentials in the optic tectum was increased after neuraminidase injection up to 200% of control level for 20--40 min, whereas the amplitude of summed action potentials of retino-tectal afferents remained unchanged. 3. Similar effects were observed in single cell responses of the optic tectum with some differences in the degree of increase in activity, as well as latency and final depression of the stimulus response. 4. The extent of neuraminic acid liberation following neuraminidase treatment was determined biochemically. In both tissues investigated the amount of free neuraminic acid was increased significantly (4--5.5 fold) after enzyme treatment. Whereas after enzyme injection into spinal cord and optic tectum the percentage release of total glycoprotein- and glycolipidbound neuraminic acid was 12% and 15%, respectively, liberation from enzyme incubated tissue homogenates was somewhat higher (20.5% and 24%).