Abstract
Summary
Effects of thyroxine and thio-urea upon optically evoked potentials in the midbrain of goldfish were tested. Thyroid hormone treatment reduced latency, time to reach maximum response, and time to complete the response, and it increased response amplitude. Thiourea had the opposite effects. Thyroxine shortened the “recovery” time between successive stimuli, and thiourea prolonged it. Supramaximal second responses were found when light flash stimuli were repeated at 1/5 to 1/10 second intervals in some of the thyroxine-treated fishes. The data suggest that thyroxine has a facilitating action upon tectal synaptic events.
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