A New Spinal Flexor Reflex

IN the acute spinal animal L-3,4-dihydroxyphenyl-alanine (DOPA) gives a marked increase in the flexor reflex which can be evoked on pinching the skin1,2. An electrophysiological analysis revealed that DOPA depresses the transmission of single volleys from the flexor reflex afferents to motoneurones and to primary afferents3,4. DOPA is more effective in depressing the path from the flexor reflex afferents to primary afferents than to motoneurones. Hence there was the possibility that DOPA, by eliminating the negative feed-back of presynaptic inhibition (the primary afferent depolarization in the flexor reflex afferents), might give more effective transmission to motoneurones despite its inhibitory action on this path3. However, further experiments have shown that this explanation is not correct.