Different effects of norepinephrine and serotonin on the electrical toe stimulation-induced reflexes in the rat spinal cord.

1. Electrical toe stimulation was shown to elicit reflex potentials in the ipsilateral common peroneal nerve in the rat. 2. This reflex consisted of the spinal reflex and the spino-bulbo-spinal reflex (SBS reflex). 3. Administration of norepinephrine into the subarachnoid space enhanced the spinal reflex but depressed the SBS reflex. On the other hand, serotonin enhanced both reflexes. 4. These different effects of norepinephrine and serotonin suggest different control of nociceptive reactions by these biogenic amines.