The Effect of DOPA on the Spinal Cord 3. Depolarization Evoked in the Central Terminals of Ipsilateral Ia Afferents by Volleys in the Flexor Reflex Afferents

Abstract

AbstractIn unanaesthetized spinal cats, injected with 1‐DOPA, volleys in the flexor reflex afferents (FRA) evoke a long latency, long lasting dorsal root potential (DRP). Measurements of excitability of ispilateral primary afferent terminals show a corresponding depolarization of Ia, but not Ib or cutaneous, afferent terminals. Volleys in the FRA have no effect on Ia afferent terminals in the normal acute spinal cat, presumably because the neuronal pathway transmitting the effect from the FRA to Ia afferents is inhibited by activity in another pathway from the FRA. Results are presented showing that after intravenous injection of DOPA volleys in the FRA can inhibit transmission from the FRA to Ia afferents. It is suggested that this inhibitory effect from the FRA also is responsible for the hyperpolarization of Ia afferent terminals that sometimes is evoked from the FRA after DOPA and is probably caused by a removal of depolarization.