脊髄反射に対する5-hydroxytryptophanおよびL-3, 4-dihydroxyphenylalanineの作用

抄録

It was reported that axons originated from 5-HT or NA containing neurons in brain stem especially medulla ended in spinal cord and that both 5 HT and NA influenced on spinal reflex. However it was also reported that these compounds exerted the inhibitory effect on spinal reflex and the excitatory effect on motoneuron.
In present study, it was founded that these inhibitory and excitatory actions of 5-HTP and DOPA could be separated by the applied concentrations of these compounds.
The low concentrations of DOPA and 5-HTP augmented the spinal reflex discharges of frog without changing dorsal root potential, while the higher concentrations of these drugs inhibited reflex discharges reducing dorsal root potential. These effects last for more than 2 hours.
The facilitatory and inhibitory effects by DOPA were observed in the spinal reflex discharges of short latency, while the spinal reflex with long latency was only responded to increase the duration of discharges by large doses of DOPA.
From these results the followings were postulated that 1) DOPA and 5-HTP depolarized both presynaptic nerve terminals and post synaptic membrane. 2) The depolarization of the nerve terminals decreased the action potential of nerve terminals and hence decreased the release of transmitter. As a result, spinal reflex was inhibited.
If depolarization of motoneuron induced by these compounds was under the thresholdal membrane potential, spinal reflex should be facilitated. In this regard, the facilitatory and inhibitory effects were separated by applied doses of these compounds.