Abstract
The effects of several 5-hydroxytryptamine (5-HT) antagonists were studied on potentials evoked in acute spinal cats by supramaximal stimulation of an L7 dorsal root or peripheral nerve and recorded from the ipsilateral L7 ventral root. The effects of the different 5-HT antagonists on the evoked potentials varied from marked depression to slight facilitation. Since these actions still appeared in animals depleted of endogenous 5-HT, they apparently are not associated with the antagonism of 5-HT. The 5-hydroxytryptophan (5-HTP)-induced increase in the monosynaptic spike amplitude and spontaneous motoneuronal discharge and decreased stimulus-response latency were immediately antagonized by the injection of the 5-HT antagonists, methysergide, 2-brom-d-lysergic acid diethylamide, d-lysergic acid diethylamide, cinanserin and cyproheptadine. The amount of antagonist necessary for complete reversal was directly proportional to the dose of 5-HTP. None of the 5-HT antagonists effectively antagonized the depressant actions of 5-HTP on polysynaptic and dorsal root reflexes. Pretreatment with a 5-HT antagonist also prevented the excitatory effects of 5-HTP. It is concluded that the 5-HT antagonists will effectively antagonize the excitatory, but not the depressant, effects of 5-HTP on evoked potentials in the spinal cord.
Footnotes
- Received November 15, 1967.
- Accepted March 24, 1968.
- © 1968 by The Williams & Wilkins Co.
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