Action of 5-hydroxytryptamine on isolated spinal cord of bullfrogs.
Slow depolarizations of dorsal root nerve terminals and motoneurons, which were produced by 5-hydroxytryptamine (5-HT) applied directly to isolated bullfrog spinal cords, were recorded by the sucrose-gap method. These depolarizations were eliminated in the Ca-deficient Ringer's solution containing Mg, suggesting that these 5-HT depolarizations were not caused by a direct action of 5-HT on dorsal root nerve terminals or motoneurons but rather by actions of transmitters released from interneurons. Indeed, mephenesin, which is a selective blocker of polysynaptic transmission in the spinal cord, inhibited more markedly the 5-HT depolarization than the L-glutamate or GABA depolarization. The transmitter directly responsible for the generation of the 5-HT depolarization of dorsal root nerve terminals was not considered to be GABA as the 5-HT depolarization was not antagonized by picrotoxin. It would thus appear that 5-HT stimulates interneurons in the amphibian spinal cord and unknown transmitters released from these interneurons depolarize the dorsal root nerve terminals.
D000818:Animals; D001001:Anura; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists; D005971:Glutamates / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008615:Mephenesin / Q000494:pharmacology; D009046:Motor Neurons / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects; D010852:Picrotoxin / Q000494:pharmacology; D011892:Rana catesbeiana; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists; D013116:Spinal Cord / Q000187:drug effects*; D013126:Spinal Nerve Roots / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D002118:Calcium; D018756:GABA Antagonists; D005971:Glutamates; D008615:Mephenesin; D010852:Picrotoxin; D012701:Serotonin; D012702:Serotonin Antagonists; D005680:gamma-Aminobutyric Acid