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  • Title: Action of 5-hydroxytryptamine on isolated spinal cord of bullfrogs.
    Author: Shirasawa Y, Koketsu K.
    Journal: Jpn J Pharmacol; 1977 Feb; 27(1):23-9. PubMed ID: 194076.
    Abstract:
    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.
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