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Presynaptic serotonin 5-HT1B/D receptor-mediated inhibition of glycinergic transmission to the frog spinal motoneurons

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Abstract

Endogenous monoamine 5-hydroxytryptamine (5-HT, serotonin) is a phylogenetically ancient neurotransmitter present in vertebrates. The functions of 5-HT in central nervous system are intensively studied; however, the presynaptic effects of 5-HT in frog spinal motoneurons are practically unexplored. We have previously shown that 5-HT decreases the frequency of glycinergic miniature inhibitory postsynaptic potentials (mIPSPs), but does not affect the frequency of GABAergic mIPSPs and increases the frequency of glutamatergic postsynaptic potentials. In the present study, using pharmacological methods and intracellular recordings in motoneurons from an adult frog’s isolated spinal cord, we aimed to identify the 5-HT receptor subtype responsible for inhibiting the release of glycine. Аn agonist of 5-HT1A and 5-HT7 receptors, 8-OH-DPAT, and a selective agonist of 5-HT2 receptors, α-Ме-5-НТ, did not show any significant effect on inhibitory transmission, indicating that 5-HT1A, 5-HT2, and 5-HT7 receptors are not involved in the modulation of glycine release in the adult frog spinal cord. An agonist of 5-HT1B/D receptors sumatriptan decreased the frequency (but not the amplitude) of glycinergic mIPSPs similar to 5-HT. An antagonist of 5-HT1,2 receptors, methysergide, abolished the effect of sumatriptan. Together our results suggest that 5-HT inhibits the release of glycine by activation of 5-HT1B/D receptors.

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Abbreviations

5-HT-serotonin:

5-hydroxytryptamine;

8-OH-DPAT:

(±)-8-Hydroxy-2-(dipropylamino)tetralin hydrobromide;

Sum:

3-[2-(Dimethylamino)ethyl]-N-methyl-1H-indole-5-methanesulfonamide succinate (sumatriptan succinate)

α-Ме-5-НТ:

α-Methyl-5-hydroxytryptamine maleate;

Methysergide maleate:

[8β(S)]-9,10-Didehydro-N-[1-(hydroxymethyl)propyl]-1,6-dimethylergoline-8-carboxamide maleate;

CNQX:

6-Cyano-7-nitroquinoxaline-2,3-dione;

D-AP5:

D-(−)-2-Amino-5-phosphonopentanoic acid;

mIPSPs:

Miniature inhibitory postsynaptic potentials;

RMP:

Resting membrane potential;

TTX:

Tetrodotoxin

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Acknowledgements

This study was funded by Russian Foundation for Basic Research (RFBR, Grant number 15-04-05782).

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Correspondence to Aleksey V. Zaitsev.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.

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The authors declare that they have no conflict of interest.

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Kalinina, N.I., Zaitsev, A.V. & Vesselkin, N.P. Presynaptic serotonin 5-HT1B/D receptor-mediated inhibition of glycinergic transmission to the frog spinal motoneurons. J Comp Physiol A 204, 329–337 (2018). https://doi.org/10.1007/s00359-017-1244-y

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  • DOI: https://doi.org/10.1007/s00359-017-1244-y

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