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The Journal of Neuroscience, January 19, 2005, 25(3):584-593; doi:10.1523/JNEUROSCI.3797-04.2005

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Behavioral/Systems/Cognitive
Membrane Receptors Involved in Modulation of Responses of Spinal Dorsal Horn Interneurons Evoked by Feline Group II Muscle Afferents

Kimberly J. Dougherty,¹ B. Anne Bannatyne,² Elzbieta Jankowska,¹ Piotr Krutki,¹ and David J. Maxwell²

¹Department of Physiology, Göteborg University, 405 30 Göteborg, Sweden, and ²Spinal Cord Group, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom

Modulatory actions of a metabotropic 5-HT_1A&7 membrane receptor agonist and antagonist [(+/-)-8-hydroxy-2-(di-n-propylamino)-tetralin; N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane-carboxamide] and an ionotropic 5-HT₃ membrane receptor agonist and antagonist [2-methyl-serotonin (2-Me 5-HT); N-(1-azabicyclo[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride] were investigated on dorsal horn interneurons mediating reflex actions of group II muscle afferents. All drugs were applied ionophoretically in deeply anesthetized cats. Effects of agonists were tested on extracellularly recorded responses of individual interneurons evoked by electrical stimulation of group II afferents in a muscle nerve. Effects of antagonists were tested against the depression of these responses after stimulation of raphe nuclei. The results show that both 5-HT_1A&7 and 5-HT₃ membrane receptors are involved in counteracting the activation of dorsal horn interneurons by group II afferents. Because only quantitative differences were found within the sample of the tested neurons, these results suggest that modulatory actions of 5-HT on excitatory and inhibitory interneurons might be similar. The relationship between 5-HT axons and axons immunoreactive for the 5-HT_3A receptor subunit, which contact dorsal horn interneurons, was analyzed using immunofluorescence and confocal microscopy. Contacts from both types of axons were found on all interneurons, but their distribution and density varied, and there was no obvious relationship between them. In two of six interneurons, 5-HT_3A-immunoreactive axons formed ring-like arrangements around the cell bodies. In previous studies, axons possessing 5-HT₃ receptors were found to be excitatory, and as 2-Me 5-HT depressed transmission to dorsal horn interneurons, the results indicate that 5-HT operates at 5-HT₃ receptors presynaptic to these neurons to depress excitatory transmission.

Key words: spinal cord; dorsal horn interneurons; membrane receptors; serotonin; group II afferents; confocal microscopy

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Received Sep 14, 2004; revised November 25, 2004; accepted November 26, 2004.

This article has been cited by other articles:

				B. A. Bannatyne, S. A. Edgley, I. Hammar, E. Jankowska, and D. J. Maxwell Differential projections of excitatory and inhibitory dorsal horn interneurons relaying information from group II muscle afferents in the cat spinal cord. J. Neurosci., March 15, 2006; 26(11): 2871 - 2880. [Abstract] [Full Text] [PDF]

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