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The actions of monoamines and distribution of noradrenergic and serotoninergic contacts on different subpopulations of commissural interneurons in the cat spinal cord.

Journal article
Authors Ingela Hammar
B Anne Bannatyne
David J Maxwell
Stephen A Edgley
Elzbieta Jankowska
Published in The European journal of neuroscience
Volume 19
Issue 5
Pages 1305-16
ISSN 0953-816X
Publication year 2004
Published at Institute of Physiology and Pharmacology, Dept of Physiology
Pages 1305-16
Language en
Links dx.doi.org/10.1111/j.1460-9568.2004...
Keywords Action Potentials, drug effects, physiology, Animals, Biogenic Monoamines, pharmacology, physiology, Cats, Female, Interneurons, drug effects, physiology, Male, Norepinephrine, pharmacology, physiology, Serotonin, pharmacology, physiology, Spinal Cord, drug effects, physiology
Subject categories Neurophysiology

Abstract

Modulatory actions of monoamines were investigated on spinal commissural interneurons which coordinate left-right hindlimb muscle activity through direct projections to the contralateral motor nuclei. Commissural interneurons located in Rexed lamina VIII, with identified projections to the contralateral gastrocnemius-soleus motor nuclei, were investigated in deeply anaesthetized cats. Most interneurons had dominant input from either the reticular formation or from group II muscle afferents; a small proportion of neurons had input from both. Actions of ionophoretically applied serotonin and noradrenaline were examined on extracellularly recorded spikes evoked monosynaptically by group II muscle afferents or reticulospinal tract fibres. Activation by reticulospinal fibres was facilitated by both serotonin and noradrenaline. Activation by group II afferents was also facilitated by serotonin but was strongly depressed by noradrenaline. To investigate the possible morphological substrates of this differential modulation, seven representative commissural interneurons were labelled intracellularly with tetramethylrhodamine-dextran and neurobiotin. Contacts from noradrenergic and serotoninergic fibres were revealed by immunohistochemistry and analysed with confocal microscopy. There were no major differences in the numbers and distributions of contacts among the interneurons studied. The findings suggest that differences in modulatory actions of monoamines, and subsequent changes in the recruitment of subpopulations of commissural interneurons in various behavioural situations, depend on intrinsic interneuron properties rather than on the patterns of innervation by monoaminergic fibres. The different actions of noradrenaline on different populations of interneurons might permit reconfiguration of the actions of the commissural neurons according to behavioural context.

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