The Modification of Lumbar Motoneurone Excitability by Stimulation of a Putative 5‐hydroxytryptamine Pathway

Abstract

1Changes in lumbar motoneurone excitability were monitored by recording spinal reflex activity from the ventral roots of rats anaesthetized with fluothane. 2 Electrical stimulation of nucleus raphes medianus increased the amplitude of the monosynaptic reflex via a pathway having a slow conduction velocity. Stimulation elsewhere in the lower brain stem was less effective. This increase in motoneurone excitability was potentiated by the intravenous injection of L-tryptophan and reduced by intravenous injections of lysergic acid diethylamide (LSD), methysergide or Cinanserin. 3 Extracellular field potential responses to stimulation of dorsal or ventral roots were recorded with six barrelled microiontophoresis electrodes. Stimulation of nucleus raphes medianus and iontophoretic application of 5-hydroxytryptamine (5-HT) both increased the excitability of lumbar motoneurones as reflected by an increase in field potential amplitude. 4 Responses to both stimulation of raphe nuclei and iontophoretic application of 5-HT were reduced by iontophoretic application of Cinanserin and methysergide. 5 The similarities of the responses of lumbar motoneurones to applied 5-HT and activity within the raphe-spinal pathway are discussed. It is suggested that activity within the raphe-spinal pathway can increase lumbar motoneurone excitability via the release of 5-HT in the ventral horn of the spinal cord.

Increased Lower Limb Spasticity but Not Strength or Function Following a Single-Dose Serotonin Reuptake Inhibitor in Chronic Stroke

“…Increased stretch reflexes with enhanced 5-HT transmission are consistent with results from animal models with increased descending 5-HT after decerebration, raphe electrical stimulation, 45 or spinalization with 5-HT precursors. 46 We believe increased 5-HT was the likely primary determinant of increased velocity-dependent stretch reflexes accessed by following the link in the citation at the bottom of the page.…”

Up-regulation of 5-HT2 receptors is involved in the increased H-reflex amplitude after contusive spinal cord injury

“…The effects of serotonin or serotonergic agents on spinal cord locomotor output have been studied in various models ranging from in vitro postnatal spinal cord preparations to kinematic analysis in freely moving adult animals (Antri, et al, 2002, Cazalets, et al, 1995. In particular, 5-HT 2 R agonists have received a lot of attention due to their ability to increase the excitability of motoneurons (Barasi and Roberts, 1974, Elliott and Wallis, 1992, Machacek, et al, 2001. The 5-HT 2 R agonists, quipazine and m-CPP, have been shown to significantly improve treadmill-trained locomotion after complete transection in rats (Antri, et al, 2002, Kim, et al, 2001).…”

Inhibition of reflex responses of neonate rat lumbar spinal cord by 5‐hydroxytryptamine

“…Although 5-HT has a direct depolarizing action on spinal motoneurones Elliott & Wallis, 1990a) and increases their excitability (Ahlman et al, 1971;Barasi & Roberts, 1974;Roberts et al, 1988), 5-HT and 5-HT agonists, such as 5-methoxy-dimethyltryptamine and 8-hydroxy-2-(di-n-propylamino)tetralin , are reported to depress reflex responses evoked by dorsal root stimulation (Saito et al, 1982;Nagano et al, 1988). On the other hand, facilitation of reflex responses can occur on stimulation of the nucleus raphe medianus and this effect is blocked by 5-HT antagonists (Barasi & Roberts, 1974). It is clear that the role of 5-HT in regulating motoneurone activity remains to be clarified.…”