1
|
D'Amico JM, Butler AA, Héroux ME, Cotel F, Perrier JFM, Butler JE, Gandevia SC, Taylor JL. Human motoneurone excitability is depressed by activation of serotonin 1A receptors with buspirone. J Physiol 2016; 595:1763-1773. [PMID: 27859267 DOI: 10.1113/jp273200] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 11/14/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS In the adult turtle spinal cord, action potential generation in motoneurones is inhibited by spillover of serotonin to extrasynaptic serotonin 1A (5-HT1A ) receptors at the axon initial segment. We explored whether ingestion of the 5-HT1A receptor partial agonist, buspirone, decreases motoneurone excitability in humans. Following ingestion of buspirone, two tests of motoneurone excitability showed decreases. F-wave areas and persistence in an intrinsic muscle of the hand were reduced, as was the area of cervicomedullary motor evoked potentials in biceps brachii. Our findings suggest that activation of 5-HT1A receptors depresses human motoneurone excitability. Such a depression could contribute to decreased motoneurone output during fatiguing exercise if there is high serotonergic drive to the motoneurones. ABSTRACT Intense serotonergic drive in the turtle spinal cord results in serotonin spillover to the axon initial segment of the motoneurones where it activates serotonin 1A (5-HT1A ) receptors and inhibits generation of action potentials. We examined whether activation of 5-HT1A receptors decreases motoneurone excitability in humans by determining the effects of a 5-HT1A receptor partial agonist, buspirone, on F waves and cervicomedullary motor evoked potentials (CMEPs). In a placebo-controlled double-blind study, 10 participants were tested on two occasions where either placebo or 20 mg of buspirone was administered orally. The ulnar nerve was stimulated supramaximally to evoke F waves in abductor digiti minimi (ADM). CMEPs and the maximal M wave were elicited in biceps brachii by cervicomedullary stimulation and brachial plexus stimulation, respectively. Following buspirone intake, F-wave area and persistence, as well as CMEP area, were significantly decreased. The mean post-pill difference in normalized F-wave areas and persistence between buspirone and placebo days was -27% (-42, -12; 95% confidence interval) and -9% (-16, -2), respectively. The mean post-pill difference in normalized CMEP area between buspirone and placebo days showed greater variation and was -31% (-60, -2). In conclusion, buspirone reduces motoneurone excitability in humans probably via activation of 5-HT1A receptors at the axon initial segment. This has implications for motor output during high drive to the motoneurones when serotonin may spill over to these inhibitory receptors and consequently inhibit motoneurone output. Such a mechanism could potentially contribute to fatigue with exercise.
Collapse
Affiliation(s)
- Jessica M D'Amico
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia
| | - Annie A Butler
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | - Martin E Héroux
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | | | | | - Jane E Butler
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | - Simon C Gandevia
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | - Janet L Taylor
- Neuroscience Research Australia, Barker Street, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| |
Collapse
|
2
|
Müller AC, Daya S. Acyclovir inhibits rat liver tryptophan-2,3-dioxygenase and induces a concomitant rise in brain serotonin and 5-hydroxyindole acetic acid levels. Metab Brain Dis 2008; 23:351-60. [PMID: 18665439 DOI: 10.1007/s11011-008-9095-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Accepted: 06/25/2008] [Indexed: 10/21/2022]
Abstract
Viral diseases of the brain may induce changes in neurotransmitter synthesis and metabolism. In experimental herpes simplex encephalitis, brain serotonin is reduced, whilst it's major metabolite, 5-hydroxyindole acetic acid and turnover is increased. It is well established that reduced levels of brain monoamines, serotonin and norepinephrine may contribute to the symptoms of clinical depression, which raises the possibility that this condition is prevalent in herpes simplex encephalitis. An inverse relationship exists between liver tryptophan-2,3-dioxygenase activity and brain serotonin levels and there is an interdependency between serotonin and norepinephrine levels. The aim of this study is to determine the effect of acyclovir, an antiviral used in the treatment of herpes simplex encephalitis, on rat liver tryptophan-2,3-dioxygenase activity in vitro and in vivo as well as on rat forebrain serotonin, 5-hydroxyindole acetic acid and norepinephrine levels. The results show that acyclovir inhibits tryptophan-2,3-dioxygenase activity in vitro and in vivo, with a concomitant rise in serotonin and 5-hydroxyindole acetic acid levels. However, acyclovir reduces the turnover of serotonin to 5-hydroxyindole acetic acid, without any effect on norepinephrine levels. It appears that acyclovir may have the potential to reduce the clinical symptoms of depression in herpes simplex encephalitis. However, a greater turnover of serotonin to 5-hydroxyindole acetic acid could possibly be masked by conversion of serotonin to 5-hydroxytryptophol, which needs to be investigated further.
Collapse
Affiliation(s)
- Adrienne C Müller
- Division of Pharmacology, Faculty of Pharmacy, Rhodes University, P.O. Box 94, Grahamstown, 6140 Eastern Cape, South Africa
| | | |
Collapse
|
3
|
Lorivel T, Hilber P. Motor effects of delta 9 THC in cerebellar Lurcher mutant mice. Behav Brain Res 2007; 181:248-53. [PMID: 17531329 DOI: 10.1016/j.bbr.2007.04.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Revised: 04/13/2007] [Accepted: 04/19/2007] [Indexed: 10/23/2022]
Abstract
The present study evaluated the effects of the principal active component of marijuana (delta 9 THC) on motor abilities and motor learning in mice with cerebellar dysfunction. For this purpose, spontaneous locomotor activity, equilibrium abilities, muscular tone, motor coordination and motor learning were investigated in Lurcher mutant and non-mutant B6/CBA mice 20 min after i.p. administration of 4 or 8 mg kg(-1) of delta 9 tetra hydro cannabinol (delta 9 THC). The performances were compared to those obtained by Lurcher and non-mutant mice injected with vehicle (Tween 80). The results showed that at the dose of 4 mg kg(-1) but not at the dose of 8 mg kg(-1), the cannabinoid (CB) substance reduced deficits in motor coordination, equilibrium and muscular tone and facilitated motor learning in Lurcher mice. On the other hand, only a muscular strength decrease was observed in control B6/CBA mice injected with the dose of 8 mg kg(-1) of delta 9 THC. These results suggested that cannabinoid derivative could represent a new field of investigation concerning the treatment of cerebellar ataxic syndrome in humans.
Collapse
Affiliation(s)
- T Lorivel
- UPRES PSY.CO EA 1780, Laboratoire de Neurobiologie de l'Apprentissage, Université de Rouen, Faculté des Sciences, 76821 Mont Saint Aignan Cedex, France
| | | |
Collapse
|
4
|
Reader TA, Hébert C, Ase AR, Le Marec N. Distribution of serotonin, its metabolites and 5-HT transporters in the neostriatum of Lurcher and weaver mutant mice. Neurochem Int 2001; 39:169-77. [PMID: 11434974 DOI: 10.1016/s0197-0186(01)00031-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Serotonin (5-HT) uptake sites, or transporters, were measured in the neostriatum (caudate putamen) of wild type (+/+) mice and heterozygous (wv/+) and homozygous (wv/wv) weaver, as well as in heterozygous Lurcher (Lc/+) mutants. These topological surveys were carried out by quantitative ligand binding autoradiography using the uptake site antagonist [3H]-citalopram as a probe of innervation densities in four quadrants of the rostral neostriatum and in two halves of the caudal neostriatum. In addition, tissue concentrations of 5-HT, 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol were measured by high-performance liquid chromatography with electrochemical detection in these neostriatal divisions. In +/+ mice and in Lc/+ mutants there was a dorso-ventral gradient of increasing 5-HT levels, and they exhibited a similar heterogeneity of [3H]-citalopram labeling. In contrast, the gradients of 5-HT concentrations and [3H]-citalopram binding disappeared in the weaver mutants, suggesting a rearrangement of the 5-HT innervation. This reorganization of the 5-HT system in the neostriatum was more obvious in the wv/wv and is compatible with the hypothesis that the postnatal dopaminergic deficiencies that characterize weaver mutants lead to a sprouting of fibers and thus constitute a genetic model of dopaminergic denervation that leads to a 5-HT hyperinnervation.
Collapse
Affiliation(s)
- T A Reader
- Centre de Recherche en Sciences Neurologiques, Département de Physiologie, Faculté de Médecine, Université de Montréal, CP6128 Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
| | | | | | | |
Collapse
|