1
|
Fauss GNK, Hudson KE, Grau JW. Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia. BIOLOGY 2022; 11:234. [PMID: 35205100 PMCID: PMC8869318 DOI: 10.3390/biology11020234] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/27/2022] [Accepted: 01/29/2022] [Indexed: 12/12/2022]
Abstract
As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.
Collapse
Affiliation(s)
| | | | - James W. Grau
- Department of Psychological and Brain Sciences, Texas A&M University, College Station, TX 77843, USA; (G.N.K.F.); (K.E.H.)
| |
Collapse
|
2
|
Lucas-Osma AM, Li Y, Murray K, Lin S, Black S, Stephens MJ, Ahn AH, Heckman CJ, Fenrich KK, Fouad K, Bennett DJ. 5-HT 1D receptors inhibit the monosynaptic stretch reflex by modulating C-fiber activity. J Neurophysiol 2019; 121:1591-1608. [PMID: 30625007 DOI: 10.1152/jn.00805.2018] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The monosynaptic stretch reflex (MSR) plays an important role in feedback control of movement and posture but can also lead to unstable oscillations associated with tremor and clonus, especially when increased with spinal cord injury (SCI). To control the MSR and clonus after SCI, we examined how serotonin regulates the MSR in the sacrocaudal spinal cord of rats with and without a chronic spinal transection. In chronic spinal rats, numerous 5-HT receptor agonists, including zolmitriptan, methylergonovine, and 5-HT, inhibited the MSR with a potency highly correlated to their binding affinity to 5-HT1D receptors and not other 5-HT receptors. Selective 5-HT1D receptor antagonists blocked this agonist-induced inhibition, although antagonists alone had no action, indicating a lack of endogenous or constitutive receptor activity. In normal uninjured rats, the MSR was likewise inhibited by 5-HT, but at much higher doses, indicating a supersensitivity after SCI. This supersensitivity resulted from the loss of the serotonin transporter SERT with spinal transection, because normal and injured rats were equally sensitive to 5-HT after SERT was blocked or to agonists not transported by SERT (zolmitriptan). Immunolabeling revealed that the 5-HT1D receptor was confined to superficial lamina of the dorsal horn, colocalized with CGRP-positive C-fibers, and eliminated by dorsal rhizotomy. 5-HT1D receptor labeling was not found on large proprioceptive afferents or α-motoneurons of the MSR. Thus serotonergic inhibition of the MSR acts indirectly by modulating C-fiber activity, opening up new possibilities for modulating reflex function and clonus via pain-related pathways. NEW & NOTEWORTHY Brain stem-derived serotonin potently inhibits afferent transmission in the monosynaptic stretch reflex. We show that serotonin produces this inhibition exclusively via 5-HT1D receptors, and yet these receptors are paradoxically mostly confined to C-fibers. This suggests that serotonin acts by gating of C-fiber activity, which in turn modulates afferent transmission to motoneurons. We also show that the classic supersensitivity to 5-HT after spinal cord injury results from a loss of SERT, and not 5-HT1D receptor plasticity.
Collapse
Affiliation(s)
- Ana M Lucas-Osma
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Yaqing Li
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Katie Murray
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Shihao Lin
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Sophie Black
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Marilee J Stephens
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Andrew H Ahn
- Teva Pharmaceuticals, Clinical Development, North Wales, Pennsylvania
| | - C J Heckman
- Department of Physiology, Northwestern University, Feinberg School of Medicine , Chicago, Illinois
| | - Keith K Fenrich
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - Karim Fouad
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| | - David J Bennett
- Neuroscience and Mental Health Institute and Faculty of Rehabilitation Medicine, University of Alberta , Edmonton, Alberta , Canada
| |
Collapse
|
3
|
D'Amico JM, Li Y, Bennett DJ, Gorassini MA. Reduction of spinal sensory transmission by facilitation of 5-HT1B/D receptors in noninjured and spinal cord-injured humans. J Neurophysiol 2012; 109:1485-93. [PMID: 23221401 DOI: 10.1152/jn.00822.2012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Activation of receptors by serotonin (5-HT1) and norepinephrine (α2) on primary afferent terminals and excitatory interneurons reduces transmission in spinal sensory pathways. Loss or reduction of descending sources of serotonin and norepinephrine after spinal cord injury (SCI) and the subsequent reduction of 5-HT1/α2 receptor activity contributes, in part, to the emergence of excessive motoneuron activation from sensory afferent pathways and the uncontrolled triggering of persistent inward currents that depolarize motoneurons during muscle spasms. We tested in a double-blind, placebo-controlled study whether facilitating 5-HT1B/D receptors with the agonist zolmitriptan reduces the sensory activation of motoneurons during an H-reflex in both noninjured control and spinal cord-injured participants. In both groups zolmitriptan, but not placebo, reduced the size of the maximum soleus H-reflex with a peak decrease to 59% (noninjured) and 62% (SCI) of predrug values. In SCI participants we also examined the effects of zolmitriptan on the cutaneomuscular reflex evoked in tibialis anterior from stimulation to the medial arch of the foot. Zolmitriptan, but not placebo, reduced the long-latency, polysynaptic component of the cutaneomuscular reflex (first 200 ms of reflex) by ∼50%. This ultimately reduced the triggering of the long-lasting component of the reflex (500 ms poststimulation to end of reflex) known to be mediated by persistent inward currents in the motoneuron. These results demonstrate that facilitation of 5-HT1B/D receptors reduces sensory transmission in both monosynaptic and polysynaptic reflex pathways to ultimately reduce long-lasting reflexes (spasms) after SCI.
Collapse
Affiliation(s)
- Jessica M D'Amico
- Centre for Neuroscience, Univ. of Alberta, 5-005 Katz Group - Rexall Centre, Edmonton, AB, Canada T6G 2E1
| | | | | | | |
Collapse
|
4
|
Hueletl‐Soto ME, Carro‐Juárez M, Rodríguez‐Manzo G. Fluoxetine Chronic Treatment Inhibits Male Rat Sexual Behavior by Affecting Both Copulatory Behavior and the Genital Motor Pattern of Ejaculation. J Sex Med 2012; 9:1015-26. [DOI: 10.1111/j.1743-6109.2011.02339.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
5
|
Nogueira-Neto FDS, Amorim RL, Brigatte P, Picolo G, Ferreira WA, Gutierrez VP, Conceição IM, Della-Casa MS, Takahira RK, Nicoletti JLM, Cury Y. The analgesic effect of crotoxin on neuropathic pain is mediated by central muscarinic receptors and 5-lipoxygenase-derived mediators. Pharmacol Biochem Behav 2008; 91:252-60. [DOI: 10.1016/j.pbb.2008.08.016] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 07/24/2008] [Accepted: 08/12/2008] [Indexed: 01/05/2023]
|
6
|
Gajendiran M. In vivo evidence for serotonin 5-HT2C receptor-mediated long-lasting excitability of lumbar spinal reflex and its functional interaction with 5-HT1A receptor in the mammalian spinal cord. Brain Res Bull 2008; 75:674-80. [DOI: 10.1016/j.brainresbull.2007.11.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Revised: 10/30/2007] [Accepted: 11/05/2007] [Indexed: 01/03/2023]
|
7
|
Honda M, Imaida K, Tanabe M, Ono H. Endogenously released 5-hydroxytryptamine depresses the spinal monosynaptic reflex via 5-HT1D receptors. Eur J Pharmacol 2005; 503:55-61. [PMID: 15496296 DOI: 10.1016/j.ejphar.2004.09.045] [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: 06/03/2004] [Revised: 09/06/2004] [Accepted: 09/10/2004] [Indexed: 10/26/2022]
Abstract
In the spinal cord, various 5-hydroxytryptamine (5-HT) receptor subtypes are involved in the modulation of motor output. Previously, we have shown that 5-HT1B receptors mediate the monosynaptic reflex depression induced by exogenously applied 5-HT that was formed from the precursor L-5-hydroxytryptophan in spinalized rats. In this study, we determined the effects of endogenous 5-HT, which was released from serotonergic terminals by DL-p-chloroamphetamine, on spinal reflexes. DL-p-chloroamphetamine depressed the monosynaptic reflex and increased the polysynaptic reflex. The depletion of 5-HT abolished the monosynaptic reflex depression, but the increase in polysynaptic reflexes was maintained, suggesting that endogenous 5-HT released by DL-p-chloroamphetamine mediates depression of the monosynaptic reflex in the spinal cord. The depression of the monosynaptic reflex was antagonized by GR127935 (N-[methoxy-3-(4-methyl-l-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide; 5-HT1B/1D receptor antagonist) and BRL15572 (3-[4-(4-chlorophenyl)piperazin-1-yl]-1,1-diphenyl-2-propanol; 5-HT1D receptor antagonist) but not by isamoltane (5-HT(1B) receptor antagonist). These results suggest that 5-HT released from serotonergic terminals depresses monosynaptic reflex transmission via 5-HT1D receptors.
Collapse
Affiliation(s)
- Motoko Honda
- Laboratory of CNS Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan.
| | | | | | | |
Collapse
|