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Amann M, Wan HY, Thurston TS, Georgescu VP, Weavil JC. On the Influence of Group III/IV Muscle Afferent Feedback on Endurance Exercise Performance. Exerc Sport Sci Rev 2020; 48:209-216. [PMID: 32658041 DOI: 10.1249/jes.0000000000000233] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This review discusses evidence suggesting that group III/IV muscle afferents affect locomotor performance by influencing neuromuscular fatigue. These neurons regulate the hemodynamic and ventilatory response to exercise and, thus, assure appropriate locomotor muscle O2 delivery, which optimizes peripheral fatigue development and facilitates endurance performance. In terms of central fatigue, group III/IV muscle afferents inhibit motoneuronal output and thereby limit exercise performance.
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Affiliation(s)
| | - Hsuan-Yu Wan
- Department of Anesthesiology, University of Utah
| | - Taylor S Thurston
- Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT
| | - Vincent P Georgescu
- Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT
| | - Joshua C Weavil
- Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT
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Ishii K, Asahara R, Komine H, Liang N, Matsukawa K. Pivotal role of the ventral tegmental area in spontaneous motor activity and concomitant cardiovascular responses in decerebrate rats. Brain Res 2020; 1729:146616. [DOI: 10.1016/j.brainres.2019.146616] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 12/11/2019] [Accepted: 12/16/2019] [Indexed: 10/25/2022]
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Sidhu SK, Weavil JC, Rossman MJ, Jessop JE, Bledsoe AD, Buys MJ, Supiano MS, Richardson RS, Amann M. Exercise Pressor Reflex Contributes to the Cardiovascular Abnormalities Characterizing: Hypertensive Humans During Exercise. Hypertension 2019; 74:1468-1475. [PMID: 31607174 DOI: 10.1161/hypertensionaha.119.13366] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We investigated the impact of hypertension on circulatory responses to exercise and the role of the exercise pressor reflex in determining the cardiovascular abnormalities characterizing patients with hypertension. After a 7-day drug washout, 8 hypertensive (mean arterial pressure [MAP] 130±4 mm Hg; 65±3 years) and 8 normotensive (MAP 117±2 mm Hg; 65±2 years) individuals performed single-leg knee-extensor exercise (7 W, 15 W, 50%, 80%-Wpeak) under control conditions and with lumbar intrathecal fentanyl impairing feedback from µ-opioid receptor-sensitive leg muscle afferents. Femoral artery blood flow (QL), MAP (femoral artery), leg vascular conductance, and changes in cardiac output were continuously measured. While the increase in MAP from rest to control exercise was significantly greater in hypertension compared with normotension, the exercise-induced increase in cardiac output was comparable between groups, and QL and leg vascular conductance responses were ≈18% and ≈32% lower in the hypertensive patients (P<0.05). The blockade-induced decreases in MAP were significantly larger during exercise in hypertensive (≈11 mm Hg) compared with normotensive (≈6 mm Hg). Afferent blockade attenuated the central hemodynamic response to exercise similarly in both groups resulting in a ≈15% lower cardiac output at each workload. With no effect in normotensive, afferent blockade significantly raised the peripheral hemodynamic response to exercise in hypertensive, resulting in ≈14% and ≈23% higher QL and leg vascular conductance during exercise. Finally, QL and MAP during fentanyl-exercise in hypertensive were comparable to that of normotensive under control conditions (P>0.2). These findings suggest that exercise pressor reflex abnormalities largely account for the exaggerated MAP response and the impaired peripheral hemodynamics during exercise in hypertension.
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Affiliation(s)
- Simranjit K Sidhu
- From the Department of Internal Medicine, Division of Geriatrics (S.K.S., M.J.R., M.S.S., R.S.R., M.A.), University of Utah, Salt Lake City.,Discipline of Physiology, Adelaide Medical School, The University of Adelaide, Australia (S.K.S.)
| | - Joshua C Weavil
- Geriatric Research, Education, and Clinical Center, VAMC Salt Lake City, UT (J.C.W., M.S.S., R.S.R., M.A.)
| | - Matthew J Rossman
- From the Department of Internal Medicine, Division of Geriatrics (S.K.S., M.J.R., M.S.S., R.S.R., M.A.), University of Utah, Salt Lake City
| | - Jacob E Jessop
- Department of Anesthesiology (J.E.J., A.D.B., M.J.B., M.A.), University of Utah, Salt Lake City
| | - Amber D Bledsoe
- Department of Anesthesiology (J.E.J., A.D.B., M.J.B., M.A.), University of Utah, Salt Lake City
| | - Michael J Buys
- Department of Anesthesiology (J.E.J., A.D.B., M.J.B., M.A.), University of Utah, Salt Lake City
| | - Mark S Supiano
- From the Department of Internal Medicine, Division of Geriatrics (S.K.S., M.J.R., M.S.S., R.S.R., M.A.), University of Utah, Salt Lake City.,Geriatric Research, Education, and Clinical Center, VAMC Salt Lake City, UT (J.C.W., M.S.S., R.S.R., M.A.)
| | - Russell S Richardson
- From the Department of Internal Medicine, Division of Geriatrics (S.K.S., M.J.R., M.S.S., R.S.R., M.A.), University of Utah, Salt Lake City.,Geriatric Research, Education, and Clinical Center, VAMC Salt Lake City, UT (J.C.W., M.S.S., R.S.R., M.A.)
| | - Markus Amann
- From the Department of Internal Medicine, Division of Geriatrics (S.K.S., M.J.R., M.S.S., R.S.R., M.A.), University of Utah, Salt Lake City.,Department of Anesthesiology (J.E.J., A.D.B., M.J.B., M.A.), University of Utah, Salt Lake City.,Geriatric Research, Education, and Clinical Center, VAMC Salt Lake City, UT (J.C.W., M.S.S., R.S.R., M.A.)
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Liang N, Iwamoto GA, Downey RM, Mitchell JH, Smith SA, Mizuno M. The Pressor Response to Concurrent Stimulation of the Mesencephalic Locomotor Region and Peripheral Sensory Afferents Is Attenuated in Normotensive but Not Hypertensive Rats. Front Physiol 2019; 10:95. [PMID: 30814955 PMCID: PMC6381028 DOI: 10.3389/fphys.2019.00095] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 01/25/2019] [Indexed: 11/29/2022] Open
Abstract
Central command (CC) and the exercise pressor reflex (EPR) regulate blood pressure during exercise. We previously demonstrated that experimental stimulation of the CC and EPR pathways independently contribute to the exaggerated pressor response to exercise in hypertension. It is known that CC and EPR modify one another functionally. Whether their interactive relationship is altered in hypertension, contributing to the generation of this potentiated blood pressure response, remains unknown. To address this issue, the pressor response to activation of the CC pathway with and without concurrent stimulation of the EPR pathway, and vice versa, was examined in normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. In decerebrated, paralyzed animals, activation of the CC pathway was evoked by electrical stimulation of the mesencephalic locomotor region (MLR; 20–50 μA in 10-μA steps). Electrical stimulation of the sciatic nerve (SN, 3, 5, and 10 × motor threshold; MT) was used to activate hindlimb afferents known to carry EPR sensory information. In both WKY and SHR, the algebraic sum of the pressor responses to individual stimulation of the MLR and SN were greater than when both inputs were stimulated simultaneously. Although the blood pressure response to a constant level of SN stimulation was not significantly affected by concurrent MLR stimulation at variable intensities, the pressor response to a constant level of MLR simulation was significantly attenuated by concurrent SN stimulation in WKY but not in SHR. These findings suggest the interactive relationship between CC and the EPR is inhibitory in nature in both WKY and SHR. However, the neural occlusion between these central and peripheral pressor mechanisms is attenuated in hypertension.
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Affiliation(s)
- Nan Liang
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Gary A Iwamoto
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Ryan M Downey
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Pharmacology and Physiology, Georgetown University, Washington, DC, United States
| | - Jere H Mitchell
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Scott A Smith
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Masaki Mizuno
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States
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Mueller PJ, Clifford PS, Crandall CG, Smith SA, Fadel PJ. Integration of Central and Peripheral Regulation of the Circulation during Exercise: Acute and Chronic Adaptations. Compr Physiol 2017; 8:103-151. [DOI: 10.1002/cphy.c160040] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Laurin J, Pertici V, Dousset E, Marqueste T, Decherchi P. Group III and IV muscle afferents: Role on central motor drive and clinical implications. Neuroscience 2015; 290:543-51. [DOI: 10.1016/j.neuroscience.2015.01.065] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 01/27/2015] [Accepted: 01/28/2015] [Indexed: 12/12/2022]
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Koba S, Hisatome I, Watanabe T. Central command dysfunction in rats with heart failure is mediated by brain oxidative stress and normalized by exercise training. J Physiol 2014; 592:3917-31. [PMID: 24973409 DOI: 10.1113/jphysiol.2014.272377] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Sympathoexcitation elicited by central command, a parallel activation of the motor and autonomic neural circuits in the brain, has been shown to become exaggerated in chronic heart failure (CHF). The present study tested the hypotheses that oxidative stress in the medulla in CHF plays a role in exaggerating central command-elicited sympathoexcitation, and that exercise training in CHF suppresses central command-elicited sympathoexcitation through its antioxidant effects in the medulla. In decerebrate rats, central command was activated by electrically stimulating the mesencephalic locomotor region (MLR) after neuromuscular blockade. The MLR stimulation at a current intensity greater than locomotion threshold in rats with CHF after myocardial infarction (MI) evoked larger (P < 0.05) increases in renal sympathetic nerve activity and arterial pressure than in sham-operated healthy rats (Sham) and rats with CHF that had completed longterm (8–12 weeks) exercise training (MI + TR). In the Sham and MI + TR rats, bilateral microinjection of a superoxide dismutase (SOD) mimetic Tempol into the rostral ventrolateral medulla (RVLM) had no effects on MLR stimulation-elicited responses. By contrast, in MI rats, Tempol treatment significantly reduced MLR stimulation-elicited responses. In a subset of MI rats, treatment with Tiron, another SOD mimetic, within the RVLM also reduced responses. Superoxide generation in the RVLM, as evaluated by dihydroethidium staining, was enhanced in MI rats compared with that in Sham and MI + TR rats. Collectively, these results support the study hypotheses. We suggest that oxidative stress in the medulla in CHF mediates central command dysfunction, and that exercise training in CHF is capable of normalizing central command dysfunction through its antioxidant effects in the medulla.
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Affiliation(s)
- Satoshi Koba
- Division of Integrative Physiology, Faculty of Medicine, Tottori University, Yonago, Japan
| | - Ichiro Hisatome
- Division of Regenerative Medicine and Therapeutics, Graduate School of Medical Science, Tottori University, Yonago, Japan
| | - Tatsuo Watanabe
- Division of Integrative Physiology, Faculty of Medicine, Tottori University, Yonago, Japan
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Leal AK, Williams MA, Garry MG, Mitchell JH, Smith SA. Evidence for functional alterations in the skeletal muscle mechanoreflex and metaboreflex in hypertensive rats. Am J Physiol Heart Circ Physiol 2008; 295:H1429-38. [PMID: 18641268 DOI: 10.1152/ajpheart.01365.2007] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exercise in hypertensive individuals elicits exaggerated increases in mean arterial pressure (MAP) and heart rate (HR) that potentially enhance the risk for adverse cardiac events or stroke. Evidence suggests that exercise pressor reflex function (EPR; a reflex originating in skeletal muscle) is exaggerated in this disease and contributes significantly to the potentiated cardiovascular responsiveness. However, the mechanism of EPR overactivity in hypertension remains unclear. EPR function is mediated by the muscle mechanoreflex (activated by stimulation of mechanically sensitive afferent fibers) and metaboreflex (activated by stimulation of chemically sensitive afferent fibers). Therefore, we hypothesized the enhanced cardiovascular response mediated by the EPR in hypertension is due to functional alterations in the muscle mechanoreflex and metaboreflex. To test this hypothesis, mechanically and chemically sensitive afferent fibers were selectively activated in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) decerebrate rats. Activation of mechanically sensitive fibers by passively stretching hindlimb muscle induced significantly greater increases in MAP and HR in SHR than WKY over a wide range of stimulus intensities. Activation of chemically sensitive fibers by administering capsaicin (0.01-1.00 microg/100 microl) into the hindlimb arterial supply induced increases in MAP that were significantly greater in SHR compared with WKY. However, HR responses to capsaicin were not different between the two groups at any dose. This data is consistent with the concept that the abnormal EPR control of MAP described previously in hypertension is mediated by both mechanoreflex and metaboreflex overactivity. In contrast, the previously reported alterations in the EPR control of HR in hypertension may be principally due to overactivity of the mechanically sensitive component of the reflex.
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Affiliation(s)
- Anna K Leal
- Department of Biomedical Engineering, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9174, USA
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Volatile anesthetic effects on midbrain-elicited locomotion suggest that the locomotor network in the ventral spinal cord is the primary site for immobility. Anesthesiology 2008; 108:1016-24. [PMID: 18497602 DOI: 10.1097/aln.0b013e3181730297] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Volatile anesthetics produce immobility primarily by action in the spinal cord; however, anesthetic effects among different neuronal classes located in different spinal regions, and how they relate to immobility, are not understood. METHODS In decerebrated rats, effects of isoflurane and halothane on movement elicited by electrical microstimulation of the mesencephalic locomotor region (MLR) were assessed in relation to minimum alveolar concentration (MAC). Anesthetic effects on step frequency and isometric limb force were measured. The authors also examined effects of MLR stimulation on responses of nociceptive dorsal horn neurons and limb force responses to tail clamp. RESULTS Mean isoflurane requirements to block MLR-elicited stepping were slightly but significantly greater than MAC by 10%. Mean halothane requirements to block MLR-elicited stepping were greater than those for isoflurane and exceeded MAC by 20%. From 0.4 to 1.3 MAC (but not 0.0 to 0.4 MAC), there was a dose-dependent reduction in the frequency and force of hind limb movements elicited by MLR stimulation during both anesthetics. MLR stimulation inhibited noxious stimulus evoked responses of dorsal horn neurons by approximately 80%. Aptly, MLR stimulation produced analgesia that outlasted the midbrain stimulus by at least 15 s, as indicated by an 81% reduction in hind limb force elicited noxious tail clamp. CONCLUSIONS Because electrical stimulation of the MLR elicits movement independent of dorsal horn activation, the immobilizing properties of isoflurane and halothane are largely independent of action in the dorsal horn. The results suggest that volatile anesthetics produce immobility mainly by action on ventral spinal locomotor networks.
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Smith SA, Williams MA, Leal AK, Mitchell JH, Garry MG. Exercise pressor reflex function is altered in spontaneously hypertensive rats. J Physiol 2006; 577:1009-20. [PMID: 17023501 PMCID: PMC1890389 DOI: 10.1113/jphysiol.2006.121558] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
In hypertension, exercise elicits excessive elevations in mean arterial pressure (MAP) and heart rate (HR) increasing the risk for adverse cardiac events and stroke during physical activity. The exercise pressor reflex (a neural drive originating in skeletal muscle), central command (a neural drive originating in cortical brain centres) and the tonically active arterial baroreflex contribute importantly to cardiovascular control during exercise. Each of these inputs potentially mediates the heightened cardiovascular response to physical activity in hypertension. However, given that exercise pressor reflex overactivity is known to elicit enhanced circulatory responses to exercise in disease states closely related to hypertension (e.g. heart failure), we tested the hypothesis that the exaggerated cardiovascular response to exercise in hypertension is mediated by an overactive exercise pressor reflex. To test this hypothesis, we used a rat model of exercise recently developed in our laboratory that selectively stimulates the exercise pressor reflex independent of central command and/or the arterial baroreflex. Activation of the exercise pressor reflex during electrically induced static muscle contraction in the absence of input from central command resulted in significantly larger increases in MAP and HR in male spontaneously hypertensive rats as compared to normotensive Wistar-Kyoto rats over a wide range of exercise intensities. Similar findings were obtained in animals in which input from both central command and the arterial baroreflex were eliminated. These findings suggest that the enhanced cardiovascular response to exercise in hypertension is mediated by an overactive exercise pressor reflex. Potentially, effective treatment of exercise pressor reflex dysfunction may reduce the cardiovascular risks associated with exercise in hypertension.
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Affiliation(s)
- Scott A Smith
- Department of Physical Therapy, Allied Health Sciences School, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9174, USA.
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Bell HJ, Feenstra W, Duffin J. The initial phase of exercise hyperpnoea in humans is depressed during a cognitive task. Exp Physiol 2005; 90:357-65. [PMID: 15665147 DOI: 10.1113/expphysiol.2004.028779] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Increased wakefulness is known to suppress the initial ventilatory response to passive movement and the steady-state ventilatory response to exercise. However, the effect of increased wakefulness upon the integrated ventilatory response at the onset of exercise is not known. We hypothesized that increasing wakefulness via a cognitive task would attenuate the initial ventilatory response to exercise, and so we examined the response to active leg extensions under two conditions: with and without concurrently solving a puzzle. At rest before exercise, subjects demonstrated greater minute ventilation while solving a puzzle (mean +/- S.E.M., 12.38 +/- 0.55 versus 10.12 +/- 0.51 l min(-1), P < 0.001), due to a higher mean breathing frequency (mean +/- S.E.M., 17.1 +/- 0.93 versus 13.6 +/- 0.59 breaths min(-1), P < 0.001). At the start of exercise, subjects did not increase their ventilation significantly while solving the puzzle (P = 0.170), but did by a mean +/-s.e.m. of 6.16 +/- 1.12 l min(-1) (P < 0.001) when not puzzle solving. The ventilation achieved at the start of exercise in absolute terms was also lower while solving the puzzle (14.6 +/- 1.1 versus 16.3 +/- 1.3 l min(-1), P = 0.047). Despite differences in the rapid ventilatory response to exercise between conditions, the steady-state responses were not different. We conclude that the performance of a cognitive task decreases the initial phase of exercise hyperpnoea, and suggest that this might occur because of either a competitive interaction between drives to breathe or a behavioural distraction from the 'task' of exercise.
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Affiliation(s)
- Harold J Bell
- Department of Physiology, Medical Sciences Building, 1 King's College Circle, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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Bell HJ, Duffin J. Respiratory response to passive limb movement is suppressed by a cognitive task. J Appl Physiol (1985) 2004; 97:2112-20. [PMID: 15273238 DOI: 10.1152/japplphysiol.00302.2004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Feedback from muscles stimulates ventilation at the onset of passive movement. We hypothesized that central neural activity via a cognitive task source would interact with afferent feedback, and we tested this hypothesis by examining the fast changes in ventilation at the transition from rest to passive leg movement, under two conditions: 1) no task and 2) solving a computer-based puzzle. Resting breathing was greater in condition 2 than in condition 1, evidenced by an increase in mean +/- SE breathing frequency (18.2 +/- 1.1 vs. 15.0 +/- 1.2 breaths/min, P = 0.004) and ventilation (10.93 +/- 1.16 vs. 9.11 +/- 1.17 l/min, P < 0.001). In condition 1, the onset of passive movement produced a fast increase in mean +/- SE breathing frequency (change of 2.9 +/- 0.4 breaths/min, P < 0.001), tidal volume (change of 233 +/- 95 ml, P < 0.001), and ventilation (change of 6.00 +/- 1.76 l/min, P < 0.001). However, in condition 2, the onset of passive movement only produced a fast increase in mean +/- SE breathing frequency (change of 1.3 +/- 0.4 breaths/min, P = 0.045), significantly smaller than in condition 1 (P = 0.007). These findings provide evidence for an interaction between central neural cognitive activity and the afferent feedback mechanism, and we conclude that the performance of a cognitive task suppresses the respiratory response to passive movement.
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Affiliation(s)
- Harold J Bell
- Dept. of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada M5S 1A8
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Nojima H, Carstens E. Quantitative assessment of directed hind limb scratching behavior as a rodent itch model. J Neurosci Methods 2003; 126:137-43. [PMID: 12814838 DOI: 10.1016/s0165-0270(03)00074-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Hind limb scratching is used increasingly as an itch model in rodents. Scratching is usually quantified as the number of scratching bouts over a 60 min period. Since the antipruritic effect of scratching should depend on the total time of skin contact, then the duration of scratching bouts and within-bout scratching frequency may also be important factors. Therefore, we measured these parameters during episodes of scratching directed toward the site (nape of neck) of intradermal injection of serotonin in Sprague-Dawley rats. Serotonin elicited significantly more scratching bouts than saline. There was a biphasic pattern of scratching over time, with peaks at 10-20 and 40-50 min. Although cumulative bout duration (2-min intervals) had a similar biphasic distribution, the mean individual bout duration (2.1 s) did not change significantly over time. Within-bout scratching frequency remained constant over time at 8 Hz. The number of scratching bouts was suppressed in a dose dependent manner by naltrexone (3 and 5 mg/kg), while the individual bout duration and the within-bout frequency were not significantly different compared with serotonin-evoked scratching without naltrexone. These results validate the total number of scratching bouts as an indicator of the magnitude of itch-related scratching.
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Affiliation(s)
- Hiroshi Nojima
- Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan
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Beyaert CA, Haouzi P, Marchal F. Inhibition of midbrain-evoked tonic and rhythmic motor activity by cutaneous stimulation in decerebrate cats. Exp Brain Res 2003; 149:159-66. [PMID: 12610683 DOI: 10.1007/s00221-002-1347-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2002] [Accepted: 11/01/2002] [Indexed: 12/18/2022]
Abstract
The effect of mechanical and electrical stimulation of cervical cutaneous afferents was analysed on both the centrally induced tonic and rhythmic activities in hindlimb antagonist muscle nerves of 16 decerebrate paralysed cats. Electrical stimulation of dorsal midbrain evoked in the nerve to the tibialis anterior muscle (TAn) either rhythmic discharges (n=14), associated with tonic discharges in ten cats, or only tonic discharges (n=4). Centrally induced activity in the ipsilateral nerve to gastrocnemius medialis (GMn) occurred in fewer cats (n=12) and displayed similar patterns as in TAn. Manual traction of the scruff of the neck reduced the TAn tonic and rhythmic discharges (n=6) by 73% (P<0.05) and 71% (P<0.05), respectively, and reduced only the tonic component of GMn discharges (by 41%, n=3). Electrical stimulation (impulses 0.1-0.5 ms, 50 Hz) of cervical nerves belonging to C5 or C6 dermatomes, the intensity (0.4-4 mA) of which induced minimal inhibition of both TAn and GMn discharges, reduced significantly the tonic component of TAn discharges (by 39%, n=4). At higher intensities of electrical cervical nerve stimulation (2-6 mA) inducing maximal inhibitory effect, both tonic and rhythmic activities in TAn and GMn were both significantly reduced by, respectively, 81% and 94% in TAn (n=7), and by 49% and 43% in GMn (n=7). Electrical cervical nerve stimulation consistently reduced the isolated tonic discharge in TAn by 66% (n=4, P<0.05) and in GMn by 23% (n=3) when present. Thus the tonic component was more sensitive to inhibition than the rhythmic component of hindlimb muscle nerve activity.
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Affiliation(s)
- C A Beyaert
- Laboratoire de Physiologie, Faculté de Médecine, 9 Avenue de la Forêt de Haye, 54500 Vandoeuvre-lès-Nancy, France.
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Degtyarenko AM, Kaufman MP. Spinoreticular neurons that receive group III input are inhibited by MLR stimulation. J Appl Physiol (1985) 2002; 93:92-8. [PMID: 12070191 DOI: 10.1152/japplphysiol.00072.2002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In decerebrate paralyzed cats, we examined the responses of 18 spinoreticular neurons to electrical stimulation of the mesencephalic locomotor region. The activity of each of the spinoreticular neurons was recorded extracellularly from laminae IV through VI of the L(7) and S(1) spinal cord. In addition, each of the 18 spinoreticular neurons received group III afferent input from the tibial nerve. Spinoreticular projections were established for each of 18 neurons by antidromic invasion of the ventro lateral medulla at the P11 though P14 levels. The onset latencies and current thresholds for antidromic invasion from the ventro lateral medulla averaged 15.0 +/- 3.8 ms and 117 +/- 11 microA, respectively. Electrical stimulation of the mesencephalic locomotor region attenuated the spontaneous activity or the responses of each of the spinoreticular neurons to tibial nerve stimulation at currents that recruited group III afferents. Our data support the notion that thin-fiber muscle afferent input to the ventrolateral medulla is gated by a central command to exercise.
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Affiliation(s)
- Alexandr M Degtyarenko
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis 95616, USA.
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