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Cutaneous silent period in hand muscles is lengthened by tramadol: Evidence for monoaminergic modulation?
Neuroscience Letters 528 (2012) 78–82
Contents lists available at SciVerse ScienceDirect
Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet
Cutaneous silent period in hand muscles is lengthened by tramadol: Evidence for monoaminergic modulation? Francesco Pujia a,∗ , Gianluca Coppola b , Maria G. Anastasio a , Marianna Brienza a , Elisa Vestrini b , Gabriele O. Valente a , Leoluca Parisi a , Mariano Serrao c , Francesco Pierelli c,d a
“Sapienza” University of Rome, Department of Medico-surgical Sciences and Biotechnologies, Neurology Section, Rome, Italy G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy c “Sapienza” University of Rome, Polo Pontino, Department of Medico-surgical Sciences and Biotechnologies, Latina, Italy d IRCCS-Neuromed, Italy b
h i g h l i g h t s Tramadol has low affinity for opioid receptors and inhibits serotonin and noradrenaline reuptake. Tramadol increased duration of the cutaneous silent period. Monoamines may play a major role as neurotransmitters mediating CSPs.
a r t i c l e
i n f o
Article history: Received 20 June 2012 Accepted 13 August 2012 Keywords: Cutaneous silent period Tramadol Noxious withdrawal flexor reflex Monoamines Brainstem descending system
a b s t r a c t The purpose of this study was to shed light on the neurochemical modulatory mechanisms of the noxious spinal inhibitory cutaneous silent period (CSP). We study the effects of 100 mg of oral tramadol in 11 healthy volunteers. Tramadol has low affinity for opioid receptors and has the ability to inhibit serotonin and noradrenaline reuptake. We elicited CSPs in the first dorsal interosseus muscle and noxious withdrawal flexor reflexes (NWR) in the right biceps femoris muscle before, 30 min and each hour up to the 6th after tramadol. Subjective pain sensation was checked on an 11-point numerical scale. Tramadol increased duration of CSP, and reduced the NWR area under the curve maximally 2 h after tramadol and paralleled the reduction of subjective pain perception. We suggest that the monoaminergic action of tramadol reinforces the activity of spinal inhibitory interneurons on ␣-motoneurons for the hand muscles. © 2012 Elsevier Ireland Ltd. All rights reserved.
The cutaneous silent period (CSP) is a spinal inhibitory reflex elicited in hand muscles by noxious electrical digital nerve stimulation, mainly mediated by A␦-fibers [32,29,26]. The afferents of CSPs induce, through a spinal oligosynaptic circuit, a transient suppression of voluntary muscle contraction that could be produced either by post- or pre-synaptic inhibition of excitatory inputs on C7-T1 motoneurons [14]. Interneurons mediating the CSP may be considered as part of the circuitry that mediates also noxious withdrawal flexor reflexes (NWR) [18,20]. Whereas the NWR is mainly expressed in the proximal muscles, the CSP is mainly present in distal ones. Such a differential distribution appears to fit well into a protective mechanism. The functional significance of these reflexes may be to
∗ Corresponding author at: Department of Medico-surgical Sciences and Biotechnologies, “Sapienza” University of Rome, Viale dell’Università 30, 00185 Rome, Italy. Tel.: +39 06 49914984; fax: +39 06 49914809. E-mail address: [email protected] (F. Pujia). 0304-3940/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neulet.2012.08.064
‘prepare’ the upper limbs to rapidly move away from an offending object by preferentially inhibiting muscles that mediate reaching and grasping (hand muscles), while allowing activation of the most important muscles that mediate the NWR (biceps and deltoid) [27]. The CSP and NWR seem to be synchronously controlled by descending inhibitory pathways because both of them are inhibited by the activation of diffuse inhibitory controls (DNICs) induced by cold pressor test [27]. This evidence suggests that the gain of the “CSP–NWR complex” may be modulated (either decreased or increased) depending on the peripheral context. It raises also the question of whether there is a separate modulation of the two reflexes. Inghilleri et al. [14] showed that, in healthy subjects, fentanyl, a potent synthetic opioid with short-acting analgesic activity, did not affect CSP parameters, while, conversely, it reduced the NWR magnitude. This finding suggests that the CSP and NWR may be distinctively modulated and that they are mediated by different neurochemical substrates. Although the NWR has been widely investigated in both animal and humans (for review see [28,1]), the neurochemical
F. Pujia et al. / Neuroscience Letters 528 (2012) 78–82
modulation of the CSP is still poorly understood. Few authors explored the CSP physiology by investigating its modifications after specific drugs administration. Oral administration of H1 antihistaminic cetirizine failed to modify the CSP in healthy subjects [17]. Furthermore, in patients with focal dystonia, botulinum toxin did not modify the basal prolonged CSP [23]. Finally, baclofen, GABA(b) receptors agonist, does not influence the CSP excitability in a single case observation [15]. Conversely, there are some evidences that dopaminergic pathways are involved in the modulation of the CSP. Indeed, dopaminergic medication is able to shorten the abnormally prolonged CSP duration in idiopathic Parkinson’s disease [30] as well as in restless legs syndrome [12]. The dopamine-related changes may indicate that monoaminergic pathways may play a role in the integration of peripheral inputs regulating the CSP reflex. Tramadol is one of the most used central acting pain relieving drug, with a low affinity for opioid receptors and with the ability to inhibit serotonin and noradrenaline reuptake [6]. Since CSP, unlike NWR, is a non-opiate-sensitive nociceptive reflex [14], it would be of interest to see if tramadol, through its monoaminergic activity, is able to modulate the CSP. In healthy humans, tramadol was already revealed to be able to influence spinal NWRs [7]. However, whether the potential effect of tramadol on the CSP be either the same or be the opposite, than that on the NWR, needs to be explored. In this study we investigated whether and how tramadol administration influences both CSPs and NWRs. To do this, we tested the CSP duration and NWR area under the curve in eleven healthy subjects before and up to 6 h after a 100 mg oral dose of tramadol. We reasoned that, on the one hand, tramadol administration would inhibit the NWR RIII response by virtue of its opiatergic activity, but, on the other hand, would reinforce the activity of the spinal inhibitory interneurons mediating CSP due to its concomitant monoaminergic action. Thirteen right-handed healthy volunteers (7 women, 6 men) gave their written informed consent and participated in the study, which had the approval of the local ethics committee. Inclusion criteria were: absence of any medical condition and, in particular, no personal or family history of neurological diseases. The age and bodyweight of the subjects ranged from 23 to 34 years (mean 28.7 ± 2.7 years) and from 59 to 71 kg (mean 66.2 kg), respectively. The mean body max index was 24.8. Subjects were not allowed to take drugs on a regular basis, nor caffeine or alcohol-containing beverage less than 72 h before the recording. To avoid bias due to hormonal effects, females were recorded outside of menses. Before the beginning of the study and 15 days after its completion, participants were determined to be healthy by a medical history and a physical examination. Before the formal measurements for the study were started, the subjects underwent an initial training session to familiarize them with the assessment procedures. All of the participants signed informed consent in accordance with the Helsinki Declaration relating to human experimentation. The study was approved by the Ethics Committee of the Faculty of Medicine, Sapienza University of Rome. The cutaneous silent period (CSP) was recorded during an isometric contraction of the first dorsal interosseous (FDI) muscle on a horizontal plane against a fixed bar, while cutaneous electrical stimuli (monopolar square-wave pulses with a duration of 0.2 ms) were delivered through ring electrodes over the interphalangeal joints of the fifth digit of the hand. Sensitivity was set at 500–1000 V/division, with a 30–3000 Hz bandpass. The oscilloscope screen was calibrated, for each subject, to display a force level corresponding to 50% of the maximal force, which was the level used for all the experiments. The stimulus intensity used to evoke the CSP was 20 times the value of the individual sensory threshold (mean: 2.2 ± 0.8 mA). Ten consecutive CSPs were
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full-wave rectified and averaged. During stimulations subjects were instructed to perform a constant isometric contraction of the FDI muscle for about 3 s. Interstimulus intervals of 10 s were used to avoid muscle fatigue. CSP duration was obtained by measuring the arithmetic difference between the CSP onset and offset latencies, which were taken respectively when the averaged signal dropped below and returned to above 80% of the baseline electromyographic level (obtained during a 100 ms epoch preceding the stimulus). For the nociceptive withdrawal reflex (NWR), subjects were seated comfortably and their lower limbs were positioned with the knee flexed at 130◦ and the ankle at 90◦ so as to achieve muscle relaxation. The NWR was elicited by delivering, using a pair of standard surface electrodes (Ag/AgCl), a constant-current pulse train of five individual 1 ms pulses, delivered at 200 Hz, randomly applied every 35–40 s to the retromalleolar sural nerve. Electromyographic reflex responses (NWR) were recorded from the caput brevis of the biceps femoris by surface electrodes (Ag/AgCl), sensitivity was set at 100 V/div with a 3 Hz and 3 kHz bandpass. The staircase method was used to evaluate the NWR threshold (Th), defined as the stimulus intensity which generated stable reflex responses. The stimulus intensity was fixed at 1.2× Th (mean: 28.1 ± 13.7 mA). The left side only was examined in all the subjects. Each response was full-wave rectified and integrated between set points from 90 to 130 ms after the start of the test stimulus, in accordance with previous studies that have indicated the occurrence of a specific nociceptive response in this time window [4]. Ten consecutive responses of 300 ms duration were averaged and full-wave rectified and the mean NWR area under the curve (ms × mV) was computed. During the study, room temperature was maintained between 21 and 24 ◦ C, skin temperature was kept above 31 ◦ C. All subjects started to be tested in the morning (between 9 and 10 AM). All of the participants observed a 10 h overnight fast. All of the meals consumed during the study were prepared with a low fat content. Tramadol chlorhydrate was administered orally at a 100 mg dose (Contramal© Farmaceutici Formenti, Italy). Since tramadol peak serum levels occur 2 h after administration and since the elimination kinetic was 5 ± 1 h [6], CSP and NWR recordings were performed in random order during a single session before, 1, 2, 4, and 6 h after tramadol administration. Subjects remained under observation in the study unit until 10 h from the tramadol administration. Vital signs (respiration, heart rate, sitting blood pressure, oral temperature) were taken and recorded every one hour after drug administration. Subjects rated the subjective intensity of the peripheral pain sensation, after every recording, on an 11-point numerical scale (11PNS), graded from 0 = no pain to 10 = unbearable pain. The Statistical Package for the Social Sciences (SPSS) for Windows, version 19.0, was used for all the analyses (SPSS Inc., Chicago, IL, USA). Data were first analyzed through the Kolmogorov–Smirnov test for normal distribution. The changes in the electrophysiological parameters pre- and post-tramadol administration were analyzed by Friedman repeated measures analysis of variance (ANOVA) on ranks. Tukey’s test was used for post hoc analyses. Wilcoxon Signed Ranks test was used to compare 11 PNS scores pre- and post-tramadol. Results were considered significant at p < 0.01. Eleven healthy subjects completed the study (6 women and 5 men, range age 23–34; mean age: 28.6 ± 2.9 years; weight range between 60 and 71 kg, BMI range between 20.7 and 27.9, mean 24.8). Two subjects (one woman and one man) withdrew from the study because of side effects (nausea/vomiting) and their data were excluded from the analysis.
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Fig. 1. Illustrative recordings of cutaneous silent period (CSP) before (A) and 2 h after (B) tramadol administration.
Examples of CSP and NWR recordings after tramadol administration in a representative subject are shown in Figs. 1 and 2, respectively. Friedman’s test did not reveal any repetition effect on CSP onset latency (Chi-square = 5.936, p = 0.204) (upper in Fig. 3). Conversely, a significant repetition effect was disclosed on CSP duration (Chi-square = 17.009, p = 0.002). Post hoc analysis revealed that CSP duration increased already at 1 h, becoming significantly different from the baseline at the 2nd one (q = 4.863, p < 0.01) and then it tended numerically to return to the baseline duration values in the subsequent hours (p > 0.05) (Figs. 1 and 3A). There was a significant repetition effect on NWR area (Chisquare = 17.174, p = 0.002). NWR area decreased already at the 1st hour, but significantly only at the 2nd hour (post hoc q = 5.721, p < 0.01) post-tramadol administration, after which it tended to return to the baseline values (p > 0.05) (Figs. 2 and 4A). Fig. 3. CSP onset latency, duration and 11PNS score before and their change over six hours after tramadol administration (data expressed as mean ± SEM, *p < 0.01).
Fig. 2. Illustrative recordings of nociceptive withdrawal reflex (NWR) before (A) and 2 h after (B) tramadol administration.
Friedman’s ANOVA test revealed a significant repetition effect on 11PNS during both the CSP (Chi-square = 12.217, p = 0.016) and the NWR (Chi-square = 11.972, p = 0.018) sessions. Post hoc analysis revealed that the 11PNS score was significantly reduced only at 2 h (q = 4.386, p = 0.01; q = 3.989, p = 0.01 for CSP and NWR, respectively) after tramadol administration compared to baseline (Figs. 3C and 4B). The main finding of our experiment shows that a 100 mg oral dose of tramadol induces a significant increase of the duration of the CSP as well as a decrease of the NWR magnitude. Tramadol is a centrally acting pain reliever with a weak link for the -opioid receptors and an additional non-opioid mechanism that contributes to its pharmacological action [6]. Indeed, besides its weak opiatergic activity, tramadol is able to strongly reinforce the extraneural concentrations of the monoamine neurotransmitters norepinephrine and serotonin, interfering with their re-uptake and release mechanisms [2,8,9,24,25,3]. A single oral dose of tramadol reaches peak serum concentrations within 2 h and has a half-life of approximately 5 h (9 h for the M1 derivative), whereas the duration of analgesia after a dose of 100 mg is approximately 6 h [6].
F. Pujia et al. / Neuroscience Letters 528 (2012) 78–82
Fig. 4. (A) R3 NWR area-under-the-curve (AUC) and (B) 11PNS score before and their change over six hours after tramadol administration (data expressed as mean ± SEM, *p < 0.05).
In the present study, the CSP duration changes fit well with the pharmacokinetic profile of tramadol. Indeed, at 2 h after tramadol administration, we found a significant increase in the duration of the CSP (Fig. 3), which corresponded to the presumed peak serum concentration of the drug, followed by a slow recovery, which paralleled the half-life of tramadol (approximately 6 h). It is likely that the main effect of tramadol on the CSP duration is exerted by its monoaminergic activity. Indeed, while opioid -agonist fentanyl significantly suppresses the NWR [5], it leaves the duration of the CSP unchanged [14], indicating that the circuitry mediating the CSP is neither directly mediated by -opiate receptors nor indirectly modulated. We speculate that the weak opiatergic activity of tramadol is probably responsible also for the reduced NWR area at 2 h after drug administration, which also paralleled subjective perceived analgesia (Fig. 4). Previous studies have shown that drugs with monoaminergic properties reduce the NWR excitability (for a review see [28]). Thus a synergistic effect of both monoaminergic and opiatergic activity of tramadol in reducing the NWR magnitude at the 2nd hours is likely to occur. It is well known that monoamines, particularly noradrenaline and serotonin, are widely involved in the control of spinal pain mechanisms by supraspinal descending pathways coming from brainstem neural structures such as the nucleus reticularis gigantocellularis, nucleus raphe magnus, PAG, and diffuse noxious inhibitory controls (DNICs) [33]. A major role of brainstem monoaminergic systems clearly emerges from animal models where monoamines, particularly noradrenaline, inhibit spontaneous activity of dorsal horn neurons and their excitation after noxious stimuli [10,13]. In humans, supraspinal influence on CSPs has been postulated based on studies in patients with spinal cord injury, minor stroke, amyotrophic lateral sclerosis, compressive cervical myelopathy and syringomyelia [21,16,11,31]. All these diseases are characterized by corticospinal tract dysfunctions and influence the CSP by
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delaying onset or shortening its duration. Conversely, in extrapyramidal disorders such Parkinson’s disease and brachial dystonia [23,30] the duration of the CSP is prolonged suggesting that the descending pathways conveying the basal ganglia output, e.g. reticulo-spinal pathways, produce a different effect onto the neuronal substrate mediating the CSP compared to the corticospinal ones. Altogether these results indicate that the CSP and NWR can be modulated either in the same or in the opposite way depending on the on-off balance of the descending modulating systems. It makes sense, in a functional way, because the “CSP–NWR complex” excitability can be tuned according to the peripheral context. For instance, in some circumstances, there is not need to withdraw the whole limb but just to strongly inhibits the hand muscles to leave the grip on an offending object. It appears reasonable to think that ‘pre-motoneuronal’ spinal interneurons mediating NWR and CSP responses represent the final, common pathway subserving various aspects of motor control. In this light, the “NWR–CSP system” may provide a wide and complex neuronal substrate to modulate the excitatory and inhibitory responses in both proximal and distal muscles according to the motor context. In our study the CSP duration was increased suggesting that the monoaminergic activity of tramadol exerts its action probably by reinforcing the activity of the spinal inhibitory interneurons on ␣-motoneurons for the hand muscles. However, for the sake of completeness, it must be mentioned that prolongation of CSP could be explained also by a drug-mediated inhibition of excitatory EMG activity, through the descending cortico-motoneuronal command [19,22]. Finally should be acknowledged that we were not able to perform measure of serum concentrations of tramadol to ensure that concentrations had been achieved. Such a missing data should not be considered detrimental since we controlled for all the confounding factors which may have interfere with the drug pharmacokinetics, for instance respiration, diet and thus bodyweight. In conclusion we observed that 100 mg of orally administered tramadol significantly changed the CSP, since it increased its duration. These drug-induced modifications occurred maximally at the presumed serum compound peak concentration and slowly disappeared following its half-life. Interestingly, tramadol modifies the CSP and NWR excitability in the opposite way. It increases the inhibitory tone of the circuit mediating the CSP and suppresses that mediating the NWR. References [1] O.K. Andersen, Studies of the organization of the human nociceptive withdrawal reflex. Focus on sensory convergence and stimulation site dependency, Acta Physiologica (Oxford) 189 (Suppl. (654)) (2007) 1. [2] T.A. Bamigbade, C. Davidson, R.M. Langford, J.A. Stamford, Actions of tramadol, its enantiomers and principal metabolite, O-desmethyltramadol, on serotonin (5-HT) efflux and uptake in the rat dorsal raphe nucleus, British Journal of Anaesthesia 79 (1997) 352. [3] E. Berrocoso, M.D. De Benito, J.A. Mico, Role of serotonin 5-HT1A and opioid receptors in the antiallodynic effect of tramadol in the chronic constriction injury model of neuropathic pain in rats, Psychopharmacology (Berlin) 193 (2007) 97. [4] D. Bouhassira, D. Le Bars, F. Bolgert, D. Laplane, J.C. Willer, Diffuse noxious inhibitory controls in humans: a neurophysiological investigation of a patient with a form of Brown-Séquard syndrome, Annals of Neurology 34 (1993) 536. [5] C. Chabal, L. Jacobson, J. Little, Intrathecal fentanyl depresses nociceptive flexion reflexes in patients with chronic pain, Anesthesiology 70 (1989) 226. [6] P. Dayer, J. Desmeules, L. Collart, Pharmacology of Tramadol, Drugs 53 (Suppl. (2)) (1997) 18. [7] J.A. Desmeules, V. Piguet, L. Collart, P. Dayer, Contribution of monoaminergic modulation to the analgesic effect of tramadol, British Journal of Clinical Pharmacology 41 (1996) 7. [8] B. Driessen, W. Reimann, Interaction of the central analgesic, tramadol, with the uptake and release of 5-hydroxytryptamine in the rat brain in vitro, British Journal of Pharmacology 105 (1992) 147.
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[9] B. Driessen, W. Reimann, H. Giertz, Effects of the central analgesic tramadol on the uptake and release of noradrenaline and dopamine in vitro, British Journal of Pharmacology 108 (1993) 806. [10] S.M. Fleetwood-Walker, R. Mitchell, P.J. Hope, V. Molony, A. Iggo, An alpha 2 receptor mediates the selective inhibition by noradrenaline of nociceptive responses of identified dorsal horn neurones, Brain Research 334 (1985) 243. [11] F. Gilio, C.M. Bettolo, A. Conte, E. Iacovelli, V. Frasca, M. Serrao, E. Giacomelli, M. Gabriele, M. Prencipe, M. Inghilleri, Influence of the corticospinal tract on the cutaneous silent period: a study in patients with pyramidal syndrome, Neuroscience Letters 433 (2008) 109. [12] J.K. Han, K. Oh, B.J. Kim, S.B. Koh, J.Y. Kim, K.W. Park, D.H. Lee, Cutaneous silent period in patients with restless leg syndrome, Clinical Neurophysiology 118 (2007) 1705. [13] P. Headley, Noradrenergic receptors in the dorsal horn of the spinal cord, in: J. Besson, G. Guilbaud (Eds.), Towards the Use of Noradrenergic Agonists for the Treatment of Pain, Elsevier, Amsterdam, 1992, pp. 169–181. [14] M. Inghilleri, A. Conte, V. Frasca, A. Berardelli, M. Manfredi, G. Cruccu, Is the cutaneous silent period an opiate-sensitive nociceptive reflex? Muscle and Nerve 25 (2002) 695. [15] M. Kofler, J. Wissel, J. Müller, C. Brenneis, Influence of intrathecal baclofen on silent periods in dystonia, Muscle and Nerve 23 (2000) 1145. [16] M. Kofler, M.F. Kronenberg, C. Brenneis, A. Felber, L. Saltuari, Cutaneous silent periods in intramedullary spinal cord lesions, Journal of the Neurological Sciences 216 (2003) 67. [17] M. Kofler, H. Kumru, I. Stetkarova, S. Rüegg, P. Fuhr, A.A. Leis, Cutaneous silent periods are not affected by the antihistaminic drug cetirizine, Clinical Neurophysiology 120 (2009) 1016. [18] A.A. Leis, Cutaneous silent period, Muscle and Nerve 21 (1998) 1243. ´ D.S. Stokic, ´ Spinal motor neuron excitability [19] A.A. Leis, I. St˘etkárová, A. Beric, during the cutaneous silent period, Muscle and Nerve 18 (1995) 1464. [20] A.A. Leis, D.S. Stokic, P. Fuhr, M. Kofler, M.F. Kronenberg, J. Wissel, F.X. Glocker, C. Seifert, I. Stetkarova, Nociceptive fingertip stimulation inhibits synergistic motoneuron pools in the human upper limb, Neurology 55 (2000) 1305.
[21] E.L. Logigian, G.M. Plotkin, J.M. Shefner, The cutaneous silent period is mediated by spinal inhibitory reflex, Muscle and Nerve 22 (1999) 467. [22] O. Öz, C¸. Erdo˘gan, M. Yücel, H. Akgün, Y. Kütükc¸ü, Z. Gökc¸il, Z. Odabas¸i, Effect of pramipexole on cutaneous-silent-period parameters in patients with restless legs syndrome, Clinical Neurophysiology 123 (2012) 154. [23] S.L. Pullman, B. Ford, B. Elibol, A. Uncini, P.C. Su, S. Fahn, Cutaneous electromyographic silent period findings in brachial dystonia, Neurology 46 (1996) 503. [24] R.B. Raffa, E. Friderichs, W. Reimann, R.P. Shank, E.E. Codd, J.L. Vaught, Opioid and nonopioid components independently contribute to the mechanism of action of tramadol, an ‘atypical’ opioid analgesic, Journal of Pharmacology and Experimental Therapeutics 260 (1992) 275. [25] M.O. Rojas-Corrales, E. Berrocoso, J.A. Micó, Role of 5-HT1A and 5-HT1B receptors in the antinociceptive effect of tramadol, European Journal of Pharmacology 511 (2005) 21. [26] A. Romaniello, A. Truini, F. Galeotti, C. De Lena, J.C. Willer, G. Cruccu, Cutaneous silent period in hand muscle is evoked by laser stimulation of the palm, but not the hand dorsum, Muscle and Nerve 29 (2004) 870. [27] P. Rossi, F. Pierelli, L. Parisi, A. Perrotta, M. Bartolo, G. Amabile, M. Serrao, Effect of painful heterotopic stimulation on the cutaneous silent period in the upper limbs, Clinical Neurophysiology 114 (2003) 1. [28] G. Sandrini, M. Serrao, P. Rossi, A. Romaniello, G. Cruccu, J.C. Willer, The lower limb flexion reflex in humans, Progress in Neurobiology 77 (2005) 353. [29] M. Serrao, L. Parisi, F. Pierelli, P. Rossi, Cutaneous afferents mediating the cutaneous silent period in the upper limbs: evidences for a role of low-threshold sensory fibres, Clinical Neurophysiology 112 (2001) 2007. [30] M. Serrao, L. Parisi, G. Valente, A. Martini, F. Fattapposta, F. Pierelli, P. Rossi, l-Dopa decreases cutaneous nociceptive inhibition of motor activity in Parkinson’s disease, Acta Neurologica Scandinavica 105 (2002) 196. [31] I. Stetkarova, M. Kofler, Cutaneous silent periods in the assessment of mild cervical spondylotic myelopathy, Spine 34 (2009) 34. [32] A. Uncini, T. Kujirai, B. Gluck, S. Pullman, Silent period induced by cutaneous stimulation, Electroencephalography and Clinical Neurophysiology 81 (1991) 344. [33] C.J. Woolf, Pain, Neurobiology of Disease 7 (2000) 504.
Contents lists available at SciVerse ScienceDirect
Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet
Cutaneous silent period in hand muscles is lengthened by tramadol: Evidence for monoaminergic modulation? Francesco Pujia a,∗ , Gianluca Coppola b , Maria G. Anastasio a , Marianna Brienza a , Elisa Vestrini b , Gabriele O. Valente a , Leoluca Parisi a , Mariano Serrao c , Francesco Pierelli c,d a
“Sapienza” University of Rome, Department of Medico-surgical Sciences and Biotechnologies, Neurology Section, Rome, Italy G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy c “Sapienza” University of Rome, Polo Pontino, Department of Medico-surgical Sciences and Biotechnologies, Latina, Italy d IRCCS-Neuromed, Italy b
h i g h l i g h t s Tramadol has low affinity for opioid receptors and inhibits serotonin and noradrenaline reuptake. Tramadol increased duration of the cutaneous silent period. Monoamines may play a major role as neurotransmitters mediating CSPs.
a r t i c l e
i n f o
Article history: Received 20 June 2012 Accepted 13 August 2012 Keywords: Cutaneous silent period Tramadol Noxious withdrawal flexor reflex Monoamines Brainstem descending system
a b s t r a c t The purpose of this study was to shed light on the neurochemical modulatory mechanisms of the noxious spinal inhibitory cutaneous silent period (CSP). We study the effects of 100 mg of oral tramadol in 11 healthy volunteers. Tramadol has low affinity for opioid receptors and has the ability to inhibit serotonin and noradrenaline reuptake. We elicited CSPs in the first dorsal interosseus muscle and noxious withdrawal flexor reflexes (NWR) in the right biceps femoris muscle before, 30 min and each hour up to the 6th after tramadol. Subjective pain sensation was checked on an 11-point numerical scale. Tramadol increased duration of CSP, and reduced the NWR area under the curve maximally 2 h after tramadol and paralleled the reduction of subjective pain perception. We suggest that the monoaminergic action of tramadol reinforces the activity of spinal inhibitory interneurons on ␣-motoneurons for the hand muscles. © 2012 Elsevier Ireland Ltd. All rights reserved.
The cutaneous silent period (CSP) is a spinal inhibitory reflex elicited in hand muscles by noxious electrical digital nerve stimulation, mainly mediated by A␦-fibers [32,29,26]. The afferents of CSPs induce, through a spinal oligosynaptic circuit, a transient suppression of voluntary muscle contraction that could be produced either by post- or pre-synaptic inhibition of excitatory inputs on C7-T1 motoneurons [14]. Interneurons mediating the CSP may be considered as part of the circuitry that mediates also noxious withdrawal flexor reflexes (NWR) [18,20]. Whereas the NWR is mainly expressed in the proximal muscles, the CSP is mainly present in distal ones. Such a differential distribution appears to fit well into a protective mechanism. The functional significance of these reflexes may be to
∗ Corresponding author at: Department of Medico-surgical Sciences and Biotechnologies, “Sapienza” University of Rome, Viale dell’Università 30, 00185 Rome, Italy. Tel.: +39 06 49914984; fax: +39 06 49914809. E-mail address: [email protected] (F. Pujia). 0304-3940/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neulet.2012.08.064
‘prepare’ the upper limbs to rapidly move away from an offending object by preferentially inhibiting muscles that mediate reaching and grasping (hand muscles), while allowing activation of the most important muscles that mediate the NWR (biceps and deltoid) [27]. The CSP and NWR seem to be synchronously controlled by descending inhibitory pathways because both of them are inhibited by the activation of diffuse inhibitory controls (DNICs) induced by cold pressor test [27]. This evidence suggests that the gain of the “CSP–NWR complex” may be modulated (either decreased or increased) depending on the peripheral context. It raises also the question of whether there is a separate modulation of the two reflexes. Inghilleri et al. [14] showed that, in healthy subjects, fentanyl, a potent synthetic opioid with short-acting analgesic activity, did not affect CSP parameters, while, conversely, it reduced the NWR magnitude. This finding suggests that the CSP and NWR may be distinctively modulated and that they are mediated by different neurochemical substrates. Although the NWR has been widely investigated in both animal and humans (for review see [28,1]), the neurochemical
F. Pujia et al. / Neuroscience Letters 528 (2012) 78–82
modulation of the CSP is still poorly understood. Few authors explored the CSP physiology by investigating its modifications after specific drugs administration. Oral administration of H1 antihistaminic cetirizine failed to modify the CSP in healthy subjects [17]. Furthermore, in patients with focal dystonia, botulinum toxin did not modify the basal prolonged CSP [23]. Finally, baclofen, GABA(b) receptors agonist, does not influence the CSP excitability in a single case observation [15]. Conversely, there are some evidences that dopaminergic pathways are involved in the modulation of the CSP. Indeed, dopaminergic medication is able to shorten the abnormally prolonged CSP duration in idiopathic Parkinson’s disease [30] as well as in restless legs syndrome [12]. The dopamine-related changes may indicate that monoaminergic pathways may play a role in the integration of peripheral inputs regulating the CSP reflex. Tramadol is one of the most used central acting pain relieving drug, with a low affinity for opioid receptors and with the ability to inhibit serotonin and noradrenaline reuptake [6]. Since CSP, unlike NWR, is a non-opiate-sensitive nociceptive reflex [14], it would be of interest to see if tramadol, through its monoaminergic activity, is able to modulate the CSP. In healthy humans, tramadol was already revealed to be able to influence spinal NWRs [7]. However, whether the potential effect of tramadol on the CSP be either the same or be the opposite, than that on the NWR, needs to be explored. In this study we investigated whether and how tramadol administration influences both CSPs and NWRs. To do this, we tested the CSP duration and NWR area under the curve in eleven healthy subjects before and up to 6 h after a 100 mg oral dose of tramadol. We reasoned that, on the one hand, tramadol administration would inhibit the NWR RIII response by virtue of its opiatergic activity, but, on the other hand, would reinforce the activity of the spinal inhibitory interneurons mediating CSP due to its concomitant monoaminergic action. Thirteen right-handed healthy volunteers (7 women, 6 men) gave their written informed consent and participated in the study, which had the approval of the local ethics committee. Inclusion criteria were: absence of any medical condition and, in particular, no personal or family history of neurological diseases. The age and bodyweight of the subjects ranged from 23 to 34 years (mean 28.7 ± 2.7 years) and from 59 to 71 kg (mean 66.2 kg), respectively. The mean body max index was 24.8. Subjects were not allowed to take drugs on a regular basis, nor caffeine or alcohol-containing beverage less than 72 h before the recording. To avoid bias due to hormonal effects, females were recorded outside of menses. Before the beginning of the study and 15 days after its completion, participants were determined to be healthy by a medical history and a physical examination. Before the formal measurements for the study were started, the subjects underwent an initial training session to familiarize them with the assessment procedures. All of the participants signed informed consent in accordance with the Helsinki Declaration relating to human experimentation. The study was approved by the Ethics Committee of the Faculty of Medicine, Sapienza University of Rome. The cutaneous silent period (CSP) was recorded during an isometric contraction of the first dorsal interosseous (FDI) muscle on a horizontal plane against a fixed bar, while cutaneous electrical stimuli (monopolar square-wave pulses with a duration of 0.2 ms) were delivered through ring electrodes over the interphalangeal joints of the fifth digit of the hand. Sensitivity was set at 500–1000 V/division, with a 30–3000 Hz bandpass. The oscilloscope screen was calibrated, for each subject, to display a force level corresponding to 50% of the maximal force, which was the level used for all the experiments. The stimulus intensity used to evoke the CSP was 20 times the value of the individual sensory threshold (mean: 2.2 ± 0.8 mA). Ten consecutive CSPs were
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full-wave rectified and averaged. During stimulations subjects were instructed to perform a constant isometric contraction of the FDI muscle for about 3 s. Interstimulus intervals of 10 s were used to avoid muscle fatigue. CSP duration was obtained by measuring the arithmetic difference between the CSP onset and offset latencies, which were taken respectively when the averaged signal dropped below and returned to above 80% of the baseline electromyographic level (obtained during a 100 ms epoch preceding the stimulus). For the nociceptive withdrawal reflex (NWR), subjects were seated comfortably and their lower limbs were positioned with the knee flexed at 130◦ and the ankle at 90◦ so as to achieve muscle relaxation. The NWR was elicited by delivering, using a pair of standard surface electrodes (Ag/AgCl), a constant-current pulse train of five individual 1 ms pulses, delivered at 200 Hz, randomly applied every 35–40 s to the retromalleolar sural nerve. Electromyographic reflex responses (NWR) were recorded from the caput brevis of the biceps femoris by surface electrodes (Ag/AgCl), sensitivity was set at 100 V/div with a 3 Hz and 3 kHz bandpass. The staircase method was used to evaluate the NWR threshold (Th), defined as the stimulus intensity which generated stable reflex responses. The stimulus intensity was fixed at 1.2× Th (mean: 28.1 ± 13.7 mA). The left side only was examined in all the subjects. Each response was full-wave rectified and integrated between set points from 90 to 130 ms after the start of the test stimulus, in accordance with previous studies that have indicated the occurrence of a specific nociceptive response in this time window [4]. Ten consecutive responses of 300 ms duration were averaged and full-wave rectified and the mean NWR area under the curve (ms × mV) was computed. During the study, room temperature was maintained between 21 and 24 ◦ C, skin temperature was kept above 31 ◦ C. All subjects started to be tested in the morning (between 9 and 10 AM). All of the participants observed a 10 h overnight fast. All of the meals consumed during the study were prepared with a low fat content. Tramadol chlorhydrate was administered orally at a 100 mg dose (Contramal© Farmaceutici Formenti, Italy). Since tramadol peak serum levels occur 2 h after administration and since the elimination kinetic was 5 ± 1 h [6], CSP and NWR recordings were performed in random order during a single session before, 1, 2, 4, and 6 h after tramadol administration. Subjects remained under observation in the study unit until 10 h from the tramadol administration. Vital signs (respiration, heart rate, sitting blood pressure, oral temperature) were taken and recorded every one hour after drug administration. Subjects rated the subjective intensity of the peripheral pain sensation, after every recording, on an 11-point numerical scale (11PNS), graded from 0 = no pain to 10 = unbearable pain. The Statistical Package for the Social Sciences (SPSS) for Windows, version 19.0, was used for all the analyses (SPSS Inc., Chicago, IL, USA). Data were first analyzed through the Kolmogorov–Smirnov test for normal distribution. The changes in the electrophysiological parameters pre- and post-tramadol administration were analyzed by Friedman repeated measures analysis of variance (ANOVA) on ranks. Tukey’s test was used for post hoc analyses. Wilcoxon Signed Ranks test was used to compare 11 PNS scores pre- and post-tramadol. Results were considered significant at p < 0.01. Eleven healthy subjects completed the study (6 women and 5 men, range age 23–34; mean age: 28.6 ± 2.9 years; weight range between 60 and 71 kg, BMI range between 20.7 and 27.9, mean 24.8). Two subjects (one woman and one man) withdrew from the study because of side effects (nausea/vomiting) and their data were excluded from the analysis.
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Fig. 1. Illustrative recordings of cutaneous silent period (CSP) before (A) and 2 h after (B) tramadol administration.
Examples of CSP and NWR recordings after tramadol administration in a representative subject are shown in Figs. 1 and 2, respectively. Friedman’s test did not reveal any repetition effect on CSP onset latency (Chi-square = 5.936, p = 0.204) (upper in Fig. 3). Conversely, a significant repetition effect was disclosed on CSP duration (Chi-square = 17.009, p = 0.002). Post hoc analysis revealed that CSP duration increased already at 1 h, becoming significantly different from the baseline at the 2nd one (q = 4.863, p < 0.01) and then it tended numerically to return to the baseline duration values in the subsequent hours (p > 0.05) (Figs. 1 and 3A). There was a significant repetition effect on NWR area (Chisquare = 17.174, p = 0.002). NWR area decreased already at the 1st hour, but significantly only at the 2nd hour (post hoc q = 5.721, p < 0.01) post-tramadol administration, after which it tended to return to the baseline values (p > 0.05) (Figs. 2 and 4A). Fig. 3. CSP onset latency, duration and 11PNS score before and their change over six hours after tramadol administration (data expressed as mean ± SEM, *p < 0.01).
Fig. 2. Illustrative recordings of nociceptive withdrawal reflex (NWR) before (A) and 2 h after (B) tramadol administration.
Friedman’s ANOVA test revealed a significant repetition effect on 11PNS during both the CSP (Chi-square = 12.217, p = 0.016) and the NWR (Chi-square = 11.972, p = 0.018) sessions. Post hoc analysis revealed that the 11PNS score was significantly reduced only at 2 h (q = 4.386, p = 0.01; q = 3.989, p = 0.01 for CSP and NWR, respectively) after tramadol administration compared to baseline (Figs. 3C and 4B). The main finding of our experiment shows that a 100 mg oral dose of tramadol induces a significant increase of the duration of the CSP as well as a decrease of the NWR magnitude. Tramadol is a centrally acting pain reliever with a weak link for the -opioid receptors and an additional non-opioid mechanism that contributes to its pharmacological action [6]. Indeed, besides its weak opiatergic activity, tramadol is able to strongly reinforce the extraneural concentrations of the monoamine neurotransmitters norepinephrine and serotonin, interfering with their re-uptake and release mechanisms [2,8,9,24,25,3]. A single oral dose of tramadol reaches peak serum concentrations within 2 h and has a half-life of approximately 5 h (9 h for the M1 derivative), whereas the duration of analgesia after a dose of 100 mg is approximately 6 h [6].
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Fig. 4. (A) R3 NWR area-under-the-curve (AUC) and (B) 11PNS score before and their change over six hours after tramadol administration (data expressed as mean ± SEM, *p < 0.05).
In the present study, the CSP duration changes fit well with the pharmacokinetic profile of tramadol. Indeed, at 2 h after tramadol administration, we found a significant increase in the duration of the CSP (Fig. 3), which corresponded to the presumed peak serum concentration of the drug, followed by a slow recovery, which paralleled the half-life of tramadol (approximately 6 h). It is likely that the main effect of tramadol on the CSP duration is exerted by its monoaminergic activity. Indeed, while opioid -agonist fentanyl significantly suppresses the NWR [5], it leaves the duration of the CSP unchanged [14], indicating that the circuitry mediating the CSP is neither directly mediated by -opiate receptors nor indirectly modulated. We speculate that the weak opiatergic activity of tramadol is probably responsible also for the reduced NWR area at 2 h after drug administration, which also paralleled subjective perceived analgesia (Fig. 4). Previous studies have shown that drugs with monoaminergic properties reduce the NWR excitability (for a review see [28]). Thus a synergistic effect of both monoaminergic and opiatergic activity of tramadol in reducing the NWR magnitude at the 2nd hours is likely to occur. It is well known that monoamines, particularly noradrenaline and serotonin, are widely involved in the control of spinal pain mechanisms by supraspinal descending pathways coming from brainstem neural structures such as the nucleus reticularis gigantocellularis, nucleus raphe magnus, PAG, and diffuse noxious inhibitory controls (DNICs) [33]. A major role of brainstem monoaminergic systems clearly emerges from animal models where monoamines, particularly noradrenaline, inhibit spontaneous activity of dorsal horn neurons and their excitation after noxious stimuli [10,13]. In humans, supraspinal influence on CSPs has been postulated based on studies in patients with spinal cord injury, minor stroke, amyotrophic lateral sclerosis, compressive cervical myelopathy and syringomyelia [21,16,11,31]. All these diseases are characterized by corticospinal tract dysfunctions and influence the CSP by
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delaying onset or shortening its duration. Conversely, in extrapyramidal disorders such Parkinson’s disease and brachial dystonia [23,30] the duration of the CSP is prolonged suggesting that the descending pathways conveying the basal ganglia output, e.g. reticulo-spinal pathways, produce a different effect onto the neuronal substrate mediating the CSP compared to the corticospinal ones. Altogether these results indicate that the CSP and NWR can be modulated either in the same or in the opposite way depending on the on-off balance of the descending modulating systems. It makes sense, in a functional way, because the “CSP–NWR complex” excitability can be tuned according to the peripheral context. For instance, in some circumstances, there is not need to withdraw the whole limb but just to strongly inhibits the hand muscles to leave the grip on an offending object. It appears reasonable to think that ‘pre-motoneuronal’ spinal interneurons mediating NWR and CSP responses represent the final, common pathway subserving various aspects of motor control. In this light, the “NWR–CSP system” may provide a wide and complex neuronal substrate to modulate the excitatory and inhibitory responses in both proximal and distal muscles according to the motor context. In our study the CSP duration was increased suggesting that the monoaminergic activity of tramadol exerts its action probably by reinforcing the activity of the spinal inhibitory interneurons on ␣-motoneurons for the hand muscles. However, for the sake of completeness, it must be mentioned that prolongation of CSP could be explained also by a drug-mediated inhibition of excitatory EMG activity, through the descending cortico-motoneuronal command [19,22]. Finally should be acknowledged that we were not able to perform measure of serum concentrations of tramadol to ensure that concentrations had been achieved. Such a missing data should not be considered detrimental since we controlled for all the confounding factors which may have interfere with the drug pharmacokinetics, for instance respiration, diet and thus bodyweight. In conclusion we observed that 100 mg of orally administered tramadol significantly changed the CSP, since it increased its duration. These drug-induced modifications occurred maximally at the presumed serum compound peak concentration and slowly disappeared following its half-life. Interestingly, tramadol modifies the CSP and NWR excitability in the opposite way. It increases the inhibitory tone of the circuit mediating the CSP and suppresses that mediating the NWR. References [1] O.K. Andersen, Studies of the organization of the human nociceptive withdrawal reflex. Focus on sensory convergence and stimulation site dependency, Acta Physiologica (Oxford) 189 (Suppl. (654)) (2007) 1. [2] T.A. Bamigbade, C. Davidson, R.M. Langford, J.A. Stamford, Actions of tramadol, its enantiomers and principal metabolite, O-desmethyltramadol, on serotonin (5-HT) efflux and uptake in the rat dorsal raphe nucleus, British Journal of Anaesthesia 79 (1997) 352. [3] E. Berrocoso, M.D. De Benito, J.A. Mico, Role of serotonin 5-HT1A and opioid receptors in the antiallodynic effect of tramadol in the chronic constriction injury model of neuropathic pain in rats, Psychopharmacology (Berlin) 193 (2007) 97. [4] D. Bouhassira, D. Le Bars, F. Bolgert, D. Laplane, J.C. Willer, Diffuse noxious inhibitory controls in humans: a neurophysiological investigation of a patient with a form of Brown-Séquard syndrome, Annals of Neurology 34 (1993) 536. [5] C. Chabal, L. Jacobson, J. Little, Intrathecal fentanyl depresses nociceptive flexion reflexes in patients with chronic pain, Anesthesiology 70 (1989) 226. [6] P. Dayer, J. Desmeules, L. Collart, Pharmacology of Tramadol, Drugs 53 (Suppl. (2)) (1997) 18. [7] J.A. Desmeules, V. Piguet, L. Collart, P. Dayer, Contribution of monoaminergic modulation to the analgesic effect of tramadol, British Journal of Clinical Pharmacology 41 (1996) 7. [8] B. Driessen, W. Reimann, Interaction of the central analgesic, tramadol, with the uptake and release of 5-hydroxytryptamine in the rat brain in vitro, British Journal of Pharmacology 105 (1992) 147.
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