Sensory Stimulation of the Triceps Surae Muscle Complex Modulates Spinal Reflex Responses-A Comparison between Tapotement Massage and Repetitive Peripheral Magnetic Stimulation (rPMS)

BACKGROUND

The reduction of muscular hypertonia is important in the treatment of various diseases or rehabilitation. This study aims to test the efficacy of a 5 Hz mechanical muscle stimulation (tapotement massage) in comparison to a 5 Hz repetitive peripheral magnetic stimulation (rPMS) on the neuromuscular reflex response.

METHODS

In a randomized control trial, 15 healthy volunteers were administered with either 5 Hz rPMS, tapotement massage, or rPMS sham stimulation. The posterior tibial nerve was stimulated with rPMS and sham stimulation. The Achilles tendon was exposed to a mechanically applied high-amplitude 5 Hz repetitive tendon tapotement massage (rTTM). The tendon reflex (TR) was measured for the spinal response of the soleus muscle.

RESULTS

After rPMS, there was a reduction of the TR response (-9.8%, p ≤ 0.034) with no significant changes after sham stimulation. Likewise, TR decreased significantly (-17.4%, p ≤ 0.002) after Achilles tendon tapotement intervention.

CONCLUSIONS

These findings support the hypothesis that both afferent 5 Hz sensory stimulations contributed to a modulation within the spinal and/or supraspinal circuits, which resulted in a reduction of the spinal reflex excitability. The effects could be beneficial for patients with muscle hypertonia and could improve the functional results of rehabilitation programs.

Aβ-CT affective touch: Touch pleasantness ratings for gentle stroking and deep pressure exhibit dependence on A-fibers

Gentle stroking of the skin is a common social touch behavior with positive affective consequences. A preference for slow versus fast stroking of hairy skin has been closely linked to the firing of unmyelinated C-tactile (CT) somatosensory afferents. Because the firing of CT afferents strongly correlates with touch pleasantness, the CT pathway has been considered a social-affective sensory pathway. Recently, ablation of the spinothalamic pathway- thought to convey all C-fiber sensations- in patients with cancer pain impaired pain, temperature, and itch, but not ratings of pleasant touch. This suggested integration of afferent A and CT fiber input in the spinal cord, or mechanoreceptive A-fiber contributions to computations of touch pleasantness in the brain. However, contribution of mechanoreceptive A-fibers to touch pleasantness- in humans without pain- remains unknown. In the current, single-blinded study we performed two types of peripheral nerve blocks in healthy adults to temporarily eliminate the contribution of A-fibers to touch perception. Our findings show that when mechanoreceptive A-fiber function is greatly diminished, the perceived intensity and pleasantness of both gentle stroking and deep pressure are nearly abolished. These findings demonstrate that explicit perception of the pleasantness of CT-targeted brushing and pressure both critically depend on afferent A-fibers.Significance StatementIn the current study we performed two types of peripheral nerve blocks in healthy adults to temporarily eliminate the contribution of A-fiber afferents to touch perception. We show that when afferent A-fiber function is greatly diminished, the perceived intensity and pleasantness of gentle stroking are nearly abolished. These findings demonstrate for the first time that explicit perception of the pleasantness of C-tactile (CT)-targeted touch critically depends upon A-fiber afferents. In addition, we show the same outcome for deep pressure (similar to hugs and massage), another form of social-affective touch we have previously validated in the lab. Together these findings demonstrate that social touch is not conveyed solely by the CT pathway.

The structure of sensory afferent compartments in health and disease

Primary sensory neurons are a heterogeneous population of cells able to respond to both innocuous and noxious stimuli. Like most neurons they are highly compartmentalised, allowing them to detect, convey and transfer sensory information. These compartments include specialised sensory endings in the skin, the nodes of Ranvier in myelinated axons, the cell soma and their central terminals in the spinal cord. In this review, we will highlight the importance of these compartments to primary afferent function, describe how these structures are compromised following nerve damage and how this relates to neuropathic pain.

Activation of TRPM8 channel inhibits contraction of the isolated human ureter

AIMS

The transient receptor potential melastin-8 (TRPM8) channel is a "cooling" receptor expressed in primary sensory neurons and can be activated by compounds like menthol or icilin. TRPM8 is involved in the regulation of urinary bladder sensory function and contraction, but the role of TRPM8 in the ureter, particularly in the human ureter, is poorly understood. The aim of this study is to examine the effects of TRPM8 activation on human ureter contraction.

METHODS

Human ureters were acquired from 20 patients undergoing radical nephrectomy. Contractions of ureter strips were recorded by an isometric transducer in the organ bath. Ureteral TRPM8 expression in the human ureter was examined by immunofluorescence and western blot.

RESULTS

The two TRPM8 agonists menthol and icilin both reduced the frequency of spontaneous, electrical field stimulation, or neurokinin A-evoked ureteral contractions in a dose-dependent manner. The inhibitory effects were decreased by 10-fold in mucosa-denuded strips. The inhibitory effects of TRPM8 agonists were mimicked by calcitonin gene-related peptide (CGRP), and were blocked by KRP2579 (a TRPM8 antagonist), tetrodotoxin (a sodium channel blocker), olcegepant (BIBN, a CGRP receptor antagonist), SQ22536 (an adenylate cyclase antagonist), or H89 (a nonspecific cAMP-dependent protein kinase A inhibitor). TRPM8 was coexpressed with CGRP on the nerves located in the suburothelial and intermuscular regions and was not expressed in the urothelium.

CONCLUSIONS

The TRPM8 channel expressed on sensory nerve terminals of the human ureter is involved in the inhibitory sensory neurotransmission and modulate ureter contraction via the CGRP-adenylyl cyclase-protein kinase A pathway. TRPM8 may be involved in stone-induced changes in ureter contraction or pain.

Cardiac sensory afferents modulate susceptibility to anxio-depressive behaviour in a mouse model of chronic heart failure

AIM

Impairments in cerebral structure and cognitive performance in chronic heart failure (CHF) are critical components of its comorbidity spectrum. Autonomic afferents that arise from cardiac sensory fibres show enhanced activity with CHF. Desensitization of these fibres by local application of resiniferatoxin (RTX) during myocardial infarction (MI) is known to prevent cardiac hypertrophy, sympathetic hyperactivity and CHF. Whether these afferents mediate cerebral allostasis is unknown.

METHODS

CHF was induced by myocardial infarction. To evaluate if cardiac afferents contribute to cerebral allostasis, RTX was acutely applied to the pericardial space in controls (RTX) and in MI treated animals (MI/RTX). Subjects were then evaluated in a series of behavioural tests recapitulating different symptoms of depressive disorders. Proteomics of the frontal cortices (FC) was performed to identify contributing proteins and pathways responsible for behavioural allostasis.

RESULTS

Desensitization of cardiac afferents relieves hallmarks of an anxio/depressive-like state in mice. Unique protein signatures and regulatory pathways in FCs isolated from each treatment reveal the degree of complexity inherent in the FC response to stresses originating in the heart. While cortices from the combined treatment (MI/RTX) did not retain protein signatures from the individual treatment groups, all three groups suffer dysregulation in circadian entrainment.

CONCLUSION

CHF is comorbid with an anxio/depressive-like state and ablation of cardiac afferents relieves the despair phenotype. The strikingly different proteomic profiles observed in FCs suggest that MI and RTX lead to unique brain-signalling patterns and that the combined treatment, potentially through destructive interference mechanisms, most closely resembles controls.

Pain in Endometriosis

Endometriosis is a chronic and debilitating condition affecting ∼10% of women. Endometriosis is characterized by infertility and chronic pelvic pain, yet treatment options remain limited. In many respects this is related to an underlying lack of knowledge of the etiology and mechanisms contributing to endometriosis-induced pain. Whilst many studies focus on retrograde menstruation, and the formation and development of lesions in the pathogenesis of endometriosis, the mechanisms underlying the associated pain remain poorly described. Here we review the recent clinical and experimental evidence of the mechanisms contributing to chronic pain in endometriosis. This includes the roles of inflammation, neurogenic inflammation, neuroangiogenesis, peripheral sensitization and central sensitization. As endometriosis patients are also known to have co-morbidities such as irritable bowel syndrome and overactive bladder syndrome, we highlight how common nerve pathways innervating the colon, bladder and female reproductive tract can contribute to co-morbidity via cross-organ sensitization.

Sympathoexcitation in response to cardiac and pulmonary afferent stimulation of TRPA1 channels is attenuated in rats with chronic heart failure

Excessive sympathoexcitation characterizes the chronic heart failure (CHF) state. An exaggerated cardiac sympathetic afferent reflex (CSAR) contributes to this sympathoexcitation. Prior studies have demonstrated that the CSAR to capsaicin [transient receptor potential (TRP) vanilloid 1 agonist] is exaggerated in CHF animal models. We recently discovered that capsaicin application to the lung visceral pleura in anesthetized, vagotomized, open-chested rats increases mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA). We named this response the pulmonary spinal afferent reflex (PSAR). Due to the similarities between TRP vanilloid 1 and TRP ankyrin 1 (TRPA1) channels as well as the excessive sympathoexcitation of CHF, we hypothesized that stimulation of the CSAR and PSAR with a specific TRPA1 agonist would result in an augmented response in CHF rats (coronary ligation model) compared with sham control rats. In response to a TRPA1 agonist, both CSAR and PSAR in sham rats resulted in biphasic changes in MAP and increases in HR and RSNA 10-12 wk postmyocardial infarction (post-MI). These effects were blunted in CHF rats. Assessment of TRPA1 expression levels in cardiopulmonary spinal afferents by immunofluorescence, quantitative RT-PCR, and Western blot analysis 10-12 wk post-MI all indicates reduced expression in CHF rats but no reduction at earlier time points. TRPA1 protein was reduced in a dorsal root ganglia cell culture model of inflammation and simulated tissue ischemia, raising the possibility that the in vivo reduction of TRPA1 expression was, in part, caused by CHF-related tissue ischemia and inflammation. These data provide evidence that reflex responses to cardiopulmonary spinal afferent TRPA1 stimulation may be attenuated in CHF rather than enhanced. NEW & NOTEWORTHY Excessive sympathoexcitation characterizes chronic heart failure (CHF). The contribution of transient receptor potential ankyrin 1 (TRPA1) channel-mediated reflexes to this sympathoexcitation is unknown. We found that application of TRPA1 agonist to the heart and lung surface resulted in increased heart rate and sympathetic output and a biphasic change in mean arterial pressure in control rats. These effects were attenuated in CHF rats, decreasing the likelihood that TRPA1 channels contribute to cardiopulmonary afferent sensitization in CHF.

Voltage-gated sodium channels: (NaV )igating the field to determine their contribution to visceral nociception

Chronic visceral pain, altered motility and bladder dysfunction are common, yet poorly managed symptoms of functional and inflammatory disorders of the gastrointestinal and urinary tracts. Recently, numerous human channelopathies of the voltage-gated sodium (NaV ) channel family have been identified, which induce either painful neuropathies, an insensitivity to pain, or alterations in smooth muscle function. The identification of these disorders, in addition to the recent utilisation of genetically modified NaV mice and specific NaV channel modulators, has shed new light on how NaV channels contribute to the function of neuronal and non-neuronal tissues within the gastrointestinal tract and bladder. Here we review the current pre-clinical and clinical evidence to reveal how the nine NaV channel family members (NaV 1.1-NaV 1.9) contribute to abdominal visceral function in normal and disease states.

Cross-organ sensitization between the colon and bladder: to pee or not to pee?

Chronic abdominal and pelvic pain are common debilitating clinical conditions experienced by millions of patients around the globe. The origin of such pain commonly arises from the intestine and bladder, which share common primary roles (the collection, storage, and expulsion of waste). These visceral organs are located in close proximity to one another and also share common innervation from spinal afferent pathways. Chronic abdominal pain, constipation, or diarrhea are primary symptoms for patients with irritable bowel syndrome or inflammatory bowel disease. Chronic pelvic pain and urinary urgency and frequency are primary symptoms experienced by patients with lower urinary tract disorders such as interstitial cystitis/painful bladder syndrome. It is becoming clear that these symptoms and clinical entities do not occur in isolation, with considerable overlap in symptom profiles across patient cohorts. Here we review recent clinical and experimental evidence documenting the existence of "cross-organ sensitization" between the colon and bladder. In such circumstances, colonic inflammation may result in profound changes to the sensory pathways innervating the bladder, resulting in severe bladder dysfunction.

Cross-organ sensitization between the colon and bladder: to pee or not to pee?

Chronic abdominal and pelvic pain are common debilitating clinical conditions experienced by millions of patients around the globe. The origin of such pain commonly arises from the intestine and bladder, which share common primary roles (the collection, storage, and expulsion of waste). These visceral organs are located in close proximity to one another and also share common innervation from spinal afferent pathways. Chronic abdominal pain, constipation, or diarrhea are primary symptoms for patients with irritable bowel syndrome or inflammatory bowel disease. Chronic pelvic pain and urinary urgency and frequency are primary symptoms experienced by patients with lower urinary tract disorders such as interstitial cystitis/painful bladder syndrome. It is becoming clear that these symptoms and clinical entities do not occur in isolation, with considerable overlap in symptom profiles across patient cohorts. Here we review recent clinical and experimental evidence documenting the existence of "cross-organ sensitization" between the colon and bladder. In such circumstances, colonic inflammation may result in profound changes to the sensory pathways innervating the bladder, resulting in severe bladder dysfunction.

Role of DSCAM in the development of the spinal locomotor and sensorimotor circuits

Locomotion is controlled by spinal circuits that generate rhythm and coordinate left-right and flexor-extensor motoneuronal activities. The outputs of motoneurons and spinal interneuronal circuits are shaped by sensory feedback, relaying peripheral signals that are critical to the locomotor and postural control. Several studies in invertebrates and vertebrates have argued that the Down syndrome cell adhesion molecule (DSCAM) would play an important role in the normal development of neural circuits through cell spacing and targeting, axonal and dendritic branching, and synapse establishment and maintenance. Although there is evidence that DSCAM is important for the normal development of neural circuits, little is known about its functional contribution to spinal motor circuits. We show here that adult DSCAM(2J) mutant mice, lacking DSCAM, exhibit a higher variability in their locomotor pattern and rhythm during treadmill locomotion. Retrograde tracing studies in neonatal isolated spinal cords show an increased number of spinal commissural interneurons, which likely contributes to reducing the left-right alternation and to increasing the flexor/swing duration during neonatal and adult locomotion. Moreover, our results argue that, by reducing the peripheral excitatory drive onto spinal motoneurons, the DSCAM mutation reduces or abolishes spinal reflexes in both neonatal isolated spinal cords and adult mice, thus likely impairing sensorimotor control. Collectively, our functional, electrophysiological, and anatomical studies suggest that the mammalian DSCAM protein is involved in the normal development of spinal locomotor and sensorimotor circuits.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Spinal activation of serotonin 1A receptors enhances latent respiratory activity after spinal cord injury

BACKGROUND/OBJECTIVE

Hemisection of the cervical spinal cord results in paralysis of the ipsilateral hemidiaphragm. Removal of sensory feedback through cervical dorsal rhizotomy activates latent respiratory motor pathways and restores hemidiaphragm function. Because systemic administration of serotonin 1A receptor (5HT1A) agonists reversed the altered breathing patterns after spinal cord injury (SCI), we predicted that 5HT1A receptor activation after SCI (C2) would activate latent crossed motor pathways. Furthermore, because 5HT1 A receptors are heavily localized to dorsal horn neurons, we predicted that spinal administration of 5HT1A agonists should also activate latent motor pathways.

METHODS

Hemisection of the C2 spinal cord was performed 24 to 48 hours, 1 week, or 16 weeks before experimentation. Bilateral phrenic nerve activity was recorded in anesthetized, vagotomized, paralyzed Sprague-Dawley rats, and 8-OH-DPAT (5HT1A agonist) was applied to the dorsal aspect of the cervical spinal cord (C3-C7) or injected systemically.

RESULTS

Systemic administration of 8-OH-DPAT led to a significant increase in phrenic frequency and amplitude, whereas direct application to the spinal cord increased phrenic amplitude alone. Both systemic and spinal administration of 8-OH-DPAT consistently activated latent crossed phrenic activity. 8-OH-DPAT induced a greater respiratory response in spinal injured rats compared with controls.

CONCLUSION

The increase in crossed phrenic output after application of 8-OH-DPAT to the spinal cord suggests that dorsal horn inputs, respiratory and/or nonrespiratory, may inhibit phrenic motor output, especially after SCI. These findings support the idea that the administration of 5HT1A agonists may be a beneficial therapy in enhancing respiratory neural output in patients with SCI.