Somatic Afferent Nerves Research Articles

The Sympathorenal Axis in Hypertension and Heart Failure

Excessive sympathetic drive is undoubtedly a major contributing factor to the pathophysiology of hypertension and heart failure. Much of the excessive sympathetic drive in these conditions is directed to the kidney, where it leads to inappropriate sodium retention, renin stimulation, and diminished renal function. Less well appreciated is the role the kidney itself plays in the generation of increased sympathetic activity by way of the renal somatic afferent nerves. The kidney therefore is both target and contributor to increased sympathetic activity in these conditions. Although some current pharmacotherapy indirectly targets this “sympathorenal axis,” resistant hypertension remains a common problem, and the prognosis in heart failure remains poor, especially in more severe cases. It is now possible to directly target this axis via procedures, which directly interrupt renal sympathetic efferent and afferent signaling. Other procedures involving chronic carotid nerve stimulation may indirectly influence renal sympathetic tone and so improve renal sodium handling. These techniques have demonstrated early promise in hypertension and offer significant potential in heart failure as well. Should their early promise be borne out in controlled studies, the “sympathorenal axis” will have been proven to be a key element in the pathophysiology of these 2 very common, and dangerous, conditions.

Randomized Trial of Percutaneous Tibial Nerve Stimulation Versus Sham Efficacy in the Treatment of Overactive Bladder Syndrome: Results From the SUmiT Trial

The Study of Urgent PC vs Sham Effectiveness in Treatment of Overactive Bladder Symptoms (SUmiT) was a multicenter, double-blind, randomized, controlled trial comparing the efficacy of percutaneous tibial nerve stimulation to sham through 12 weeks of therapy. The improvement in global response assessment, voiding diary parameters, and overactive bladder and quality of life questionnaires was evaluated. A total of 220 adults with overactive bladder symptoms were randomized 1:1 to 12 weeks of treatment with weekly percutaneous tibial nerve stimulation or sham therapy. Overactive bladder and quality of life questionnaires as well as 3-day voiding diaries were completed at baseline and at 13 weeks. Subject global response assessments were completed at week 13. The 13-week subject global response assessment for overall bladder symptoms demonstrated that percutaneous tibial nerve stimulation subjects achieved statistically significant improvement in bladder symptoms with 54.5% reporting moderately or markedly improved responses compared to 20.9% of sham subjects from baseline (p <0.001). All individual global response assessment subset symptom components demonstrated statistically significant improvement from baseline to 13 weeks for percutaneous tibial nerve stimulation compared to sham. Voiding diary parameters after 12 weeks of therapy showed percutaneous tibial nerve stimulation subjects had statistically significant improvements in frequency, nighttime voids, voids with moderate to severe urgency and urinary urge incontinence episodes compared to sham. No serious device related adverse events or malfunctions were reported. This pivotal multicenter, double-blind, randomized, sham controlled trial provides level I evidence that percutaneous tibial nerve stimulation therapy is safe and effective in treating overactive bladder symptoms. The compelling efficacy of percutaneous tibial nerve stimulation demonstrated in this trial is consistent with other recently published reports and supports the use of peripheral neuromodulation therapy for overactive bladder.

Delta and Kappa Opioid Receptors as Suitable Drug Targets for Pain

Similar to mu opioid receptors, kappa and delta opioid receptors reside in the periphery, the dorsal root ganglion, the spinal cord, and in supraspinal regions associated with pain modulation. Both delta and kappa opioid agonists have been shown to activate pain inhibitory pathways in the central nervous system. Yet, currently there are only a few pharmacologic agents that target kappa receptors, and none that target delta receptors. Spurred by the need for an efficacious analgesic without the unwanted side effects associated with the typical clinical profile of mu opioid agonists, new research has provided insight into why the development of effective kappa and delta opioid receptor agonists has remained elusive thus far, and importantly, how these obstacles may be overcome. For example, for delta opioid agonists to be effective, a state of inflammation may be required as this induces delta opioid receptors to migrate to the surface of neuronal cells and thereby become accessible to delta opioid agonists. Studies have shown that delta opioid agonists can provide relief of inflammatory pain and malignant bone pain. Meanwhile, peripherally restricted kappa opioid agonists have been developed to target kappa opioid receptors located on visceral and somatic afferent nerves for relief of inflammatory, visceral, and neuropathic chronic pain. The recently shown efficacy of these analgesics combined with a possible lower abuse potential and side effect burden than mu opioid receptor agonists makes delta and peripherally restricted kappa opioid receptor agonists promising targets for treating pain.

Randomized Trial of Percutaneous Tibial Nerve Stimulation Versus Extended-Release Tolterodine: Results From the Overactive Bladder Innovative Therapy Trial

The Overactive Bladder Innovative Therapy trial was a randomized, multicenter, controlled study that compared the effectiveness of percutaneous tibial nerve stimulation to extended-release tolterodine. The reduction in overactive bladder symptoms along with global response assessments was evaluated. A total of 100 adults with urinary frequency were randomized 1:1 to 12 weeks of treatment with weekly percutaneous tibial nerve stimulation or to 4 mg daily extended-release tolterodine. Voiding diaries and an overactive bladder questionnaire were completed at baseline and at the end of therapy to compare 24-hour voiding frequency, urinary urge incontinence episodes, voids causing waking, volume voided, urgency episodes and quality of life indices. Global response assessments were completed by subjects and investigators after 12 weeks of therapy. The global response assessment demonstrated that subject assessment of overactive bladder symptoms compared to baseline was statistically significant in the percutaneous tibial nerve stimulation arm with 79.5% reporting cure or improvement compared to 54.8% of subjects on tolterodine (p = 0.01). Assessments by investigators were similar but did not reach statistical significance (p = 0.05). After 12 weeks of therapy objective measures improved similarly in both groups for reductions in urinary frequency, urge urinary incontinence episodes, urge severity and nighttime voids, as well as for improvement in voided volume. There were no serious adverse events or device malfunctions. This multicenter, randomized trial demonstrates that percutaneous tibial nerve stimulation is safe with statistically significant improvements in patient assessment of overactive bladder symptoms, and with objective effectiveness comparable to that of pharmacotherapy. Percutaneous tibial nerve stimulation may be considered a clinically significant alternative therapy for overactive bladder.

Electro-acupuncture improves responsiveness to insulin via excitation of somatic afferent fibers in diabetic rats

The effects of electro-acupuncture (EA) on plasma concentration of glucose and on responsiveness to insulin were examined in an animal model of diabetes, the streptozotocin-treated rat. Two weeks after treatment with streptozotocin, rats were anesthetized with urethane-chloralose and subjected to the EA for 10 min delivered to the tibialis anterior muscle of one side. The stimulation produced no significant changes in plasma glucose concentration. In contrast, EA increased the response of plasma glucose to insulin (0.2 U kg−1). The effect of EA on the responsiveness to insulin was abolished by section of both sciatic and femoral nerves ipsilateral to the side of the EA. These results show that EA in diabetic rats has no effect on plasma glucose concentration while it augments the responsiveness to insulin, and we show that this occurs via a mechanism that involves the somatic afferent nerves.

Brain Derived Neurotrophic Factor (BDNF) Contributes to the Pain Hypersensitivity Following Surgical Incision in the Rats

BackgroundThe pathogenic role of brain derived neurotrophic factor (BDNF) in the incisional pain is poorly understood. The present study explores the role of the BDNF in the incision-induced pain hypersensitivity.MethodsA longitudinal incision was made in one plantar hind paw of isoflurane-anesthetized rats. Dorsal root ganglias (DRG) and spinal cords were removed at various postoperative times (1–72 h). Expression pattern of BDNF was determined by immunohistochemistry and double-labeling immunofluorescence. Lidocaine-induced blockade of sciatic nerve function was used to determine the importance of afferent nerve activity on BDNF expression in the DRG and spinal cord after incision. BDNF antibody was administered intrathecally (IT) or intraperitoneal (IP) to modulate the spinal BDNF or peripheral BDNF after incision.ResultsAfter hind-paw incision, the BDNF was upregulated in the ipsilateral lumbar DRG and spinal cord whereas thoracic BDNF remained unchanged in response to incision. The upregulated BDNF was mainly expressed in the large-sized neurons in DRG and the neurons and the primary nerve terminals in the spinal cord. Sciatic nerve blockade prevented the increase of BDNF in the DRG and spinal cord. IT injection of BDNF antibody greatly inhibited the mechanical allodynia induced by incision whereas IP administration had only marginal effect.ConclusionThe present study showed that incision induced the segmental upregulation of BDNF in the DRG and spinal cord through somatic afferent nerve transmission, and the upregulated BDNF contributed to the pain hypersensitivity induced by surgical incision.

Acupuncture Affects Regional Blood Flow in Various Organs

In this review, our recent studies using anesthetized animals concerning the neural mechanisms of vasodilative effect of acupuncture-like stimulation in various organs are briefly summarized. Responses of cortical cerebral blood flow and uterine blood flow are characterized as non-segmental and segmental reflexes. Among acupuncture-like stimuli delivered to five different segmental areas of the body; afferent inputs to the brain stem (face) and to the spinal cord at the cervical (forepaw), thoracic (chest or abdomen), lumbar (hindpaw) and sacral (perineum) levels, cortical cerebral blood flow was increased by stimuli to face, forepaw and hindpaw. The afferent pathway of the responses is composed of somatic groups III and IV afferent nerves and whose efferent nerve pathway includes intrinsic cholinergic vasodilators originating in the basal forebrain. Uterine blood flow was increased by cutaneous stimulation of the hindpaw and perineal area, with perineal predominance. The afferent pathway of the response is composed of somatic group II, III and IV afferent nerves and the efferent nerve pathway includes the pelvic parasympathetic cholinergic vasodilator nerves. Furthermore, we briefly summarize vasodilative regulation of skeletal muscle blood flow via a calcitonin gene-related peptide (CGRP) induced by antidromic activation of group IV somatic afferent nerves. These findings in healthy but anesthetized animals may be applicable to understanding the neural mechanisms improving blood flow in various organs following clinical acupuncture.

Endothelin Stimulates Cardiac Sympathetic Afferents during Myocardial Ischemia

Myocardial ischemia activates cardiac sympathetic afferents that transmit nociceptive information to the brain leading to chest pain and excitatory cardiovascular reflexes. Previous studies have demonstrated an increase in endothelin (ET) concentrations during myocardial ischemia and unstable angina. ET-1 can elicit pain in animal models through stimulation of somatic sensory nerve fibers. Therefore, the present study tested the hypothesis that ET stimulates ischemically sensitive cardiac afferents and thus contributes to activation of this pathway during ischemia. Nerve activity of single unit cardiac afferents was recorded from the left sympathetic chain or rami communicans (T2 - T5) in anesthetized cats. Receptive fields of 11 afferents (CV= 0.31–3.25 m/s) were identified in the left ventricle with a stimulating electrode. Five min of myocardial ischemia stimulated all 11 cardiac afferents (2 Aδ, 9 C-fibers), increasing their activity from 0.52±0.23 to 2.34±0.45 imp/s. Injection of ET-1 (2–4 μg) into the left atrium (LA) stimulated five ischemically sensitive cardiac afferents, after a latency of 17±2.6 s, significantly increasing the activity of these afferents from 0.31±0.04 to 1.41±0.34 imp/s. BQ123, a selective ETA receptor antagonist, eliminated the responses of three cardiac afferents to ET-1 (4 μg, LA), and attenuated the ischemia-related increase in activity of three other afferents by 38%. These data suggest that during ischemia endothelin contributes to stimulation of cardiac sympathetic afferent nerve endings through an ETA receptor mechanism. (Supported by NIH HL66217)

Differential Neuropathies in Hyperglycemic and Hypoglycemic Diabetic Rats

We investigated the effects of hyperglycemia and hypoglycemia on development of peripheral neuropathy in somatic motor and sensory nerves in type 1 diabetic BB/Wor rats. The animals were maintained in a hyper- or hypoglycemic state by treatment with insulin for 3 months. Nondiabetic siblings served as controls. Qualitative analysis of the gastrocnemius and sural nerves by light and electron microscopy revealed signs of Wallerian-type axonal degeneration and regeneration of large myelinated fibers in the hypoglycemic but not the hyperglycemic animals. Degeneration was more common in the gastrocnemius nerve than in the sural nerve. In hypoglycemic rats, myelinated fibers in both the gastrocnemius and sural nerves had significantly shorter internodes and smaller diameters. The decreased fiber diameter was related (r = -0.9) to the duration of severe hypoglycemia (</=2.5 mmol/L). Myelinated fiber occupancy was also decreased without any significant changes in fiber counts in both the gastrocnemius and sural nerves. In hyperglycemic rats, myelinated fibers in the sural nerve but not the gastrocnemius nerve had smaller diameters compared with controls. We conclude that hypoglycemia has a more severe impact on somatic motor nerves than on somatic sensory nerves, whereas hyperglycemia affects only somatic sensory nerves.

A- and C- reflexes elicited in ovarian sympathetic nerves by single shock to a somatic afferent nerve include spinal and supraspinal components in anesthetized rats.

A- and C- reflexes elicited in ovarian sympathetic nerves by single shock to a somatic afferent nerve include spinal and supraspinal components in anesthetized rats.

Peripheral nerve functions may deteriorate parallel to the progression of microangiopathy in diabetic patients

Our aim was to obtain information to help in the early detection of impaired nerve function and to assess the severity of diabetic symmetric polyneuropathy (DPN). Various somatic and autonomic nerve functions in 40 diabetics and 20 age-matched healthy volunteers were evaluated using six objective examinations: nerve conduction study, quantitative vibratory perception threshold, heart rate variability, Valsalva test, head-up tilt and quantitative sudomotor axonal reflex test (QSART). The diabetics were divided into three groups according to the severity of their microangiopathy. The nerve function data and level of impairment were compared between a healthy control and three diabetic groups. The relationships between nerve function data and clinical background were also examined using multivariate analysis. Results were as follows: (1) all nerve dysfunctions seemed to develop parallel to the progression of microangiopathy, (2) reduced nerve conduction velocity and elevated vibratory perception thresholds in the feet might be early detectable signs of DPN, (3) vasomotor and sudomotor sympathetic functions and cardiovagal functions seemed to deteriorate with the appearance of microangiopathy, (4) lowered compound muscle action potential seemed to appear at the advanced microangiopathic condition, (5) hypohydrosis was closely related to diabetic foot ulcers. In conclusion, nerve dysfunction in diabetics might generally progress with microangiopathy from somatic sensory nerve dysfunction to autonomic nerve dysfunction and then to somatic motor nerve dysfunction. Sympathetic sudomotor dysfunction might be a sensitive predictor of diabetic foot ulcer.

Responses of hepatic glucose output to electro-acupuncture stimulation of the hindlimb in anaesthetized rats

Responses of hepatic glucose output (HGO) to electro-acupuncture (EA) stimulation of the hindlimb were investigated in anaesthetized rats, focusing on involvement of the somatic afferent and autonomic efferent nerves. HGO was measured with a microdialysis probe implanted into the left lateral lobe of the liver. Stainless steel needles with a diameter of 0.25 mm were inserted into the right tibialis anterior muscle and connected to an electrical stimulator. The EA stimulation was delivered for 10 min at 10 mA, 20 Hz. Atropine was injected in order to block the action of the parasympathetic nerves, whereas phentolamine and propranolol were injected in order to block the action of the sympathetic nerves. Furthermore, adrenal sympathetic nerves were crushed bilaterally to block the reflex secretion of adrenal medullary hormones. The EA stimulation significantly increased HGO for 20 min after the onset of stimulation. The increases of HGO were abolished by severing the femoral and sciatic nerves, demonstrating that the responses are elicited via activation of somatic afferent nerves. Furthermore, the increases were diminished after severance of the adrenal sympathetic nerves, which regulate catecholamine secretion from the adrenal medulla. The increases were totally abolished after pretreatment with phentolamine, an α-adrenergic blocker, and propranolol, a β-adrenergic blocker. On the other hand, the increases of HGO in response to the EA stimulation were augmented after pretreatment with atropine, a muscarinic cholinergic blocker. The present results demonstrate that EA stimulation to a hindlimb can reflexly increase HGO via activation of somatic afferents and, thereby, sympathetic efferents, including sympathetic efferents to the adrenal medulla. The present results further show that the increases of HGO in responses to EA stimulation are simultaneously reflexly inhibited via the parasympathetic nerves.

Origin and course of nerves immunoreactive for calcitonin gene-related peptide surrounding the femoral artery in rat.

Appreciation of anatomic relationships between perivascular nerve fibers and blood vessels is essential in reconstructive surgery. We examined the origin and neural connections of perivascular nerve fibers containing calcitonin gene-related peptide surrounding the femoral artery that regulate vascular tone. We used immunohistochemistry, denervation, and retrograde labeling methods. Peptide-immunoreactive fibers surrounding the femoral artery formed a complex network, with numerous small fibers extending from nerve fiber bundles located in the perivascular connective tissue. In middle and distal arterial segments, these fibers originated from the femoral nerve, the artery's main accompanying nerve. More proximally, fibers arose from the genitofemoral nerve and sympathetic nerves. Nerve branches terminating in various arterial segments had origins corresponding to those of somatic sensory nerve fibers, although pathways innervating the femoral artery took different courses.

Inspiratory coupling to cardiac activity and to somatic afferent nerve stimulation in the anaesthetised rat

We examined the ability of somatic afferent nerve stimulation to entrain inspiratory onset in the anaesthetized spontaneously breathing rat, and compared features of this stimulus–ventilatory coupling to entrainment of inspiratory onset by cardiac activity. In 14 rats prior to stimulation, we commonly observed a constant temporal alignment between ECG R waves and inspiratory onset (cardioventilatory coupling). Stimulation of a hamstring nerve at rates close to the heart rate also caused coupling (a constant stimulus to inspiratory onset interval), although this was highly dependent upon frequency of stimulation, with small changes in frequency causing a loss of coupling. In experiments where stimuli were given at constant intervals after ECG R waves, we observed no augmentation of coupling. Our results indicate that both cardiac and somatic afferent nerve activity is able to entrain inspiratory onset. We have suggested that coupling causes respiratory frequency to increase, and it is possible that this is a general mechanism whereby non-respiratory afferents act as stimulants or pacemakers to respiratory rhythm. The role of non-respiratory activity in initiating inspiration needs to be more fully recognised and studied.

Effect of moxibustion stimulation of various skin areas on cortical cerebral blood flow in anesthetized rats.

The effect of moxibustion stimulation of various skin areas (cheek, forepaw, upper arm, chest, back, lower leg, hindpaw and perineum) on cerebral blood flow (CBF) of the parietal cortex was examined in anesthetized rats after eliminating emotional influences. Moxibustion stimulation was performed by burning a moxa cone of about 4 mg weight placed on the shaved skin. CBF of the parietal cortex was measured using a laser Doppler flowmeter. Stimulation of the cheek, forepaw, upper arm and hindpaw produced significant increases in CBF, but stimulation of the other areas did not produce significant responses. Moxibustion stimulation of the forepaw and hindpaw produced an increase in the mean arterial pressure (MAP), while stimulation of the other areas did not. After spinal transection at the 2nd thoracic level, the MAP response to stimulation of the forepaw was abolished, whereas the CBF response to stimulation of the forepaw remained. The CBF response in spinalized rats was not affected by cutting cervical sympathetic and facial parasympathetic nerves, while it was almost abolished by intravenous administration of muscarinic and nicotinic cholinergic blocking agents. The CBF response was abolished by crushing the brachial plexus ipsilateral to the stimulated side. It is suggested that the increase in CBF, independent of MAP and emotional responses, elicited by moxibustion stimulation is a reflex response whose afferent pathway is composed of somatic afferent nerves, and whose efferent pathway involves intracerebral cholinergic nerves. A contribution of endogenous opioids in the present CBF responses was neglected, because naloxone did not influence the CBF responses.

Cardiovascular responses to sciatic nerve stimulation are blocked by paratrigeminal nucleus lesion

The paratrigeminal nucleus (Pa5) receives primary sensory inputs from the vagus, glossopharyngeal, and trigeminal nerves and has efferent projections to the nucleus of the solitary tract (NTS), rostroventrolateral reticular nucleus (RVL), as well as to the nucleus ambiguus (Amb), lateral reticular (LRt), parabrachial (PB) and ventral posteromedial thalamic (VPM) nuclei, suggesting that it may play a significant role in cardiovascular responses to nociceptive stimuli. The aim of the present study was to evaluate the effects of unilateral lesions of the Pa5 on cardiovascular alterations induced by afferent somatic sensory nerve stimulation (SNS), also known as the somatosympathetic reflex (SSR). Cardiovascular responses were recorded in rats following either sham operation or unilateral lesions of the Pa5 with ibotenic acid. Mean arterial blood pressure (MAP) increased after SNS, which in sham-lesioned animals raised from 95±4 to 115±2 mmHg. Ipsilateral Pa5 lesion did not significantly reduce the pressor response to SNS (from 91±7 to 107±4 mmHg increase of baseline MAP). On the other hand, contralateral Pa5 lesion significantly reduced the response to SNS (from 99±5 to 104±2 mmHg). Sciatic nerve stimulation did not alter heart rate (HR) neither did ipsi- or contralateral Pa5 lesion HR baseline response level. These findings support a crucial role for the Pa5 in cardiovascular regulation, by relaying SSR input evoked by peripheral nerve stimulation.

Denervation impairs healing of the rabbit medial collateral ligament

Little is known about the contribution of innervation to ligament healing after traumatic disruption, although there is good evidence of an important role for the peripheral nervous system in the healing of fractures and skin injuries. Tissues such as ligament, with a low resting blood supply, are dependent on substantial increases in blood flow and vascular volume during the initial stages of repair. We hypothesized that this initial healing response would be strongly promoted by neurogenic inflammation. Since the saphenous nerve (a major sensory branch of the femoral nerve) supplies the medial half of the knee joint, we elected to use femoral nerve transection as a model to determine the role of sensory and autonomic innervation in the initial outcome of repair of the injured medial collateral ligament. Twelve adult, female NZW rabbits underwent right medial collateral ligament transection. Of these, six rabbits underwent right femoral nerve transection to disrupt the somatic sensory and autonomic nerve supply to the knee joint and six were kept neurologically intact (controls). At six weeks post-injury, the animals were assessed by laser Doppler perfusion imaging (LDI) to determine the local blood flow, at both the injury site and at the uninjured contralateral ligament. The animals were then killed, the knee joints were removed and the biomechanical characteristics of the healing bone–median collateral ligament (MCL)–bone complexes assessed. In a separate cohort of 16 rabbits, vascular volumes of the injured ligaments were measured by infusion of a carmine red/gelatin solution. At six weeks post-injury, in vivo measurement of perfusion with LDI revealed that normally innervated ligaments had an almost three-fold higher average blood flow. Carmine red/gelatin infusion revealed a 50% higher density of blood vessels as compared to denervated ligaments. The force required for ultimate failure was found to be 50% higher in normally innnervated MCL's as compared to denervated MCL's: 153.14±20.71 N versus 101.29±17.88 N ( p<0.05). Static creep was increased by 66% in denervated MCL's: 2.83±0.45% versus 1.70±0.12% ( p<0.05). Total creep was increased by 45% in denervated MCL's: 5.29±0.62% compared to 3.64±0.31% in innervated MCL's ( p<0.05). We conclude that intact innervation makes a critical contribution to the early healing responses of the MCL of adult rabbits.

Modification of the cardiovascular response to hemorrhage by somatic afferent nerve stimulation with special reference to gut and skeletal muscle blood flow.

Tissue injury modifies heart rate and blood pressure responses to hemorrhage. The effect of concomitant injury on the hemorrhage-induced redistribution of cardiac output is much less clear. However, if injury elicits the visceral alerting response of the defense reaction, then a change in this redistribution of peripheral blood flow might be expected. If such a change compromised the gut circulation, then it might explain the deleterious effects of injury on the ability to withstand hemorrhage. Immature pigs anesthetized with Saffan were bled 30% of blood volume with or without concomitant somatic afferent (brachial) nerve stimulation (to mimic injury). In addition to global cardiovascular and oxygen transport variables, blood flow was measured in the cranial mesenteric (gut) and right femoral (skeletal muscle) arteries after a 60-minute stabilization period after surgery, at the end of the 30-minute hemorrhage, and after a 30-minute shock period. Hemorrhage induced the expected cardiovascular and oxygen transport changes accompanied by a reduction in skeletal muscle blood flow and a 55% increase in skeletal muscle vascular resistance, but gut blood flow and vascular resistance were unchanged. However, in the presence of brachial nerve stimulation, the pattern of response to hemorrhage was modified, such that gut blood flow was now reduced and gut vascular resistance increased. The sparing of the gut circulation after hemorrhage was abolished in the presence of "injury." This finding is consistent with injury eliciting the defense reaction and may help explain the deleterious effects of injury on resistance to hypovolemia.

Neural mechanisms of autonomic responses elicited by somatic sensory stimulation.

All evidence introduced here indicates that, in anesthetized animals in which emotional factors have been eliminated, somatic afferent nerve stimulation can regulate various visceral functions by responses that are reflex in nature. One conclusion emerging from the evidence presented is that the effects of somatic afferent stimulation are dependent upon the particular organs and on the spinal afferent segments. When the central nervous system is intact, the responses are sometimes general, as seen in cerebral cortical blood flow, heart rate, and adrenal medullary hormonal secretion and splenic immune function, whereas sometimes they have a strong segmental organization, as seen in gastric motility and urinary vesical contractility (Fig. 8). Needless to say, in the spinalized preparation all responses are strongly segmental. The contribution of the sympathetic and parasympathetic efferent nerves to the somato-visceral reflexes depends on the organs. It is difficult for us to state specifically or to generalize upon which autonomic component, the sympathetic or parasympathetic, will dominate as the efferent path in these reflexes, because this depends on the individual organ, the site being stimulated, and the nature or mode of the stimulation. The somatically-induced reflex responses of autonomic, hormonal and immune functions demonstrated in anesthetized animals, as have been discussed herein, appear to function even during conscious states. We need further studies to evaluate the physiological meaning of these somato-autonomic reflex responses. The analysis of neural mechanisms of these reflex responses seems to be very important for clinical application to regulate visceral function by physical treatment.

Effects of remote deep somatic noxious stimuli on a jaw reflex in man

The effects on an inhibitory jaw reflex of activating deep somatic afferent nerves in a remote part of the body (the arm) were studied in 13 humans. Electromyographic recordings were made from the active masseter of the long-latency (mean 42.0 ± 1.1 ms) inhibitory reflex evoked by electrical stimulation of the upper lip. Immediately after a 1-min conditioning period during which the participants compressed a hand-held spring once a second while ischaemia was produced in the arm with an inflated pneumatic cuff, the magnitude of the inhibitory reflex decreased significantly (by 43%). The reflex recovered within 5 min to a magnitude that was not significantly different from its pre-conditioning value. The arm exercise or the ischaemia alone produced no significant changes in the reflex. Furthermore, neither of these last two conditions was reported to be painful, whereas the ischaemic exercise produced pain in all but one participant. It is concluded that activation of remote nociceptive, but not non-nociceptive, deep somatic nerves can modulate jaw reflexes in man.