Gastrocnemius Nerve Research Articles

Purification and Characterization of a Nonenzymatic Neurotoxin fromHippasa partita(Lycosidae) Spider Venom Gland Extract

India is a habitat for nearly one thousand four hundred forty-seven species of spiders under three hundred and sixty-five genera and sixty families. Our initial survey on toxic bite by spider revealed severe edema, itching, acute pain, and hemorrhage following tissue necrosis, which are the general symptoms of envenomation, but there are no reports of mortality. Significantly,Hippasa partitaspider, commonly called “funnel web spider,” which is endemic in hilly regions of the Western Ghats is responsible for envenomation. In this study, a nonenzymatic neurotoxin has been purified fromH. partitavenom gland extract. Gel filtration and ion exchange chromatography were used to purify the toxin into homogeneity as shown by SDS-PAGE, RP-HPLC, and MALDI-TOF. Neurotoxin is devoid of enzymatic activities but causes intense neurotoxic symptoms. Neurotoxin is found to inhibit the twitch response of sciatic nerve gastrocnemius muscle preparation and is found to be postsynaptic in action. Neurotoxin is devoid of coagulant activity, edema, and hemorrhage and is nonlethal to mice (up to 5 mg/kg body weight). In conclusion, a neurotoxin, which is a principle agent in whole venom responsible for induced neurotoxic symptoms, has been purified and characterized.

Purification, Characterization, and Chemical Modification of Neurotoxic Peptide from Daboia russelii Snake Venom of India

Comprehensive knowledge of venom composition is very important for effective management of snake envenomation and antivenom preparation. Daboia russelii venom from the eastern region of India is the most neurotoxic among the four venom samples investigated. From the eastern D. russelii venom sample, neurotoxic peptide has been purified by combined method of ion exchange gel permeation chromatography and reversed phase high performance liquid chromatography. Molecular weight of Daboia neurotoxin III (DNTx-III) found to be 6,849 Da (as measured on matrix-assisted laser desorption/ionisation-time of flight mass spectrometer), and N-terminal amino acid sequences is I K C F I T P D U T S Q A. Approximate LD50 dosage was 0.24 mg/kg body weight. It produced concentration- and time-dependent inhibition of indirectly stimulated twitches of Rana hexadactyla sciatic nerve gastrocnemius muscle preparations. Chemical modification of DNTx-III tryptophan residue(s) reduced the twitch height inhibition property of toxin, signifying the importance of tryptophan residues for the neurotoxic function. This type of neurotoxic peptide is unique to east Indian regional D. russelii venom.

Function of Group IB Inhibition During Assisted Stepping in Human Spinal Cord Injury

The aim of this study was to investigate the function of group Ib inhibition exerted between ankle synergists during assisted stepping in people with chronic motor incomplete spinal cord injury (SCI). During stepping, the soleus (SOL) H-reflex was conditioned by percutaneous stimulation of the medialis gastrocnemius (MG) nerve by a bipolar electrode placed distal and medial to the cathode electrode for the tibial nerve. Stimulation was delivered at 0.95 times MG M-wave motor threshold with a pulse train at short conditioning-test intervals. To counteract movement of recording and stimulating electrodes, a supramaximal stimulus at 80 to 100 milliseconds after the test H-reflex was delivered. Stimuli were randomly dispersed across the step cycle, which was divided into 16 equal bins. The conditioned SOL H-reflex was significantly facilitated throughout the stance phase, while it was depressed during the swing phase when compared with the unconditioned SOL H-reflex. Ankle clonus during the stance phase may have affected the excitability state of spinal motoneuronal and interneuronal circuits, but the presence of group Ib inhibition in the swing phase suggests that in the absence of loading this spinal circuit is modulated in a physiologic manner in human incomplete SCI. Repetitive body loading and unloading promotes functional integration of sensory signals mediating load in human SCI.

Variation: use it or misuse it – replication and its variants

In a previous article (Drummond & Vowler, 2012a), we discussed variation between individuals, termed variance. When measurements are taken of subjects in separate groups, the variance of the measurements within the group can be compared with the variance that exists between groups. This allows us to estimate the likelihood that groups were drawn from the same population. Commonly, a treatment has been applied to these groups, and the aim would be to find if this had increased the variance between the groups, which might then indicate that the treatment had caused an effect (Fig. 1A).

Kv1.1 knock-in ataxic mice exhibit spontaneous myokymic activity exacerbated by fatigue, ischemia and low temperature

Episodic ataxia type 1 (EA1) is an autosomal dominant neurological disorder characterized by myokymia and attacks of ataxic gait often precipitated by stress. Several genetic mutations have been identified in the Shaker-like K+ channel Kv1.1 (KCNA1) of EA1 individuals, including V408A, which result in remarkable channel dysfunction. By inserting the heterozygous V408A, mutation in one Kv1.1 allele, a mouse model of EA1 has been generated (Kv1.1V408A/+). Here, we investigated the neuromuscular transmission of Kv1.1V408A/+ ataxic mice and their susceptibility to physiologically relevant stressors. By using in vivo preparations of lateral gastrocnemius (LG) nerve–muscle from Kv1.1+/+ and Kv1.1V408A/+ mice, we show that the mutant animals exhibit spontaneous myokymic discharges consisting of repeated singlets, duplets or multiplets, despite motor nerve axotomy. Two-photon laser scanning microscopy from the motor nerve, ex vivo, revealed spontaneous Ca2+ signals that occurred abnormally only in preparations dissected from Kv1.1V408A/+ mice. Spontaneous bursting activity, as well as that evoked by sciatic nerve stimulation, was exacerbated by muscle fatigue, ischemia and low temperatures. These stressors also increased the amplitude of compound muscle action potential. Such abnormal neuromuscular transmission did not alter fiber type composition, neuromuscular junction and vascularization of LG muscle, analyzed by light and electron microscopy. Taken together these findings provide direct evidence that identifies the motor nerve as an important generator of myokymic activity, that dysfunction of Kv1.1 channels alters Ca2+ homeostasis in motor axons, and also strongly suggest that muscle fatigue contributes more than PNS fatigue to exacerbate the myokymia/neuromyotonia phenotype. More broadly, this study points out that juxtaparanodal K+ channels composed of Kv1.1 subunits exert an important role in dampening the excitability of motor nerve axons during fatigue or ischemic insult.

Peripheral nerve inflammation in ALS mice: cause or consequence

Neuroinflammation is a prominent pathologic feature in the spinal cord of patients with amyotrophic lateral sclerosis (ALS), and is characterized by glial activation and infiltrating T cells.1 A similar inflammatory response is present in spinal cords of ALS mice1 and is preceded by evidence of a “dying back phenomenon” which includes motor axon degeneration and alterations of the neuromuscular junction.2 The presence of monocytes/macrophages surrounding the degenerating peripheral nerve fibers is an early event that occurs prior to the onset of clinical signs of motor weakness,3 and thus raises the question whether the peripheral nerve inflammatory response initiates, or is in response to, the neurodegenerative process. To address this question, we evaluated the time course of denervation and accompanying inflammatory responses in the lumbar spinal cord–sciatic nerve–gastrocnemius and the cervical spinal cord–phrenic nerve–diaphragm motor units of ALS mice, and found that denervation occurred prior to inflammation; also, both denervation and inflammation occurred earlier in the sciatic nerve motor unit than in the phrenic nerve motor unit. Therefore, peripheral nerve inflammation is probably not the cause of denervation, but rather a response to the neurodegenerative process.

Stump Rotation in a Nerve Autograft by 2 Factors

The aim of this study was to determine the influence of stump rotation (fascicular cross-connection) on nerve autograft functional recovery. Thirty rat sciatic nerves were transected and repaired by autograft. The rats were divided into 3 groups according to the number of stump rotations of the autograft: (1) plain graft (PG-g, with no change in fascicular orientation, no difference in diameter), (2) graft rotation (GR-g, with no change in fascicular orientation, and diameter difference between fascicles), (3) stump rotation (SR-g, with cross-connection and diameter difference between fascicles). Relative gastrocnemius muscle weight and nerve fiber count were examined as anatomic recovery indices, and autotomy score (ATS) and toe-out angle as functional recovery indices. The results showed that SR-g had a significantly low functional recovery compared with PG-g and GR-g. However, there was no difference found in the anatomic recovery. These findings suggest that the stump rotation in nerve autograft had no effect on neural regeneration and muscle reinnervation; however, it had a negative effect on functional recovery. Because GR-g was similar to PG-g rather than SR-g in functional recovery, the diameter difference between fascicles appears to have had little effect on the functional recovery. The results of this study suggest that a novel approach to ATS interpretation is needed. It is recommended that (1) ATS 2 be considered the onset of autotomy instead of ATS 1; and (2) the frequency of "ATS 2 and above" should be considered for the comparison of the autotomy rather than the mean ATS.

Analysis of dynamics of degenerative and regenerative processes in the flexor and extensor collaterals of crushed sciatic nerve: Effects of parathyroid hormone

We performed morphological, histochemical, and electrophysiological analysis of changes in the state of the rat sciatic nerve after nerve crushing. The activity of Ca2+-dependent acidic phosphatase (AP) was measured in sections of the nerve fibers to trace the recovery of the nerve after its injury. The systemic application of parathyroid hormone (PTH) resulted in the acceleration of injured nerve recovery. Proliferation of both endoneurium and Schwann cells was observed on the 3rd day after the crushing of the ipsilateral extensor (N. peroneus communis) and flexor (N. gastrocnemius) nerve bundles. A complete recovery of the AP enzymatic activity was found on the 7–9th days after the crushing. From the 5th to 35th days after the crushing, we performed online registration and mathematical analysis of pulse activity. In the control experiments, from the 35th to 70th days, high-frequency stimulation of the nerves showed the regeneration of the extensor nerve only accompanied by alterations in fiber direction. In the presence of PTH, the regeneration was significantly accelerated and it was associated with early regeneration of the flexor nerve and more structured fiber morphology. We found a correlation between the electrophysiological and morphological data.

Lidocaine Hyperselective Motor Blocks of the Triceps Surae Nerves

This prospective study was designed to evaluate the clinical and gait parameter changes induced by two types of hyperselective motor blocks of the triceps surae nerves (superior soleus and gastrocnemius nerves) and their ability to predict the results of selective tibial neurotomy. Seven adult patients (four males and three females, mean age of 41 yrs old) with spastic foot were included in this study. Clinical (equinus foot score, ankle range of motion, spasticity, pain, and comfort wearing shoes), and gait analysis (kinematic and electromyographic parameters) assessment were performed before and after each motor block (superior soleus nerve and gastrocnemius nerve) and 1 mo after selective tibial neurotomy. The superior soleus nerve block was effective on clinical parameters (triceps surae stretch reflex scores decreased from 2.57 to 0.9, and mean walking time decreased from 44 to 32.1 secs) and on kinematics parameters (the total duration of the gait cycle was decreased because of a reduction of the R3 and swing phases). The same results are observed after soleus neurotomy. This work confirms the practical value of selective superior soleus nerve motor block and that this block provides a useful prediction of the effect of selective soleus neurotomy. It constitutes an additional argument in favor of the predominant role of the soleus in spastic foot.

Survival and regeneration of cutaneous and muscular afferent neurons after peripheral nerve injury in adult rats

Peripheral nerve injury induces the retrograde degeneration of dorsal root ganglion (DRG) cells, which affects predominantly the small-diameter cutaneous afferent neurons. This study compares the time-course of retrograde cell death in cutaneous and muscular DRG cells after peripheral nerve transection as well as neuronal survival and axonal regeneration after primary repair or nerve grafting. For comparison, spinal motoneurons were also included in the study. Sural and medial gastrocnemius DRG neurons were retrogradely labeled with the fluorescent tracers Fast Blue (FB) or Fluoro-Gold (FG) from the homonymous transected nerves. Survival of labeled sural and gastrocnemius DRG cells was assessed at 3 days and 1-24 weeks after axotomy. To evaluate axonal regeneration, the sciatic nerve was transected proximally at 1 week after FB-labeling of the sural and medial gastrocnemius nerves and immediately reconstructed using primary repair or autologous nerve grafting. Twelve weeks later, the fluorescent tracer Fluoro-Ruby (FR) was applied 10 mm distal to the sciatic lesion in order to double-label sural and gastrocnemius neurons that had regenerated across the repair site. Counts of labeled gastrocnemius DRG neurons did not reveal any significant retrograde cell death after nerve transection. In contrast, sural axotomy induced a delayed loss of sural DRG cells, which amounted to 22% at 4 weeks and 43-48% at 8-24 weeks postoperatively. Proximal transection of the sciatic nerve at 1 week after injury to the sural or gastrocnemius nerves neither further increased retrograde DRG degeneration, nor did it affect survival of sural or gastrocnemius motoneurons. Primary repair or peripheral nerve grafting supported regeneration of 53-60% of the spinal motoneurons and 47-49% of the muscular DRG neurons at 13 weeks postoperatively. In the cutaneous DRG neurons, primary repair or peripheral nerve grafting increased survival by 19-30% and promoted regeneration of 46-66% of the cells. The present results suggest that cutaneous DRG neurons are more sensitive to peripheral nerve injury than muscular DRG cells, but that their regenerative capacity does not differ from that of the latter cells. However, the retrograde loss of cutaneous DRG cells taking place despite immediate nerve repair would still limit the recovery of cutaneous sensory functions.

Magnetic resonance microneurography of rabbit sciatic nerve on a 1.5‐T clinical MR system correlated with gross anatomy

This study was performed to investigate the feasibility and accuracy of magnetic resonance (MR) microneurography of the rabbit sciatic nerve on a 1.5-T clinical MR system by correlation with the gross anatomy. The 3D T2-weighted imaging (3D-T2WI), 3D T2-weighted imaging plus spectral presaturation with inversion recovery (SPIR), and T1-weighted imaging (T1WI) of the sciatic nerve in ten rabbits were performed on a 1.5-T MR system. The radiological anatomy of the sciatic nerve was observed and correlated with the gross anatomy. The anterior-posterior diameter of the sciatic nerve trunk was measured on 3D T2WI and on gross anatomy. The T1 and T2 relaxation times were also measured with multiecho spin echo and mixed sequence, respectively. The tibial nerve and peroneal nerve in the sciatic nerve trunk in all ten rabbits could be clearly displayed on T2WI and T2WI. The fine branches of the gastrocnemius nerve, posterior femoral cutaneous nerve, and the posterior gluteal nerve could be clearly depicted on T2WI. The T1 and T2 relaxation times of the sciatic nerves were 915 and 40 ms, respectively. The anterior-posterior diameter of sciatic nerve trunk was measured grossly, and on T2WI was 3.17 +/- 0.21 mm and 3.15 +/- 0.19 mm, respectively. There was no statistically significant difference (t = 0.768, P = 0.462). With the 1.5-T clinical MR system, the microneurography of the sciatic nerve could be revisualized, and the finer structure of the sciatic nerve trunk could be clearly and accurately delineated.

Studies of the protective effect of the hypothalamic peptide PRP-3 on spinal cord neurons at different periods after lateral hemisection

The protective effect of a new neurosecretory cytokine, proline-rich peptide (PRP-3) that is produced by the cells of the hypothalamic paraventricular and supraoptical nuclei was studied after lateral hemisection of the spinal cord. Experiments were performed at different postoperative periods (3, 4, and 5 weeks) under conditions of daily administration of PRP-3 in order to study dynamics of the development of rehabilitation states. Flow of single impulse activity induced by stimulation of the mixed (N. ischiadicus), extensor (N. peroneus communis), and flexor (N. gastrocnemius) nerves, at the level of the transection site and lower than it, on the damaged and symmetrical intact sides of the spinal cord was observed in comparison with the control in the interneurons and motoneurons of the spinal cord after daily administration of PRP-3 for 3–4 weeks. PRP-3 was shown to restore activity of the neurons of the lumbar part of the spinal cord and to cause more pronounced early and late postimpulse manifestations of the activity of spinal cord neurons. Morphological studies demonstrated that PRP-3 exhibited a powerful effect on the migration of motoneurons to the transection site and on intensification of proliferation of glial elements. Moreover, PRP-3 stimulated the migration of motoneurons to more distant regions along with penetration to the white matter at the level of the symmetrical undamaged side of the spinal cord. Glial and neurite penetration into places without symphysis, predominantly in the grey matter of the spinal cord, and the prevention of scar formation in the regions of damage were demonstrated. PRP-3 facilitated active ingrowth of vessels in the damaged regions. This process, in turn, favors regeneration with the restoration of locomotor activity at the rehabilitation stage. PRP-3 prevented scar formation and favored ingrowth of nerve fibers of the white matter in the damaged area and thus prevented degeneration of neuroglial elements. This fact was confirmed by recording activity at the level of the injury and by restoration of locomotor activity on the damaged side. This properties of PRP-3 may allow its use in clinical practice for the prevention of neurodegeneration induced by craniocerebral and spinal trauma.

Stochastic Resonance in the Motor System: Effects of Noise on the Monosynaptic Reflex Pathway of the Cat Spinal Cord

In sensory systems, the presence of a particular nonzero level of noise may significantly enhance the ability of an individual to detect weak sensory stimuli through a phenomenon known as stochastic resonance (SR). The aim of this study was to demonstrate if such phenomenon is also exhibited by the motor system; in particular, in the Ia-motoneuron synapse of the cat spinal cord. Monosynaptic reflexes elicited by periodic electrical stimulation to the medial gastrocnemius nerve were recorded in the L(7) ventral root (or in single motoneurons) of decerebrated cats. Random stretches (mechanical noise) were applied to the lateral gastrocnemius plus soleus muscle by means of a closed-loop mechanical stimulator-transducer. In all cats, we observed the SR phenomenon. The amplitude of the monosynaptic reflexes (or number of action potentials recorded in the motoneurons) evoked by the weak electrical stimuli applied to the medial gastrocnemius nerve were an inverted U-like function of the mechanical noise applied to the lateral gastrocnemius plus soleus muscle. A significant maximum value in the amplitude of the monosynaptic responses was reached with a particular noise amplitude value. Numerical simulations on a model of the monosynaptic reflex pathway qualitatively reproduce this stochastic resonance behavior. We conclude that the monosynaptic reflex response elicited by Ia afferents is optimized by the noisy stretching of a synergistic muscle. Our study provides the first direct demonstration that the motor system, and not only the sensory systems, exhibits the SR phenomenon.

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.

Recovery of Electromyographic Activity After Transection and Surgical Repair of the Rat Sciatic Nerve

The recovery of soleus (SOL), gastrocnemius (GAS), and tibialis anterior (TA) electromyographic activity (EMG) after transection and surgical repair of the sciatic nerve was studied in Sprague-Dawley rats using chronically implanted stimulation and recording electrodes. Spontaneous EMG activity in SOL and GAS and direct muscle (M) responses to posterior tibial nerve stimulation persisted for < or =2 days after sciatic nerve transection, but SOL and GAS H-reflexes disappeared immediately. Spontaneous EMG activity began to return 2-3 wk after transection, rose nearly to pretransection levels by 60 days, and persisted for the duration of the study period (120 days). Recovery of stimulus-evoked EMG responses began about 30 days after sciatic nerve transection as multiple small responses with a wide range of latencies. Over time, the latencies of these fractionated responses shortened, their amplitudes increased, and they merged into a distinct short-latency component (the putative M response) and a distinct long-latency component (the putative H-reflex). The extent of recovery of stimulation-evoked EMG was modest: even 100 days after sciatic nerve transection, the responses were still much smaller than those before transection. Similar gradual development of responses to posterior tibial nerve stimulation was also seen in TA, suggesting that some regenerating fibers sent branches into both tibial and common peroneal nerves.

Phantom reflexes: Muscle contractions at a frequency not physically present in the input stimuli

In the motor system, the periodic stimulation of one Ia-afferent input produces reflex muscle contractions at the input frequency. However, we observed that when two Ia monosynaptic reflex-afferent inputs are involved the periodic muscle contractions may occur at a frequency physically not present in the afferent inputs even when these inputs are sub-threshold. How can the muscles respond with such phantom reflex contractions at a frequency physically absent in the sub-threshold Ia-afferent input stimuli? Here we provide an explanation for this phenomenon in the cat spinal cord, that we termed “ghost motor response”. We recorded monosynaptic reflexes in the L7 ventral root, intracellular potentials in the motoneurons, and the associated muscular contractions elicited by stimulation of the lateral and medial gastrocnemius nerves. By stimulating with periodic pulses of sub-threshold intensities and distinct frequencies of 2 and 3 Hz the lateral and medial gastrocnemius nerves, respectively, we observed monosynaptic responses and phantom reflex muscle contractions occurring at the fundamental frequency (1 Hz), which was absent in the input stimuli. Thus we observed a reflex ghost motor response at a frequency not physically present in the inputs. We additionally studied the inharmonic case for sub-threshold stimuli and observed muscular contractions occurring at much lower frequencies, which were also conspicuously absent in the inputs. This is the first experimental evidence of a phantom reflex response in the nervous system. The observed behavior was modeled by numerical simulations of a pool of neurons subjected to two different input pulses.

Pre- and post-alpha motoneuronal control of the soleus H-reflex during sinusoidal hip movements in human spinal cord injury

The aim of this study was to establish the contribution of hip-mediated sensory feedback to spinal interneuronal circuits during dynamic conditions in people with incomplete spinal cord injury (SCI). Specifically, we investigated the effects of synergistic and antagonistic group I afferents on the soleus H-reflex during imposed sinusoidal hip movements. The soleus H-reflex was conditioned by stimulating the common peroneal nerve (CPN) at short (2, 3, and 4 ms) and long (80, 100, and 120 ms) conditioning test (C-T) intervals to assess the reciprocal and pre-synaptic inhibition of the soleus H-reflex, respectively. The soleus H-reflex was also conditioned by medial gastrocnemius (MG) nerve stimulation at C-T intervals ranging from 4 to 7 ms to assess changes in autogenic Ib inhibition during hip movement. Sinusoidal hip movements were imposed to the right hip joint at 0.2 Hz by the Biodex system while subjects were supine. The effects of sinusoidal hip movement on five leg muscles along with hip, knee, and ankle joint torques were also established during sensorimotor conditioning of the reflex. Phase-dependent modulation of antagonistic and synergistic muscle afferents was present during hip movement, with the reciprocal, pre-synaptic, and Ib inhibition to be significantly reduced during hip extension and reinforced during hip flexion. Reflexive muscle and joint torque responses – induced by the hip movement – were entrained to specific phases of hip movement. This study provides evidence that hip-mediated input acts as a controlling signal of pre- and post-alpha motoneuronal control of the soleus H-reflex. The expression of these spinal interneuronal circuits during imposed sinusoidal hip movements is discussed with respect to motor recovery in humans after SCI.

Barosensory cells in the nucleus tractus solitarius receive convergent input from group III muscle afferents and central command

Some neural mechanism must prevent the full expression of the baroreceptor reflex during static exercise because arterial blood pressure increases even though the baroreceptors are functioning. Two likely candidates are central command and input from the thin fiber muscle afferents evoking the exercise pressor reflex. Recently, activation of the mesencephalic locomotor region, an anatomical locus for central command, was found to inhibit the discharge of nucleus tractus solitarius cells that were stimulated by arterial baroreceptors in decerebrated cats. In contrast, the effect of thin fiber muscle afferent input on the discharge of nucleus tractus solitarius cells stimulated by baroreceptors is not known. Consequently in decerebrated unanesthetized cats, we examined the responses of barosensory nucleus tractus solitarius cells to stimulation of thin fiber muscle afferents and to stimulation of the mesencephalic locomotor region, a maneuver which evoked fictive locomotion. We found that electrical stimulation of either the mesencephalic locomotor region or the gastrocnemius nerve at current intensities that recruited group III afferents inhibited the discharge of nucleus tractus solitarius cells receiving baroreceptor input. We also found that the inhibitory effects of both gastrocnemius nerve stimulation and mesencephalic locomotor region stimulation converged onto the same barosensory nucleus tractus solitarius cells. We conclude that the nucleus tractus solitarius is probably the site whereby input from both central command and thin fiber muscle afferents function to reset the baroreceptor reflex during exercise.

Inhibition from the plantar nerve to soleus muscle during the stance phase of walking

The purpose of this study is to investigate the effect and the circuit from the branch of tibial (plantar) nerve to soleus muscle and its modulation during walking in humans. Stimulation of the plantar nerve produced short latency inhibition of soleus EMG activity and the H-reflex in humans. The threshold of afferent fibers was lower than that of motor fibers. This inhibition did not converge to disynaptic reciprocal Ia inhibition nor did inhibition from the cutaneous nerve of the big toe, but to Ib inhibition from the medial gastrocnemius nerve. The inhibitory pathway from the plantar nerve therefore is considered to include Ib inhibitory interneurones. Modulation of the inhibition was investigated during walking. Less EMG depression after plantar nerve stimulation occurred in the stance phase of walking than for tonic or dynamic plantar flexion at similar background EMG activity level. The inhibition of the soleus H-reflex after plantar nerve stimulation was also decreased during the stance phase. For investigating the influence of load on the inhibition from the plantar nerve, more EMG depression occurred in the stance phase with body unloading. Similar findings were observed in Ib inhibition from the medial gastrocnemius nerve, but not in disynaptic reciprocal Ia inhibition to soleus muscle. It is concluded that transmission of inhibition from the plantar nerve to soleus muscle is modulated during walking. It would minimize this inhibition during the stance phase of walking and might enhance soleus muscle activity via this reflex pathway for the support of weight.

Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: A clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle

Objective To evaluate clinically and electrophysiologically the effects of selective anesthetic blocks of motor nerve branches to the triceps surae muscle on lower limb stretch reflex in patients with spastic equinus foot. Methods Eleven patients were assessed before and after selective anesthetic block of the superior soleus nerve or the gastrocnemius nerves, performed by lidocaine injection. The stretch reflex (SR) of the ankle with the knee flexed or extended and the Achilles tendon reflex (TR) were scored clinically. Additionally, the direct M response and the H reflex to tibial nerve stimulation were recorded on the three heads of the triceps surae muscle. The ratio of H reflex to M response of maximal amplitudes ( H max/ M max) was calculated. Results The SR and TR mean scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Electrophysiologically, H max and H max/ M max ratios were significantly reduced for the soleus muscle after soleus nerve block and for the lateral (but not medial) gastrocnemius muscle after gastrocnemius nerve block. Conclusions Soleus nerve block appeared more appropriate than gastrocnemius nerve block to relieve spasticity clinically. In addition, the decrease in H max/ M max ratio suggested that lidocaine preferentially blocked proprioceptive Ia fibers rather than A-alpha motor fibers. Significance Selective anesthetic blocks of nerve branches to the triceps surae muscle are useful in the assessment of lower limb spasticity and can benefit from H reflex investigation. H reflex recordings showed a preferential susceptibility of muscle spindle afferents to local anesthetics and supported the hypothesis of a prominent role of the soleus muscle in spastic ankle. The clinical and electrophysiological effects induced by anesthetic blocks may help to guide therapeutic interventions, such as neurotomy, neurolysis or botulinum toxin injection.