The Inhibitory Effects of Pudendal Nerve Stimulation on Bladder Overactivity in Spinal Cord Injury Dogs: Is Early Stimulation Necessary?

Objective: To determine the inhibitory effects of pudendal nerve stimulation (5 Hz) on bladder overactivity at early and late stages of spinal cord injury in dogs. Materials and Methods: The study was performed in eight dogs with chronic spinal cord transection at the T9‐T10 level. Group 1 (four dogs) underwent electrical stimulation of pudendal nerve one month after spinal cord transection. Group 2 (four dogs) underwent stimulation six months after spinal cord transection. The bladders were removed for histological examination of fibrosis after the stimulation. Results: The bladder capacity and the compliance were significantly increased (p < 0.05) by pudendal nerve stimulation in group 1, but not in group 2. The nonvoiding contractions were inhibited in both groups by electrical stimulation. Collagen fiber was increased, while elastic fiber was significantly decreased (p < 0.05) in group 2 when compared with group 1. Conclusion: Pudendal nerve stimulation can increase the bladder capacity and compliance only during the early period before the bladder wall becomes fibrosit and can inhibit the nonvoiding contraction during two stages.     

Influence of naloxone on inhibitory pudendal-to-bladder reflex in cats

To determine the involvement of opioid receptors in the inhibitory pudendal-to-bladder reflex, the effect of naloxone (0.01-1 mg/kg, i.v.), an opioid receptor antagonist, on the inhibition of bladder activity evoked by pudendal nerve stimulation was investigated in α-chloralose anesthetized cats. The inhibition of reflex isovolumetric bladder contractions induced by pudendal nerve stimulation (5-10 Hz) at intensity threshold (T) for producing complete inhibition was significantly suppressed by naloxone at a high dose (0.3 mg/kg). However, the inhibition elicited at higher intensities (1.5-3 T) was not changed. Naloxone (1 mg/kg) did not alter the frequency dependence of the inhibitory effect of pudendal stimulation. During cystometrograms (CMGs) pudendal nerve stimulation significantly increased bladder capacity to 155.1 ± 24.5% and 163.4 ± 10% of the control at stimulation intensities of 1 T and 1.5-3 T, respectively. After administration of naloxone (1 mg/kg), the bladder capacity during pudendal nerve stimulation at inhibition threshold (1 T) was not significantly different from control, but it was significantly increased at higher intensities (1.5-3 T). Naloxone alone markedly reduced bladder capacity to 43 ± 11.1% of the control, and pudendal stimulation completely reversed this facilitatory effect. This study revealed that activation of opioid receptors contributes to or facilitates the inhibitory pudendal-to-bladder reflex. The reduction in bladder capacity after naloxone treatment also indicates that endogenous opioid peptides mediate a tonic inhibition of micturition. Understanding the neurotransmitter mechanisms involved in the inhibitory pudendal-to-bladder reflex could promote the development of new treatments for bladder overactivity and incontinence.     

Pudendal-to-bladder reflex in chronic spinal-cord-injured cats

The effects of pudendal nerve stimulation on reflex bladder activity were investigated in cats with chronic spinal cord injury (6-12 months) under alpha-chloralose anesthesia. Electrical stimulation of the pudendal nerve on one side at different frequencies and intensities induced either inhibitory or excitatory effects on bladder activity. The inhibitory effect peaked at a stimulation frequency of 3 Hz and gradually decreased at lower or higher frequencies. The inhibitory effect could occur at stimulation intensities between 0.3 and 1 V (pulse width 0.1 ms) and increased at intensities up to 10 V. Stimulation of the central end of transected pudendal nerve also inhibited bladder activity, indicating that afferent axons in pudendal nerve are involved. Nerve transections also showed that both hypogastric and pelvic nerves might be involved in the inhibitory pudendal-to-bladder spinal reflex. Pudendal nerve stimulation at 20 Hz and at the same intensities (1-10 V) elicited a bladder excitatory response. Although this excitatory effect could not sustain a long lasting bladder contraction at small bladder volumes, it did induce continuous rhythmic bladder contractions at large bladder volumes. This study indicated the possibility of developing a neuroprosthetic device based on pudendal nerve electrical stimulation to restore micturition function after spinal cord injury.     

Electrical stimulation of dog pudendal nerve regulates the excitatory pudendal-to-bladder relfex

Pudendal nerve plays an important role in urine storage and voiding. Our hypothesis is that a neuroprosthetic device placed in the puden-dal nerve trunk can modulate bladder function after suprasacral spinal cord injury. We had conifrmed the inhibitory pudendal-to-bladder relfex by stimulating either the branch or the trunk of the pudendal nerve. This study explored the excitatory pudendal-to-bladder relfex in beagle dogs, with intact or injured spinal cord, by electrical stimulation of the pudendal nerve trunk. The optimal stimulation frequency was approximately 15–25 Hz. This excitatory effect was dependent to some extent on the bladder volume. We conclude that stimulation of the pudendal nerve trunk is a promising method to modulate bladder function.     

Plasticity of urinary bladder reflexes evoked by stimulation of pudendal afferent nerves after chronic spinal cord injury in cats

Bladder reflexes evoked by stimulation of pudendal afferent nerves (PudA-to-Bladder reflex) were studied in normal and chronic spinal cord injured (SCI) adult cats to examine the reflex plasticity. Physiological activation of pudendal afferent nerves by tactile stimulation of the perigenital skin elicits an inhibitory PudA-to-Bladder reflex in normal cats, but activates an excitatory reflex in chronic SCI cats. However, in both normal and chronic SCI cats electrical stimulation applied to the perigenital skin or directly to the pudendal nerve induces either inhibitory or excitatory PudA-to-Bladder reflexes depending on stimulation frequency. An inhibitory response occurs at 3–10 Hz stimulation, but becomes excitatory at 20–30 Hz. The inhibitory reflex activated by electrical stimulation significantly (P < 0.05) increases the bladder capacity to about 180% of control capacity in normal and chronic SCI cats. The excitatory reflex significantly (P < 0.05) reduces bladder capacity to about 40% of control capacity in chronic SCI cats, but does not change bladder capacity in normal cats. Electrical stimulation of pudendal afferent nerves during slow bladder filling elicits a large amplitude bladder contraction comparable to the contraction induced by distension alone. A bladder volume about 60% of bladder capacity was required to elicit this excitatory reflex in normal cats; however, in chronic SCI cats a volume less than 20% of bladder capacity was sufficient to unmask an excitatory response. This study revealed the co-existence of both inhibitory and excitatory PudA-to-Bladder reflex pathways in cats before and after chronic SCI. However our data combined with published electrophysiological data strongly indicates that the spinal circuitry for both the excitatory and inhibitory PudA-to-Bladder reflexes undergoes a marked reorganization after SCI.     

Improved bladder emptying in urinary retention by electrical stimulation of pudendal afferents

Urinary retention is the inability to empty the bladder completely, and may result from bladder hypocontractility, increases in outlet resistance or both. Chronic urinary retention can lead to several urological complications and is often refractory to pharmacologic, behavioral and surgical treatments. We sought to determine whether electrical stimulation of sensory fibers in the pudendal nerve could engage an augmenting reflex and thereby improve bladder emptying in an animal model of urinary retention. We measured the efficiency of bladder emptying with and without concomitant electrical stimulation of pudendal nerve afferents in urethane-anesthetized rats. Voiding efficiency (VE = voided volume/initial volume) was reduced from 72 +/- 7% to 29 +/- 7% following unilateral transection of the sensory branch of the pudendal nerve (UST) and from 70 +/- 5% to 18 +/- 4% following bilateral transection (BST). Unilateral electrical stimulation of the proximal transected sensory pudendal nerve during distention-evoked voiding contractions significantly improved VE. Low-intensity stimulation at frequencies of 1-50 Hz increased VE to 40-51% following UST and to 39-49% following BST, while high-intensity stimulation was ineffective at increasing VE. The increase in VE was mediated by increases in the duration of distention-evoked voiding bladder contractions, rather than increases in contraction amplitude. These results are consistent with an essential role for pudendal sensory feedback in efficient bladder emptying, and raise the possibility that electrical activation of pudendal nerve afferents may provide a new approach to restore efficient bladder emptying in persons with urinary retention.     

A gentle mechanical skin stimulation technique for inhibition of micturition contractions of the urinary bladder

Effects of gentle skin stimulation of various segmental areas on the micturition contractions of the urinary bladder were examined in anesthetized male rats. The bladder was expanded by infusing saline via urethral cannula until the bladder produced rhythmic micturition contractions as a consequence of rhythmic burst discharges of vesical pelvic efferent nerves. Gentle stimulation was applied for 1 min by slowly rolling on top of skin with an elastomer "roller". Rolling on the perineal area inhibited both micturition contractions and pelvic efferent discharges during and after stimulation. Stimulation of the hindlimb, abdomen and forelimb inhibited micturition contractions after stimulation ended, in this order of effectiveness. During stimulation of the perineal skin, the reflex increase in pelvic efferent discharges in response to bladder distension to a constant pressure was also inhibited up to 45% of its control response. The inhibition of the micturition contractions induced by perineal stimulation was abolished, to a large extent by the opioid receptor antagonist naloxone and completely by severing cutaneous nerves innervating the perineal skin. We recorded unitary afferent activity from cutaneous branches of the pudendal nerve and found that the fibers excited by stimulation were low-threshold mechanoreceptive Aβ, Aδ and C fibers. Discharge rates of afferent C fibers (7.9 Hz) were significantly higher than those of Aβ (2.2 Hz) and Aδ (2.9 Hz) afferents. The results suggest that low frequency excitation of low threshold cutaneous mechanoreceptive myelinated and unmyelinated fibers inhibits a vesico-pelvic parasympathetic reflex, mainly via release of opioids, leading to inhibition of micturition contraction.     

Changes in vesical function produced by cutaneous stimulation in rats.

(1) The effect of stimulation of various skin areas on the function of the bladder was examined in anesthetized rats with the CNS intact, in decerebrated non-anesthetized rats and in spinal rats. The tone and contraction of the bladder was measured by the intravesical ballon method. (2) When the volume of the intravesical ballon was expanded so that the resting vesical pressure was increased from O to approximately 40 mm H2O level, the bladder revealed small spontaneous contractions in all experiments. Under these conditions intravesical pressure was increased approximately 40 mm H2O by application of tactile or nociceptive stimulation of the skin in the perineal area. This excitatory perneal-bladder response existed befor and after spinal transection and was shown to be a propriospinal reflex for which reflexly increased nerve discharges of vesical branches of the pelvic nerves were responsible. (3) When the volume of the intravesical ballon was further expanded so that the resting vesical pressure was kept about 200 mm H2O, the bladder had the usual large rhythmic contractions (micturition contractions) with amplitudes of about 610 mm H2O, and rhythms of 1--3/min in the CNS intact or decrebrated rats. These large contractions were driven by the rhythmic bust discharges of the vesical nerve branches of the pelvic nerves. The occurrence of the large contractions of the bladder could be inhibited by nociceptive stimulation which was localized in the perineal area. This inhibition of the large contractions was caused by disappearance of the rhythmic burst discharges in the vesical branches of the pelvic nerves. (4) On some occasions in the CNS intact anesthetized and in the decerebrated non-anesthetized rats the large contractions of the bladder disappeared during experiments even when the bladder was expanded enough for producing normal large contractions and kept at high intravesical pressure. Regardless of whether the large contractions existed or not at the high intravesical pressure, the vesical pressure was increased by perineal stimulation due to the same neural mechanism mentioned in (2) above.     

Bladder and urethral sphincter responses evoked by microstimulation of S2 sacral spinal cord in spinal cord intact and chronic spinal cord injured cats

Urinary bladder and urethral sphincter responses evoked by bladder distention, ventral root stimulation, or microstimulation of S2 segment of the sacral spinal cord were investigated under alpha-chloralose anesthesia in cats with an intact spinal cord and in chronic spinal cord injured (SCI) cats 6-8 weeks after spinal cord transection at T9-T10 spinal segment. Both SCI and normal cats exhibited large amplitude reflex bladder contractions when the bladder was fully distended. SCI cats also exhibited hyperreflexic bladder contractions during filling and detrusor-sphincter dyssynergia during voiding, neither was observed in normal cats. Electrical stimulation of the ventral roots revealed that the S2 sacral spinal cord was the most effective segment for evoking large amplitude bladder contractions or voiding in both types of cats. Microstimulation with a stimulus intensity of 100 microA and duration of 30-60 s via a single microelectrode in the S2 lateral ventral horn or ventral funiculus evoked large amplitude bladder contractions with small urethral contractions in both normal and SCI cats. However, this stimulation evoked incomplete voiding due to either co-activation of the urethral sphincter or detrusor-sphincter dyssynergia. Stimulation in the S2 dorsal horn evoked large amplitude sphincter responses. The effectiveness of spinal cord microstimulation with a single electrode to induce prominent bladder and urethral sphincter responses in SCI animals demonstrates the potential for using microstimulation techniques to modulate lower urinary tract function in patients with neurogenic voiding dysfunctions.     

Modulation of motor cortex excitability by different levels of whole-hand afferent electrical stimulation

Objective

In a previous transcranial magnetic stimulation (TMS) study we demonstrated that suprathreshold mesh-glove (MG) whole-hand stimulation elicits lasting changes in motor cortical excitability. Currently, there is no consensus with regard to the optimal parameters for the induction of sensorimotor cortical plasticity using peripheral electrical stimulation. Thus, in the present study we explore the modulatory effects of MG stimulation at different stimulus intensities and different frequencies in order to identify an optimal stimulation protocol.

Methods

MG stimulation was performed on 12 healthy subjects in separate sessions at different stimulation levels: sub-sensory at 50 Hz, sensory at 50 Hz and motor at 2 Hz. To verify if stimulation at lower frequencies is less effective, an additional experiment at sensory level with 2 Hz was performed. TMS was used to assess motor threshold (MT), motor evoked potentials (MEPs) recruitment curve (RC), short latency intracortical inhibition (SICI) and intracortical facilitation (ICF) to paired-pulse TMS at baseline (T0), immediately after (T1) and 1 h (T2) after 30 min of MG stimulation. F-wave studies were performed to assess spinal motoneuron excitability.

Results

MG stimulation at sub-sensory/50 Hz and sensory/2 Hz level determines no significant cortical excitability changes; at sensory/50 Hz level and at motor/2 Hz level we found decreased MT, increased MEP RC as well as reduced SICI and increased ICF at T1 and T2.

Conclusions

MG stimulation at sensory/50 Hz and motor/2 Hz level induces similar long-lasting modulatory effects on motor cortical excitability. Both the strength of the corticospinal projections and the intracortical networks are influenced to the same extend.

Significance

The study provides further evidence that stimulation intensity and frequency can independently modulate motor cortical plasticity. The selection of optimal stimulation parameters has potentially important implications for the neurorehabilitation of patients after brain damage (e.g. stroke, traumatic brain injury) with hand motor deficits.     

Effects of pudendal nerve stimulation on neurons in pericruciate cerebral cortex of male domestic cats

The pudendal nerve, which innervates the anogenital region, has been implicated in micturition and in male sexual behavior. Electrical stimulation of this nerve in chloralose-anesthetized male cats evoked activity thoughout the anterior and posterior sigmoid, anterior ectosylvian, and anterior marginal gyri. The influence was bilateral at every site examined; no contralateral focus was found on the dorsum of the anterior hemisphere. The influence was not only bilateral, but of the same magnitude and nearly the same latency in both hemispheres. Furthermore, the gross potentials evoked by stimulation of either pudendal nerve were similar in configuration and amplitude to those evoked by ipsilateral forepaw and ipsilateral hind paw stimulation. Single-neuron recordings from four sites—medial and lateral precruciate and postcruciate—revealed that 17% of the sa neurons, 55% of the sb neurons, and 98% of the m neurons could be excited by pudendal nerve stimulation. Of the neurons tested and found to respond to the contralateral pudendal nerve, fully 98% also responded to the ipsilateral pudendal nerve. Some sa neurons that failed to respond to pudendal nerve stimulation were rendered less excitable to paw stimulation by conditioning stimulation of that nerve. These same sa neurons were also rendered less excitable to paw stimulation by conditioning stimulation of any of the other (nonexcitatory) paws. The property of coadunate behavior among the m neurons clearly included their responses to pudendal nerve stimulation. The numerous sensory inputs to m neurons—cutaneous, visual, auditory, vestibular, thoracic and pelvic splanchnic, and now pudendal—arrive via markedly different pathways, suggesting that the mechanism underlying coadunate behavior is to be found within the cerebral cortex itself. It is argued that in the intact, behaving animal these disparate sensory influences onto cerebral m neurons function to modulate the excitability of these neurons, their effective driving input arriving via the local sa (small-field) neurons that reside in layers II and III. It is further argued that some of these m neurons act to depress the excitability of certain sa neurons in their neighborhood.     

Pudendal Nerve Block by Low-Frequency (≤1 kHz) Biphasic Electrical Stimulation

ObjectivesTo test the hypothesis that poststimulation block of nerve conduction can be achieved by low-frequency (≤1 kHz) biphasic stimulation (LFBS).Materials and MethodsA tripolar cuff electrode was placed around the pudendal nerve in cats to deliver LFBS (1 kHz, 500 Hz, and 100 Hz). Two bipolar hook electrodes were placed central and distal to the cuff electrode to induce external urethral sphincter (EUS) contractions. A catheter was inserted into the urethra to record EUS contraction pressure. Pudendal nerve block by LFBS was confirmed by the failure of the central hook electrode stimulation to induce EUS contractions, while the distal hook electrode stimulation still induced contractions.ResultsPudendal nerve conduction was completely blocked by LFBS at different frequencies (1 kHz, 500 Hz, and 100 Hz) after terminating LFBS. The post-LFBS block induced at the minimal stimulation intensity and duration was fully reversible within the same time period (10–15 min on average) for the three frequencies. However, the stimulation duration to induce block significantly (p < 0.05) increased from 23 ± 8 sec to 95 ± 14 sec when frequency increased from 100 Hz to 1 kHz.ConclusionThis study discovered that LFBS (≤1 kHz), like high-frequency (≥5 kHz) biphasic stimulation (HFBS), can induce poststimulation block. The result provides support for the theory that biphasic stimulation waveforms block axonal conduction by changing intracellular and extracellular ion concentrations. The post-LFBS block provides the opportunity to develop new neuromodulation devices for clinical applications where initial nerve firing is acceptable.     

Brief post-surgical electrical stimulation accelerates axon regeneration and muscle reinnervation without affecting the functional measures in carpal tunnel syndrome patients

Electrical stimulation (ES) of injured peripheral nerves accelerates axonal regeneration in laboratory animals. However, clinical applicability of this intervention has never been investigated in human subjects. The aim of this pilot study was to determine the effect of ES on axonal regeneration after surgery in patients with median nerve compression in the carpal tunnel causing marked motor axonal loss. A randomized control trial was conducted to provide proof of principle for ES-induced acceleration of axon regeneration in human patients. Carpel tunnel release surgery (CTRS) was performed and in the stimulation group of patients, stainless steel electrode wires placed alongside the median nerve proximal to the surgical decompression site for immediate 1 h 20 Hz bipolar ES. Subjects were followed for a year at regular intervals. Axonal regeneration was quantified using motor unit number estimation (MUNE) and sensory and motor nerve conduction studies. Purdue Pegboard Test, Semmes Weinstein Monofilaments, and Levine's Self-Assessment Questionnaire were used to assess functional recovery. The stimulation group had significant axonal regeneration 6-8 months after the CTRS when the MUNE increased to 290 ± 140 (mean ± SD) motor units (MU) from 150 ± 62 MU at baseline (p < 0.05). In comparison, MUNE did not significantly improve in the control group (p > 0.2). Terminal motor latency significantly accelerated in the stimulation group but not the control group (p > 0.1). Sensory nerve conduction values significantly improved in the stimulation group earlier than the controls. Other outcome measures showed a significant improvement in both patient groups. We conclude that brief low frequency ES accelerates axonal regeneration and target reinnervation in humans.     

Serotonergic modulation of spinal ascending activity and sacral reflex activity evoked by pelvic nerve stimulation in cats

Serotonin (5-HT) may be inhibitory to micturition at a spinal level. A potential mechanism of action for serotonergic inhibition of bladder function is a depression of the ascending limb of the supraspinal reflex mediating micturition. Ascending activity evoked by pelvic nerve stimulation was recorded in the thoracic spinal cord of anesthetized cats. For comparison, spinal reflex activity evoked by pelvic nerve stimulation was recorded on the pudendal nerve. The effects of intrathecal administration of serotonergic agents were examined to determine whether spinal and supraspinal responses to bladder afferent activation were modulated by 5-HT. Methysergide (60 nmol), a non-selective serotonergic antagonist, increased ascending activity by 61±7% and depressed spinal reflex activity by 38±6%. Zatosetron (10 nmol), a 5-HT₃ antagonist had a similar effect on both activities (increased by 93±24% and decreased by 77±7%, respectively). The effect on ascending activity of blocking 5-HT₃ receptors was also confirmed with ICS 205930 and MDL 72222. 2-Methyl-5-HT (800 nmol), a 5-HT₃ agonist, depressed ascending activity to 46±9% of control, but enhanced spinal reflex activity by 73±92%. These results demonstrate that stimulation of 5-HT₃ and methysergide-sensitive 5-HT receptors can inhibit ascending activity and facilitate spinal reflex activity elicited by activation of bladder afferents. It is suggested that descending serotonergic pathways may participate in the spinal coordination of urinary continence.     

Transmission of afferent information from urinary bladder, urethra and perineum to periaqueductal gray of cat

The micturition reflex pathway is a supraspinal pathway. Anatomical tracing evidence is compatible with an involvement of the periaqueductal gray (PAG) in the ascending limb of this reflex. We tested the involvement of the PAG in receiving urinary tract- or perineum-related information and attempted to characterize this ascending path in terms of what type of information is being conveyed. Electrical stimulation of the pelvic nerves, which carry afferent information from the urinary bladder, evoked maximum field potentials in the caudal third of the PAG, primarily in the dorsal part of the lateral PAG and in the ventrolateral PAG. Since the regions activated by pelvic nerve stimulation differed from those activated by stimulation of the sensory pudendal or superficial perineal nerves, it is possible that specific pathways for different nerve inputs to the PAG exist. Sacral spinal cord neurons ascending to the PAG were identified by antidromic activation and then tested for inputs from pelvic, sensory pudendal or superficial perineal nerves. Of 18 units identified, only five received inputs from any of the peripheral nerves tested and only two projecting neurons received a pelvic nerve input. Thus the PAG may receive inputs from bladder and perineum, but the small proportion of cells with direct projections to the PAG receiving inputs from our test nerves implies that the major part of this pathway is not directly related to lower urinary tract function.     

Depression and recovery of reflex amplitude during electrical stimulation after spinal cord injury

ObjectiveThe aim of this study was to quantify, for the first time, H-reflexes evoked during prolonged trains of wide-pulse neuromuscular electrical stimulation (WP-NMES) in individuals with chronic spinal cord injury (SCI). We hypothesised that after the first H-reflex, reflex amplitudes would be depressed (due to post-activation depression), but would recover and this recovery would be enhanced after a “burst” of 100 Hz WP-NMES.MethodsSoleus M-waves and H-reflexes evoked during WP-NMES (1 ms pulse width) of the tibial nerve were quantified in nine individuals with SCI. WP-NMES was delivered in two patterns: “constant-frequency” (15 or 20 Hz for 12 s) and “burst-like” (15-100-15 Hz or 20-100-20 Hz; 4 s each phase) at an intensity that evoked an M-wave between 10% and 15% of the maximal M-wave (M_max).ResultsDuring constant frequency stimulation, after the initial depression from the first to the second H-reflex (1st: 57% M_max; 2nd: 25% M_max), H-reflexes did not recover significantly and were 37% M_max at the end of the stimulus train. During the burst-like pattern, after the initial depression (1st: 62% M_max; 2nd: 30%), reflexes recovered completely by the end of the stimulation (to 55% M_max) as they were not significantly different from the first H-reflex. M-waves were initially depressed (1st: 12% M_max; 2nd: 7% M_max) then did not change throughout the stimulation and were not significantly different between stimulation patterns. An analysis of covariance indicated that the depression in M-wave amplitude did not account for the depression in H-reflex amplitude.ConclusionsRelatively large H-reflexes were recorded during both patterns of NMES. The brief burst of 100 Hz stimulation restored H-reflexes to their initial amplitudes, effectively reversing the effects of post-activation depression.SignificanceFor individuals with chronic SCI, generating contractions through central pathways may help reduce muscle atrophy and produce contractions that are more fatigue-resistant for rehabilitation, exercise programs, or to perform activities of daily living.     

Peripheral nerve abnormalities in pediatric patients with spinal muscular atrophy

We examined the specific nerve conduction deficits distinguishing spinal muscular atrophy (SMA) subtypes I and II. Five SMA I patients (age, 0.2–1.1 years) and 10 SMA II patients (age, 1.0–2.8 years) were examined. Patients were compared to age-matched controls for motor and sensory conduction velocity (MCV and SCV) changes, compound muscle and sensory nerve action potential amplitudes (CMAP and SNAP), and F-wave occurrence (FO). Slower MCVs were found in three of five SMA I patients; all five exhibited markedly decreased CMAP amplitudes. Tibial nerve CMAP amplitudes significantly reduced in SMA II patients (p < 0.01). Slower SCVs and decreased SNAP amplitudes were observed in three of five SMA I patients but not in SMA II patients. Although FOs were reduced in both extremities of SMA I patients, the reduction was prominent in the tibial nerve of SMA II patients (p = 0.031). Loss of motor units may be widespread in the early stage of SMA I, while specific to the legs in young SMA II patients. SMA I showed sensory nerve degeneration, especially of large myelinated fibers. SMA II showed no sensory nerve abnormalities.     

Mouse current vocalization threshold measured with a neurospecific nociception assay: the effect of sex, morphine, and isoflurane

Sine-wave electrical stimulation at frequencies 2000, 250, and 5 Hz to respectively evaluate Aβ, Aδ, and C sensory neurons has recently been added to the armamentarium used to evaluate sensory neurons. We developed an automated nociception assay using sine-wave stimulation methodology to determine current vocalization threshold in response to 2000, 250, and 5 Hz and examine the effects of sex, analgesics, and anesthetics in mice. At baseline, males had significantly higher mean current vocalization thresholds compared with female mice at 2000, 250, and 5 Hz (p ≤ 0.019). By 1 h after intrathecal injections of morphine there were significant increases in current vocalization threshold percent changes from baseline that varied with doses (p = 0.0001) and frequency used (p < 0.0001). Specifically, with increasing doses of morphine, there were significantly greater increases in current vocalization threshold percent changes from baseline in response to 5 Hz compared with 250 and 2000 Hz stimulation in a significantly ordered pattern: 5 Hz > 250 Hz (p < 0.0001) and 250 Hz > 2000 Hz (p = 0.0002). Forty-five minutes after exposure, there were no effects of isoflurane on current vocalization thresholds at any frequency. Therefore, our findings suggest that this automated nociception assay using sine-wave stimulation in mice, can be valuable for measurements of the effects of sex, opioids, and anesthetics on the response to electrical stimuli that preferentially stimulate Aβ, Aδ, and C-sensory fibers in vivo. This investigation suggests the validation of this assay and supports its use to examine mechanisms of nociception in mice.     

Muscle Weakness, Paralysis, and Atrophy after Human Cervical Spinal Cord Injury

Muscle weakness and failure of central motor drive were assessed in triceps brachii muscles of individuals with chronic cervical spinal cord injury (SCI) and able-bodied controls. Electrical stimuli were applied to the radial nerve during rest and during triceps submaximal and maximal voluntary contractions (MVCs). The mean forces and integrated EMGs generated by SCI subjects during MVCs were significantly less than those produced by controls (P < 0.01), with 74 and 71% of muscles generating <10% control force and EMG, respectively. There was an inverse linear relationship between the evoked and voluntary forces (n = 32 muscles of SCI subjects) which, when extrapolated to zero evoked force, also showed significant whole muscle weakness for SCI compared to control subjects (P < 0.01). Severe muscle atrophy was revealed which might reflect disuse and/or muscle denervation subsequent to motoneuron loss. Many triceps muscles of SCI subjects showed no force occlusion (n = 41) or were impossible to stimulate selectively (n = 61). Force was always evoked when the radial nerve was stimulated during MVCs of SCI subjects. The force elicited by single magnetic shocks applied to the motor cortex at Cz′ during voluntary contractions of SCI subjects was also inversely related to the voluntary triceps force exerted (n = 18), but usually no force could be elicited during MVCs. Thus central motor drive was probably maximal to these muscles, and the force evoked during MVCs by below-lesion stimulation must come from activation of paralyzed muscle. SCI subjects also had significantly longer mean central nervous system (CNS) conduction times to triceps (P < 0.01) suggesting that the measured deficits reflect CNS rather than peripheral nervous system factors. Thus, the weak voluntary strength of these partially paralyzed muscles is not due to submaximal excitation of higher CNS centers, but results mainly from reduction of this input to triceps motoneurons.     

Automatic analysis of EMG during clonus

Clonus can disrupt daily activities after spinal cord injury. Here an algorithm was developed to automatically detect contractions during clonus in 24 h electromyographic (EMG) records. Filters were created by non-linearly scaling a Mother (Morlet) wavelet to envelope the EMG using different frequency bands. The envelope for the intermediate band followed the EMG best (74.8-193.9 Hz). Threshold and time constraints were used to reduce the envelope peaks to one per contraction. Energy in the EMG was measured 50 ms either side of each envelope (contraction) peak. Energy values at 5% and 95% maximal defined EMG start and end time, respectively. The algorithm was as good as a person at identifying contractions during clonus (p = 0.946, n = 31 spasms, 7 subjects with cervical spinal cord injury), and marking start and end times to determine clonus frequency (intra class correlation coefficient, α: 0.949), contraction intensity using root mean square EMG (α: 0.997) and EMG duration (α: 0.852). On average the algorithm was 574 times faster than manual analysis performed independently by two people (p ≤ 0.001). This algorithm is an important tool for characterization of clonus in long-term EMG records.