Neurophysiological evaluation of central-peripheral sensory and motor pudendal fibres

Extensive neurophysiological investigations were carried out in 18 healthy volunteer subjects, and 6 patients with neurological disease. The tests consisted of spinal and scalp somatosensory evoked potentials (SEPs) to stimulation of the dorsal nerve of penis/clitoris, motor evoked potentials (MEPs) from the bulbocavernosus muscle (BC) and anal sphincter (AS) in response to scalp and sacral root stimulation, and measurement of sacral reflex latency (SRL) from BC and AS. In the control subjects, the mean sensory total conduction time (sensory TCT), as measured at the peak of the scalp P40 wave was 40.9 msec (range: 37.8-44.2). The mean sensory central conduction time (sensory CCT = spine-to-scalp conduction time) was 27.0 msec (range: 23.5-30.4). Transcranial brain stimulation was performed by using a magnetic stimulator both at rest and during voluntary contraction of the examined muscle. Sacral root stimulation was performed at rest. Motor total conduction times (motor TCT) to BC and AS muscles were respectively 28.8 and 30.0 msec at rest, and 22.5 and 22.8 msec during contraction. Motor central conduction times (motor CCT) to sacral cord segments controlling BC and AS muscles were respectively 22.4 and 21.2 msec at rest, and 15.1 and 12.4 msec during contraction. The mean latencies of SRL were respectively 31.4 msec in the bulbocavernosus muscle and 35.9 msec in the anal sphincter. Combined or isolated abnormalities of SEPs, MEPs and SRL were found in a small group of patients with neurological disorders primarily or secondarily affecting the genito-urinary tract.     

EMG, single fibre EMG and sacral reflexes in assessment of sacral nervous system lesions.

EMG of pelvic floor muscles, single fibre EMG of external anal sphincter and both bulbocavernosus and anal reflexes were investigated in 31 men without sacral nervous system lesions and in 12 patients with neurogenic erectile impotence, of whom one had slight loss of sensitivity to pinprick in the lower sacral dermatomes. EMG and single fibre EMG abnormalities have been found concomitantly in eight patients and six of these had also prolonged bulbocavernosus reflex latencies. In two patients the prolonged bulbocavernosus reflex latency was the only abnormality. Single fibre EMG of anal sphincter muscle seems to be superfluous in routine evaluation of sacral nervous system lesions.     

Sacrolumbar intersegmental reflex circuit in men and its relation to the ejaculatory process.

OBJECTIVE: We aimed to investigate electrophysiologically the intersegmental reflex circuit from sacral to lumbar cord segments in normopotent adult men, in patients with spinal cord injury and in patients with premature ejaculation. METHODS: Reflex EMG activity of the cremasteric (CM) and bulbocavernosus (BC) muscles was recorded simultaneously by needle electrodes during electrical stimulation of the upper lumbar and sacral dermatomes, respectively. Thirty-three healthy male volunteers, 16 patients with spinal cord injury (SCI) at the thoracic or cervical levels, and 26 men with premature ejaculation (PME) were included in the study. RESULTS: In controls, upper lumbar dermatomal stimulation (ULS) at the inner side of thigh only elicited a reflex response from the CM muscle and did not produce a regular response from the lower sacral myotomes such as in the BC muscle. However lower sacral dermatomal stimulation (LSS) at the dorsal nerve of penis consistently evoked reflex responses from both CM and BC muscles. These basic electrophysiological features were not different in patients with SCI. LSS did not elicit a reflex response from the CM muscle in about 39% of patients with PME, while the BC reflex was obtained from all patients with PME. CONCLUSIONS: The neurophysiological pattern in BC and CM muscles during sacral or lumbar dermatomal stimulation reflects the sacrolumbar intersegmental reflex linkage that may be related to the ejaculatory process in men. The intersegmental sacrolumbar reflex circuit may be functionally disturbed in some patients with PME. SIGNIFICANCE: Interaction between the reflex activity of sacral to lumbar dermatomes could prove useful in defining electrophysiological mechanisms related to ejaculation in men.     

Motor potentials of bulbocavernosus muscle after transcranial and lumbar magnetic stimulation: comparative study with bulbocavernosus reflex and pudendal evoked potentials.

Motor potentials of the bulbocavernosus muscle were recorded in 17 healthy subjects after transcranial and lumbar magnetic stimulation. The latencies (SD) were respectively: 22.9 (1.8) and 5.9 (0.4) ms. The central conduction time was 17.0 (2.5) ms. The bulbocavernosus reflex presented an onset at 34.5 (3.3) ms and a negative peak at 43.1 (3.9) ms. The cortical pudendal evoked potential was W shaped: the first peak had a latency of 35.4 (2.8) ms. The concurrent recording of motor potentials, bulbocavernosus reflex, pudendal evoked potentials gives a measure of peripheral and central, afferent and efferent neurological pathways related to pudendal nerve function.     

Pudendal SEP and bulbocavernosus reflex in women.

A new simple method for the electrical stimulation of the dorsal nerve of clitoris is presented. Well-formed cortical somatosensory evoked potentials could be recorded in 12 continent adult females without nervous system involvement at a stimulus intensity of 4 times 'sensory threshold.' The procedure was well tolerated by the subjects; the bulbocavernosus reflex responses were, however, not always obtainable at this stimulus intensity.     

Somatic innervation of the human bulbocavernosus muscle.

OBJECTIVE: To demonstrate the somatic reflex innervation of the bulbocavernosus muscle (BCM), the principal muscle for ejaculation. METHODS: Genitourinary electrodiagnostic testing utilizing modifications of the standard bulbocavernosus reflex was performed in 13 healthy male volunteers ages 20-43. RESULTS: Bulbocavernosus muscle contraction was elicited by stimulation of the dorsal nerve of the penis, from both the penile skin and from the anterior urethra, and following stimulation of the perineal nerve. Latencies were variable depending on the point of stimulation. CONCLUSIONS: All 3 afferent pathways synapse on pudendal motoneurons in the conus medullaris, and provide for peripheral reflex control of BCM contractions. Based on the latencies of the urethral evoked responses, urethral innervation differs from penile shaft innervation, each having a distinct population of the dorsal nerve of the penis (DNP) fibers. The presence of an electrically-defined pathway from the anterior urethra to the BCM suggests that somatic afferents from the anterior urethra are involved with the ejaculatory reflex. These somatic reflexes are components of normal ejaculatory function. The findings contribute to understanding the neurophysiology of ejaculation, and may be applicable to the evaluation of ejaculatory disorders.     

Muscle activity during unconditioned and conditioned eye blinks in the rabbit.

EMGs were recorded from the orbicularis oculi, retractor bulbi and superior rectus muscles in rabbits to investigate the time course of muscle activation during unconditioned and conditioned eye blinks. EMGs from the three muscles showed two responses, with the responses of the orbicularis oculi and retractor bulbi showing the same latency, and the responses of the superior rectus lagging. The latency of responses to periorbital electrostimulation was about 5 ms, and to air puff stimulation about 10 ms. Results showed a tight coupling of activity between muscles, with cross-correlograms peaking at 0.65 to 0.85 and showing little time shift. Stimulus-response curves showed clear non-linearities in the response of the muscle to changes in stimulus strength. Local anesthesia of the cornea had little effect on unconditionally evoked responses. The form of unconditionally evoked responses was similar with periorbital electrostimulation and air puff stimuli but differed in latency. These results show the form of the eye blink reflex response and will be of importance in interpreting electrophysiological studies of the classically conditioned eye blink of rabbits.     

Intracranial stimulation of the trigeminal nerve in man. II. Reflex responses.

The reflex responses evoked by direct electrical stimulation of the intracranial portion of the trigeminal nerve have been studied in 16 subjects undergoing percutaneous retrogasserian thermocoagulation for the treatment of trigeminal neuralgia affecting the second or third division. In the obicularis oculi muscle, early and late responses similar to the R1 and R2 components of the blink reflex were recorded. The former could be evoked only by stimulation of the second division and its latency was consistent with intermediately fast afferents. A late reflex (50-70 ms) was occasionally recorded from the anterior belly of the digastric muscle. The response was sometimes followed by a later activity and showed the features of a polysynaptic reflex. No response was obtained in the jaw elevators when fully relaxed. With the subject voluntarily clenching his teeth, both an early "H-like" response and two silent periods in the background EMG were obtained. The second silent period was similar in the muscles ipsi- and contralateral to intracranial stimulation, while the first silent period was longer in the ipsilateral muscles. Possible mechanisms contributing to the inhibition following stimulation of the mixed portion of the nerve are discussed.     

Innervation of the human anterior urethra by the dorsal nerve of the penis

Previous neuroanatomic studies have demonstrated that branches of the dorsal nerve of the penis (DNP) innervate the anterior urethra. This study utilized electrodiagnostic techniques to confirm this finding. Electrical stimulation of the urethra resulted in responses recorded in the main trunk of the DNP, and responses were recorded from the urethra following stimulation of the DNP. A bulbocavernosus reflex was evoked after urethral stimulation. Urethral afferent impulses have a role in reflex ejaculatory function. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:514–518, 1998.     

Components of the neural circuitry of the vaginocavernosus reflex in rabbits

In mammals the mechanisms underlying female sexual and reproductive biology are poorly understood. Little attention has been paid to striated muscles and their neural regulation. The aim of the present study was to describe the components of the vaginocavernosus reflex in adult rabbits. It was found that mechanical stimulation of the glans of the clitoris and the perineal vagina induced electromyographic (EMG) responses in bulbocavernosus (Bcm) and ischiocavernosus (Icm) muscles. Unilateral and bilateral nerve transection indicated that the clitoral nerve is the main afferent path of the reflex and that it recruits ipsilateral and contralateral perineal motoneurons. Injection of horseradish peroxides‐wheat germ agglutinin (HRP‐WGA) into the Bcm and Icm labeled spinal motoneurons scattered in L7 and S1 segments. According to the results of this study and previous work, the elements of the vaginocavernosus reflex may be described as follows. Mechanical receptors are located in the glans clitoris and in the wall of the perineal vagina. The main afferent pathway is the clitoral nerve. It activates ipsilateral and contralateral Bcm and Icm motoneurons in lumbosacral segments. Axons of efferent neurons travel through the clitoral and ischiocavernosus nerves, and the effectors are the Bcm and Icm perineal muscles. Identification of neural components of the vaginocavernosus reflex in rabbits will allow the use of this animal as a model to assess the physiological characteristics of the perineal motoneurons as well as the contribution of the Bcm and Icm in female urogenital functions. J. Comp. Neurol. 518:199–210, 2010. © 2009 Wiley‐Liss, Inc.     

Head extensor reflex evoked by trigeminal stimulation in humans.

OBJECTIVE: Excitatory and inhibitory responses have been recognized in human cervical muscles following trigeminal stimulation. However, no evidence has so far been published of a crossed, short-latency, excitatory response resembling the early head extensor reflex seen in the cat. We seek its existence in humans. METHODS: The study was carried out in 14 voluntary healthy subjects. Percutaneous and surface electrical stimulation of the supraorbital and infraorbital nerves was performed with single, double and repetitive stimuli. Signals were recorded from the relaxed splenius and sternomastoid muscles bilaterally. RESULTS: Percutaneous stimulation of infraorbital nerve with single stimuli evoked an early response in the contralateral splenius muscle, with onset latency ranging from 11 to 14 ms (HR1). This response was greatly facilitated by double or repetitive stimuli. Single stimuli also gave rise to two larger responses in all 4 muscles in the latency ranges 50-70 ms (HR2) and 100-160 ms (HR3). Surface stimulation of one nerve alone could not elicit any early activity. Single surface stimuli delivered simultaneously to the supraorbital and infraorbital nerves evoked HR1 in only 5 subjects. CONCLUSIONS: We detected a crossed early reflex of the head extensor muscles to trigeminal stimuli. Its timing is similar to the 8-ms response seen in cats. The evidence provided suggests that the reflex is mediated by an oligosynaptic circuit and that it needs a strong spatial summation at central synapses.     

Electrophysiological evaluation of genito-sphincteric dysfunction in multiple system atrophy

Thirteen patients with multiple system atrophy underwent multimodality neurophysiological evaluation, including sphincteric needle electromyography (EMG), sacral reflexes, pudendal nerve terminal latency, pudendal (PSEPs) and tibialis posterior nerve somatosensory evoked potentials (TPSEPs), and perineal motor evoked potentials (PMEPs). EMG revealed denervation or neurogenic changes, with reduction in spontaneous tonic activity at rest and abnormal pudendal nerve terminal latency in 10 patients (76.9%); anal reflex was delayed in 7 patients (53.8%). TPSEPs scalp responses were clearly abnormal in 4 patients (30.7%), whereas PSEPs exhibited changes in 9 (69.2%): in 6 patients responses were delayed at lumbar level (46.2%), and in 5 over the scalp (38.4%). PMEPs showed an increase in latency with a mild prolongation of central motor conduction time (CMCT) in 2 cases (15.3%); 1 patient had prolonged latencies following both cortical and sacral stimulation, but a normal CMCT. Even if diagnostic yield is not improved using these investigations they provide evidence of multiple lesion sites other than Onuf's nucleus.     

Lipoma of the cauda equina selectively involving lower sacral roots. Case report.

A 44-year-old male patient suffering from sexual and voiding dysfunction did not exhibit any sensorimotor deficit except for a lax anal sphincter with loss of the bulbocavernosus reflex (BCR). The absence of both the electrically induced BCR and cortical evoked responses to stimulation of the dorsal penile nerve as well as partial denervation of the pelvic floor musculature suggested damage to the lower sacral roots. The site of the lesion as indicated by electrophysiological findings was confirmed by computerized tomography and magnetic resonance imaging. The operation revealed a lipoma involving a few cauda fibers which produced a distension in the region of the conus medullaris.     

ELECTROPHYSIOLOGICAL EVALUATION OF GENITO-SPHINCTERIC DYSFUNCTION IN MULTIPLE SYSTEM ATROPHY

Thirteen patients with multiple system atrophy underwent multimodality neurophysiological evaluation, including sphincteric needle electromyography (EMG), sacral reflexes, pudendal nerve terminal latency, pudendal (PSEPs) and tibialis posterior nerve somatosensory evoked potentials (TPSEPs), and perineal motor evoked potentials (PMEPs). EMG revealed denervation or neurogenic changes, with reduction in spontaneous tonic activity at rest and abnormal pudendal nerve terminal latency in 10 patients (76.9%); anal reflex was delayed in 7 patients (53.8%). TPSEPs scalp responses were clearly abnormal in 4 patients (30.7%), whereas PSEPs exhibited changes in 9 (69.2%): in 6 patients responses were delayed at lumbar level (46.2%), and in 5 over the scalp (38.4%). PMEPs showed an increase in latency with a mild prolongation of central motor conduction time (CMCT) in 2 cases (15.3%); 1 patient had prolonged latencies following both cortical and sacral stimulation, but a normal CMCT. Even if diagnostic yield is not improved using these investigations they provide evidence of multiple lesion sites other than Onuf's nucleus.­­     

Human anal reflexes.

By perianal electrical stimulation and EMG recording from the external anal sphincter the anal reflex was constantly present in normal subjects. The latency decreased within certain limits with increasing stimulation to an average minimum latency of 50 ms (SD 10.5). There was no difference between the minimum latency in normal subjects and patients with suprasegmental lesions of the CNS. The latency may be prolonged in patients with lesion of the reflex arc. By stimulation over the posterior tibial nerve behind the medial malleolus a reflex reaction could be picked up constantly from the anal sphincter in normal subjects. This reflex had a longer latency but a lower threshold than the reflex reaction from the tibialis anterior muscle. The average minimum latency from the anal sphincter was 93 ms (SD 21.1) and from the tibialis anterior muscle 64 ms (SD 7.9). In the absence of the anal reflex it may be possible to localise the defect to the afferent or efferent parts of the reflex by using types of stimulation. Preliminary studies of spinal shock revealed a perianally elicited anal reflex in all cases, but also a response to peripheral stimulation in some of the cases, more frequently found in the anal sphincter than in the tibialis anterior muscle.     

Analysis of reflex activity in cardiac sympathetic nerve induced by myelinated phrenic nerve afferents

Electrical stimulation of the phrenic nerve afferents evoked excitatory responses in the right inferior cardiac sympathetic nerve in chloralose-anaesthetized cats. The reflex was recorded in intact and spinal cats. The latency and threshold of the volley recorded from the phrenic nerve as well as of the cord dorsum potentials evoked by electrical stimulation of the phrenic nerve indicated that group III afferents were responsible for this reflex. The phrenicocardiac sympathetic reflex recorded in intact cats was followed by a silent period. The maximum amplitude of the reflex discharges was 800 microV, the latency was 83 ms and the central transmission time 53 ms. Duration of the silent period lasted up to 0.83 s. In spinal cats the reflex was recorded 5.5-8 h after spinalization. The maximum amplitude of the spinal reflex discharges ranged from 22 to 91 microV and the latency from 36 to 66 ms.     

Significance of coil orientation for motor evoked potentials from nasalis muscle elicited by transcranial magnetic stimulation.

OBJECTIVE: In transcranial magnetic stimulation (TMS) of the motor cortex, the optimal orientation of the coil on the scalp is dependent on the muscle under investigation, but not yet known for facial muscles. METHODS: Using a figure-of-eight coil, we compared TMS induced motor evoked potentials (MEPs) from eight different coil orientations when recording from ipsi- and contralateral nasalis muscle. RESULTS: The MEPs from nasalis muscle revealed three components: The major ipsi- and contra-lateral middle latency responses of approximately 10 ms onset latency proved entirely dependent on voluntary pre-innervation. They were most easily obtained from a coil orientation with posterior inducing current direction, and in this respect resembled the intrinsic hand rather than the masseter muscles. Early short duration responses of around 6 ms onset latency were best elicited with an antero-lateral current direction and not pre-innervation dependent, and therefore most probably due to stimulation of the nerve roots. Late responses (>18 ms) could inconsistently be elicited with posterior coil orientations in pre-innervated condition. CONCLUSIONS: By using the appropriate coil orientation and both conditions relaxed and pre-innervated, cortically evoked MEP responses from nasalis muscle can reliably be separated from peripheral and reflex components and also from cross talk of masseter muscle activation.     

Neurophysiological testing in anorectal disorders

The neurophysiological techniques currently available to evaluate anorectal disorders include concentric needle electromyography (EMG) of the external anal sphincter, anal nerve terminal motor latency (TML) measurement in response to transrectal electrical stimulation or sacral magnetic stimulation, motor evoked potentials (MEPs) of the anal sphincter to transcranial magnetic cortical stimulation, cortical recording of somatosensory evoked potentials (SEPs) to anal nerve stimulation, quantification of electrical or thermal sensory thresholds (QSTs) within the anal canal, sacral anal reflex (SAR) latency measurement in response to pudendal nerve or perianal stimulation, and perianal recording of sympathetic skin responses (SSRs). In most cases, a comprehensive approach using several tests is helpful for diagnosis: needle EMG signs of sphincter denervation or prolonged TML give evidence for anal motor nerve lesion; SEP/QST or SSR abnormalities can suggest sensory or autonomic neuropathy; and in the absence of peripheral nerve disorder, MEPs, SEPs, SSRs, and SARs can assist in demonstrating and localizing spinal or supraspinal disease. Such techniques are complementary to other methods of investigation, such as pelvic floor imaging and anorectal manometry, to establish the diagnosis and guide therapeutic management of neurogenic anorectal disorders.     

Segmental organization of rat lateral longissimus, a muscle involved in lordosis behavior: EMG and muscle nerve recordings

Following stimulation of lumbar cutaneous and high threshold muscle afferents in urethane-anesthetized ovariectomized rats, polysynaptic multi-unit responses were recorded from muscle nerves to lateral longissimus (LL) at a mean latency of 9.5 ms. These responses could be reciprocally evoked between segments with no apparent rostro-caudal asymmetry. Polysynaptic responses habituated to repeated stimulation within 0.5-1.5 min but could be evoked again after several minutes rest. In estradiol-treated rats, 60% of the 9.5 ms responses were followed by late discharges (greater than 40 ms) as compared to 24% in untreated control animals (P = 0.05). Following stimulation to the L3 and L4 motor nerves to lateral longissimus, EMG responses were recorded from overlapping fields of innervation. The conduction velocity of the fast muscle fibers was determined to be 7 m/s. The short length of most of the LL muscle fibers and the intersegmental recruitment of LL motoneurons by cutaneous afferents is compatible with the integrated action of axial muscles in the performance of lordosis behavior.     

Dartos reflex: a sympathetically mediated scrotal reflex

The dartos muscle is a sympathetically innervated dermal muscle layer within the scrotum, distinct from the somatically innervated cremasteric muscle. We electrophysiologically demonstrate the presence of a dartos reflex (DR), which can be used to evaluate the thoracolumbar sympathetic and genitofemoral nerve pathways. In 20 healthy men, we evoked the DR by cutaneous stimulation of the thigh and recorded the resultant scrotal skin contraction. We recorded hand, foot, and perineal sympathetic skin responses (SSRs) as controls. The DR was reliable and reproducible, as were the SSRs. The mean left DR latency was 4.8 s (SD, 2.7 s) and right DR latency was 5.4 s (SD, 3 .4), both of which were longer than the mean hand, foot, and perineal SSRs (P < 0.05). An intact reflex arc reflects the integrity of the afferent and efferent branches of the genitofemoral nerve (T12-L2). The DR test can also be used to assess scrotal autonomic innervation. Abnormalities of dartos innervation may impact testis thermoregulation and spermatogenesis.