Sensory action potentials in the ulnar and radial nerves of dogs: effect of stimulation site and voltage

The influence of stimulation site and voltage on amplitude, wave form, conduction time, and velocity of sensory action potentials in the ulnar and radial nerves was evaluated in 25 healthy dogs. A 5-fold increase in stimulation voltage above threshold caused a 300% increase in the amplitude of evoked sensory nerve potentials. An additional 2-fold increase in stimulation voltage (to 10 times threshold) resulted in an additional 40% increase in amplitude. An absolute saturation voltage was not found. Latency velocity was increased by increasing stimulation voltage, but conduction velocity was not affected. Multicomponent nerve action potentials were frequently found at the proximal recording sites. The number of components was not affected by stimulation voltage. Proximal displacement of the stimulation site resulted in an increase in amplitude of the nerve action potentials, increased latency velocity, and fewer components; conduction velocity was not affected. As a consequence of these findings, preference was given to simultaneous recording at 2 sites along the nerve, stimulation at the more proximal stimulation site distal to the carpus, and stimulation voltages between 5 and 10 times the threshold. The occurrence of multicomponent wave forms, the absence of an absolute saturation voltage, and the lowering of the number of components by proximal displacement of the site of stimulation may all be related to the relatively small number of sensory nerve fibers that can be activated at the stimulation site.     

Resistance of the Peripheral Nervous System to the Effects of Chronic Canine Hypothyroidism

Background: Hypothyroidism has been implicated in the development of multiple peripheral mono‐ and polyneuropathies in dogs. The objectives of this study were to evaluate the clinical and electrophysiologic effects of experimentally induced hypothyroidism on the peripheral nervous system of dogs. Hypothesis: Chronic hypothyroidism will induce peripheral nerve sensorimotor dysfunction. Animals: Eighteen purpose‐bred, female dogs. Methods: Prospective, longitudinal study: Hypothyroidism was induced by radioactive iodine administration in 9 dogs, and the remaining 9 served as untreated controls. Neurological examinations were performed monthly. Electrophysiologic testing consisting of electromyography (EMG); motor nerve conduction studies of the sciatic‐tibial, radial, ulnar, and recurrent laryngeal nerves; sciatic‐tibial and ulnar F‐wave studies; sensory nerve conduction studies of the tibial, ulnar, and radial nerves; and evaluation of blink reflex and facial responses were performed before and 6, 12, and 18 months after induction of hypothyroidism and compared with controls. Results: Clinical evidence of peripheral nervous dysfunction did not occur in any dog. At 6 month and subsequent evaluations, all hypothyroid dogs had EMG and histologic evidence of hypothyroid myopathy. Hypothyroid dogs had significant (P≤ .04) decreases in ulnar and sciatic‐tibial compound muscle action potentials over time, which were attributed to the concurrent myopathy. No significant differences between control and hypothyroid dogs were detected in electrophysiologic tests of motor (P≥ .1) or sensory nerve conduction velocity (P≥ .24) or nerve roots (P≥ .16) throughout the study period, with values remaining within reference ranges in all dogs. Conclusion: Chronic hypothyroidism induced by thyroid irradiation does not result in clinical or electrophysiologic evidence of peripheral neuropathy, but does cause subclinical myopathy.     

A new method for recording and analysing evoked motor potentials from dogs

Normal values for motor conduction in the tibial, ulnar and fibular nerves of dogs have been determined using a new method for recording and analysing evoked motor potentials. The use of an alligator clip as a roving surface electrode for recording, and a personal computer to analyse the evoked potentials has facilitated faster and more reproducible motor conduction studies. Compound muscle action potential (CMAP) and motor nerve conduction velocity data are in good agreement with previous studies. Normal values for CMAP area, residual latency and proximal to distal ratios for CMAP area and amplitude are presented for the first time.     

Assessment of dorsal nerve root and spinal cord dorsal horn function in clinically normal dogs by determination of cord dorsum potentials

OBJECTIVE: To establish normal predictive values for cord dorsum potential (CDP) onset latency after thoracic and pelvic limb sensory or mixed nerve stimulation in adult dogs. ANIMALS: 26 clinically normal adult dogs. PROCEDURE: Sensory nerve action potentials (SNAP) were recorded proximally from tibial and lateral superficial radial nerves after distal stimulation. The CDP were recorded from the L4-L5 interarcuate ligament for the tibial nerve and from the C7-T1 interarcuate ligament for the radial nerve. Linear regression analyses were performed for CDP onset latency, and mean +/- SD was calculated for CDP onset to peak latency differences and sensory nerve conduction velocities (SNCV). RESULTS: For the tibial nerve, expected CDP onset latency (CDPOL) = -1.194 + 0.014 X pelvic limb length (mm; R2 = 0.912); CDPOL = -2.156 + 0.011 X pelvic limb/spinal length (mm; R2 = 0.911); and CDPOL = 0.941 + 2.197 X tibial nerve SNAP latency (milliseconds; R2 = 0.903). For the radial nerve, CDPOL = -0.9 + 0.014 x thoracic limb length (mm; R2 = 0.873); and CDPOL = 1.454 + 1.874 X radial nerve SNAP latency (milliseconds; R2 = 0.903). Mean +/- SD for CDP onset to peak latency difference for tibial and radial nerves was 3.1+/-0.3 and 3.0+/-0.4 milliseconds, respectively. CONCLUSIONS: Strong linear associations exist between CDPOL and a number of easily measured peripheral independent variables in dogs. There is also a narrow range of normal values for CDP onset to peak latency differences that is independent of limb length. CLINICAL RELEVANCE: CDP evaluation can be used to accurately assess functional severity and distribution of abnormalities in proximal sensory nerves, dorsal nerve roots, and spinal cord dorsal horns in dogs with suspected neuropathy, radiculopathy, or myelopathy involving the brachial or lumbosacral intumescences.     

Conduction velocities and reflexes of the proximal and distal parts of the saphenous nerve of the dog

The maximal conduction velocities of compound-action potentials in the proximal and distal parts of the saphenous nerve were determined by averaging potentials evoked and recorded through needle electrodes. Antidromic, triphasic compound-action potentials unipolarly recorded from the distal part of the saphenous nerve were of the same minimal latency as potentials having 4 phases which were recorded bipolarly from the same site. However, the unipolarly recorded potentials were of greater amplitude. Monophasic compound-action potentials were recorded through bipolar chlorided silver electrodes from the surface of fascicles of the distal part of the saphenous nerve. The maximal conduction velocity of these potentials was in agreement with the conduction velocity of compound-action potentials of the distal part of the saphenous nerve which were evoked and recorded through subcutaneous needle electrodes. The specificities of the stimulating and recording sites were verified by recording before and after the saphenous nerve was cut between the stimulating and recording sites. Mean conduction velocities were 62.3 +/- 2.0 m/s for the distal part of the saphenous nerve and 66.3 +/- 2.2 m/s for the proximal part of the saphenous nerve. Reflex-evoked muscle activity was elicited in the ipsilateral tensor muscle of the fascia lata and semimembranous muscle after electrical stimulation of the saphenous nerve through subcutaneous needle electrodes. The effects of various stimulus intensities on the latency and duration of these reflex-evoked muscle potentials were determined.     

Myelinated axons in peripheral nerves of adult beagle dogs: morphometric and electrophysiological measurements

The myelinated fibre composition and conduction velocities were measured for the ulnar, saphenous and caudal cutaneous sural nerves of 10 healthy beagle dogs. A systematic random sampling technique was used to estimate the fibre diameter frequency distributions and densities. Conduction velocities were measured from evoked compound nerve action potentials. All nerves showed bimodal diameter frequency distributions with modes being approximately the same for each nerve (2 to 4 microns and 8 to 10 microns or 10 to 12 microns). The variation in the average densities and in the shapes of histograms of the different nerves was slight; however, there was a wide variation for the same nerve in different individuals. The conduction velocities for the fastest conducting axons in the nerves ranged from 63 to 79 m s-1. These normal quantitative processes affecting peripheral nerves in the dog.     

Sensory nerve conduction velocities in forelimb of ponies

Normal nerve conduction velocity values in 10 ponies were determined for sensory nerve fibers in the median and ulnar nerves. A percutaneous signal-averaging technique was developed and used. Medial and lateral palmar digital nerves on the abaxial surface of the proximal sesamoid bones were used as the sites for percutaneous stimulation, whereas recording sites included the medial and lateral palmar nerves just distal to the carpus and the median and ulnar nerves in the middle of the radius. Sensory nerve conduction velocities can be evaluated simply and clinically in the limbs of horses, using percutaneous signal-averaging techniques.     

Electrophysiological evaluation of traumatic forelimb paralysis of the dog

The results of clinical neurological, electromyographic and electroneurographic examinations in 26 dogs with traumatic forelimb paralysis are presented. The results of neurological examination varied considerably among the cases. Electromyographic evidence of denervation in the epaxial muscles was observed in 22 dogs. A post ganglionic dorsal root lesion was diagnosed in 14 cases by the presence of an evoked sensory nerve action potential in association with loss of conscious pain perception in the appropriate area. Motor nerve studies in the ulnar nerve were not helpful in discriminating root lesions from spinal nerve involvement. It was concluded that electromyographic examination of the ipsilateral epaxial muscles under general anaesthesia is essential for the detection of root involvement. Sensory conduction studies in the radial nerve are indicated if conscious pain perception is absent in the fifth digit. Motor and sensory conduction studies of the ulnar nerve system seldom provide additional diagnostic information seldom provide additional diagnostic information. The absence of electrophysiological signs of root involvement does not exclude a post ganglionic dorsal root lesion.     

Sensory nerve conduction velocities in the cutaneous afferents of the ulnar and peroneal nerves of the dog: Tissue temperature-dependent reference ranges

Sensory nerve conduction velocities in the cutaneous afferents of the ulnar and peroneal nerves of the neurologically normal adult dog were determined by stimulation at stimulus intensities of 15, 20 and 25 V through subcutaneously placed electrodes and by the averaged evoked response technique. Stimulus intensities of 15 V for the ulnar nerve and 20 V for the peroneal nerve were adequate to measure the sensory nerve conduction velocities of these nerves. A linear relationship was seen between sensory nerve conduction velocity (y in m/s) and tissue temperature (x in °C) and the regression equations were expressed as follows: y=1.6x+12.3 at a stimulus intensity of 15 V for the ulnar nerve and y=2.0x–10.6 at 20 V for the peroneal nerve, respectively. The 95% confidence limits of the regressions of the sensory nerve conduction velocities against tissue temperature, obtained at a stimulus intensity of 15 V for the ulnar nerve or at a stimulus intensity of 20 V for the peroneal nerve, were proposed for a tissue temperature-dependent reference range to enable the clinician to evaluate graphically the sensory nerve conduction velocity in a diseased dog.     

MOTOR AND SENSORY NERVE CONDUCTION STUDY IN THE FERRET

Ferrets are considered a popular small mammal pet, and like other companion animals they are reported to suffer from diseases affecting the neuromuscular system. There currently is a lack of comprehensive electrodiagnostic study regarding the appendicular nerves of ferrets. In this research investigation, 25 domestic ferrets were used for electromyography and motor nerve conduction studies of the tibial, fibular, ulnar, and radial nerves, including H reflexes of the tibial and ulnar nerves, as well as sensory conduction of the fibular nerve. Mean and standard deviations for motor and sensory nerve studies were established. The hypothesis that weight would be correlated with all distal and proximal compound muscle action potential latencies was tested and confirmed for the tibial, fibular, and radial nerves but not the ulnar nerve.     

Compound-action potentials of myelinated fibers in the saphenous nerve of the dog: in situ electrophysiologic and behavioral studies

Compound-action potentials (CAP) were recorded directly from the surface of fascicles of the distal portion of the saphenous nerve (SN) of dogs in situ. Potentials were evoked through needle electrodes and were recorded through bipolar stainless steel electrodes. Stimuli of 10-microseconds duration and of 0.4 +/- 0.15-mA amplitude evoked a monophasic CAP. Sensory conduction velocities of afferent fibers, the action potentials of which contributed to this evoked compound potential, ranged from 62.4 +/- 2.8 m/s for the most rapidly conducting fibers to 30.5 +/- 2.4 m/s for the least rapidly conducting fibers. Stimuli of 25-microseconds duration and of 2.2 +/- 0.8-mA amplitude evoked a second, longer latency CAP in addition to the first CAP. Sensory conduction velocities of afferent fibers, the action potentials of which contributed to this evoked compound potential, ranged from 20.4 +/- 2.9 m/s for the most rapidly conducting fibers to 13.7 +/- 1.0 m/s for the least rapidly conducting fibers. Low-amplitude, negative peaks were recorded between the first and second major potentials elicited by the longer duration stimuli. Stimuli of still longer duration and higher currents induced contractions of the caudal part of the sartorius muscle by current spread in 9 of 12 dogs. In 3 dogs, a third monophasic CAP was evoked, having a maximal conduction velocity of 1.7 +/- 0.2 m/s. After section of the distal portion of the SN on one side in each of 2 dogs, an absence of signs of sensory deficit was found on clinical neurologic examination. The area of cutaneous innervation of the cranial branch of the distal portion of the SN was determined electrophysiologically.     

Motor nerve conduction velocity and latency in the dog

Supramaximal percutaneous nerve stimulation was used in motor nerve conduction velocity studies conducted in ten middle-aged, clinically normal dogs. Dogs were separated into two groups; dogs in one group weighted less than or equal to 7.5 kg and dogs in the other group weighted greater than or equal to 15.9 kg. Mean values and SEM were recorded for radial (72.1 +/- 1.9 m/s), median 65.6 +/- 2.1 m/s), ulnar (58.9 +/- 1.0 m/s), tibial (68.2 +/- 1.4 m/s), and peroneal (79.8 +/- 1.8 m/s) nerves. Values for latency, amplitude, and duration for proximal and distal evoked potentials were recorded. Analysis of mean nerve conduction velocity values for all nerves between the two groups indicated no statistical difference (P greater than 0.05). However, the two groups were statistically different (P less than 0.05) when values for distal latency and measurements of nerve length were compared. These data suggest that if latency is substituted for velocity measurements, various populations of dogs must be considered to clarify interpretation.     

Histological assessment of puberty in dogs in the Zaria area of northern Nigeria

The ages of puberty and sexual maturity were histologically determined in 300 dogs, comprising 115 local Nigerian dogs and 185 crosses of local with exotic breeds. The ages ranged from six months to eight and a half years. The age at puberty was estimated to be seven to eight months and the age of sexual maturity to be 10 to 11 months for all the dogs, both local and exotic. Testicular and epididymal dimensions and weights, on average, increased progressively from before puberty until sexual maturity. The same trend was observed in the diameters of seminiferous tubules, the percentage of spermatogenesis and the epididymal sperm reserves. At puberty an average of 51.8 per cent of the caudal epididymal sperm cells of the local dogs had morphological defects compared with 54.5 per cent in the exotic cross breeds. The defects were mostly coiled tails and proximal cytoplasmic droplets. These defects had decreased to an average of 12.8 per cent in all breeds by the time the dogs had attained a mean age of one and a half years. In general the post-pubertal pattern of spermatogenesis in the dogs resembled that of the bull, and the ages at onset of puberty and sexual maturity fall within the range determined for exotic breeds of dogs. There were no significant differences between the local Nigerian dogs and the local cross exotic breeds in the parameters studied.     

Normal values for radial,peroneal and tibial motor nerve conduction velocities in adult sheep,with comparison to adult dogs

A technique for measuring motor nerve conduction velocities (NCV) in sheep was developed using 15 clinically normal ewes. Mean ±SD values were determined for the radial (76.3±12.5 m/s), peroneal (103.9±12.7 m/s), and tibial (98.6±13.1 m/s) nerves. The recording needle electrode was located in the extensor carpi radialis, tibialis cranialis, and gastrocnemius muscles, respectively. Latencies, amplitudes and durations of the proximal and distal evoked compound muscle action potentials are given. To investigate further the unexpectedly high NCVs calculated for the peroneal and tibial nerves, analogous stimulating and recording electrode sites were used in 7 clinically normal dogs. The corresponding canine peroneal (88.1±8.3 m/s) and tibial (89.2±12.4 m/s) NCVs were higher than the standard sciatic-tibial NCV recorded from the interosseous Myelinated nerve fiber diameters were measured on semithin transverse sections of peroneal and tibial nerve specimens taken from a clinically normal ewe and bitch. A possible explanation for the relative species difference in the proximal peroneal and tibial NCV values is the presence of fibers in both the peroneal and tibial nerves of the sheep which were as much as 3 wider than the largest fibers found in the dog.     

Electrophysiological evidence of peripheral nerve dysfunction in six dogs with botulism type C

In six dogs with botulism type C electrophysiological examinations showed: fibrillation potentials and prolonged insertional activity; low amplitude of the evoked muscle action potential; decrease in amplitude of the compound muscle action potential with slow repetitive stimulation; slowing of motor and sensory velocities in the peripheral nerve; and restoration of velocity and amplitude corresponding to clinical improvement. These findings indicate peripheral nerve dysfunction which cannot be explained adequately by current knowledge of the action of botulinum toxin on cholinergic nerve endings. It is therefore suggested that botulinum toxin also interferes with peripheral nerve conduction.     

Fascicular nerve biopsy in the dog

A nerve fascicular biopsy technique that preserves the functional integrity of the parent nerve is reported in the dog. Fascicular biopsies from ulnar and peroneal nerves did not produce clinical sensory or motor deficits. Electrodiagnostic testing for the modalities of latency, duration, amplitude, and conduction velocities were not markedly altered after fascicular biopsies. Morphometric analysis of muscle fiber types, delineated by histochemic techniques, revealed no statistical (P greater than 0.05) difference between muscles from biopsied or control limbs. Fascicular biopsies resulted in small neuromas in all dogs.     

Electrophysiologic Assessment of Acute Polyradiculoneuropathy in Dogs: Comparison with Guillain-Barré Syndrome in People

Electrophysiologic investigations of motor and sensory nerve as well as ventral nerve root function were performed on 12 dogs with suspected acute canine polyradiculoneuropathy (ACP) at different stages and with different severity of disease. The most reliable electrophysiologic indicators of ACP were electromyographic changes (occurring in 100% of affected dogs), significantly decreased compound muscle action potential amplitudes (in 75, 90, and 100% of affected dogs at all sites along the sciatic/tibial, radial, and ulnar nerves, respectively), increased minimum F-wave latencies (67%), increased F ratios (92%), and decreased F-wave amplitudes (67%). These findings suggest that ACP represents a peripheral motor axonopathy, with demyelination and axonal involvement also occurring in ventral nerve roots. Evidence of peripheral demyelination was present in some dogs although it was overshadowed by the prominent axonopathy. ACP more closely resembles the acute axonal or intermediate forms of Guillain-Barré syndrome in people.     

Conduction velocities and myelinated fiber diameter spectra of the infraorbital and palpebral nerves of the dog

Maximum conduction velocities of compound-action potentials of the infraorbital (ION) and palpebral (PN) nerves were determined by averaging potentials evoked and recorded through subcutaneous needle electrodes. The specificity of the stimulating and recording sites was verified by recording before and after cutting the nerves. Conduction times for orthodromically and antidromically conducted potentials of the ION were essentially the same. The unipolarly recorded antidromic compound-action potentials of the ION were of higher peak-to-peak amplitude and were more reliably recorded than were the bipolarly recorded orthodromic action potentials. Areas of cutaneous innervation were not found for the PN. Neuromuscular blockade eliminated the volume-conducted muscle action potentials that were recorded after PN stimulation, allowing triphasic nerve action potentials to be recorded unobscured. Mean conduction velocities were: ION = 83.9 +/- 3.5 m/s; PN = 56.4 +/- 2.8 m/s. Distributions of the external diameters of myelinated fibers within the ION and the PN were determined.     

Evaluation of repetitive nerve stimulation in young dogs

Evaluation of neuromuscular transmission requires a complete electrodiagnostic evaluation including repetitive nerve stimulation. Supra-maximal stimulation of the peroneal nerve and recording of the compound muscle action potentials from the cranial tibial muscle were under-taken in 25 young dogs of two to 18 months of age. Proximal stimulation in the trochanteric fossa and distal stimulation in the popliteal fossa were chosen for small and large breeds, respectively. Highly consistent results were obtained when the examined muscle was kept at a constant temperature and the limb was firmly fixed. Neither sex- (14 females, 11 males) nor age- related (mean = 4·4 months] differences in neuromuscular transmission were found, but frequency-dependent phenomena were observed. These became more distinct with high frequency stimulation. Pseudofacilitation (n = 16/15 Hz; n = 7/50 Hz), was found to range within certain limits (6 to 26 per cent/15 Hz; 13 to 31 per cent/50 Hz). Its mean values at 50 Hz stimulation were apparently higher (26·88 per cent) than those at 15 Hz stimulation (11·3 per cent). Decremental responses occurred mainly with application of tetanic stimulation frequency (n = 1/15 Hz; n = 12/50 Hz) and may represent blocking of neuromuscular transmission. Each of these reaction patterns usually started to occur at the fourth potential of a series (81 per cent/15 Hz; 94 per cent/50 Hz) and remained constant during the second half of the stimulation train in most cases. The occurrence of post-tetanic phenomena in healthy dogs is poorly understood. Post-tetanic potentiation observed in the present material (24 per cent) may represent pseudofacilitation following high stimulation frequency (50 Hz/100 pulses).     

Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs

Spinal-evoked potentials were recorded from 2 litters of clinically normal mixed-breed dogs between 35 and 300 days of age. Summated responses to tibial nerve stimulation were recorded from percutaneous needle electrodes placed at L7-S1, L4-5, T13-L1, C7-T1, and the cisterna cerebellomedullaris. The ulnar nerve was stimulated with recordings at C7-T1 and the cisterna cerebellomedullaris. Amplitudes did not change significantly with age, but were significantly (P less than 0.05) different between various recording sites. On day 35, segmental and overall (L7-cisterna cerebellomedullaris) conduction velocities were less than half of the adult values. Spinal cord conduction velocities increased with age, reaching adult values at approximately 9 months of age. It was determined that quadratic equations best predicted the conduction velocities during maturation.