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1. The effect of temperature (20-37.5 degrees C) on the potentiation of twitch tension was examined during and after the staircase (250 stimuli, 5/sec) and after the tetanus (188 stimuli, 125/sec) in the extensor digitorum longus muscle of adult Lewis rats.2. During the staircase at 20 degrees C the twitch tension decreased (negative staircase) by 10-20%. At 25-30 degrees C the staircase was initially negative and later positive. At 37.5 degrees C the staircase was positive throughout the train. Both at the end of the staircase and 2 sec after the tetanus the potentiation increased linearly with increasing temperature.3. After the staircase and the tetanus at 20-30 degrees C the twitch tension increased initially rapidly and later after the staircase at a slower rate. Maximal potentiation at 20 degrees C was attained 3 min after the staircase (+ 30 +/- 3%, n = 10, s.e. of mean) and 1 min after the tetanus (+ 16 +/- 1%, n = 10, s.e. of mean). At 37.5 degrees C the potentiation decayed rapidly after the staircase and the tetanus.4. During the staircase the time course of the twitch was shortened twice as much at 20 as at 37.5 degrees C. At the end of the staircase and 2 sec after the tetanus the contraction time was the more prolonged the greater the potentiation. At maximal potentiation the contraction time was prolonged three times as much at 20 degrees C (+ 19 +/- 3%, n = 10, s.e. of mean) as at 37.5 degrees C (P < 0.005). The half-relaxation time at the end of the staircase was prolonged 10 times more at 20 than at 37.5 degrees C (P < 0.02).5. When extrapolated to time zero after the staircase and the tetanus the potentiation at 20 degrees C was still marked (20-50%). The rate of decay of potentiation (time constant, 20 degrees C, 561.2 +/- 37.4 sec, n = 20, s.e. of mean) increased with increasing temperature (Q(10) = 2.6). The event of potentiation with a fast rate of decay, present after the tetanus but not after the staircase at 37.5 degrees C, was abolished below 30 degrees C.6. The increase in twitch tension after the staircase and the tetanus at 20-30 degrees C was taken to indicate the recovery of events that diminished the twitch, occurring simultaneously with potentiation.7. (i) One process of diminution, present after the staircase but not after the tetanus, increased on cooling and was assumed to be due to fatigue. The rate of recovery of the process (time constant, 20 degrees C, 79.6 +/- 7.4 sec, n = 10, s.e. of mean) increased with increasing temperature (Q(10) = 1.9). The half-relaxation time of the last twitch in the staircase was the more prolonged the greater the process. (ii) Another process causing diminution was present after the staircase and the tetanus at 20-30 degrees C. It recovered at 20 degrees C with a time constant of 14.9 +/- 2.2 sec (n = 10, s.e. of mean). This process, possibly responsible for the initially negative staircase, was not thought to be due to fatigue. It may reflect a diminished depolarization of the transverse tubules by repetitive stimuli.

The compound muscle action potential and isometric twitch tension evoked by single and repetitive electrical stimuli are indicators of the number of motor units activated and of the contractile properties of the muscle. The action potentials and mechanical responses were recorded in proximal and distal muscles in patients with myasthenia gravis and myopathy and compared with findings in normal subjects. In normal muscle, at low rates of stimulation (2-3 s-1) the decrement was at most 5% in the action potential and 15-24% in the twitch tension. Tetanic stimuli (50 s-1) were unsuitable for diagnostic purposes because of movement artefact. In patients with myasthenia gravis, the incidence and size of the decrement of evoked responses were greater in the platysma than in the elbow flexors and the adductor pollicis (ADP) muscles. The 2-3 times greater post-tetanic facilitation (PTF) of the action potential in the platysma than in extremity muscles also indicates a more severe functional block in facial muscle. The PTF is an indicator of recruitment of blocked fibres. The maximal decrement was grossly related to the titre of antibodies against the acetylcholine receptor. To reveal failure of neuromuscular transmission in patients with myasthenia gravis without a decrement, a small dose of d-tubocurarine (0.2 mg in 30 ml of saline) was injected i.v. in the upper arm in a regional curare test. The sensitivity was greater in patients with myasthenia gravis than in controls and in patients with myopathy. Potentiation of twitch tension reflects contractile properties. In normal muscle twitch potentiation in the staircase (1-3 s-1, 100 s in duration) and after tetanus (50 s-1, 1.5 s in duration) was 2-3 times greater in the platysma than in the elbow flexors and ADP, presumably related to the greater proportion of fast-twitch fibers in facial muscle. The amplitude of the action potential and the twitch tension varied proportionally with the number of fibers activated and the difference in the decrements of the action potential and the twitch during the staircase in some patients with myasthenia gravis showed that the staircase phenomenon was diminished suggesting abnormalities in the excitation-contraction coupling. The diminution of the staircase and post-tetanic potentiation (PTP) in myopathy also indicates impairment of the excitation-contraction coupling. In rats with severe chronic myasthenia gravis, the staircase and PTP were decreased even when the failing neuromuscular transmission was circumvented by applying direct stimuli to the extensor digitorum longus muscle (EDL).

Eleven thymectomized and ten non-thymectomized patients with myasthenia gravis, matched with respect to sex, age, duration and severity of the disease were investigated with respect to routine clinical features, electrophysiological examination, HLA-typing, auto-antibodies, lymphocyte subpopulations in peripheral blood, Concanavalin A-induced release of leucocyte migration inhibitory factor (LIF), in vitro lymphocyte activation by mitogens and antigens and response to primary immunization with dinitrochlorobenzene measured in vivo and in vitro. The following conclusions could be drawn. The immune response to external antigens seems to be normal in myasthenia gravis and thymectomy is not followed by general defects in immune competence; at least as investigated by current techniques. The only reduction of responsiveness demonstrable in the thymectomized group was a decreased release of LIF by Concanavalin A-stimulated lymphocytes. Primary immune responses appear to be increased after adult thymectomy, which may be due to a decrease in suppressor T-lymphocyte activity. A hypothesis is formulated that Concanavalin A-induced release of LIF may reflect the competence of suppressor T-lymphocytes in man.

Electrical and mechanical responses of the elbow flexors (EFs) and the adductor pollicis muscle (ADP) were evoked in 31 patients with myasthenia gravis (MG). Thirteen patients with moderate or severe involvement showed a decrement during trains of repetitive stimuli in both muscle types, greater in the proximal ones than in the distal one. Seven of 18 patients with mild generalized or ocular MG showed abnormalities in the EFs, and 4 patients showed abnormalities in the ADP. A regional curare test was performed in the EFs of 11 patients with borderline or no abnormalities in the EFs and the ADP. All patients were more sensitive to curare than were control subjects; in 2, a decrement outside the range of controls could only be provoked in the partly curarized muscle during posttetanic exhaustion. Excitation-contraction coupling, as evidenced by the staircase phenomenon and after correction for blackade of fibers, was abnormal in 5 of 31 patients in the EFs, and in 11 patients in the ADP. In both muscles, the action potential was a more sensitive criterion of abnormality than the mechanical response. The decrement in the action potentials during 3/sec stimuli gave the largest diagnostic yield.

Silicone rubber cuff and patch electrodes with multiple contacts were implanted along the sciatic-tibial-plantar nerves in cat for repeated studies of conduction properties of normal peripheral nerve over periods of time. The contacts were used in various combinations for precise localization of changes in conduction velocities and excitability along the extent of normal nerves. In this paper the particular characteristics and limitations associated with cuff-electrode recordings of neural activity are discussed. The nerve action potential was recorded using a tripolar configuration with a central lead flanked by two shunted leads at symmetrical distances. This configuration records the spatial derivative of the action potential and rejects potentials from sources outside the cuff. The voltage changes are restricted by the silicone cuff, and the dynamic range is therefore very high, allowing detection from single myelinated fibers to whole nerve responses. The electrodes are well suited for following the development of regeneration and degeneration following experimental lesions.

Occult lesions of the spine in children are a rare but recognizable cause of neurogenic dysfunction involving the lower extremities, and lower urinary and gastrointestinal tracts. We report the preoperative and postoperative urodynamic findings in 40 children with varying spinal abnormalities. Of these patients 28 were neonates or infants (average age 8.7 months) and 12 were older children (average age 11.7 years). Preoperative urodynamic testing revealed normal function in 18 of 28 children (64 per cent) in the younger age group in contrast to 1 of 12 (8 per cent) in the older age group. Of the 10 infants with abnormal studies postoperative urodynamic findings returned to normal in 6, while 2 others remained abnormal but were improved. In contrast, of 11 older children with abnormal preoperative evaluations 3 (27 per cent) reverted to normal postoperatively. The neurourological changes seen in these occult lesions are variable, may occur at any age, are progressive and are potentially reversible by surgical correction but this reversibility diminishes with age.

Arrays of chronically implanted electrodes were used to examine the time course of elongation and maturation of peripheral nerve fibers in the cat after crush of the tibial nerve in the proximal calf. Regeneration after crush alone was compared with crush 5 mm proximal to a tight constriction of the nerve. Regeneration was monitored by the progression of excitability along the electrode arrays on the tibial and plantar nerves. The sensitivity was sufficient to record the averaged activity in single nerve fibers allowing detection of the earliest regeneration. The diameters of the fastest regenerating fibers were estimated from the conduction velocity proximal to the site of crush. Both after crush alone, and after crush constriction, small myelinated fibers regenerated in front of large fibers. The rate of elongation after crush alone was 3.2 mm/day, whereas it was slower (P less than 0.02) distal to crush + constriction (2.2 mm/day). In both lesions, the extrapolated delay to onset of regeneration was 8 days. In observations up to 300 days after crush, maturation was delayed or impaired by the constriction, and the compound nerve action potential had a smaller amplitude and a dispersed shape. Transverse sections of nerves after crush + constriction showed a diminished number of large and an increased number of small fibers compared with crush alone, possibly due to persistent branching of regenerated fibers. After both crush alone and crush + constriction, regenerated fibers had similar g ratios, suggesting that myelination developed fully in fibers of diminished diameters.

Seventy-nine newborns with myelodysplasia were followed up for 1 1/2 to six years with serial roentgenographic, neurologic, and urodynamic evaluations. Twenty-nine infants (37%) demonstrated changes in external urethral sphincter innervation during the first three years of life. Of the group who changed, 896% (25/29 infants) did so in the first year, 10% (3/29 infants) in the second year, and 4% (1/29 infants) in the third. The risk factor for change was 32%, 6%, and 2%, respectively, during each of these three years. Fifteen infants (19% of the total) experienced neurourologic deterioration while 14 infants (18%) improved. Seven newborns underwent a second neurosurgical procedure resulting in improvement in four, stabilization in two, and further deterioration in one. These findings underline the importance of early and continued neurologic and urologic surveillance in children with myelodysplasia because it is a dynamic disease process.

A 24-year-old male with idiopathic acute aching of the right wrist, weakness of ulnar innervated muscles of the forearm and hand, and numbness of the ulnar two digits, was examined electrophysiologically. Conduction studies showed almost complete conduction block of motor fibers of the ulnar nerve distally in the brachial plexus. Sensory fibers were less affected. The symptoms and pathophysiological findings improved over a period of 1-2 months and were normal at the final study performed 7 months after presentation. There was mild evidence of chronic partial denervation of the abductor digiti V and the flexor digitorum profundus of the two ulnar digits. There were additional mild EMG changes of the abductor pollicis muscle indicating minor involvement of the median nerve. There was no traumatic or other obvious cause for these findings. It is suggested that the patient had a mild and abortive form of brachial plexus neuropathy presenting as a demyelinating lesion rather than the more typical wallerian degeneration seen in most established cases.

In chronic experimental myasthenia gravis (EAMG) in rat, the decrement of electrical and mechanical responses evoked by maximal repetitive (3-167/sec) stimuli to the nerve was greater in the slow-twitch soleus (SOL) than in the fast-twitch extensor digitorum longus (EDL) muscle. Excitation-contraction coupling was impaired in moderate to severe EAMG, as evidenced by a diminished staircase phenomenon and by diminished posttetanic potentiation (PTP) of twitch tension in two EDLs. The only morphologic abnormality observed was an increase in length of the endplates in the EDLs of those animals that had had an acute phase of EAMG. The latter had more than a 90% reduction in the amplitude of the action potential and in the twitch tension of the EDL when stimuli were applied to the nerve. Stimuli applied directly to the muscle evoked a tetanic tension that was one-third of normal. The staircase and PTP were normal. Necrosis occurred in the endplate and in the adjacent segment of muscle fiber; outside the endplate region, the muscle fiber was normal.

Electrical and mechanical responses were evoked in the elbow flexors (EFs) of normal subjects and myopathy patients by maximal stimulation of the musculocutaneous nerve by a wire electrode in the axilla. In normals, the decrement in the mechanical responses during short trains of twitches was small (10%). The potentiation during a staircase decreased with increasing frequency of stimuli, but the potentiation 30 sec after the 100-sec staircase was the same at all frequencies. Posttetanic potentiation was twice as large as the maximal potentiation attained during the staircase. The staircase phenomenon probably results from two opposing events, diminution and potentiation. Findings in 11 patients with myopathy varied according to the severity of involvement. Slight weakness of the EFs was associated with an increased twitch:tetanus ratio, decreased tetanic tension, and decrease in the staircase and posttetanic potentiation. Additionally, severe weakness of the EFs was associated with a diminution in twitch tension.

A 31-year-old male developed paresthesia and numbness of mainly the right foot following exposure to nonfreezing temperatures under moist conditions over a period of 1 week. The symptoms gradually improved over several months. When seen for electrophysiological studies 6 months after the injury, there was no sensory loss on clinical examination, although he continued to complain of distal numbness of the right foot. The right extensor digitorum brevis muscle was atrophic, and the distal motor latency in the peroneal nerve was prolonged. Conduction studies of the right sural nerve showed a predominantly distal diminution of the SAP evoked by electrical stimulation at the dorsum pedis. Action potentials evoked by tactile stimulation of Pacinian corpuscles showed a prolonged latency on the symptomatic side, suggesting that the most pronounced pathological changes in immersion injury may be localized to the very distal portion of the nerve at the nerve fiber-receptor junction.