The static sensitivity of tendon organs during recovery from nerve injury

Tremor in the human hand following peripheral nerve transection and reinnervation

Slow movements and position holding by the digits are both characterised by 8-10 Hz tremor which appears to be centrally generated. Denervation and subsequent reinnervation lead to significant alterations in peripheral connectivity and reflex organisation. We have tested the hypothesis that 8-10 Hz tremor is present in the digits of subjects following a complete nerve lesion. The frequency content of abduction and adduction movements was recorded in 12 index fingers and nine little fingers reinnervated subsequent to a complete ulnar nerve transection. An optical position laser transducer was used to measure digital movements, minimising mechanical interference to the system. Concurrently, surface electromyograms (EMG) were also recorded from first dorsal interosseus muscles (1DI) and abductor digiti minimi brevis (ADMB) muscles for index and little fingers, respectively. The maximal voluntary contraction (MVC) of the reinnervated muscles varied from 5.9% to 100% of those of the unimpaired, contralateral hands. The subjects performed abduction-adduction movements of the index and little fingers and a position holding task. Significant peaks in PSD curves of acceleration and rectified integrated EMG traces were identified. Tremor in the 8-10 Hz range was evident in both the acceleration and EMG signals for the majority of digits during both the slow movement and position holding tasks. These findings demonstrate the robust nature of these 8-10 Hz oscillations, even following the significant changes in peripheral connectivity of muscle and nerve resulting from nerve transection and reinnervation.

Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

H reflex restitution and facilitation after different types of peripheral nerve injury and repair

This study addresses the restitution of monosynaptic H reflex after nerve injuries and their role in the recovery of walking. Adult rats were submitted to sciatic crush, complete section repaired by aligned or crossed fascicular suture, or an 8-mm resection repaired by autograft or tube repair. The sciatic nerve was stimulated proximal to the injury site and the M and H waves were recorded from gastrocnemius (GCm) and plantar (PLm) muscles at monthly intervals during 3 months postoperation. Walking track tests were also carried out and the sciatic functional index (SFI) calculated to assess gait recovery. The M and H waves reappeared in all the animals at the end of the follow-up. The H/M amplitude ratio increased during the first stages of regeneration and tended to decrease to control values as muscle reinnervation progressed. However, final values of the H/M ratio for the PLm remained significantly higher in all the groups except that with a nerve crush. The walking track pattern showed an appreciable recovery only after crush injury. Final SFI values correlated positively with the M wave amplitude and negatively with the H/M ratio. In conclusion, H reflex is facilitated after peripheral nerve injury and regeneration and tends to return to normal excitability with time. Changes in the H reflex circuitry and excitability correlated positively with the deficient recovery of walking pattern after severe nerve injury.

Long-term evaluation of functional nerve recovery after reconstruction with a thin-walled biodegradable poly (DL-lactide-epsilon-caprolactone) nerve guide, using walking track analysis and electrostimulation tests

This study was performed to evaluate the long-term functional nerve recovery after reconstruction of a 10-mm gap in the sciatic nerve of the rat, with a thin-walled nerve guide, composed of a biodegradable copolymer of DL-lactide and epsilon-caprolactone [p(DLLA-epsilon-CL)]. To evaluate both motor and sensory nerve recovery, walking track analysis and electrostimulation tests were carried out after implantation periods ranging from 3 to 52 weeks postoperatively. The first signs of both motor and sensory nerve recovery could be observed after 5 weeks. After 15 weeks, 70% of the sciatic function and 90% of the sensory nerve function had been recovered. After this period, the sciatic function index (SFI) did not improve further, whereas the sensory nerve function appeared to return to normal. When the results of the SFI measurements, minus those obtained from rats with severe automutilation, are extrapolated, further improvement of the SFI might be expected after 52 weeks. The fact that 100% sensory nerve recovery was obtained, as measured by the electrostimulation test, could be explained by sensory reinnervation from surrounding areas. The SFI was not fully reestablished because automutilation had a great impact on the use of walking track assessment.

The dynamic response of feline Golgi tendon organs during recovery from nerve injury

The dynamic response of tendon organs to isometric contractions of activating motor units has been examined during recovery from nerve crush or nerve transection followed by suture repair. After nerve crush the characteristic response was rapidly restored, although the early and late phases of the dynamic response were altered differentially. Following nerve transection, recovery was much poorer and many responses were abnormal. Normal responses were only observed in a minority of tendon organ-motor unit interactions but every tendon organ studied did respond normally to at least one motor unit, with a range of dynamic sensitivities similar to normal. This suggests that the abnormalities observed reflect changes in the mechanical input to the organ, due to motor unit reorganisation, rather than abnormalities of the transduction process.