The effect of denervated muscle and Schwann cells on axon collateral sprouting

The effects of denervated muscle and Schwann cells on collateral sprouting from peripheral nerve were studied in the peroneal and tibial nerves of 48 Sprague-Dawley rats. Three groups were prepared. In group MSW (muscle-Schwann cell-window), the peroneal nerves were transected 3 mm below the sciatic bifurcation. The proximal stumps were sealed in a blocked tube to prevent regeneration and the distal stumps were implanted into denervated muscle cells that were wrapped around the ipsilateral tibial nerve, which had a window of perineurium resected. Schwann cells from the ipsilateral sural nerve were implanted into the muscle. Group MS (muscle-Schwann cell) was similar to group MSW, except that the tibial nerve perineurium was kept intact. In group MW (muscle-window), the muscle was prepared without Schwann cells and the tibial nerve perineurium was windowed. S-100 immunostain was used to identify the Schwann cells surviving 1 week after transplantation. After 16 weeks of regeneration, horseradish peroxidase tracer was used to label motor neurons and sensory neurons reinnervating the peroneal nerve. Myelinated axons of the reinnervated peroneal nerves were quantified with the Bioquant OS/2 computer system (R&M Biometrics, Nashville, TN). A mean of 169 motor neurons in group MSW, 64 in group MW, and 26 in group MS reinnervated the peroneal nerve. In the dorsal root ganglion, the mean number of labeled sensory neurons was 1,283 in group MSW, 947 in group MS, and 615 in group MW. The mean number of myelinated axons in the reinnervated peroneal nerve was 1,659 in group MSW, 359 in group MS, and 348 in group MW. Reinnervated anterolateral compartment muscles in group MSW were significantly heavier than those in group MS or MW. This study demonstrates that the transplantation of denervated muscle and Schwann cells promotes motor and sensory nerve collateral sprouting through a perineurial window.     

Isolation and characterisation of a diverse family of Arabidopsis two and three-fingered C2H2 zinc finger protein genes and cDNAs

The motor nerve transplantation (MNT) technique is used to transfer an intact nerve into a denervated muscle by harvesting a neurovascular pedicle of muscle containing motor endplates from the motor endplate zone of a donor muscle and implanting it into a denervated muscle. Thirty-six adult New Zealand White rabbits underwent reinnervation of the left long peroneal (LP) muscle (fast twitch) with a motor nerve graft from the soleus muscle (slow twitch). The right LP muscle served as a control. Reinnervation was assessed using microstimulatory single-fiber electromyography (SFEMG), alterations in muscle fiber typing and grouping, and isometric response curves. Neurofilament antibody was used for axon staining. The neurofilament studies provided direct evidence of nerve growth from the motor nerve graft into the adjacent denervated muscle. Median motor endplate jitter was 13 microsec preoperatively, and 26 microsec at 2 months, 29.5 microsec at 4 months, and 14 microsec at 6 months postoperatively (p < 0.001). Isometric tetanic tension studies showed a progressive functional recovery in the reinnervated muscle over 6 months. There was no histological evidence of aberrant reinnervation from any source outside the nerve pedicle. Isometric twitch responses and adenosine triphosphatase studies confirmed the conversion of the reinnervated LP muscle to a slow-type muscle. Acetylcholinesterase studies confirmed the presence of functioning motor endplates beneath the insertion of the motor nerve graft. It is concluded that the MNT technique achieves motor reinnervation by growth of new nerve fibers across the pedicle graft into the recipient muscle.     

Motor and sensory fibres of neck muscle nerves in the cat

The numbers and sizes of nerve fibres to the dorsal neck muscles, splenius, complexus and biventer cervicis have been examined in the cat. The total number of fibres is unusually high as is the content of sensory fibres (estimated as the loss of fibres after ganglionectomy). The fibre spectra of these sensory nerves has an unusually large number of fibres in the group II and III range (3-7 mum) and differs markedly in this way from other muscle nerves. The motor fibres contain a high proportion (64-99%) in the gamma fibre size range. Large motor fibres are absent in the nerves to biventer cervicis (a slow muscle). The ratio of unmyelinated to myelinated fibres in neck muscle nerves is similar to that in hind legs at about 2.5:1.     

Acute adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps in the pig

The objective of the present project was to investigate the efficacy and mechanism of acute (10-minute) adenosine treatment for augmentation of ischemic tolerance in muscle flaps in pigs. Varying doses of adenosine were infused into 28 latissimus dorsi muscle flaps through the axillary artery (0, 0.5, or 2.0 mg per flap) and 22 gracilis muscle flaps through the medial circumflex femoral artery (0, 10, or 20 mg per flap) over 10 minutes. Ten minutes after adenosine infusion, these muscle flaps were subjected to 4 hours of sustained warm global ischemia. In addition, one group of latissimus dorsi muscle flaps (n = 6) received a 10-minute intraarterial adenosine infusion (0.5 mg) at the beginning of reperfusion. Muscle biopsies (n = 4 or 5) for adenosine triphosphate (ATP) analysis were obtained before and after adenosine infusion and at the end of 4 hours of ischemia. The extent of muscle infarction was assessed at 48 hours of reperfusion by the tetrazolium dye staining technique. Muscle blood flow in latissimus dorsi muscle flaps was measured at the end of adenosine infusion (0 or 0.5 mg per flap, n = 8) by the radioactive microsphere (15-microns) technique. It was observed that adenosine, at all doses tested, significantly (p < 0.05) reduced the extent of muscle infarction in latissimus dorsi muscle flaps (control, 40.3 +/- 2.2 percent; 0.5 mg, 20.6 +/- 1.6 percent; 2.0 mg, 18.2 +/- 1 percent) and gracilis muscle flaps (control, 31.0 +/- 1.5 percent; 10 mg, 14.3 +/- 3 percent; 20 mg, 11.6 +/- 1.2 percent). Preischemic adenosine treatment (0.5 mg per flap) was associated with maintenance of a significantly (p < 0.05) higher muscle content of ATP in latissimus dorsi muscle flaps at the end of 4 hours of ischemia compared with saline-treated ischemic controls. Postischemic adenosine treatment did not protect latissimus dorsi muscle flaps against infarction. Furthermore, adenosine treatment did not have any significant effect on mean systemic arterial blood pressure or muscle blood flow in latissimus dorsi muscle flaps. It is concluded that acute (10-minute) preischemic adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps and that this protective effect of adenosine may be, at least in part, the result of slowing muscle ATP depletion during sustained ischemia. The possible mechanisms of this adenosine-induced energysparing effect are discussed.     

Skeletal muscle regeneration during aging and after long-term denervation

Data accumulated in recent years strongly suggest that the basis for at least part of the muscle atrophy seen in old age is related to the diminution of motor innervation in normal muscle and a decreased effectiveness of reinnervation of regenerating muscle fibers. Thus, attempts to stabilize reverse the decline of the skeletal musculature during aging must take into account both the effects of aging on the peripheral nervous system and the presence of populations of denervated muscle fibers in the aging muscles. Of considerable importance is the question of how long muscle fibers in old animals can remain denervated before they begin to lose their capacity for restoration if they ultimately become reinnervated. The experimental studies reviewed here have shown that normal muscles in old animals are capable of a high degree of restoration as long as their motor nerve supply remains undamaged. After a certain period of time, denervated muscle in young animals steadily loses the capacity to restore or repair itself. To date, so little information is available on the properties of denervated muscle in old animals that meaningful comparisons cannot be made. Ultimately, ensuring that normal or injured muscle in old individuals is supplied by an effective motor innervation may be a real key to the problems of muscle loss in old age, but if such could be provided, it will be important that the old musculature, whether normal or injured, is capable of adequately responding to the innervation.     

Neurophysiological assessment of children with obstetric brachial plexus palsy]

INTRODUCTION: The objectives of the neurophysiological evaluation of infants with brachial plexus palsy are to determine the time of occurrence of the lesion, to locate the lesion and to determine its course. METHODS AND CONCLUSIONS: These objectives are achieved by studying affected upper extremity muscles by needle electromiography (EMG) and affected nerves by motor and sensory conduction studies. EMG is performed in the first week of life in those patients with brachial plexus palsy of unknown etiology to determine the age of the lesion for medico-legal reasons. EMG is performed before surgery for tendon transfer in the selected muscles to assure that they are normal. EMG and motor and sensory conduction studies are performed at the age of 3 and 6 months in infants with less than 4 muscle weakness to determine candidates for surgical exploration. Motor and sensory nerve conduction studies are performed intraoperative to determine the functional status of the affected axons and the best surgical procedure (neurotization, neurolysis and/or neuroma resection and homologous nerve graft).     

Use of ultrasonography to evaluate muscle thickness and blood flow in free flaps

The purpose of this study was to investigate the common belief that a microvascular transfer of a non-innervated free muscle flap loses muscle bulk over time. Sixteen patients (latissimus dorsi = 8, rectus abdominis = 7, and gracilis muscle = 1) were evaluated an average of 41 months after free flap transfer. Latissimus dorsi and lower extremity flaps displayed significantly more swelling than the other flaps. Flap bulk was measured by ultrasound. The mean thickness of upper extremity flaps was 10.3 +/- 1.8 mm (control muscles 11.8 +/- 2.8), lower-extremity 14.5 +/- 3.7 mm (control muscles 10.9 +/- 0.7), latissimus dorsi 14.3 +/- 2.2 mm (control muscles 10.3 +/- 0.8, P = 0.018), and rectus abdominis 11.2 +/- 1.2 mm (control muscles 12.4 +/- 1.9). Color Doppler ultrasonography was used to detect the pedicles of the free flaps and also to measure the peak velocity of blood flow intramuscularly and in the pedicles. In the upper extremities (n = 5) the pedicles could be found in only 20% of cases whereas in the lower extremities (n = 11) 91% of pedicles were located. (P = 0.013). Peak flow within the free flaps was significantly higher in the lower extremity (50% of the peak flow of the common femoral artery) than in the upper extremity (5% of the peak flow of the common femoral artery, P = 0.013). This study demonstrated that non-innervated free muscle flaps in the extremities maintain the original muscle thickness, although lower extremity and latissimus dorsi flaps have a trend to be thicker. Most pedicles of free muscle flaps in the upper extremities could not be located by ultrasound. However, flaps in the lower extremities most often have patent pedicles and also more vigorous intramuscular blood flow.     

End-to-side neurorrhaphy with removal of the epineurial sheath: an experimental study in rats

Terminolateral neurorrhaphies were used up to the beginning of this century. After that, they were no longer reported. We tested the efficacy of a new type of end-to-side neurorrhaphy. A group of 20 rats had the peroneal nerve sectioned, and the distal ending was sutured to the lateral face of the tibial nerve after removing a small epineural window. All experiments were made on the right side, the left one remaining untouched in half the animals of each group. The other half was denervated by sectioning and inverting the endings of the peroneal nerves. In this way, tibial cranial muscles were either normal or denervated on the left side and reinnervated through end-to-side neurorrhaphies on the right side. After 7.8 months, the animals were subjected to electrophysiologic tests, sacrificed, and the nerves and muscles were taken for histologic examination. A response of the tibial cranial muscle was obtained in 90 percent of the animals. The distal ending of the peroneal nerve showed an average of 861 nerve fibers. The average areas of the reinnervated tibial cranial muscles were (microns 2) 1617.81 for M2n (when the contralateral side was normal) and 1579.19 for M2d (when the contralateral was denervated). We conclude that the terminolateral neurorrhaphy is functional, conducting electrical stimuli and allowing the passage of axons from the lateral surface of a healthy nerve, to reconstitute the distal segment of a sectioned nerve. The absence of an incision on the axons of the donor nerve was no impediment to axonal regeneration or to the passage of electrical stimuli. The results demonstrate the possibility of using end-to-side and terminolateral neurorrhaphies for reconstituting neural lesions when only a distal end is available; the reinnervation can be obtained from the lateral face of a healthy nerve.     

Lower extremity muscle activation during horizontal and uphill running

To provide more comprehensive information on the extent and pattern of muscle activation during running, we determined lower extremity muscle activation by using exercise-induced contrast shifts in magnetic resonance (MR) images during horizontal and uphill high-intensity (115% of peak oxygen uptake) running to exhaustion (2.0-3.9 min) in 12 young women. The mean percentage of muscle volume activated in the right lower extremity was significantly (P <0.05) greater during uphill (73 +/- 7%) than during horizontal (67 +/- 8%) running. The percentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphill running. During horizontal running, the muscles or groups most activated were the adductors (90 +/- 5%), semitendinosus (86 +/- 13%), gracilis (76 +/- 20%), biceps femoris (76 +/- 12%), and semimembranosus (75 +/- 12%). During uphill running, the muscles most activated were the adductors (83 +/- 8%), biceps femoris (79 +/- 7%), gluteal group (79 +/- 11%), gastrocnemius (76 +/- 15%), and vastus group (75 +/- 13%). Compared with horizontal running, uphill running required considerably greater activation of the vastus group (23%) and soleus (14%) and less activation of the rectus femoris (29%), gracilis (18%), and semitendinosus (17%). We conclude that during high-intensity horizontal and uphill running to exhaustion, lasting 2-3 min, muscles of the lower extremity are not maximally activated, suggesting there is a limit to the extent to which additional muscle mass recruitment can be utilized to meet the demand for force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.     

Neurotrophin-3-enhanced nerve regeneration selectively improves recovery of muscle fibers expressing myosin heavy chains 2b

The purpose of this study was to evaluate the effect of neurotrophin 3 (NT-3) enhanced nerve regeneration on the reinnervation of a target muscle. Muscle fibers can be classified according to their mechanical properties and myosin heavy chain (MHC) isoform composition. MHC1 containing slow-type and MHC2a or 2b fast-type fibers are normally distributed in a mosaic pattern, their phenotype dictated by motor innervation. After denervation, all fibers switch to fast-type MHC2b expression and also undergo atrophy resulting in loss of muscle mass. After regeneration, discrimination between fast and slow fibers returns, but the distribution and fiber size change according to the level of reinnervation. In this study, rat gastrocnemius muscles (ipsilateral and contralateral to the side of nerve injury) were collected up to 8 mo after nerve repair, with or without local delivery of NT-3. The phenotype changes of MHC1, 2a, and 2b were analyzed by immunohistochemistry, and fiber type proportion, diameter, and grouping were assessed by computerized image analysis. At 8 mo, the local delivery of NT-3 resulted in significant improvement in gastrocnemius muscle weight compared with controls (NT-3 group 47%, controls 39% weight of contralateral normal muscle; P < 0.05). NT-3 delivery resulted in a significant increase in the proportion (NT-3 43.3%, controls 35.7%; P < 0.05) and diameter (NT-3 87.8 micron, controls 70.8 micron; P < 0.05) of fast type 2b fibers after reinnervation. This effect was specific to type 2b fibers; no normalization was seen in other fiber types. This study indicates that NT-3-enhanced axonal regeneration has a beneficial effect on the motor target organ. Also, NT-3 may be specifically affecting a subset of motoneurons that determine type 2b muscle fiber phenotype. As NT-3 was topically applied to cut nerves, our data suggest a discriminating effect of the neurotrophin on neuro-muscular interaction. These results would imply that muscle fibers may be differentially responsive to other neurotrophic factors and indicate the potential clinical role of NT-3 in the prevention of muscle atrophy after nerve injury.     

Recovery of muscle after different periods of denervation and treatments

Three aspects of reinnervation and recovery of skeletal muscle following various periods of denervation were investigated: (1) the effect of duration of denervation; (2) the effect of hyperthyroidism on recovery; and (3) whether the muscle or the nerve limits recovery. The rat medial gastrocnemius (MG) nerve was cut and then resutured after 0, 3, 7, 21, or 56 days. In a second group of animals, the MG muscle was denervated and, in addition, the animal received triiodothyronine (T3) supplementation during reinnervation. The third group of animals had the denervated MG muscle reinnervated by a larger number of newly transected foreign axons. The force produced by the reinnervated muscle depends on the period that the muscle was denervated. Recovery was impaired when the period of denervation exceeded 7 days. T3 treatment did not benefit the return of force production, nor did providing the muscle with a larger number of newly transected axons.     

Functioning muscle transplantation after wide excision of sarcomas in the extremity

Free functioning muscle transplantation was performed after resection of 23 sarcomas in the extremity. There were 21 soft tissue sarcomas and two malignant bone tumors. The tumor resection was performed with a wide margin in all except two patients who had a marginal margin in a limited area. The consequent extensive soft tissue defect received free musculocutaneous flaps, the motor nerve of which was repaired in the recipient site. The most frequent procedure was latissimus dorsi transplantation to replace thigh muscles in 17 cases. The other donors included gracilis, tensor fascia lata, and rectus femoris, which were selected according to the site of defects. Patients were followed up for a mean of 60 months (range, 13-119 months). The grafted muscles showed reinnervation at a mean of 6 months postoperatively in all patients except for a 75-year-old patient. Obtained contraction of the muscles was powerful in 18 patients and fair in four patients. Performance of the salvaged limb significantly improved after recovery of the muscles. Although there were five distant recurrences, local recurrence was seen in one patient with systemic metastases. Because muscle loss could be compensated functionally for by the innervated free muscle transfer, the method encouraged surgeons to perform more radical tumor excisions and this may have contributed to the excellent local tumor control that was achieved. Thus, functioning muscle transplantation was extremely useful in limb salvage surgery from the functional and oncologic viewpoints.     

Use of a rapid intraoperative parathyroid hormone assay in the surgical management of parathyroid disease

We present recent developments in the area of glycosaminoglycans (GAGs) and their possible interaction with insulin-like growth factor-I (IGF-I). GAGs are constituents of proteoglycans, and the combination of a core protein and a specific GAG makes a unique proteoglycan with a precise developmental pattern and with the ability to bind growth factors. This process is apparently regulated by the moiety of the peripheral GAGs. The supplementation of GAGs promotes neuritogenesis in vitro and stimulates nerve regrowth and muscle reinnervation, an effect correlated with an increase in trophic factor mRNA expression. In the case of neonatal nerve lesion, there is in addition an enhanced motor neuron survival, accompanied by higher levels of IGF-I in plasma and denervated muscle. The neurotrophic and neuroregenerative effects of exogenous GAGs were also observed in motor neuron disease in the wobbler mouse.     

Neurotrophic regulation of insulin-sensitive amino acid uptake in rat fast muscle

Our object was to determine how innervation regulates muscle insulin sensitivity. Insulin-stimulated uptake of the nonmetabolized amino acid, 2-amino-isobutyric acid, was used as a measure of insulin sensitivity in denervated rat extensor digitorum longus muscles retaining either a similar 2.5-cm ("proximal denervation') or a similar to 0.5-cm ("distal denervation') length of distal nerve stump. Because both muscles were inactive in the first 24 h, any difference in insulin sensitivity could be due only to some trophic influence of the distal nerve stump. Fifteen hours after either type of denervation, 2-aminoisobutyric acid uptake was refractory to insulin. However, at 24 h, insulin sensitivity of distally denervated muscles (with or without a second ipsilateral proximal denervation) was normal, whereas that of proximally denervated muscles was still relatively insensitive. In the absence of insulin, the two types of denervated muscles at 24 h showed no difference in 2-aminoisobutyric acid uptake. Finally, organ culture of paired muscles with or without long nerve stumps showed corresponding differences in insulin-stimulated 2-aminoisobutyric acid uptake after 48 h in vitro. Thus, a neurotrophic factor, independent of impulse activity, stretch, or changes in blood flow, regulates one type of muscle insulin sensitivity.     

Neonatal de-afferentation of capsaicin-sensitive sensory nerves increases in vivo insulin sensitivity in conscious adult rats

Sensory neuropeptides, released from the peripheral nervous system, might modulate glucose homeostasis by antagonizing insulin action. The effects of de-afferentation of functional small diameter unmyelinated C-fibres (sensory nerves) on in vivo insulin-mediated intracellular glucose metabolism were investigated by using euglycaemic insulin (6 and 18 mU/kg x min) clamps with [3-(3)H]-glucose infusion in 24 adult rats, treated neonatally with either capsaicin (CAP) (50 mg/kg) or vehicle (CON). Following the clamp, skeletal muscle groups, liver and adipose tissue were freeze-clamped. At plasma insulin levels of approximately 90 mU/l, CAP-rats showed a 21% increase in whole body glucose uptake compared with CON (24.4 +/- 1.6 vs 20.1 +/- 0.8 mg/kg min, p < 0.02), which was paralleled by a 20% increase in whole body glycolysis (12.6 +/- 0.8 vs 10.5 +/- 0.5 mg/ kg.min p < 0.05) (concentration of 3H2O in plasma). Whole body skeletal muscle glycogenesis was increased by 80% in CAP-rats (5.7 +/- 0.7 vs 3.1 +/- 0.7 mg/kg x min, p < 0.05) with increased muscle glycogen synthase activity. Whole body (muscle, liver and adipose tissue combined) de novo lipogenesis also was increased in CAP-rats compared with CON (0.69 +/- 0.10 vs 0.44 +/- 0.06 mg/kg x min, p < 0.05) (incorporation of [3-(3)H]-glucose counts into glycogen or fat). Hepatic glucose production was lower in CAP-rats compared with CON (0.6 +/- 0.6 vs 2.1 +/- 0.7 mg/kg x min, p < 0.05). Plasma glucagon, corticosterone, epinephrine and norepinephrine levels were reduced in CAP-rats: 43 +/- 2 compared with 70 +/- 6 pg/ml, 855 +/- 55 compared with 1131 +/- 138 nmol/l, 513 +/- 136 compared with 1048 +/- 164 pmol/l and 928 +/- 142 compared with 1472 +/- 331 pmol/l, respectively, p < 0.05. At plasma insulin levels of approximately 400 mU/l, CAP-rats showed no differences in peripheral and hepatic insulin action compared with CON. We conclude that the removal of endogenous sensory neuropeptides, by de-afferentation of capsaicin-sensitive sensory nerves, increases in vivo insulin sensitivity, but not responsiveness: 1) primarily through an increased sensitivity of skeletal muscle glycogen synthesis to insulin; 2) through a reduction in the levels of counter-regulatory hormones, thereby creating a milieu which favours overall in vivo insulin sensitivity with respect to glucose uptake, glucose production, glycolysis, glycogenesis and lipogenesis.     

The effect of putative insulin-like substances released by the motor nerve on glucose transport in perfused rat muscle

Motor nerves have been claimed to contain and release immunoreactive insulin. We studied whether release of insulin or other non-acetylcholine substances is important for (1) the increase in glucose transport normally seen during motor nerve activated contraction, and (2) the increase in insulin sensitivity induced by contractions. Ad 1:Rat hindquarters were perfused and one sciatic nerve was stimulated during motor nerve end plate blockade (Pancuronium bromide, 33 micrograms ml-1). Muscle glucose transport (3-O-[14C]-methylglucose (3-O-MG) uptake, 3 mM) was identical (P > 0.05) in stimulated compared with nonstimulated white gastrocnemius, red gastrocnemius and soleus muscle. This was also true when, prior to end plate blockade, muscles had been stimulated to contract to increase insulin sensitivity. No immunoreactive insulin was found in venous perfusate. Ad 2: Rats had both sciatic nerves cut. One week later hindquarters were perfused and calf muscles of one leg were directly stimulated to contract. Subsequently, 3-O-MG uptake in muscle was determined with and without submaximal insulin (100 microU ml-1). In contrast to previous findings in innervated muscle, responses to insulin were identical (P > 0.05) with and without prior contractions. Conclusions: The increase in muscle glucose transport normally seen in response to motor nerve stimulation is related to the contraction process and not even partly mediated by release of insulin-like substances from the nerve. In contrast, release of a non-acetylcholine substance from the motor nerve may be involved in the exercise induced increase in insulin sensitivity.     

Peripheral nerve repair in the hand with and without motor sensory differentiation

To investigate the value of motor sensory differentiated nerve repair, we examined a group of 9 patients with motor sensory differentiated nerve repair and a group of 13 patients without motor sensory differentiated nerve repair. The clinical and electroneurographic findings were compared. For the clinical examination, Millesi's scoring system was used. The hand function after motor sensory differentiated median nerve repair was 72% +/- 16% compared with 57% +/- 14% without motor sensory differentiation. The hand function after motor sensory differentiated median and ulnar nerve repair was 53% +/- 12% compared with 43% +/- 24% without motor sensory differentiation. After ulnar nerve repair the achieved values for hand function were high even without motor sensory differentiation. Our results indicate that intraoperative motor sensory differentiation of injured nerves is helpful to reestablish particularly the sensory function in median nerve injuries.     

Motor versus sensory neuron regeneration through collagen tubules

Differences in regeneration of sensory and motor nerves were studied in rats to determine the effects of entubulation with collagen conduits. The rat sciatic nerve was repaired either with a 10-mm saline-filled gap or with a no-gap end-to-end repair cuffed within collagen tubules. These repairs were compared with the standard epineurial repairs. The populations of regenerated motor and sensory neurons in the peroneal nerves of all repairs were compared against the populations of normal peroneal neurons using horseradish peroxidase retrograde labeling. The epineurial repair resulted in regeneration of 65 percent (409 +/- 150) of motor neurons and 79 percent (2127 +/- 516) of sensory neurons (n = 6). The no-gap end-to-end repair in a collagen tubule resulted in regeneration of 53 percent (338 +/- 203) of motor and 70 percent (1893 +/- 794) of sensory neurons (n = 7). In the 10-mm gap repair, only 6.2 percent (39 +/- 18) of motor neurons but 63 percent (1710 +/- 557) of sensory neurons regenerated (n = 5). These results show that collagen entubulation supports nerve regeneration in end-to-end nerve repairs comparably to standard epineurial suture repairs. With the 10-mm gap repairs in collagen tubules, sensory neurons regenerated consistently better than motor neurons in the same environment. Therefore, intrinsic differences exist between motor and sensory neuron regeneration in the same nerve.     

Femoral nerve transfer for treatment of brachial plexus root avulsion

Femoral nerve transfer to the muscular branches of the thenar and hypothenar muscles was performed to determine its protective effect on the hand intrinsic muscles. Seven cases of brachial plexus root avulsion treated from May of 1989 to October of 1991 were involved. The femoral nerve transfer to the muscular branches of the thenar and hypothenar muscles was done at the same stage of multiple neurotization. The muscular branches derived from the femoral nerve were isolated and coapted with the thenar muscle branch of the median nerve and the deep branch of the ulnar nerve. A groin flap was harvested simultaneously to form a skin-tube pedicle that covered the nerve bridge. At the second stage, when regeneration of the median and ulnar nerves was found to reach as far as the level of the wrist, the femoral nerve was divided and the muscular branches of the thenar and hypothenar muscles were anastomosed with the regenerated median and ulnar nerves. All the cases were followed up for more than 6 years. Six months after femoral nerve transfer, muscle power of the interosseous muscles and adductor pollicis recovered to MRC3, whereas that of the abductor pollicis brevis recovered to MRC1 to 2. Five cases underwent second-stage transfer. Four to five years of follow-up revealed that the muscle power of the interosseous muscles and adductor pollicis was MRC2 in one case, MRC1 in three cases, and MRC0 in one case. As for the donor area, muscle power of the quadriceps femoris reduced to M3 to 4 within 1 month after femoral nerve transfer and recovered to normal at 3 months. In conclusion, femoral nerve transfer to the muscular branches of the thenar and hypothenar muscles has some protective effect on the hand intrinsic muscles. The outcome of the second stage, however, is not satisfactory.     

Reinnervation of motor endplates and increased muscle fiber size after human insulin-like growth factor I gene transfer into the paralyzed larynx

Current surgical strategies for the treatment of laryngeal paralysis are limited by the muscle atrophy associated with denervation. Moreover, attempts at reinnervation have not effected significant change in surgical outcome. To address this clinical problem, we have developed a rat laryngeal paralysis model to study novel gene transfer strategies. Using this model, the human insulin-like growth factor I (hIGF-I) gene was introduced into paralyzed rat laryngeal muscle to assess the benefit of sustained local hIGF-I production. A muscle-specific nonviral vector containing the alpha-actin promoter and hIGF-I gene was used in formulation with a polyvinyl-based delivery system and injected into paralyzed adult rat laryngeal muscle. Twenty-eight days after a single injection, gene transfer efficiency, muscle fiber size, motor endplate length, and nerve-to-motor endplate contact were evaluated. Gene transfer was detected in 100% of injected animals by PCR. Gene transfer with expression, as measured by RT-PCR for hIGF-I mRNA, occurred in 81.3 % of injected animals. When compared with controls, hIGF-I-transfected animals presented a significant increase in muscle fiber diameter [17.56 (+/-0.97 SD) microm versus 14.70 (+/-1.43 SD) microm; p = 0.0002], a significant decrease in motor endplate length [20.88 (+/-1.42 SD) microm versus 25.41 (+/-3.19 SD) microm; p = 0.0025], and a significant increase in percentage of endplates with nerve contact (20.3% (+/-13.9 SD) versus 4.4% (+/-4.2 SD); p = 0.0079). In the context of laryngeal paralysis, gene therapy represents a tremendous opportunity to augment current surgical treatment modalities by preventing or reversing muscle atrophy, and by enhancing nerve sprouting and reinnervation.