Cold preservation of nerve grafts decreases expression of ICAM-1 and class II MHC antigens

Cold preservation has previously been shown to decrease the antigenicity of nerve allografts, while Schwann cells remain viable. The expression of intercellular adhesion molecule-1 (ICAM-1) and class II MHC antigens, both of which have been shown to play a major role in initiating graft rejection, was studied in fresh rat nerve, and after 2 and 7 weeks of cold preservation. Ten sciatic nerves harvested from Lewis rats were cut into three segments. One segment was processed immediately, while the other ones were preserved at 5 degrees C for 2 and 7 weeks, respectively, before processing. Immunostains using specific monoclonal antibodies and alkaline phosphatase development were performed on each sample. The relative level of expression of these antigens was compared using computer-assisted densitometry. Expression of ICAM-1 was significantly decreased at 7 weeks, as compared to fresh and 2-week groups, with no statistically significant difference between fresh and 2-week nerves. Expression of class II MHC was significantly decreased at 2 and 7 weeks, compared to fresh nerves, with no statistically significant difference between the preserved groups. The decrease in antigenicity of cold-preserved nerve allografts appears to be linked to a down-regulation of ICAM-1 and MHC class II expression.

Peripheral nerve injection injury with antiemetic agents

Antiemetics are widely used drugs, frequently administered to alleviate postoperative and postchemotherapeutic nausea and vomiting. While antiemetics do not induce peripheral neurotoxicity when administered systemically, it is not known whether peripheral nerve injury can occur as a result of inadvertent intraneural injection during intramuscular administration. The purpose of this study was to characterize the neurotoxic effect of three commonly used antiemetic agents (promethazine, dimenhydrinate, and prochlorperazine) as compared to saline in the rat sciatic nerve model. Intrafascicular and extrafascicular injection as well as direct application of the antiemetic drugs were performed. Nerves were harvested at 2 weeks postoperatively for histology and morphometry, with an additional sacrifice point at 8 weeks for the intrafascicular injection group. Injection injuries caused by antiemetic drugs differed depending on the agent injected and the location of injection. Extrafascicular injection and direct application caused no damage. Intrafascicular injection caused diffuse axonal injury in the promethazine and dimenhydrinate groups, while prochlorperazine caused only focal injury. Regeneration was prominent at 8 weeks in all intrafascicular injection groups in this rat model. Prochlorperazine thus appears to be less neurotoxic when injected intraneurally and should preferentially be used for intramuscular injections.

Cold preserved nerve allografts: changes in basement membrane, viability, immunogenicity, and regeneration

Rat sciatic nerve graft segments were harvested and pretreated by either placement in the University of Wisconsin Cold Storage Solution at 5 degrees C and storage from 1 to 26 weeks, or repeatedly freezing (-40 degrees C) and thawing (20 degrees C). Following pretreatment, grafts were transplanted as either syngeneic or allogeneic nerve grafts. Storage and freeze-thawing did not affect the Schwann cell basal lamina or laminin distribution of the peripheral nerve. Graft cell viability decreased with increasing time of storage, with some viable cells detectable even after 3 weeks of storage. Freeze-thawed grafts were not viable. Increasing time of storage led to decreasing immune response and graft rejection, but improved regeneration. Freeze-thawed and 26-week stored allografts were nonimmunogenic and rejection was not seen, but regeneration was delayed compared to autografts. Graft storage may become a useful adjunct to clinical nerve allografting to permit elective scheduling of surgery, provide greater time for preoperative tissue testing, and possibly blunt the immune response.

Long-term observation of the effect of peripheral nerve injury in neonatal and young rats

The purpose of this study was to observe functional recovery and motoneuron death after nerve transection-and-repair in neonatal versus young animals. One hundred nine Lewis rats underwent posterior tibial nerve transection-and-repair at 6 or 22 days of age. Fifty-two and fifty-seven nerves at the 6- and 22-day times were used for endpoint analysis at 1, 3, 10, and 14 months. These assessments included serial functional walking track analysis, electrophysiologic studies, muscle mass evaluation, motoneuron counts with retrograde horseradish peroxidase tracing, and histologic and morphometric nerve analysis. Walking track analysis and nerve conduction velocity indicated significantly poorer functional regeneration in the 6-day-old group than in the 22-day-old group. Muscle mass in the 6-day-old group did not recover as well as in the 22-day-old group. Motoneuron numbers stained with horseradish peroxidase were less in the 6-day-old group than in the 22-day-old group. In contrast, morphometric analysis did not reach significance. This study suggests that the same nerve injury sustained in a neonatal rat is less likely to demonstrate functional recovery than one sustained in a young rat.

End-to-side neurorraphy: a long-term study of neural regeneration in a rat model

This study evaluated long-term reinnervation of an end-to-side neurorraphy and the resultant functional recovery in a rat model. The divided distal posterior tibial nerve was repaired to the side of an intact peroneal nerve. Control groups included a cut-and-repair of the posterior tibial nerve and an end-to-end repair of the peroneal nerve to the posterior tibial nerve. Evaluations included walking-track analysis, nerve conduction studies, muscle mass measurements, retrograde nerve tracing, and histologic evaluation. Walking tracks indicated poor recovery of posterior tibial nerve function in the experimental group. No significant difference in nerve conduction velocities was seen between the experimental and control groups. Gastrocnemius muscle mass measurements revealed no functional recovery in the experimental group. Similarly, retrograde nerve tracing revealed minimal motor neuron staining in the experimental group. However, some sensory staining was seen within the dorsal root ganglia of the end-to-side group. Histologic study revealed minimal myelinated axonal regeneration in the experimental group as compared with findings in the other groups. These results suggest that predominantly sensory regeneration occurs in an end-to-side neurorraphy at an end point of 6 months.

Nicotine replacement therapy

OBJECTIVE

To review the literature on nicotine dependence, nicotine pharmacology, health consequences associated with the use of nicotine, and nicotine replacement therapies used to aid smokers who are nicotine dependent.

DATA SOURCES

A review of articles, book bibliographies, and published studies identified by a search of the MEDLINE database from 1982 to 1996 on nicotine dependence, nicotine addiction, nicotine withdrawal, smoking, smoking cessation, smoking intervention, nicotine pharmacology, nicotine pharmacokinetics, nicotine pharmacodynamics, and nicotine replacement therapies.

STUDY SELECTION AND DATA EXTRACTION

Inclusion criteria were published randomized, double-blind trials of at least 12 weeks' duration, meta-analyses, and panel consensus guidelines.

DATA SYNTHESIS

Cigarette smoking and tobacco use have met the surgeon general's primary criteria as well as additional criteria for drug dependence. Drug dependence requires that the drug produce psychoactive effects. Nicotine has been identified as the cause of tobacco dependence. First, nicotine provides positive reinforcement by stimulating nicotinic receptors to promote high self-administration rates. Second, nicotine causes a negative reinforcement in the form of withdrawal symptoms when nicotine is withheld after chronic use. Nicotine replacement therapy reduces the severity of withdrawal symptoms in smokers abstaining from tobacco. Nicotine replacement therapy allows the smoker to focus on psychosocial aspects of tobacco abstinence while receiving relief from withdrawal symptoms. The long-term effectiveness and health benefits of nicotine replacement therapy coupled with nonpharmacologic approaches have been clearly established. Smoking cessation has received wide attention from the public and medical communities; it is complex and has several interwoven factors to be considered. The psychological, behavioral, and physical components have to be understood before designing a treatment plan. The most successful approaches to smoking cessation involve multicomponent, multisession behavioral treatment programs as a foundation coupled with pharmacologic intervention. Pharmacists can play a key role in initiating behavior change and ensuring the safe and proper use of nicotine replacement in order to produce the desired outcome.

CONCLUSIONS

The optimum choice in nicotine replacement depends on the individual's needs and coping abilities. Individualized nicotine replacement coupled with nonpharmacologic interventions produces the highest rate of success for abstinence from nicotine.

Stability of albuterol in continuous nebulization

Due to the emergent nature of situations requiring continuous nebulization of albuterol a premixed albuterol solution would provide faster access to the therapy when required. The purpose of this study was to evaluate the stability of albuterol solutions at a concentration (200 micrograms/mL) used in continuous nebulization when stored in various containers of polyvinyl chloride bags, polyolefin bags, polypropylene syringes and tubes and borosilicate glass tubes. Solutions were prepared in triplicate in 0.9% sodium chloride stored under refrigerated and room temperatures for seven days. Samples were removed and analyzed using a stability-indicating high-performance liquid chromatrography assay method. Albuterol was found to be stable (greater than 90% of the initial concentration remaining) for at least seven days in all five types of containers under the conditions tested.

Nerve injection injury with botulinum toxin

The therapeutic use of botulinum toxin (Botox) is increasing in popularity. Previous studies have shown that various drugs, especially when injected intrafascicularly, can cause major nerve damage. This study evaluates the potential for neurotoxicity of botulinum toxin in a rat sciatic nerve model. Lewis rats were randomly assigned to one of six groups (n = 10/group). Group 1, 2, and 3 rats received, respectively, an intrafascicular, extrafascicular, and extraneural injection of 50 microl of botulinum toxin (50 UI/ml). Group 4, 5, and 6 rats received 50 microl of 10% phenol as a positive control. Five animals received saline as a negative control. Animals were sacrificed at 2 and 7 weeks. Nerves were harvested and processed for histology and morphometry. Nerves in all botulinum toxin groups retained a normal architecture without cellular infiltration or demyelination. The number and diameter of fibers, the thickness of myelin, and the percentage of neural tissue were comparable with normal controls. Nerves injected intraneurally with phenol presented with severe damage, demyelination, and inflammation at 2 weeks and showed signs of early regeneration at 7 weeks. This study demonstrates that in a rat model, even direct intraneural injection of botulinum toxin caused no damage. This information should encourage the reconstructive surgeon to consider broader applications of this drug.

Intrafascicular injection of ammonium sulfate and bupivacaine in peripheral nerves of neonatal and juvenile rats

BACKGROUND AND OBJECTIVES

Regional nerve blocks are often used for the treatment of postoperative pain in children. Ammonium sulfate is a non-narcotic anesthetic agent, which has been reported to provide pain relief lasting days to weeks, with few reported side effects in adult studies. Prior to considering clinical use in children, the neurotoxicity of ammonium sulfate in 4-day and 3-week old rats was assessed and compared with that of bupivacaine.

METHODS

Each rat received a posterior tibial nerve intrafascicular injection (0.01 mL in 4-day-old and 0.02 mL in 3-week-old rats) using either 10% ammonium sulfate (n = 24 per age group), 0.5% bupivacaine (n = 18 per age group), 0.9% saline (n = 18 per age group), or 5% phenol (n = 18 per age group). A functional assessment by serial walking track analysis and a morphologic assessment by neurohistology were made.

RESULTS

No abnormalities in serial walking track analysis and no structural nerve damage were detected after ammonium sulfate, bupivacaine, or saline injection. Bupivacaine caused mild focal changes in both age groups, which recovered by 8 weeks.

CONCLUSIONS

Intrafascicular injection of ammonium sulfate was as safe as bupivacaine in this animal model. Further animal studies must be made before human trials are initiated.

The effect of ammonium sulfate injection on peripheral nerve

Local anesthetic drugs with prolonged nerve-block effect would have clinical application for postoperative or neuromatous pain relief. This study evaluated the possibility of peripheral nerve neurotoxicity by injection of 10 percent ammonium sulfate. Both intrafascicular and extrafascicular injection of 10 percent ammonium sulfate were tested in the rat sciatic nerve model. One percent lidocaine HCl, 5 percent phenol, and normal saline were similarly injected for comparison. Using histologic studies and motor function evaluation with walking-track analysis, 10 percent ammonium sulfate was found to be neurotoxic when it is injected intrafascicularly; however, extrafascicular injection of this drug did not cause significant nerve injury. The neurotoxicity of the 10 percent ammonium sulfate solution was intermediate between the neurotoxicity of 0.1 percent lidocaine hydrochloride and the marked neurotoxicity of 5 percent phenol solution.

The effect of duration of muscle denervation on functional recovery in the rat model

The effect of long-term denervation on neuromuscular recovery was studied in a rat hind limb model. The posterior tibial nerve was transected and repaired immediately or after denervation periods of 2 weeks, or 1, 3, 6, 9, or 12 months. Six months following reconstruction excellent axonal regeneration was seen across all nerve repairs irrespective of periods of denervation. However, there was a precipitous and profound decrease in the recovery of both muscle mass and integrated motor function if the reconstruction was delayed for longer than 1 month. Rather than a progressive change proportional to the length of the denervation period, significant, more discrete changes occurred sometime after 1 month of denervation that precluded a full recovery of muscle mass. Integrated motor function quantified using walking track analysis was impaired even after immediate nerve repair.

End-to-side neurorrhaphy resulting in limited sensory axonal regeneration in a rat model

This study evaluated reinnervation of an end-to-side neurorrhaphy and the resultant functional recovery in a rat model. The cut distal posterior tibial nerve was repaired to the side of an intact peroneal nerve. In one group, the epineurium of the peroneal nerve was left intact; in another group, the epineurium was stripped; in the third experimental group, a perineurial slit was created. Evaluations included walking track analysis, nerve conduction studies, muscle mass measurements, retrograde nerve tracing, and histologic evaluation. Walking tracks indicated poor functional recovery. No significant difference in nerve conduction between the experimental and control groups was seen. Gastrocnemius muscle mass measurements revealed no functional recovery in the end-to-side groups. Retrograde nerve tracing revealed minimal staining of motor neurons. However, sensory neuronal staining of the dorsal root ganglia occurred in all groups. Histology revealed minimal myelinated axonal regeneration. These results suggest that predominantly sensory neural regeneration occurs in an end-to-side neurorrhaphy at an end point of 16 weeks.

Long-segment nerve allograft regeneration in the sheep model: experimental study and review of the literature

Experimental work in the field of nerve allotransplantation has dealt with the feasibility of nerve allografts reconstructing nerve gaps. In the majority of studies, the nerve gap studied has been short, and some degree of regeneration has been achieved, even in the untreated allograft. To better approximate clinical nerve-allograft reconstruction, a series of long-segment (8-cm) nerve allografts were performed in the ovine model. Twenty outbred ewes were randomized into two experimental groups with four experimental conditions. Animals received nerve allografts treated under one of the following conditions: fresh nerve autograft, fresh nerve allograft, cold-preserved nerve autograft, or cold-preserved nerve allograft. The nerve grafts were examined and compared at 6 and 10 months, using histological, morphometric, and electro-physiologic analyses. The results of the study demonstrated that, while excellent regeneration occurred across the nerve autograft, the long nerve allograft could not support axonal elongation. Similarly, cold nerve preservation did not enhance regeneration. The sheep animal model allows for investigation of the long nerve gap and may be beneficial in a better correlation of experimental nerve transplantation with clinical conditions.

Peripheral nerve allograft preservation improves regeneration and decreases systemic cyclosporin A requirements

Peripheral nerve allografting is limited by the need for long-term systemic immunosuppression. The purpose of this study was to determine if nerve allograft preservation reduced the requirements for systemic Cyclosporin A (CsA) immunosuppression. One hundred twenty Lewis rats were randomized to one of seven experimental groups. Group 1 received a 2-cm Lewis posterior tibial nerve autograft. Groups 2-7 received 2-cm ACI posterior tibial nerve allografts. The allograft group was then further subdivided into three groups of two receiving daily subcutaneous injections of 0, 2.5, or 5.0 mg/kg of CsA for 12 weeks. Within each CsA dose, one group received a fresh while the other received a preserved allograft. Preserved grafts were stored in University of Wisconsin solution for 7 days at 5 degrees C prior to implantation. Animals from each group were sacrificed at 6, 12, and 20 weeks postoperatively. Evaluations included histomorphometry, electrophysiology, and serial walking track analysis. Histology revealed varying degrees of nerve regeneration in all groups at 6, 12, and 20 weeks. For a given CsA dose, the group receiving the preserved graft revealed evidence of better nerve regeneration by all histomorphometric parameters including fiber width and density, percentage neural tissue, and total fiber number. There was no statistical difference in walking track analysis between groups at 4 weeks. By 20 weeks, functional recovery statistically poorer than autograft was seen only in the fresh allograft groups receiving 0 or 2.5 mg/kg of CsA. Identical electrophysiologic findings were seen at 20 weeks. These results suggest that nerve graft preservation may decrease systemic immunosuppression requirements while improving functional recovery. As well, storage of nerve grafts is feasible and would facilitate elective surgery and less costly reconstructive repair.

The dose-related effect of monoclonal antibodies against adhesion molecules ICAM-1 and LFA-1 on peripheral nerve allograft rejection in a rat model

Donor-specific immunosuppression using anti-intercellular adhesion molecule-1 (ICAM-1) and anti-lymphocyte function-associated antigen-1 (LFA-1) has been shown to inhibit nerve allograft rejection without side effects. This dose-response study evaluated several dosing regimens using a 2-week course of three monoclonal antibodies (mAbs) against ICAM-1 and LFA-1 in combination on peripheral nerve allograft rejection in a rat model. Assessments of regeneration included walking track, electrophysiological, and histomorphologic analyses. Donor (ACI)-specific tolerance induction was assessed. Toxicity and mAb serum levels were monitored. At 18 weeks post engraftment, intermediate and high-dose groups were histologically indistinguishable from isograft controls, and superior to the untreated allograft group which demonstrated a significantly lower percent nerve tissue than all other groups. There were no differences in print length factor after 12 weeks or conduction velocity at sacrifice between any groups. Tolerance induction was not demonstrated. During mAb administration, animals in higher dose groups experienced temporary systemic side effects. This study demonstrated that a short course of mAb therapy directed against ICAM-1/LFA-1 inhibits rejection in rat peripheral nerve allografts by an unknown mechanism. The use of immune modulation in nerve transplantation may eliminate the need for systemic immunosuppression.

Regeneration across preserved peripheral nerve grafts

The potential to store nerve grafts for a prolonged period of time was assessed in a rat sciatic nerve model. Three-centimeter syngeneic nerve grafts were stored in Belzer/University of Wisconsin cold storage solution at different temperatures (5 degrees C, 22 degrees C, or 37 degrees C) for varying time periods (6 h, 24 h, or 3 weeks) prior to transplantation. Functional assessment using serial walking track analyses revealed no difference between storage times and temperatures. At 14 months postengraftment, the conduction velocities and the number of myelinated fibers that had regenerated across all grafts stored at 5 degrees C for all time periods tested were superior to grafts stored at either 22 degrees C or 37 degrees C. Nerve grafts stored for up to 3 weeks at 5 degrees C acted as effective conduits for proximal regenerating fibers and resulted in histologic, electrophysiologic, and functional results equivalent to fresh nerve grafts. Nerve graft storage may be applicable to nerve allografts and potentially provide allograft material that requires reduced or no associated host immunosuppression.

Monoclonal antibodies against ICAM-1 and LFA-1 prolong nerve allograft survival

In a rat nerve allograft model, specific immunosuppression was approached with monoclonal antibodies (MAbs) against cell-surface molecules. After engraftment, recipients were treated with antiintercellular adhesion molecule-1 (ICAM-1) and antilymphocyte function-associated antigen-1 (LFA-1) MAbs for 14 days. Functional recovery was evaluated biweekly. Electrophysiological and histological assessments were performed at 6 and 16 weeks. Immunologic responsiveness in the recipients was assessed with a cytotoxic T lymphocyte (CTL) assay at 16 weeks and skin grafts at 18 weeks. The untreated allograft group demonstrated complete disruption of fascicular architecture with poor nerve regeneration. The MAb-treated allografts maintained well-organized nerve architecture with a dense population of well-myelinated fibers. These animals showed functional and electrophysiological recovery. Suppression of CTL activity was nerve donor specific and the survival time of nerve donor skin grafts was prolonged, suggesting induction of alloantigen-specific tolerance. MAbs therapy directed against ICAM-1/LFA-1 presents a new approach for the management of the peripheral nerve allograft response.

Immunosuppressive effect of monoclonal antibodies to ICAM-1 and LFA-1 on peripheral nerve allograft in mice

This study evaluated the immunosuppressive effect of monoclonal antibodies against cell surface molecules in a murine peripheral nerve allograft model. After nerve allografting, 18 recipients were treated with both anti-intercellular adhesion molecule-1 (ICAM-1) and anti-lymphocyte function-associated molecule-1 (LFA-1) monoclonal antibodies in low or high dose. Nerve allografts were harvested at 8 weeks for histologic and morphometric evaluation. Recipients were subsequently challenged with skin grafts at 9 weeks and a cytotoxic assay at 12 weeks. The majority of the antibody-treated allografts (13 of 18) showed excellent regeneration comparable to the autografts with preservation of the normal nerve architecture and scant cellular infiltrate. All untreated allografts demonstrated severe structural disorganization with cellular infiltrate consistent with acute rejection. In the high dose group, the mean skin graft survival time from nerve donor mice, but not third-party mice, was significantly prolonged. (17.5 vs. 11.3 days). Similarly, the cytotoxic activity against nerve donor alloantigen was significantly suppressed. These preliminary findings suggest that antibody therapy alone can facilitate nerve regeneration in a murine nerve allograft model.

The regulation of collagen in fetal skin wounds: mRNA localization and analysis

The deposition of collagen in fetal skin wounds has been shown in several animal models. The authors used a radiolabeled RNA antisense probe, complementary to the mRNA for the alpha-1 chain of human procollagen type I, to assess regulation of this collagen species in fetal and adult rabbit wounds. Dorsal skin wounds were placed on fetal and maternal animals at the beginning of the third trimester, and were harvested 3, 5, and 7 days later. In situ RNA/RNA hybridization was performed on suitable specimens, and morphometric analysis was carried out with a computerized LECO image analyzer. Fetal wounds exhibited an inflow of mesenchymal cells that produced collagen type I at levels higher than the surrounding tissue; this activity was highest on days 3 and 5 after wounding. Adult wounds had increased fibroblast presence by day 7, producing collagen type I at levels higher than those of adjacent unwounded tissue. Morphometric analysis of the signal produced by in situ hybridization and of the number of cells producing the signal in a given field showed that fetal wounds appear to produce collagen type I by an increase in the number of cells in the area of the wound--not by induction of the gene for procollagen type I. In contrast, adult wounds had both fibroblast migration and induction of procollagen type I mRNA synthesis. These findings imply multilevel regulation of collagen production in the adult and posttranslational regulation in the fetus.

Nerve crush injuries--a model for axonotmesis

Nerve crush is a commonly used experimental model in the rat; however, a standard method of inducing this injury has not been defined. This study examined six crush techniques that are frequently used and characterized the subsequent nerve injury. Five types of nerve crush using a No. 5 jeweler's forceps and a sixth using a 30-s single crush with a serrated hemostat were studied in the posterior tibial nerve of the Lewis rat. Regeneration was evaluated using serial walking track assessments at 1, 2, 4, 6, and 8 weeks postoperatively. Nerve conduction studies and histological examination were performed at 2 days, 2 weeks, and 8 weeks. Blood-nerve barrier breakdown was observed at 2 days and recovered by 2 weeks. By 4 weeks normal walking track patterns were obtained in all groups. A pattern of Wallerian degeneration and axonal regeneration was noted at 2 weeks, with histological recovery in all groups by 8 weeks. Nerve crush, induced by any of the six methods tested, was similar and provides a reliable model of axonotmesis.

Regeneration across 'stepping-stone' nerve grafts

The ability of small nerve segments interposed between synthetic conduits to increase the total nerve gap distance across which successful nerve regeneration would occur was studied. Fifty adult male Lewis rats were randomized into five groups. In Group I a segment of resected sciatic nerve was repaired by a nerve graft. Group II had alternating silicone tubing/nerve graft/silicone tubing replacement of the resected nerve segment (single stepping stone group). Group III had silicone tubing/nerve graft/silicone tubing/nerve graft/silicone tubing repair of the nerve deficit (double stepping stone). Group IV had a single long silicone conduit repair. Group V control underwent a sham operation. Nerve regeneration was evaluated using walking track pattern analysis, electrophysiologic assessment and histomorphological evaluation. 'Stepping stone nerve grafts' enhanced regeneration across nerve gaps in comparison to a single long conduit, but were inferior to a single long nerve graft. In the repair of long nerve gaps, the use of multiple short conduits with interposed short nerve segments could provide a source of trophic factors to enhance regeneration.

Effect of cold preservation on lymphocyte migration into peripheral nerve allografts in sheep

Lymphocyte migration into fresh and preserved peripheral nerve allografts was quantitated to assess the effect of cold preservation and freeze-thawing pretreatment on the local immunological response to nerve allografts. Out-bred ewes received multiple 1.5-cm subcutaneous heterotopic peroneal nerve autografts, fresh allografts, and pretreated allografts, implanted within the same recipient. Lymphocyte migration was studied at 7 days by injecting autologous 111indium-labeled lymphocytes intravenously. After 3 hr of recirculation, lymphocyte migration into graft tissue was quantitated by a gamma counter (epm/g, mean +/- SEM). Lymphocyte traffic into fresh nerve allografts (21,623 +/- 3783) increased an average 9.4-fold over the autograft value (2918 +/- 377, P < 0.04). Histologic studies illustrated a marked lymphocytic infiltrate of CD4+ and CD8+ cells and enhanced class I and II MHC expression in fresh allografts, but not in autografts. Short-term cold preservation, for 6 and 12 hr (5 degrees C), enhanced lymphocyte entry into pretreated allograft tissue. Conversely, cold preservation for longer periods (1 and 3 weeks) dramatically reduced lymphocyte migration to values below corresponding autograft levels (783 +/- 100 and 1,252 +/- 120, respectively, P < 0.01). A comparable reduction in lymphocyte migration into nerve allografts was observed after freeze-thawing pretreatment (P < 0.01). Cold preservation of donor allogeneic lymphocytes inhibited their capacity to induce intradermal host lymphocyte migration, implicating passenger lymphocytes as a potential cold-sensitive allogeneic component of the nerve allograft. Assessment of the local response to ovine peripheral nerve allografts, utilizing radiolabeled autologous lymphocytes, demonstrated that cold preservation and freeze-thawing pretreatment significantly reduced lymphocyte migration into nerve allografts. The mechanism(s) of reduced lymphocyte migration may involve inactivation or death of antigen-presenting cells, including passenger lymphocytes.

Walking track analysis: utilization of individual footprint parameters

Functional assessment of rat sciatic, tibial, and peroneal nerve injuries was performed using walking track analysis. Individual walking print length (PL), toe spread (TS), and intermediate toe spread (ITS) values were measured up to 24 weeks after specific nerve transection, with or without repair. Sciatic and tibial nerve manipulation initially affected all footprint measurements, consistent with loss of intrinsic and extrinsic motor function. After sciatic repair, TS demonstrated partial recovery without any substantial recovery in PL or ITS, compared with sciatic transection values. By contrast, after tibial repair, PL values recovered dramatically, between 16 and 24 weeks, to levels not significantly different from control subjects. This was not observed after tibial transection without repair. TS recovered partially, whereas ITS recovered to control levels by 20 weeks after tibial repair. Peroneal transection resulted in multiple contractures, rendering this group unmeasurable at 4 weeks. After peroneal repair, only the PL reflected significant loss of function at 2 weeks, recovering to control values by 8 weeks. Manual TS measurements in nonwalking rats did not reflect functional nerve regeneration. Thus, individual PL measurements alone can be used to characterize functional recovery after tibial and peroneal nerve injury, whereas TS reflected recovery after sciatic nerve injury.

Comparison of regeneration across nerve allografts with temporary or continuous cyclosporin A immunosuppression

The efficacy of short-term immunosuppression in a nerve allograft model was examined by comparing regeneration across peripheral nerve allografts with either temporary (12 weeks) or continuous (30 weeks) cyclosporin A treatment. One-hundred fifty Lewis rats received 2-cm nerve grafts from allogeneic ACI or syngeneic Lewis rat donors and were allocated to the following groups: allogeneic grafts and continuous cyclosporin A, with 18 weeks (20 rats) or 30 weeks (20 rats) of survival after graft placement; allogeneic grafts and temporary cyclosporin A, with 12 weeks (10 rats), 18 weeks (20 rats), or 30 weeks (20 rats) of survival; and control rats with allogeneic and syngeneic grafts, no cyclosporin A, with 12, 18, or 30 weeks (10 rats each) of survival. Functional regeneration across the nerve grafts was serially assessed with walking-track analysis. Endpoint evaluations included electrophysiological, histological, and morphometric studies. Both walking-track and electrophysiological function reached a plateau at a significantly worse level in nonimmunosuppressed allograft recipients than in syngeneic or treated allograft recipients. The group with temporary therapy experienced significant worsening in both motor and electrophysiological function at Week 18, 6 weeks after cyclosporin A withdrawal, compared to the group with continuous treatment. At Week 30, motor and electrophysiological function in the temporary-treatment group recovered to levels similar to those of the syngeneic and continuous cyclosporin A groups. Histological assessment of the graft segments from the temporary cyclosporin A group at 18 weeks showed evidence of rejection, with mononuclear cell infiltration and demyelination; morphometric evaluation demonstrated significantly decreased numbers of nerve fibers in the distal host segment. These histological and morphometric changes were no longer present in the nerves from the temporarily immunosuppressed rats at Week 30. Withdrawal of immunosuppression after successful regeneration through nerve allografts results in short-term graft rejection. Eventual restoration of graft histological and function parameters is comparable to continuously immunosuppressed rats. Temporary immunosuppression of nerve allograft recipients is feasible.