Captive diet does not influence exploration behavior upon reintroduction to the wild in a critically endangered amphibian

Exploration behavior can have profound effects on individual fitness. Consequently, knowledge of the proximate mechanisms underpinning exploration behavior may inform conservation breeding programs (CBPs) for threatened species. However, the environmental factors that influence exploration behavior in captivity and during the reintroduction process remain poorly understood. Dietary micronutrients, such as carotenoids, are known to affect the expression of energetically costly behavioral traits, and theoretically may also influence the degree of exploration behavior in various contexts. Here, we investigate whether dietary β-carotene supplementation in captivity influences exploration behavior upon reintroduction to the wild in the critically endangered southern corroboree frog, Pseudophryne corroboree. We conducted a manipulative dietary experiment where captive bred P. corroboree were supplemented with different doses of β-carotene for 40 weeks prior to release. Frogs (n = 115) were reintroduced to the wild using a soft-release approach, where they were released into field enclosures specifically designed for this species. Upon reintroduction, the frogs’ initial exploration behavior was measured using a standardized behavioral assay. There was no effect of diet treatment on any measure of exploration behavior (mean latency to leave the initial refuge, time spent mobile within the release apparatus and latency to disperse into the field enclosure). However, there was a significant relationship between individual body size and latency to leave the refuge, whereby smaller individuals left the refuge more rapidly. While these findings provide no evidence that β-carotene at the dosages tested influences P. corroboree exploration behavior in a reintroduction context, the effect of body size draws attention to the potential for bodily state to influence exploration behavior. We discuss the need for ongoing research investigating the influence of captive diet on post release behavior, and highlight how knowledge concerning state-dependent behavior might help to inform and direct reintroduction programs.

Reservoir-host amplification of disease impact in an endangered amphibian

Emerging wildlife pathogens are an increasing threat to biodiversity. One of the most serious wildlife diseases is chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd), which has been documented in over 500 amphibian species. Amphibians vary greatly in their susceptibility to Bd; some species tolerate infection, whereas others experience rapid mortality. Reservoir hosts-species that carry infection while maintaining high abundance but are rarely killed by disease-can increase extinction risk in highly susceptible, sympatric species. However, whether reservoir hosts amplify Bd in declining amphibian species has not been examined. We investigated the role of reservoir hosts in the decline of the threatened northern corroboree frog (Pseudophryne pengilleyi) in an amphibian community in southeastern Australia. In the laboratory, we characterized the response of a potential reservoir host, the (nondeclining) common eastern froglet (Crinia signifera), to Bd infection. In the field, we conducted frog abundance surveys and Bd sampling for both P. pengilleyi and C. signifera. We built multinomial logistic regression models to test whether Crinia signifera and environmental factors were associated with P. pengilleyi decline. C. signifera was a reservoir host for Bd. In the laboratory, many individuals maintained intense infections (>1000 zoospore equivalents) over 12 weeks without mortality, and 79% of individuals sampled in the wild also carried infections. The presence of C. signifera at a site was strongly associated with increased Bd prevalence in sympatric P. pengilleyi. Consistent with disease amplification by a reservoir host, P. pengilleyi declined at sites with high C. signifera abundance. Our results suggest that when reservoir hosts are present, population declines of susceptible species may continue long after the initial emergence of Bd, highlighting an urgent need to assess extinction risk in remnant populations of other declined amphibian species.

Dynamics of Chytridiomycosis during the Breeding Season in an Australian Alpine Amphibian

Understanding disease dynamics during the breeding season of declining amphibian species will improve our understanding of how remnant populations persist with endemic infection, and will assist the development of management techniques to protect disease-threatened species from extinction. We monitored the endangered Litoria verreauxii alpina (alpine treefrog) during the breeding season through capture-mark-recapture (CMR) studies in which we investigated the dynamics of chytridiomycosis in relation to population size in two populations. We found that infection prevalence and intensity increased throughout the breeding season in both populations, but infection prevalence and intensity was higher (3.49 and 2.02 times higher prevalence and intensity, respectively) at the site that had a 90-fold higher population density. This suggests that Bd transmission is density-dependent. Weekly survival probability was related to disease state, with heavily infected animals having the lowest survival. There was low recovery from infection, especially when animals were heavily infected with Bd. Sympatric amphibian species are likely to be reservoir hosts for the disease and can play an important role in the disease ecology of Bd. Although we found 0% prevalence in crayfish (Cherax destructor), we found that a sympatric amphibian (Crinia signifera) maintained 100% infection prevalence at a high intensity throughout the season. Our results demonstrate the importance of including infection intensity into CMR disease analysis in order to fully understand the implications of disease on the amphibian community. We recommend a combined management approach to promote lower population densities and ensure consistent progeny survival. The most effective management strategy to safeguard the persistence of this susceptible species might be to increase habitat area while maintaining a similar sized suitable breeding zone and to increase water flow and area to reduce drought.

Interventions for reducing extinction risk in chytridiomycosis-threatened amphibians

Wildlife diseases pose an increasing threat to biodiversity and are a major management challenge. A striking example of this threat is the emergence of chytridiomycosis. Despite diagnosis of chytridiomycosis as an important driver of global amphibian declines 15 years ago, researchers have yet to devise effective large-scale management responses other than biosecurity measures to mitigate disease spread and the establishment of disease-free captive assurance colonies prior to or during disease outbreaks. We examined the development of management actions that can be implemented after an epidemic in surviving populations. We developed a conceptual framework with clear interventions to guide experimental management and applied research so that further extinctions of amphibian species threatened by chytridiomycosis might be prevented. Within our framework, there are 2 management approaches: reducing Batrachochytrium dendrobatidis (the fungus that causes chytridiomycosis) in the environment or on amphibians and increasing the capacity of populations to persist despite increased mortality from disease. The latter approach emphasizes that mitigation does not necessarily need to focus on reducing disease-associated mortality. We propose promising management actions that can be implemented and tested based on current knowledge and that include habitat manipulation, antifungal treatments, animal translocation, bioaugmentation, head starting, and selection for resistance. Case studies where these strategies are being implemented will demonstrate their potential to save critically endangered species.

Presence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in threatened corroboree frog populations in the Australian Alps

Since the early 1980s, the southern corroboree frog Pseudophryne corroboree and northern corroboree frog P. pengilleyi have been in a state of decline from their sub-alpine and high montane bog environments on the southern tablelands of New South Wales, Australia. To date, there has been no adequate explanation as to what is causing the decline of these species. We investigated the possibility that a pathogen associated with other recent frog declines in Australia, the amphibian chytrid fungus Batrachochytrium dendrobatidis, may have been implicated in the decline of the corroboree frogs. We used histology of toe material and real-time PCR of skin swabs to investigate the presence and infection rates with B. dendrobatidis in historic and extant populations of both corroboree frog species. Using histology, we did not detect any B. dendrobatidis infections in corroboree frog populations prior to their decline. However, using the same technique, high rates of infection were observed in populations of both species after the onset of substantial population declines. The real-time PCR screening of skin swabs identified high overall infection rates in extant populations of P. corroboree (between 44 and 59%), while significantly lower rates of infection were observed in low-altitude P. pengilleyi populations (14%). These results suggest that the initial and continued decline of the corroboree frogs may well be attributed to the emergence of B. dendrobatidis in populations of these species.

Indefinite survival of peripheral nerve allografts after temporary Cyclosporine A immunosuppression

It is hypothesized that unlike solid organ transplants immunosuppression of peripheral nerve allografts is needed only for the finite time period required for regeneration of proximal host nerve axons through the allograft and subsequent re-establishment of host end-organ connections. The aim of this study was to explore the consequences of temporary and continuous systemic Cyclosporine A (CsA) immunosuppression upon peripheral nerve allograft survival. Buffalo rats received Lewis nerve allografts under CsA immunosuppression (5 mg/kg/day) either continuously for 20 weeks, or for only 10 weeks followed by abrupt withdrawal. At 20 weeks, the nerve segments from both groups were regrafted into naïve Buffalo or Lewis recipients without further immunosuppression. These grafts were compared with isografts, unimmunosuppressed allografts and allografts immunosuppressed for 10 weeks in situ. By eight weeks following regrafting, the secondary Lewis recipients had rejected the temporarily immunosuppressed allografts and accepted the continuously immunosuppressed allograft, while the secondary Buffalo recipients accepted both the temporarily and continuously immunosuppressed allografts as assessed by histology and morphometry. Functional recovery was earlier in secondary recipient strain animals that received temporarily immunosuppressed allografts in comparison to those that received continuously immunosuppressed allografts. Analysis of secondary recipients of temporarily immunosuppressed allografts demonstrated greater in vitro MLR and LDA reactivity than did those receiving continuously immunosuppressed allografts. These findings support the hypothesis that donor alloantigens are lost or replaced by the recipient after immunosuppression withdrawal. Moreover, the change to recipient antigenicity in the nerve allograft is retarded and incomplete under continuous CsA immunosuppression, resulting in acceptance by both secondary donor and recipient strains upon regraftment.

End-to-side neurorrhaphy and lateral axonal sprouting in a long graft rat model

OBJECTIVE/HYPOTHESIS

Controversy exists regarding collateral axonal sprouting across an end-to-side neurorrhaphy to provide functional motor reinnervation of a target organ without compromise of the donor nerve. Rat models may be limited in the study of end-to-side repair given potential contamination from the proximal nerve stump of the recipient distal nerve and the use of antagonistic muscle groups for donor and recipient. The current study attempts to address these issues by using a rat model in which an end-to-side coaptation is performed with a long graft interposed between the intact donor tibial nerve and the divided, distal contralateral tibial nerve.

MATERIALS AND METHODS

The graft used in proximal end-to-side coaptation consisted of both sciatic nerves in a donor syngeneic animal. The distal repair to the contralateral tibial nerve was done immediately or in a delayed fashion to allow potential motor axons to transverse the graft before division of the recipient tibial nerve.

RESULTS

After 24 weeks, axons were noted to transverse the entire distance of the graft and into the contralateral distal posterior tibial nerve. A significant increase in axonal numbers was observed in the immediate repairs compared with the delayed. No animal recovered functional motor ability on the contralateral side as assessed by walking tracks.

CONCLUSIONS

These findings suggest the importance of immediate distal neurotrophic factors in encouraging nerve regeneration even in a long graft end-to-side repair. Our model is successful in demonstrating innervation through an end-to-side coaptation but questions its use given the lack of motor recovery.

Development of the blood-nerve barrier in neonatal rats

The blood-nerve barrier (BNB) is constituted by the perineurium and the endothelium of endoneurial microvessels. We investigated the age at which the vascular component of BNB function is established in the rat and the ultrastructural modifications accompanying changes in permeability. BNB permeability was assessed with injections of Evans blue albumin (EBA) and horseradish peroxidase (HRP) in rats of different ages. Sciatic nerve sections were studied using fluorescence and electron microscopy. Nerves from animals injected with EBA indicated that the BNB is not functional before 13 days of life but that its function is established by 16 days. These results were confirmed by electron microscope examination of nerve sections from animals injected with HRP, which showed clefts between the endothelial cells of endoneurial vessels in young rats. In rats over 18 days, these clefts were occluded by tight junctions, which prevented HRP from leaving the vessel lumen and conferred BNB function. Systematic morphometric analysis of nerves from different age groups allowed the establishment of baseline normal histologic neural development with age.

Portal venous ultraviolet B-irradiated donor alloantigen prevents rejection in circumferential rat tracheal allografts

BACKGROUND

Before tracheal transplantation can be considered as a method of reconstruction in patients with extensive circumferential tracheal defects, we must achieve a state of nontoxic, donor-specific tolerance so that the risks of such a transplant do not outweigh the benefits.

OBJECTIVE

Our objective was to determine whether a single intraportal injection of modified donor alloantigen achieves donor-specific immunosuppression for major histocompatibility complex-mismatched rat tracheal allografts.

STUDY DESIGN

Buffalo (recipient) rats were pretreated with either a single portal-vein administration of ultraviolet B (UVB)-irradiated donor splenocytes (n = 4) or an intraportal inoculation of nonirradiated donor splenocytes (n = 4). Major histocompatibility complex-mismatched Lewis (donor) tracheal allograft segments were then grafted into treatment groups 7 days after donor-cell pretreatment. Tracheal rejection was assessed by histologic analysis, mucosal cilia motility, and in vitro immunologic assessment.

RESULTS

The UVB-treated group demonstrated no acute or chronic rejection as well as complete functional recovery. In vitro immunologic assessment demonstrated a donor-specific hyporesponsiveness and donor allospecificity. Untreated animals and those receiving nonirradiated donor splenocytes showed acute rejection of their tracheal allografts.

CONCLUSION

Recipient pretreatment with intraportally administered UVB-irradiated donor splenocytes prevents rejection of circumferential rat tracheal allograft segments by inducing a donor-specific immune hyporesponsiveness.

Rat-strain differences in recovery following peripheral-nerve allotransplantation

The rat model is commonly utilized in peripheral nerve research. Due to the short length of the rat limb and the animal's inherent neuroregenerative capacity, the timing of assessment of nerve regeneration is critical, and significant differences between groups can be lost if assessment is done too late. Additionally, the comparison of data from different rat-strain combinations has been questioned. This study better defines the time course of recovery after peripheral nerve grafting, and examines differences between Buffalo (BUF), Lewis (LEW), and ACI rats. Tibial-nerve isografts and allografts were performed and harvested at 6, 8, 10, or 14 weeks. Histomorphometry documented a statistically significant difference in the ACI/LEW and LEW/LEW combination at 10 weeks. No strain differences in graft rejection were noted. The optimal time to assess for histomorphometric differences in the ACI/LEW and LEW/LEW combination is at 10 weeks postoperatively.

Safe injection of cultured schwann cells into peripheral nerve allografts

The effects of cultured host Schwann cells on axonal regeneration in peripheral nerve allografts were studied. Fischer rats served as recipient animals and Buffalo rats provided nerve allografts. Animals were randomized into 9 groups. Rats receiving tibial nerve isografts were left untreated (group I), or injected with isogeneic Fischer Schwann cells (group II) or placebo suspension (group III). Allografts obtained from Buffalo rats were left untreated (group IV), or received isogeneic Fischer Schwann cells (group V), 2 mg/kg Cyclosporin A and Fischer Schwann cells (group VI), 5 mg/kg Cyclosporin A (group VII), or 5 mg/kg Cyclosporin A with Schwann cells (group VIII). No Schwann cell tumors were identified 4 or 8 weeks postoperatively. Group IX animals, harvested 3 days postoperatively, demonstrated no evidence of injection injury. Schwann cells modestly improved axonal regeneration in both isografts and allografts and may have a clinical role in the treatment of peripheral nerve allografts.

Pretreatment with portal venous ultraviolet B-irradiated donor alloantigen promotes donor-specific tolerance to rat nerve allografts

OBJECTIVE

To determine if a single intraportal inoculation of ultraviolet B-irradiated (UVB) donor splenocytes can prevent nerve allograft rejection and confer donor-specific immunotolerance to rat nerve allograft segments.

METHODS

Age-matched, class I and class II major histocompatibility complex (MHC) mismatched Buffalo (RT1b) rats were transplanted with a syngeneic nerve isograft, a Lewis (RT1l) nerve allograft, or a Brown-Norway (RT1n) rat nerve allograft segment. Control Buffalo rats in group I received a 3.0-cm Lewis (RT11) sciatic-posterior tibial interposition nerve allograft without pretreatment; group II Buffalo rats received a syngeneic Buffalo nerve isograft without pretreatment. Group III Buffalo recipients were inoculated with 2.5 x 107 UVB-irradiated Lewis donor splenocyte cells by portal venous administration 7 days before transplantation with a 3.0-cm sciatic-posterior tibial nerve allograft from a Lewis (RT11) or a third party Brown-Norway rat (RT1n) donor (group IV). Nerve graft regeneration was assessed with walking track analysis, nerve conduction studies, retrograde neural tracing, nerve graft histology, and morphometry. Recipient immune tolerance was assessed through in vitro immunological assessment.

RESULTS

Pretreatment with UVB-irradiated donor splenocytes 7 days before transplantation prevented nerve allograft rejection. Pretreated animals receiving a nerve allograft recovered limb function, and demonstrated morphological, histological, and electrophysiologic parameters of nerve regeneration similar to that measured in rats receiving a nerve isograft. In vitro immunological assessment by mixed lymphocyte culture (MLC), cytotoxic T lymphocyte (CTL) assay, limiting dilution analysis (LDA) of helper (pTH) and cytotoxic (pCTL) precursor frequencies, and IL-2 production demonstrated a marked donor-specific suppression in allografted animals pretreated with intraportal UVB-irradiated donor splenocytes. These assessments correlated with indefinite acceptance of donor nerve allografts.

CONCLUSIONS

A single pretreatment with a single intraportal dose of UVB-modified donor antigen specifically induces tolerance to peripheral nerve allografts in rats.

FK506 rescues peripheral nerve allografts in acute rejection

This study investigated the ability of the immunosuppressant FK506 to reverse nerve allograft rejection in progress. Eighty-four Buffalo rats received posterior tibial nerve grafts from either Lewis or Buffalo donor animals. Allografts were left untreated for either 7, 10, or 14 days before receiving daily subcutaneous FK506 injections (2 mg/kg). Time-matched control animals received either an isograft, an allograft with continuous FK506, or an allograft with no postoperative FK506 therapy. All animals underwent weekly evaluation of nerve function by walking track analysis. Experimental group animals were sacrificed either immediately prior to initiation of FK506 therapy (days 7, 10, or 14), after 2 weeks of immunosuppressive treatment, or 8 weeks postsurgery. Histomorphometric analysis, consisting of measurements of total number of nerve fibers, neural density, and percent of neural debris, demonstrated a statistically significant increase in regeneration in the isograft group relative to the untreated allograft group within 28 days of transplantation. Grafts harvested from animals receiving 2 weeks of FK506 after 7 or 10 days of rejection were histomorphometrically similar to time-matched isografts. By contrast, grafts from animals receiving 2 weeks of FK506 following 14 days without therapy resembled untreated allografts and demonstrated significant histomorphometric differences from isografts at the corresponding time point. Analysis of walking track data confirmed that relative to untreated allografts, functional recovery was hastened in animals receiving an isograft, or allograft treated with FK506. This study demonstrated that when started within 10 days of graft placement, FK506 could reverse nerve allograft rejection in rats evaluated following 2 weeks of treatment.

A new artificial nerve graft containing rolled Schwann cell monolayers

This study hypothesized that introducing high numbers of Schwann cells in monolayers via a novel rolled graft architecture would promote robust nerve regeneration. The objective was to place adherent Schwann cells in artificial nerve grafts and to assess regeneration through the Schwann cell-laden grafts compared with that through acellular grafts and autografts. Schwann cells were isolated from neonatal Fisher rats. Small intestinal submucosa (SIS) was harvested from adult Fisher rats, cut into 7 mm x 8 cm pieces, and pinned out. Schwann cells were plated onto the strips, allowed to reach confluence, and subsequently rolled into a laminar structure and implanted across a 7-mm gap in the rat sciatic nerve (n = 12). Control animals received SIS conduits without Schwann cells (n = 11) or autograft repair (n = 12). At 10.5 weeks, functional regeneration through the Schwann cell-laden grafts, measured by both sciatic function index and extensor postural thrust testing, exceeded that through the cell-free grafts and approached that achieved through autografts. These results highlight the role of Schwann cells in nerve regeneration. Regenerative results approaching autograft levels in the Schwann cell-laden group suggest that this methodology may ultimately be useful in clinical nerve repair.

Effects of FKBP-12 ligands following tibial nerve injury in rats

The neuroregenerative properties of FK506, an FKBP-12 ligand that inhibits calcineurin, and V-10,367, an FKBP-12 ligand that does not inhibit calcineurin, were evaluated in crush and transection models. Rats were randomly assigned to one of seven groups, including untreated controls and FK506- or V-10,367-treated experimental groups. Following crush or transection nerve injury, animals were assessed with walking tracks, and histomorphometry. FK506-treated animals demonstrated significant functional recovery 11 days following crush and 18 days following transection injury. In untreated and V-10,367 treated animals, nerves recovered 13 days following crush injury, but did not improve significantly prior to sacrifice at 28 days in animals sustaining a transection injury. No statistically significant differences in histomorphometric parameters were identified between any of the groups. The study confirms that FK506 accelerates recovery from tibial nerve injury.

Cyclosporine A inhibits lymphocyte migration into ovine peripheral nerve allografts

Lymphocyte migration into nerve allografts was measured to estimate the cyclosporine A (CsA) dose required to suppress rejection. Twelve outbred sheep received daily subcutaneous CsA at 0, 5, 10, or 15 mg/kg/day for 2 weeks prior to implantation of multiple heterotopic subcutaneous nerve grafts. Lymphocyte migration was determined after 7 days by an intravenous pulse of autologous 111indium-labeled lymphocytes and subsequent quantitation of gamma radioactivity in nerve tissue (CPM/g, mean +/- SEM). Measurement by radioimmunoassay revealed a dose-dependent increase in blood cyclosporine levels. Lymphocyte migration into autografts (404+/-44) was significantly less than migration into allografts (16,554+/-2,049), in control animals (P < 0.01). A dose-dependent inhibition of lymphocyte migration into nerve allografts was observed with counts of 7,662+/-1,692, 4,083+/-1,112, and 1,561+/-232 in sheep receiving 5, 10, or 15 mg/kg/day of CsA, respectively. Daily CsA administration produced effective blood levels and immunosuppression sufficient to inhibit lymphocyte migration into nerve allografts.

Regeneration through long nerve grafts in the swine model

We investigated regeneration across a long nerve defect in the swine model to study extensive neural loss and long nerve gap. Most experiments have been conducted in the rodent model that, while an appropriate immunological model, only allows short nerve gaps to be studied. Twelve outbred swine received either an 8-cm ulnar nerve autograft or an allograft without immunosuppression. At 6 and 10 months, histomorphometry of the autografts demonstrated excellent nerve regeneration, while very poor regeneration was noted across the allografts. This confirmed that 8 cm are an adequate challenge independent of the spontaneous regeneration potential of axons seen in rodents. The swine ulnar nerve graft model causes minimal morbidity and will now be used with immunological manipulation of inbred animals.

Regeneration across cold preserved peripheral nerve allografts

The feasibility of peripheral nerve allograft pretreatment utilizing cold storage (5 degrees C in the University of Wisconsin Cold Storage Solution) or freeze-thawing to prevent rejection was investigated. Regeneration across cold-stored (3 or 5 weeks) or freeze-thawed (FT), 3.0-cm sciatic nerve allografts were compared to fresh auto- and allografts in an inbred rat model. At 16-week post-engraftment, only FT allografts appeared similar to autografts on gross inspection; FT grafts were neither shrunken nor adherent to the surrounding tissue as seen in the other allograft groups. Qualitatively, the pattern of regeneration in the graft segments of the fresh allograft and to a lesser extent of pretreated allografts was inferior to that of autografts as evidenced by a disruption in the perineurium, more extrafascicular axons, smaller and fewer myelinated axons, increased intrafascicular collagen deposition, and the persistence of perineurial cell compartmentation and perivascular infiltrates. Distal to these grafts, the regeneration became more homogenous between groups, although areas of ongoing Wallerian degeneration, new regeneration as well as compartmentation, were more prevalent in fresh and pretreated allografts. Although the number of myelinated fibres was equivalent to autografts, the fibre diameters, the number of large diameter fibres, and the G-ratio were significantly decreased in the allograft groups, which, in part, accounted for the significant decrease in conduction velocity in the 3-week stored and fresh allograft, and the slight decrease in the 5-week stored and FT allograft groups. There was a small return in the Sciatic Function Index towards normal, but no consistent differences between groups were found. Prolonged cold storage and freeze-thawing of nerve allografts resulted in regeneration that was better than fresh allografts, but inferior to autografts. With the concomitant use of host immunosuppression or other immunotherapies, these storage techniques can provide a means of transporting nerve allografts between medical centres and for converting urgent into elective procedures.

Revascularization of peripheral nerve autografts and allografts

The timing and mechanisms of peripheral nerve revascularization were investigated using a 2-cm sciatic nerve graft model in 58 rats. Epineurial perfusion was consistently established by 48 hours and endoneurial perfusion by 72 hours. The pattern of endoneurial perfusion was "all-or-none"--either all or none of the vessels in a fascicle exhibited blood flow. Conventional allografts exhibited similar revascularization dynamics and patterns. Capping the ends of the autograft with Silastic significantly delayed revascularization; no flow was observed at 4 days, and only a peripheral rim of perfused fascicular vessels was observed at 7 days. These patterns suggested that the primary method of revascularization in the conventional graft was longitudinal inosculation; no evidence of peripheral neovascularization or dependence on the graft bed as a source of revascularization was observed. The introduction of a major histocompatibility complex barrier between the grafted tissue and the recipient animal did not alter the timing or the mechanics of blood flow reestablishment.

Strain differences in peripheral-nerve regeneration in rats

Currently, several strains of rats are used for studies of peripheral-nerve injury and repair. The purpose of this study was to determine if significant differences in regeneration between strains exist that might influence comparison of results and interpretation of scientific conclusions. One outbred (Sprague-Dawley) and four inbred stains (ACI, Wistar-Furth, Lewis, Brown-Norway) were studied. Animals were randomized to one of two experimental conditions, undergoing either posterior tibial nerve transection and repair, or Silastic conduit repair of the posterior tibial nerve (n=6/group). Endpoint evaluations at 6 and 13 weeks included histomorphometry and walking-track analysis. Evidence of excellent regeneration was noted in all rat strains undergoing primary repair. Generally, no statistically significant differences between strains were noted, regardless of endpoint evaluation used in the primary repair group. Nerve regeneration across the conduits was either poor or not present at 6 weeks, with no regeneration at all noted in any animals in the ACI and Brown-Norway groups, and regeneration in only one or two animals in the other strains. At 13 weeks, between three and five animals in each strain showed regeneration, but functional recovery was poor. Overall, few differences in peripheral-nerve recovery appear to exist between rat strains. It seems that uniform conclusions may be drawn regardless of strain used.

Expression of 1-aminocyclopropane-1-carboxylate oxidase during leaf ontogeny in white clover

We examined the expression of three distinct 1-aminocyclopropane-1-carboxylic acid oxidase genes during leaf ontogeny in white clover (Trifolium repens). Significant production of ethylene occurs at the apex, in newly initiated leaves, and in senescent leaf tissue. We used a combination of reverse transcriptase-polymerase chain reaction and 3'-rapid amplification of cDNA ends to identify three distinct DNA sequences designated TRACO1, TRACO2, and TRACO3, each with homology to 1-aminocyclopropane-1-carboxylic acid oxidase. Southern analysis confirmed that these sequences represent three distinct genes. Northern analysis revealed that TRACO1 is expressed specifically in the apex and TRACO2 is expressed in the apex and in developing and mature green leaves, with maximum expression in developing leaf tissue. The third gene, TRACO3, is expressed in senescent leaf tissue. Antibodies were raised to each gene product expressed in Escherichia coli, and western analysis showed that the TRACO1 antibody recognizes a protein of approximately 205 kD (as determined by gradient sodium dodecyl sulfate-polyacylamide gel electrophoresis) that is expressed preferentially in apical tissue. The TRACO2 antibody recognizes a protein of approximately 36.4 kD (as determined by gradient sodium dodecyl sulfate-polyacylamide gel electrophoresis) that is expressed in the apex and in developing and mature green leaves, with maximum expression in mature green tissue. No protein recognition by the TRACO3 antibody could be detected in senescent tissue or at any other stage of leaf development.

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.