Chromic Gut Research Articles

Erythropoietin and erythropoietin receptors in the peripheral nervous system: changes after nerve injury.

SPECIFIC AIMSUsing two experimental models of painful neuropathy and axonal degeneration, including one that caused enhanced TUNEL staining (apoptosis), we compared Epo/EpoR events in the peripheral nerve fibers undergoing Wallerian degeneration and in their corresponding DRG with and without apoptosis. We hypothesized that DRG neurons and Schwann cells express Epo/EpoR constitutively and that their expression is altered during painful nerve injury and includes activation of JAK2 signaling in Schwann cells.PRINCIPAL FINDINGS1. Identification of Epo/EpoR in normal and injured sciatic nervesTo identify the presence of Epo/EpoR in peripheral nerve, we performed immunohistochemistry of rat sciatic nerve sections with and without nerve injury. Nerve injury was caused by either gently crushing the rat sciatic nerve 2 mm distal to the DRG or by applying four loose, chromic gut ligatures to the distal sciatic nerve, this latter method being known as chronic constriction injury (CCI). Both forms produce Wallerian ...

One Percent Sodium Carboxymethylcellulose Prevents Experimentally Induced abdominal Adhesions in Horses

To evaluate the efficacy of 1% sodium carboxymethylcellulose (SCMC) for prevention of experimentally induced abdominal adhesions in horses. Prospective, controlled, experimental study. Twelve healthy adult horses. The effect of 1% SCMC on adhesion formation was evaluated in 12 healthy horses by using an established model of serosal trauma to induce intraabdominal adhesions. After ventral median celiotomy, 2 separate areas of the jejunum were abraded, and three 2-0 chromic gut sutures were placed in each abraded area. Jejunal resection and end-to-end anastomosis was performed at 2 sites distant to the abrasion sites. In treated horses (n = 6), 2 L of 1% SCMC was applied to the intestine before and after intestinal manipulation. In control horses (n = 6), 2 L of saline solution were applied to the intestine before and after surgical manipulation. All horses were euthanatized 10 days after surgery, and the abdominal cavity was evaluated for adhesion formation. The frequency of intraabdominal adhesions between groups was compared with a chi-square test. Statistical significance was set at P <.05. All control horses had intraabdominal adhesions. Fibrous adhesions were associated with both jejunal abrasion sites in 5 control horses. Fibrous adhesions were also associated with 1 or both jejunal anastomotic sites in 5 control horses. Only 1 treated horse developed adhesions at the jejunal abrasion sites, and no adhesions were present at the anastomotic sites in the treated horses. There were significantly fewer adhesions in the SCMC treatment group compared with the control group (P <.05). In this experimental model, application of 1% SCMC reduced the frequency of intraabdominal adhesions at areas of serosal abrasion and at jejunal anastomotic sites. In horses at an increased risk for developing intraabdominal adhesions after intestinal surgery, the use of 1% SCMC during celiotomy may decrease the frequency of adhesion formation.

Influence of painful chronic neuropathy on neurogenic inflammation

The effect of topical application of capsaicin cream on neurogenic inflammation was investigated in a neuropathic pain model in rat. The neuropathic state was induced by loose ligation of the sciatic nerve with a chromic gut suture. A marked thermal hyperalgesia was observed in response to heat stimulation applied to the operated side from 3 days through 2 weeks, followed by a gradual return to the control level 35 days after surgery. In sham-operated animals, topical application of capsaicin cream to both sides of the hind paw, the instep and sole, as well as antidromic stimulation of the sciatic nerve led to a significant increase in the amounts of Evans blue and substance P (SP) released into the perfusates. This stimulus-induced extravasation was significantly suppressed by pretreatment with RP67580, an NK 1 antagonist. On day 7 after ligation, capsaicin- and antidromic stimulation-induced extravasation were significantly reduced. At this time, both amount of SP released immediately after application of capsaicin and during antidromic stimulation were almost similar to that in sham-operated rats, whereas the basal amount of SP release significantly increased in ligated animals. In particular a major release of SP was detected immediately after the start of the perfusion compared with that in sham-operated rats. Plasma extravasation evoked by SP (10 −4 M) applied to the subcutaneous perfusate was significantly less in ligated than in sham-operated rats. These results suggest that nerve injury with chronic pain may produce increase in basal SP release into the peripheral tissues, and then such enhanced SP release cause reduction of SP-induced extravasation.

Central administration of methotrexate reduces mechanical allodynia in an animal model of radiculopathy/sciatica

We have recently reported that injury to a lumbar root in a rat model of radiculopathy produces spinal glial activation associated with elevated proinflammatory cytokines. Based on our hypothesis that central neuroinflammatory processes may manifest clinically as radicular pain, we undertook pharmacological intervention using the immunosuppressive agent methotrexate (MTX). The L5 lumbar spinal root (central to the dorsal root ganglia) was exposed unilaterally and loosely constricted with chromic gut. In the prevention (phase I) study, MTX was administered intrathecally (1 mg/kg) and around the spinal root (1 mg/kg) at surgery and at days 2 and 4 postsurgery (group A). Saline injection was employed for the control group (group B). Sham operated animals were administered MTX to determine the potential for behavioral/neural side effects (group C). In the existing pain paradigm (phase II) study, the experiment was extended to day 14 with three additional groups. The same dose and method of delivery of MTX or saline was administered as in phase I in the first week on days 0, 2, and 4 and in the second week on days 7, 9, and 11 postsurgery. To measure the effects of MTX on existing behaviors saline was administered in the first week and MTX during the second (group D; Saline:MTX). The control group received saline during both weeks (group E; Saline:Saline). To examine the possible recurrence of radicular pain after MTX termination, MTX was given in the first week and saline in the second (group F; MTX:Saline). Gait disturbance and mechanical allodynia (using von Frey filaments) were assessed up to day 7 in the prevention study (Phase I) and day 14 in the existing pain paradigm (Phase II). The L5 spinal cord segments were harvested for assessment of immunohistochemical glial activation using the antibodies OX-42 (microglial marker) and glial fibrillary acidic protein (GFAP: astrocytic marker) and for the presence of Major Histocompatibility Complex (MHC) Class II expression. Group C (Sham+MTX) did not demonstrate any evidence of gait disturbance or mechanical allodynia after MTX administration. The rats in group B (Surgery+Saline) demonstrated mechanical allodynia from one day postsurgery to the time of euthanization. When allodynia was assessed using the 12 g von Frey filament, the MTX treated rats in group A showed significantly decreased mechanical allodynia as compared to the saline treated rats (group B) (repeated measured ANOVA, P<0.0001). In the phase II study, the rats in group D (Saline:MTX) and E (Saline:Saline) showed robust allodynia in the first week after the surgery. In the second week, mechanical allodynia significantly decreased in group D, while mechanical allodynia continued in the saline treated group (repeated measured ANOVA, P=0.0121). Allodynia was significantly attenuated in group F (MTX: Saline) as compared to the response in groups D and E at day 7 (one-way ANOVA, P<0.0001) and remained significantly lower as compared to group E up to day 11 postsurgery (one-way ANOVA, P9=0.0013: P11=0.0048). OX-42 and GFAP expression were elevated in the gray matter of the L5 spinal section in all groups that underwent the root ligature with chromic gut (Groups A, B, D–F). There were no significant differences in glial activation between the groups. However, spinal expression of MHC II was markedly reduced in the MTX treated group as compared with the saline treated group. The exact mechanism of action of MTX in attenuating mechanical allodynia has not yet been elucidated. The present results indicate that MTX administration may offer a new treatment modality for radicular pain with or without disc herniation as well as directing new research into the development of novel immunomodulators for the treatment of chronic neuropathic and radicular pain.

Spinal glial activation and cytokine expression after lumbar root injury in the rat.

This study was designed to examine the behaviorial immunohistochemical changes of spinal glial cells and spinal Interleukin (IL)-1beta expression after various nerve root injuries used as models of lumbar radiculopathy. In order to better understand the role of central inflammation in the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy, this research studied the relationship between pain-related behavior associated with spinal glial activation and IL-1beta expression generated by three types of nerve root injury: loose ligation with chromic gut, loose ligation with silk, and tight ligation with silk. An animal model of lumbar radiculopathy originally described by Kawakami and Weinstein involved loose ligation of unilateral L4-L6 nerve roots with chromic gut. Characterization and establishment of such an animal model of low back pain enables further investigation of the nature of the pathophysiologic mechanisms associated with lumbar radiculopathy in humans. Seventy-three rats were divided into four treatment groups. Chromic group (n = 25): The L5 nerve roots (dorsal and ventral) were exposed by hemilaminectomy and loosely ligated with chromic gut. Tight silk group (n = 18): The exposed L5 nerve roots were tightly ligated extradurally with 5-0 silk suture. Loose silk group (n = 15): two loose ligatures of 5-0 silk were placed around the exposed L5 nerve roots. Sham group (n = 15): the rats were subjected to laminectomy alone for exposing nerve roots. Following surgery, thermal hyperalgesia and mechanical allodynia was assessed time-dependently up to 42 days post operatively. At 1, 3, 7, 14, and 42 days postoperatively, the rats in each group were perfused with fixative. The L5 spinal cord segments was harvested and cryosectioned for glial and cytokine immunohistochemistry. In the chromic and the tight silk group, an immediate and sustained mechanical allodynia was observed in the ipsilateral hind paw up to 35 days postoperatively. The loose silk group also showed an immediate mechanical allodynia that subsided by 14 days postoperatively. Sham-treated animals exhibited mild mechanicalallodynia for the initial 7 days after the surgery. Thermalhyperalgesia was evident in the three primary treatment groups, but not in the sham-treated rats. OX-42 expression was elevated in the gray matter of the L5 spinal section by 3 days in the chromic, the tight silk, and the loose silk groups as compared to the sham group. Astrocytic activation increased over time in all groups except the sham group. There was no direct correlation between degree of microglial response and severity of pain behaviors. In contrast, astrocytic activation demonstrated a direct relationship with the elevation of mechanical allodynia for the first 7 days. In addition, spinal IL-1beta protein expression was increased bilaterally in the superficial layer of the dorsal horn and cell nuclei of the ventral horns in the ligature treated groups as compared with the sham group. Direct mechanical and/or chemical injury to lumbar roots in the rat gives rise to pain behavior suggestive of lumbar radiculopathy. The finding that glial activation and enhanced IL-1beta expression are observed in the spinal cord after root injury supports a central, neuroimmune component in the generation of lumbar radiculopathy. A further understanding of the immunologic consequences of root injury may lead to further development and the novel use of selective cytokine-inflammatory inhibitors for the treatment of low back pain associated with radiculopathy.

Evaluation of a bioresorbable hyaluronate-carboxymethylcellulose membrane for prevention of experimentally induced abdominal adhesions in horses.

To evaluate the efficacy of a bioresorbable hyaluronate-carboxymethylcellulose membrane (HA-membrane) for prevention of experimentally induced abdominal adhesions in horses. Experimental study. Twelve healthy adult horses. The effect of an HA-membrane on adhesion formation was evaluated in 12 healthy horses using an established model of serosal trauma to induce adhesions. A ventral median celiotomy and two jejunal resections and end-to-end anastomoses were performed. Two separate jejunal areas were abraded, and three 2-0 chromic gut sutures placed in the abraded areas. In treated horses (n = 6), HA-membranes were applied to the jejunum to completely cover the anastomoses and abraded areas of jejunum. Nontreated horses (n = 6) served as controls. All horses were killed 10 days after surgery. The abdominal cavity was evaluated for adhesion formation. The frequency of intra-abdominal adhesions between groups was compared with a chi2 test with statistical significance set at P < .05. All control horses had intra-abdominal adhesions; fibrous adhesions were associated with both jejunal abrasion sites in 5 horses. One treated horse developed adhesions. There were significantly fewer adhesions in the HA-membrane-treated group (P < .0034). In this experimental model, application of an HA-membrane to a localized area of serosal trauma reduced the frequency of intra-abdominal adhesion formation. Application of an HA membrane may decrease the frequency of adhesions in horses at an increased risk of postoperative adhesion formation.

Strain Differences in Neuropathic Hyperalgesia

The purpose of this study was to investigate strain-related differences in the onset and maintenance of thermal hyperalgesia following the induction of peripheral nerve injury in two inbred strains of rats (Fischer 344 and Lewis) and two outbred strains of rats (Sprague–Dawley and Wistar). Neuropathic pain was induced via unilateral ligation of the left sciatic nerve with chromic gut sutures. A plantar analgesia meter was used to measure paw-withdrawal latency from the ligated vs. unligated hind paws of inbred vs. outbred strains of rats to investigate strain-related differences in nerve injury-induced thermal hyperalgesia. The results demonstrated no significant effects of animal strain on presurgical paw-withdrawal latency values. Following the sciatic nerve ligation (SNL) surgery, a significant hyperalgesic response was elicited from the Sprague–Dawley and Wistar rats (outbred strains) for at least 28 days. Conversely, data analyses from the inbred strains failed to demonstrate significant hyperalgesic responses to peripheral nerve injury, with the exception of postsurgical day 10. These data emphasize the importance of considering the strain of the rat being investigated before extrapolating the results from animals experiments to treatment strategies for humans with chronic neuropathic pain.

Brain-derived TNFα mediates neuropathic pain

Neuropathic pain is a chronic pain state that develops a central component following acute nerve injury. However, the pathogenic mechanisms involved in the expression of this central component are not completely understood. We have investigated the role of brain-associated TNF in the evolution of hyperalgesia in the chronic constriction injury (CCI) model of neuropathic pain. Thermal nociceptive threshold has been assessed in rats (male, Sprague–Dawley) that have undergone loose, chromic gut ligature placement around the sciatic nerve. Total levels of TNF in regions of the brain, spinal cord and plasma have been assayed (WEHI-13VAR bioassay). Bioactive TNF levels are elevated in the hippocampus. During the period of injury, hippocampal noradrenergic neurotransmission demonstrates a decrease in stimulated norepinephrine (NE) release, concomitant with elevated hippocampal TNF levels. Continuous intracerebroventricular (i.c.v.) microinfusion of TNF-antibodies (Abs) starting at four days, but not six days, following ligature placement completely abolishes the hyperalgesic response characteristic of this model, as assessed by the 58°C hot-plate test. Antibody infusion does not decrease spinal cord or plasma levels of TNF. Continuous i.c.v. microinfusion of rrTNFα exacerbates the hyperalgesic response by ligatured animals, and induces a hyperalgesic response in animals not receiving ligatures. Likewise, field-stimulated hippocampal adrenergic neurotransmission is decreased upon continuous i.c.v. microinfusion of TNF. These results indicate an important role of brain-derived TNF, both in the pathology of neuropathic pain, as well as in fundamental pain perception.

Surgical Pearl: Delayed intranasal knot tying for composite grafts of the ala

From the Geisinger Medical Center, Section of Dermatologic Surgery. Reprint requests: Michael L. Ramsey, MD, PennState Geisinger Health System, Geisinger Medical Center, Section of Dermatologic Surgery, Danville, PA 17822-1406. J Am Acad Dermatol 1998;39:787-8. Copyright © 1998 by the American Academy of Dermatology, Inc. 0190-9622/98/$5.00 + 0 16/74/91719 Surgical procedures within the nasal passage, such as composite grafting of the alar rim, present the challenges of visualization and maneuverability generally not encountered in cutaneous surgery. An additional challenge of composite grafting is the need for gentle and atraumatic tissue handling to improve graft survival. Delayed knot tying has been advocated to facilitate small wound closure.1,2 It allows improved visualization, gentle manipulation of tissue, and precise placement of sutures within a confined space. We performed a variation of this technique while repairing an alar defect with an interlocking composite graft. The helical rim donor site, the alar rim recipient site, and the composite graft were prepared according to the design of Ratner, Katz, and Grande.3 They secure their composite graft by first inserting the cartilaginous wings into alar tissue lateral to the defect and then suturing it in place. We chose to place all intranasal sutures first, before knot tying. We then anchored the graft wings into alar slots and tied the knots last. Using 6.0 mild chromic gut, we sutured first through the nasal mucosa. Then the needle was passed through the corresponding location on the “mucosal” side of the graft (Fig 1). We gently held the graft within our fingertips and saline-soaked gauze. We were able to use both the entire opening of the naris and the additional space afforded by the alar rim defect to access precise needle inserPEARLS

The effect of epidural injection of betamethasone or bupivacaine in a rat model of lumbar radiculopathy.

The effect of epidural injection of betamethasone or bupivacaine was investigated in an animal model of lumbar radiculopathy. To investigate the effects of an epidural steroid (betamethasone) or a local anesthetic (bupivacaine) in an animal model of radiculopathy produced by nerve root irritation. Epidural injections are commonly used for the treatment of low back pain and sciatica. However, efficacy remains controversial, and there is a paucity of basic information to support clinical use or the injections. Fifty-one rats were used. The left L4 and L5 nerve roots were loosely ligated with chromic gut, and either betamethasone, bupivacaine, betamethasone in combination with bupivacaine, or saline was injected using an epidurally placed catheter. The effects of epidural injection were evaluated using response to noxious stimuli and immunohistochemical methods. In betamethasone-treated rats (either alone or in combination with bupivacaine), thermal hyperalgesia was significantly less (P < 0.010 after surgery than that in saline- or bupivacaine-treated groups, in which the hyperalgesia was maximum at 2-3 postoperative weeks before resolving 5 weeks after surgery. Immunohistochemical analysis did not correlate with these results. Epidural steroid injection has a significant effect on the thermal hyperalgesia produced in a model of radiculopathy, which may provide clinical support for advocates of epidural steroids.

Afferent activity from myelinated inferior alveolar nerve fibres in ferrets after constriction or section and regeneration

To investigate possible peripheral mechanisms for post-injury sensory disorders in the trigeminal system, we have made electrophysiological recordings from myelinated fibres in the inferior alveolar nerve (IAN) which have previously sustained an injury. In earlier experiments we have shown that axons in ligature-induced neuromas of the IAN develop spontaneous activity and mechanical sensitivity. The present study has investigated these responses after two different types of injury. In 24 anaesthetised adult male ferrets the left IAN was either chronically constricted by four loose chromic gut ligatures (12 animals) or sectioned and regeneration permitted (12 animals). After recovery periods of 3 days, 1, 3, 6, 12 or 24 weeks, single unit recordings were made from the nerve proximal to the injury site. The proportion of units which were spontaneously active ranged from 0% to 19% after constriction injury and from 0% to 10% after nerve section and regeneration. Both groups revealed a marked variability between individual animals at similar time periods. Mechanical sensitivity was found in 0–42% of units after constriction and 0–25% of units after nerve section; both groups showed a significant negative correlation between mechanical sensitivity and recovery period. None of the fibres which had regained peripheral receptive fields was either spontaneously active or mechanically sensitive. There was no significant difference between the levels of spontaneous activity or mechanical sensitivity in the two groups or that previously found in ligature-induced neuromas. Thus we conclude that widely differing types of peripheral nerve injury are capable of initiating similar raised levels of afferent activity in myelinated inferior alveolar nerve fibres.

Chymopapain-induced reduction of proinflammatory phospholipase A2 activity and amelioration of neuropathic behavioral changes in an in vivo model of acute sciatica.

The mechanism of action underlying chymopapain (Chymodiactin) chemonucleolysis remains obscure. Radiographic studies suggest that chymopapain does not alter disc fragment size acutely; nonetheless, patients often report symptom resolution within a few days, even hours, of treatment. The authors postulate that, in addition to its chemonucleolytic action, chymopapain may possess antiinflammatory properties. To test this hypothesis, the authors assessed the ability of chymopapain to modulate the activity of the proinflammatory enzyme phospholipase A2 (PLA2) and to ameliorate behavioral changes associated with inflammatory neuropathy in an in vivo model of sciatica. Thirty-nine male Fischer rats were randomly assigned to one of three treatment groups: 1) saline, 2) betamethasone, or 3) chymopapain. All of the rats underwent unilateral sciatic nerve ligation with loose chromic gut suture to induce inflammatory mononeuropathy. The animals were tested for thermal and mechanical hyperalgesia on Days 0 (preoperation), 7 (pretreatment), and 14 (prior to death). Three animals were killed on Day 0 to determine the baseline PLA2 activity within unmanipulated rat sciatic nerves. On Day 7, three animals from each group were killed to assess PLA2 activity prior to treatment. The remainder were given a single infusion of saline, betamethasone (0.3 mg/kg), or chymopapain (100 pKat U) around the inflamed nerve. On Day 14, the remaining animals were killed and their sciatic nerves were removed. The tissue was homogenized and the PLA2 activity was determined using [14C]arachidonate-labeled Escherichia coli phospholipid membrane as a substrate. Lipids were extracted and separated by thin-layer chromatography. All animals developed behavioral changes consistent with inflammatory mononeuropathy 24 to 72 hours postoperatively; these included gait disturbance, flexion deformity, and hyperalgesia of the involved hindlimb. The degree of mechanical and thermal hyperalgesia was comparable between groups at Day 7. By Day 14, the thermal hyperalgesia had resolved; the mechanical hyperalgesia was less evident in the betamethasone- and chymopapain-treated groups than in the saline-treated controls (p = 0.003; saline- vs. chymopapain-treated groups p = 0.004; saline- vs. betamethasone-treated groups p = 0.008). The mean PLA2 activity at baseline (Day 0) was 11.6 +/- 4.9 nmol phospholipid hydrolyzed per minute per milligram of protein. The PLA2 activity at Day 7 was 74.4 +/- 18.2 (ligated side) and 21.2 +/- 11.7 (nonligated side). At Day 14, PLA2 activity was reduced in the chymopapain- (47.8 +/- 12.3) and betamethasone- (39.7 +/- 9.5) treated groups compared with the saline control group (62.3 +/- 11.2), (saline- vs. chymopapain-treated groups p < 0.05; saline- vs. betamethasone-treated groups p < 0.01). The PLA2 activity in nonligated specimens was 18.6 +/- 10.1. These data indicate that chymopapain exhibits antiinflammatory properties in vivo, reducing PLA2 activity and ameliorating mechanical hyperalgesia in this model of inflammatory sciatic neuropathy.

New experimental model of ureteropelvic junction obstruction allowing easy access for percutaneous surgery.

To assess the usefulness of an experimental model of ureteropelvic junction (UPJ) obstruction designed to facilitate subsequent percutaneous surgery, a right UPJ obstruction was created in 10 pigs by an open retroperitoneal surgical approach. With the pig in the left lateral decubitus position, a 0.038-inch Terumo guidewire was inserted via a 1-cm longitudinal upper-third ureterotomy and advanced up and down so as to bridge the UPJ from the flank to the urogenital opening. A UPJ obstruction was then induced by securing two 2-0 chromic gut ties, separated by an interval of 1 cm, over the Terumo guidewire and a 6F ureteral catheter, which was removed immediately after this procedure. After closure of the ureterotomy, the kidney was anchored horizontally to the muscle wall, and the Terumo guidewire was coiled subcutaneously in the flank and fixed to the urogenital opening. Each pig developed marked hydronephrosis, diagnosed by ultrasonography, after a mean interval of 8.3 days. Retrograde ureteropyelography confirmed this pronounced dilation of the right collecting system above a tight UPJ stricture (mean length 1.17 cm). Subsequent percutaneous access to the UPJ over the Terumo guidewire in the lateral decubitus position was facilitated by the almost-horizontal plane of dilation (mean operating time 14 minutes). Pathologic examination of the UPJ revealed mild periureteral fibrosis, but the muscle layer and urothelium remained normal. We have developed a reliable and reproducible model of secondary UPJ obstruction especially designed for percutaneous surgery. This model should provide a better understanding of current endoscopic techniques such as endopyelotomy and could help to promote new treatment concepts such as percutaneous endoscopic pyeloplasty.

Chromic gut suture reduces calcitonin-gene-related peptide and substance P levels in the spinal cord following chronic constriction injury in the rat

The chronic constriction injury (CCI) is an animal model of an experimental peripheral neuropathy. In this model, a mononeuropathy is produced by loosely ligating the left sciatic nerve of the rat with chromic gut suture (Bennett and Xie 1988). Maves et al. (1993) have proposed that chemical constituents of chromic gut suture influence the behavioral changes of rats with the CCI. Considering their results, we became interested in evaluating whether the type of suture material used to produce the CCI also affected spinal levels of calcitonin-gene-related peptide immunoreactivity (CGRP-ir) and substance P immunoreactivity (SP-ir), peptides that are associated with small primary afferent neurons. Using methods of radioimmunoassay (RIA), we measured levels of CGRP-ir and SP-ir in the dorsal quadrants of approximately the lumbar 4–5 (L4–L5) spinal segments of rats with a CCI induced using polyglactin (Vicryl ®), plain gut, or chromic gut suture. We observed bilateral decreases in CGRP-ir and SP-ir 60 days after a CCI induced with chromic gut suture, but no changes in peptide levels after a CCI induced with either polyglactin or plain gut suture. These results suggest two possibilities: (1) chromic gut suture, when used to produce the CCI, has more than just a constrictive effect on the sciatic nerve, and/or (2) different suture materials produce changes in CGRP-ir and SP-ir with a differential time-course. Our experiments are unable to distinguish between these two possibilities.

Evaluation of hindpaw position in rats during chronic constriction injury (CCI) produced with different suture materials.

Bennett and Xie (1988) described an experimental peripheral neuropathy that is produced by loosely ligating a rat's left sciatic nerve with chromic gut suture. Four ligations, which are tied tightly enough to constrict the nerve and retard epineurial blood flow, produce a chronic constriction injury (CCI). Maves et al. (1993) reported that if the ligations are tied more loosely (i.e., no retardation of blood flow) than those that produce the CCI, rats exhibit postural changes only when the ligations are of chromic gut. We decided to evaluate effects of different suture materials on the abnormalities in paw position associated with the CCI (Attal et al., 1990). Five groups of rats were included in this study. In three of the groups, the CCI was produced with chromic gut, plain gut, or polyglactin (Vicryl) suture. Rats in the fourth group served as sham injury control animals, and rats in the fifth group served as unoperated control animals. Our results indicate that the position in which the rats held the affected hindpaw varied significantly among treatment groups. Rats whose CCI was induced with chromic gut suture spent more time with the hindpaw in an abnormal position than rats in the other treatment groups. And as compared to rats in the unoperated control group, rats whose CCI was induced with either plain gut or polyglactin suture also spent more time with the hindpaw in an abnormal position. Though these different suture materials produced similar degrees of nerve constriction, the effects on paw position were greater with chromic gut suture. These results suggest that chromic gut suture, when used to produce the CCI, may have more than just a constrictive effect on the sciatic nerve. However, since all suture materials produced changes in paw position, constriction is likely to play an important role in the development of abnormalities in paw position observed in rats with the CCI.

Role of Nitric Oxide in the Development of Thermal Hyperesthesia Induced by Sciatic Nerve Constriction Injury in the Rat

Nitric oxide (NO) has been shown to be involved in mediating nociceptive information transmission in the spinal cord. It is known that the N-methyl-D-aspartate receptor plays an important role in the development of the spinal facilitation evoked by a protracted small afferent input and that this effect is mediated at least in part by NO. Recently, it has been found that N-methyl-D-aspartate receptor-mediated spinal facilitation is crucial in the development of thermal hyperesthesia evoked by a nerve constriction injury. In the current study, we investigated the role of NO in the development of thermal hyperesthesia after a nerve constriction injury. The Bennett and Xie model (four loose chromic gut ligations around the rat sciatic nerve) was used to examine the development of thermal hyperesthesia. An NO synthase inhibitor (N omega-nitro-L-arginine or N omega-nitro-L-arginine methyl ester hydrochloride), rat hemoglobin, or L-arginine was administered intrathecally 10 min before the nerve injury (pretreatment study) or 15 min after the nerve injury (posttreatment study). Pretreatment but not posttreatment administration of NO synthase inhibitor significantly delayed the development of thermal hyperesthesia. The effect of NO synthase inhibitor was reversed by the coadministration of L-arginine but not by the coadministration of D-arginine. Pretreatment with rat hemoglobin also delayed the development of thermal hyperesthesia. L-Arginine itself had no effect on the development of thermal hyperesthesia. NO may play an important role in the development of N-methyl-D-aspartate receptor-mediated spinal facilitation after a nerve constriction injury.

Characterization of Thermal Hyperalgesia, c-fos Expression, and Alterations in Neuropeptides After Mechanical Irrigation of the Dorsal Root Ganglion

This study analyzed hypersensitization in sensory systems after mechanical irritation of the dorsal root ganglion. To develop a reliable and reproducible animal model of hyperalgesia arising from the dorsal root ganglion and to understand the unique contributions of the dorsal root ganglion to clinical manifestations of sciatica. The dorsal root ganglion likely plays an important role in disorders of sciatica. However, no previous study has analyzed sciatica after irritation of the dorsal root ganglion. Thermal hyperalgesia indicates a decrease in thermal nociceptive threshold and hypersensitization in sensory systems. The left L4 and L5 dorsal root ganglia in rats (n = 22) were exposed circumferentially. Other rats (n = 22) also had the left L4 and L5 dorsal root ganglia ligated loosely with two 4-0 chromic gut sutures. Changes in thermal withdrawal latency were examined in the hindpaws across time. Substance P and vasoactive intestinal polypeptide contents were quantified in the dorsal root ganglion and spinal cord. Substance P, calcitonin gene-related peptide, and c-fos expression also were examined in the spinal cord by immunohistochemistry. In addition, histologic changes in myelinated nerve content were examined in the dorsal root ganglion. Thermal hyperalgesia occurred in rats with exposure of the dorsal root ganglion and in rats with loose ligation of the dorsal root ganglion, and was accompanied by an increase in c-fos expression and spontaneous pain-related behaviors. This experimental model reliably produced a disorder resembling an acute phase sciatica and should help further advance the understanding of pathomechanisms of spinal pain after irritation of the dorsal root ganglion in humans.

Experimental lumbar radiculopathy. Behavioral and histologic changes in a model of radicular pain after spinal nerve root irritation with chromic gut ligatures in the rat.

The recently proposed animal model of lumbar radiculopathy was used to investigate behavioral consequences and histologic changes in spinal nerve roots, dorsal root ganglia, and spinal nerves after the L4, L5, and L6 nerve roots were loosely ligated with either silk or chromic gut sutures in an attempt to better understand the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy. Little is known about the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy. The recently proposed animal model of unilateral lumbar radiculopathy, which demonstrated an association with motor paresis and thermal hyperalgesia of the affected hind limb and showed evidence of spontaneous pain has been demonstrated, may serve as a vehicle to allow direct investigation of the nature of the pathophysiological mechanisms associated with lumbar radiculopathy. Three distinct treatments of the nerve roots were initially investigated: 1) a sham intervention, where the surgery simply exposed the nerve roots and dorsal root ganglion followed by standard closing procedures; 2) 4-0 silk ligature, where two loose ligatures of 4-0 silk were placed around the nerve roots; and 3) 4-0 chromic gut 2, where four 0.3 cm pieces of 4-0 chromic gut were laid adjacent to the nerve roots and secured by two loose ligatures of 4-0 chromic gut. ANOVA techniques were used to test for differential effects across time for the three treatment groups in terms of animal function. A qualitative analysis of the histology of the ipsilateral and contralateral nerve roots, dorsal root ganglia, and spinal nerves was done to correlate histologic changes with behavioral changes. Behavioral results were consistent with the previous study. Rats treated with chromic gut, but not silk, reliably demonstrated a prolonged thermal hyperalgesia that was maximal 2 weeks after surgery and lasted for up to 12 weeks. These behavioral changes, however, were not correlated with histologic changes in myelinated fiber content in the L4, L5, and L6 nerve roots, dorsal root ganglia and spinal nerves, the ipsilateral spinal nerved, dorsal root ganglia, and nerve roots of rates ligated with silk or chromic gut showed similar, significant, decreased in the number of large diameter myelinated fibers. These results suggest that mechanical constriction of the L4, L5, and L6 spinal nerve roots, as evidenced by a loss of myelinated fibers, is not sufficient to produce the behavioral effects associated with this model of lumbar radiculopathy. It is hypothesized that chemical factors from the chromic gut play a role in the pathophysiology and development of the behavioral, but not histological, changes in this model of lumbar radiculopathy.

A Comparison of Soft-tissue Substitutes

The fate of the Zyderm II, Zyplast, Vicryl, and chromic gut was histologically examined up to 1 year following subcutaneous implantation into rats. Our data demonstrated both Zyderm II and Zyplast to be inert materials without inflammatory response; there was no difference in long-term persistence between these two collagens. Both Vicryl and chromic gut implants caused an intense inflammatory response at 1 month, and Vicryl was completely resorbed before 6 months. The degree of inflammation associated with chromic gut diminished over time, and approximately 67% of the material persisted without reaction up to 1 year.

A Variation of Composite Grafting for Reconstruction of Full-Thickness Nasal Alar Defects

REPORT OF A CASE A 72-year-old man presented with a biopsy-proven basal cell carcinoma on the right alar rim. Following resection of the tumor, the patient had a 0.9×0.4-cm full-thickness defect of the alar rim ( Figure 1 ). THERAPEUTIC CHALLENGE Removing a malignancy from the alar rim of the nose often results in destruction of the skin, the underlying cartilage, and nasal mucosal lining. These full-thickness defects are difficult to repair because of the need to replace structural support, skin, and nasal lining. SOLUTION This skin and fat variation of a composite graft uses a rectangular-shaped skin and fat graft from the inner upper arm, supraclavicular area, or the earlobe. The graft is removed from the donor site and minimally defatted to approximate the contour of the alar rim. The graft is sutured into the mucosal surface of the defect with 6-0 fast-absorbing chromic gut with the epidermis forming the ''new''