Autotomy Scores Research Articles

Dopamine receptors in the anterior insular cortex modulate long-term nociception in the rat

The rostral agranular insular cortex (RAIC) receives dopaminergic projections from the mesolimbic system, which has been involved in the modulation of nociceptive processes. In this study we determined the contribution of dopamine D 1 and D 2 receptors in the RAIC regarding nociception processing in a neuropathic pain model, as well as inflammatory articular nociception measured as pain-induced functional impairment in the rat (PIFIR). Microinjection of vehicle or substances into the RAIC was performed after the induction of nociception. The groups were treated with: a dopamine D 1 receptor antagonist (SCH-23390), a dopamine D 1 receptor agonist (SKF-38393), a dopamine D 2 receptor agonist (TNPA) and a dopamine D 2 receptor antagonist (spiperone). Chronic nociception, induced by denervation, was measured by the autotomy score in which onset and incidence were also determined. The SCH-23390 and TNPA groups showed a decrease in the autotomy score and a delay on the onset as compared to control, whereas the PIFIR groups did not show statistical differences. This work shows the differential role of dopamine receptors within the RAIC in which the activation of D 2 or the blockade of D 1 receptors elicit antinociception.

Local Nogo-66 administration reduces neuropathic pain after sciatic nerve transection in rat

Neuropathic pain after periphery nerve injury is frequently accompanied by the regeneration of the injured nerve fibers. We tested in this study whether local administration of Nogo-66, a well-studied axon growth inhibiting peptide in the central nerve system, could reduce the pain related behavior after sciatic nerve transection in rat. Nogo-66 peptide was purified as a GST fusion protein. Its inhibitory function was testified by neurite outgrowth assay of primary cultured neurons, and then it was given directly at the lesion site by a minipump for 2 weeks. Mechanical nociceptive withdrawal responses and heat hyperalgesia responses were assessed during a 4-week period, and autotomy was evaluated during a 6-week period. The results showed that the mechanical allodynia and heat hyperalgesia scores of the rats treated with GST-Nogo-66 were significantly higher than the controls between 7 and 14 days after sciatic nerve transection. The autotomy scores in the GST-Nogo-66 group were significantly lower than the controls from 28 days after surgery. Taken together, the results of our present study suggest that Nogo-66 may be utilized to decrease the neuropathic pain after periphery nerve injury.

Effects of collagen nerve guide on neuroma formation and neuropathic pain in a rat model

Background Posttraumatic neuroma formation is a major cause of neuropathic pain that can occur after elective surgery, amputation, or trauma. This study examined the use of biosynthetic collagen nerve guides to prevent the development of posttraumatic neuromas. Methods Collagen nerve guides were applied after neurectomy in a rat sciatic nerve model in an effort to stimulate linear neuronal outgrowth and reduce random axon sprouting. Animals were monitored for evidence of neuropathic pain—autotomy scores were recorded for 8 weeks posttransection—after which proximal stumps were excised and processed for histologic analyses. Results Moderate to severe autotomy was observed in 88% (7 of 8) of the control (neurectomy) animals. In contrast, 13% (1 of 8) of animals receiving collagen nerve guides developed autotomy, which was significantly less than controls ( P < .01). Qualitative analyses of neurofilament and Schwann cell–labeled nerve sections showed a significant enhancement in Schwann cell migration away from the proximal stump and advanced linear axonal regrowth in the collagen nerve guide–treated animals. Conclusions Collagen nerve guides alter the regrowth of transected nerves and reduce the severity of symptoms associated with neuropathic pain.

Taurine in the anterior cingulate cortex diminishes neuropathic nociception: A possible interaction with the glycine A receptor

Taurine is an inhibitory amino-acid which has been proposed as a nociceptive process neuromodulator. The glycine A receptor (glyR A) has been postulated as a receptor in which taurine exerts its function. Functional image studies have documented the role of the anterior cingulate cortex (ACC) in the affective component of pain. The aim of this study was to investigate the role of taurine as a glycinergic agonist in the ACC using a neuropathic pain model related to autotomy behaviour (AB). In order to test whether glyR A is responsible for taurine actions, we microinjected strychnine, a glyR A antagonist. We used taurine microinjected into the ACC, followed by a thermonociceptive stimulus and a sciatic denervation. Chronic nociception was measured by the autotomy score, onset and incidence. The administration of taurine 7 days after denervation modifies the temporal course of AB by inhibiting it. Our results showed a decreased autotomy score and incidence in the taurine groups, as well as a delay in the onset. Those experimental groups in which strychnine was microinjected into the ACC, either on its own or before the microinjection of taurine, showed no difference as compared to the control group. When taurine was microinjected prior to strychnine, the group behaved as if only taurine had been administered. Our results evidence a significant neuropathic nociception relief measured as an AB decrease by the microinjection of taurine into the ACC. Besides, the role of the glyR A is evidenced by the fact that strychnine antagonises the antinociceptive effect of taurine.

GELATIN-TRICALCIUM PHOSPHATE MEMBRANE MODIFIED WITH NGF AND CULTURED SCHWANN CELLS FOR PERIPHERAL NERVE REPAIR: A TISSUE ENGINEERING APPROACH

This study attempted to enhance the efficacy of peripheral nerve regeneration using our previously developed gelatin-tricalcium phosphate (GTG) conduits by incorporating them with nerve growth factors and cultured Schwann cells. The nerve growth factors were covalently immobilized onto the GTG conduits (GEN) using carbodiimide. Schwann cells were harvested from neonatal Lewis rats, cultured for seven days and injected into the GEN conduits. The experiment was performed in three groups: GTG conduits, GEN conduits and GEN conduits with Schwann cells injected (GEN+Sc). The effects of different conduits (GTG, GEN and GEN with Schwann cells) on the peripheral nerve regeneration were evaluated in rat sciatic nerve repair model. 24 weeks after implantation of conduits, degradation of the conduits in all groups was illustrated by the fragmentation of the conduits. All conduits were well tolerated by the host tissue. Under microscopic evaluations, regenerated nerve tissue with myelinated and unmyelinated axons presented in all groups. Histomorphometrically, the total nerve area of GEN+Sc group was significantly higher than GTG group. Conversely, the autotomy score evaluated 12 weeks after nerve repair showed better results for GTG group. Besides, GEN+Sc group had the highest average recovery index of compound muscle action potential, but the difference among each group did not reach statistical significance. Although the electrophysiological recovery of nerve was not significantly improved with GEN+Sc conduit, nerve repair using tissue engineered conduits still provided better histological results. However, it should be noticed that autotomy may be the price paid for enhanced peripheral nerve.

Genetic impairment of interleukin-1 signaling attenuates neuropathic pain, autotomy, and spontaneous ectopic neuronal activity, following nerve injury in mice

Peripheral nerve injury may lead to neuropathic pain, which is often associated with mechanical and thermal allodynia, ectopic discharge of from injured nerves and from the dorsal root ganglion neurons, and elevated levels of proinflammatory cytokines, particularly interleukin-1 (IL-1). In the present study, we tested the role of IL-1 in neuropathic pain models using two mouse strains impaired in IL-1 signaling: Deletion of the IL-1 receptor type I (IL-1rKO) and transgenic over-expression of the IL-1 receptor antagonist (IL-1raTG). Neuropathy was induced by cutting the L5 spinal nerve on one side, following which mechanical and thermal pain sensitivity was measured. Wild-type (WT) mice and the parent strains developed significant allodynia and hyperalgesia in the hind-paw ipsilateral to the injury compared with the contralateral hind-paw. The mutant strains, however, did not display decreased pain threshold in either hind-paw. Pain behavior was also assessed by cutting the sciatic and saphenous nerves and measuring autotomy scores. WT mice developed progressive autotomy, beginning at 7 days post-injury, whereas the mutant strains displayed delayed onset of autotomy and markedly reduced severity of the autotomy score. Electrophysiological assessment revealed that in WT mice a significant proportion of the dorsal root axons exhibited spontaneous ectopic activity at 1, 3, and 7 days following spinal nerve injury, whereas in IL-1rKO and IL-1raTG mice only a minimal number of axons exhibited such activity. Taken together, these results suggest that IL-1 signaling plays an important role in neuropathic pain and in the altered neuronal activity that underlies its development.

An in vivo study of tricalcium phosphate and glutaraldehyde crosslinking gelatin conduits in peripheral nerve repair

In order to modulate the mechanical properties of gelatin, we previously developed a biodegradable composite composed by tricalcium phosphate and glutaraldehyde crosslinking gelatin (GTG) feasible for surgical manipulation. In this study, we evaluated the in vivo applications of GTG conduit for peripheral nerve repair. The effect of sciatic nerve reconstruction was compared between resorbable permeable GTG conduits and durable impermeable silicone tubes. Traditional methods of assessing nerve recovery following peripheral nerve repair including histomorphometric and electrophysiologic features were conducted in our study. In addition, autotomy score and sciatic function index (SFI) in walking tract analysis were used as additional parameters for assessing the return of nerve function. Twenty-four weeks after sciatic nerve repair, the GTG conduits were harvested. Microscopically, regeneration of nerves was observed in the cross-section at the mid portion of all implanted GTG conduits. The cross-sectional area of regenerated nerve of the GTG group was significant larger than that of the silicone group. In the compound muscle action potentials (CMAP), the mean recovery index of CMAP amplitude was 0.24 +/- 0.02 for the silicone group, 0.41 +/- 0.07 for the GTG group. The mean SFI increased with time in the GTG group during the evaluation period until 24 weeks. Walking tract analysis showed a higher SFI score in the GTG group at both 12 and 24 weeks. The difference reached a significant level at 24 weeks. Thus, the histomorphometric, electrophysiologic, and functional assessments demonstrate that GTG can be a candidate for peripheral nerve repair.

Dopamine and NMDA systems modulate long-term nociception in the rat anterior cingulate cortex

The anterior cingulate cortex (ACC) plays a key role in pain processing. It has been reported that increased activity of glutamatergic projections into the ACC intensifies nociception; whereas dopaminergic projections inhibit it. The aim of this study was to evaluate the role of dopaminergic and NMDA systems of the ACC in the modulation of long-term nociception elicited by sciatic denervation in the rat. Score, onset and incidence of long-term nociception were measured by the autotomy behavior. The effects of a single microinjection into the ACC of different doses of dopamine (100 nM, 100 μM and 100 mM), a NMDA receptor antagonist (MK801 200 nM and 9.34 mM) and amantadine, a dopamine agonist and NMDA receptor antagonist (10, 100 and 1000 μM) were tested on long-term nociception. Dopamine diminished autotomy behavior in an inverse dose-dependent manner, with dopamine 100 nM as most effective concentration. MK801 and amantadine elicited a significant reduction on autotomy score. Prior injections of D1 and D2 receptor antagonists blocked the antinociceptive effects of amantadine on long-term nociceptive behavior. The present study suggests an interaction between dopaminergic and glutamatergic systems within the ACC in the genesis and maintenance of long-term nociception.

Scopolamine into the anterior cingulate cortex diminishes nociception in a neuropathic pain model in the rat: an interruption of ‘nociception-related memory acquisition’?

The cingulate cortex plays a key role in the affective component related to pain perception. This structure receives cholinergic projections and also plays a role in memory processing. Therefore, we propose that the cholinergic system in the anterior cingulate cortex is involved in the nociceptive memory process. We used scopolamine ( 10 μg in 0.25 μl/ saline ) microinjected into the anterior cingulate cortex, either before thermonociception followed by a sciatic denervation, between thermonociception and denervation or after both procedures ( n=10 each). The vehicle group (saline solution 0.9%, n=14) was microinjected before thermonociception. Chronic nociception was measured by the autotomy score, which onset and incidence were also determined. Group scopolamine–thermonociception–denervation (STD) presented the lowest autotomy score as compared to vehicle and group thermonociception–denervation–scopolamine (TDS) (vehicle vs. STD, p=0.002, STD vs. TDS, p=0.001). Group thermonociception-scopolamine-denervation (TSD) showed a diminished autotomy score when compared to TDS ( p=0.053). STD group showed a delay in the onset of AB as compared to the rest of the groups. Group TSD presented a significative delay ( p=0.048) in AB onset when compared to group TDS. There were no differences in the incidence between groups. The results show that nociception-related memory processed in the anterior cingulate cortex is susceptible of being modified by the cholinergic transmission blockade. When scopolamine is microinjected prior to the nociceptive stimuli, nociception-related memory acquisition is prevented. The evidence obtained in this study shows the role of the anterior cingulate cortex in the acquisition of nociception-related memory.

Central noradrenergic blockade prevents autotomy in rat: implication for pharmacological prevention of postdenervation pain syndrome

Following transection of peripheral nerve, rats exhibit autotomy, which is considered to be the animal model of postdenervation pain syndrome. It has been suggested that phantom limb pain is a result of peripheral denervation leading to reorganization of somatosensory pathways, particularly in the cerebral cortex, which is shown to depend upon central noradrenergic activity. In this study, sciatic and saphenous nerves were sectioned in the left hindpaw of 30 adult rats resulting in complete loss of pain sensation in the hindpaw. A group of rats received normal saline, compared to another group which received N-(2-) Chloroethyl-N-ethyl-2-bromobenzylamine (DSP4) injection 24 h prior to transection. The latter group was also compared to a third group whose central noradrenergic system were also blocked by bilateral injection of 6-OHDA into the ascending noradrenergic bundle 1 week prior to transection. A fourth group received contralateral cortical ablation in addition to peripheral nerve transection and was compared to the first group whose cortex remained intact. The animals were observed daily for 60 days and autotomy was scored in accordance to the system of Wall et al. [42]. After 1 week, control animals began to exhibit autotomy. In contrast, autotomy was absent in rats treated with DSP4, similar to rats which received 6-OHDA. Rats which had contralateral cortical ablation showed a considerably delayed onset of autotomy and a reduction in final autotomy scores. We conclude that autotomy, as a model of postdenervation pain syndrome, can be prevented by blockade of noradrenergically mediated cortical reorganization. The clinical implications of this finding are discussed.

Influence of testosterone on autotomy in castrated male rats

Sex-related differences exist in nociception and gonadal steroids influence the analgesic response in animals and humans. As we have shown previously, estrogen could modify autotomy in female rats using the sciatic nerve transection model. To further characterize the relationship between gonadal steroid and nociception, the role of testosterone on autotomy in sciatic nerve sectioned rats was investigated. Twenty male rats were subjected to orchiectomy (ORX). Then ten rats received subcutaneous sesame oil and the other ten were treated with testosterone propionate in sesame oil (TP; 500 μg/day/rat). All the rats underwent sciatic nerve resection in left hind limb. Degree of self-mutilation was measured daily for 8 weeks. TP reinstatement resulted in significantly lower autotomy scores in orchiectomized rats. The results demonstrated that testosterone could modify the autotomy behavior, an indicator of neuropathic pain, in rats after nerve injury.

Comparison of autotomy behavior induced in rats by various clinically-used neurectomy methods

When a peripheral nerve is cut, a neuroma develops at its proximal end. Nerve-end neuromas are known to be a source of ectopic sensory input. In some humans this input may cause spontaneous and evoked neuropathic pain. There is currently no available animal model for developing better methods of cutting nerves that produce less painful neuromas than those currently in clinical use. Transection of the sciatic and saphenous nerves in rats also produces nerve-end neuromas. Afferent fibers in such neuromas spontaneously emit ectopic input that coincides with the outbreak of licking, scratching and self-mutilation of the denervated limb (‘autotomy’). This behavior is considered to be the expression of spontaneous disagreeable sensations such as paresthesias, dysesthesias or neuropathic pain. We propose here that the autotomy model can be used as the first step for development of better neurectomy methods. As a demonstration, in this report we compared the course of autotomy expressed by rats following several methods of cutting peripheral nerves that are currently in clinical use. We found that the lowest extent of autotomy was caused by sciatic and saphenous neurectomy with a CO 2 laser. Tight ligation of the nerve, or a simple cut with scissors, also yielded significantly lower autotomy scores compared to cryoneurolysis and electrocut. The differing scores of autotomy caused by these neurectomy methods may derive from different properties of the injury discharge produced by these methods at the time of nerve cut. Our results raise the possibility that a higher incidence of neuropathic pain or related sensory disorders in humans may be expected following cryosurgical and electrocut neurectomies. If validated by further studies, neurectomy methods eliciting lower incidence of autotomy, and sensory disorders in models not based on autotomy may produce lower levels of neuropathic pain in humans.

Contralateral treatment with xylocaine reduces nociceptive behaviour in mononeuropathic rats.

The aim of the present study was to establish whether contralateral treatment with local anaesthetics reduces nociceptive behaviour in mononeuropathic rats. Contralateral treatment with xylocaine on day 6 and 11 following sciatic nerve ligation increased withdrawal latencies to thermal but not to mechanical stimulation for 3-4 days. Rats who received contralateral treatment with xylocaine on day 6 and 11 showed a reduced autotomy score during the following 6 weeks. To compare ipsilateral and contralateral effects another set of experiments was performed. Rats treated contralaterally on day 11 had a significantly lower autotomy score at week 4 and 6. Our results demonstrate that contralateral treatment with xylocaine reduces nociceptive behaviour in mononeuropathic rats for days or weeks.

Effects of Estrogen on Autotomy in Normal and Ovariectomized Rats

Gonadal hormones may modulate analgesia responses induced by acute stress in humans and rats. To evaluate the effects of gonadal hormones in modifying neuropathic pain, we measured autotomy changes following sciatic nerve resection in ovariectomized rats and in the presence of estrogen replacement. Two groups of female rats were subjected to ovariectomy and sham surgery. Each group was then divided into two subgroups receiving subcutaneously sesame oil with or without estradiol benzoate (5 μg/day/rat). All rats then underwent sciatic nerve resection in one hindlimb. Degree of self-mutilation was measured daily for 8 weeks. Estradiol treatment resulted in significantly lower autotomy scores in ovariectomized rats (3.6 ± 0.6 vs. 5.5 ± 0.3, p < 0.01) and in sham-operated rats (3.4 ± 0.7 vs. 5.1 ± 0.4, p < 0.05). The results of this study indicate that estrogen can modify the autotomy behavior, an indicator of neuropathic pain, in rats after nerve injury.

Substantia nigra lesion suppresses the antagonistic effects of N-methyl- d-aspartate receptor antagonist (MK-801) on the autotomy in the rat

Rats received right dorsal root ganglionectomy (DRGn) to induce autotomy, and were treated with MK-801 and/or left stantia nigra (SN) lesion after DRGn. The behavior was quantified using an autotomy grading scale. All the rats in the control groups manifested autotomy from 4 to 19 days after DRGn and attained the highest autotomy score. The group treated with MK-801 immediately after DRGn showed suppression of the development of autotomy. The groups receiving left SN lesion with 6-hydroxydopamine immediately, 2, or 4 days after DRGn showed similar patterns of autotomy as the control groups. However, when combined with the administration of MK-801 immediately after DRGn, SN lesion done immediately or 2 days after DRGn suppressed the antagonistic effect of MK-801 ( P<0.01). When the SN lesion was delayed by 4 days, the suppression effect disappeared. These data suggest that the action of the NMDA receptor antagonist on the autotomy within 4 days after DRGn depend on the integrity of the dopaminergic system.

Intrathecal administration of excitatory amino acid receptor antagonists or nitric oxide synthase inhibitor reduced autotomy behavior in rats.

Peripheral nerve injury may produce neuropathic pain. At the spinal cord level, excitatory amino acid receptors play a role in nociceptive signal modulation. N-methyl-D-aspartate (NMDA) receptor activation initiates the NO-cGMP pathway and further modulates nociceptive signal. Using the autotomy model, we examined the effect of an NMDA and a non-NMDA receptor antagonist, and nitric oxide synthase inhibitor in the treatment of autotomy behavior in rats. A right-side brachial plexus (C5-T1) transection was performed in all rats. In the treatment groups, MK-801, 1-(4-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (a non-NMDA antagonist), and L-NG-nitro arginine methyl ester (L-NAME) were infused intrathecally via an osmotic pump for 7 days at doses of 10, 4, and 400 microg/h, respectively. Saline was infused to control animals. Autotomy behavior was observed daily for 8 wk. The incidence of autotomy was 85% in the control group. MK-801, the non-NMDA antagonist, and L-NAME reduced the autotomy incidence to 10%, 20%, and 10% (P < 0.0001), respectively. All treatments delayed the onset of the autotomy behavior from 15+/-4.5 days in the control group to 52+/-3.8, 43+/-5.6, and 54+/-2.9 (P < 0.001) days in the treatment groups, respectively. The average autotomy scores were also attenuated significantly by these treatments. We conclude that the excitatory amino acid receptors and their intracellular signal messenger NO play a role in deafferentation behavior development. Inhibition of this signaling pathway may be of use for neuropathic pain relief. The excitatory amino acid receptors and their intracellular signal messenger NO play a role in deafferentation behavior development. Inhibition of this signaling pathway may be of use for neuropathic pain relief.

Colchicine treatment of the sciatic nerve reduces neurogenic extravasation, but does not affect nociceptive thresholds or collateral sprouting in neuropathic or normal rats

The effect of topical colchicine treatment of the sciatic nerve on sciatic and saphenous nociceptive thresholds and neurogenic extravasation was investigated in normal and neuropathic rats. After a pilot investigation using several different concentrations of colchicine it was determined that treating the sciatic nerve with 5 mM colchicine did not usually affect the heat nociceptive threshold over the sciatic innervated plantar surface of the hindpaw. Mechanical nociception and motor function were also unchanged. Electrical stimulation of the sciatic nerve after intravenous injection of Evans blue dye causes extravasation of the dye in the cutaneous distribution of the nerve. The area and quantity of sciatic extravasation were measured 3 weeks after treating the sciatic nerve with colchicine. This treatment results in a marked loss of neurogenic extravasation, but there were no changes in the sciatic and saphenous mediated heat and mechanical nociceptive thresholds. The area of saphenous nociceptive innervation was mapped using pinch responses and saphenous neurogenic extravasation acutely after sciatic section. There was no change in the cutaneous distribution of saphenous nociceptive fibers when measured 3 weeks after the sciatic colchicine treatment. Some rats had their sciatic nerves transected immediately after colchicine treatment (5 and 50 mM) and the saphenous nociceptive thresholds and autotomy scores were followed postoperatively. Colchicine pretreatment of the sciatic nerve has no effect on the development of hyperalgesia or autotomy. Colchicine blocks axonal transport in peripheral nerve, including the orthograde transport of tachykinins, which probably explains its ability to induce prolonged reductions in sciatic neurogenic extravasation at concentrations that spare C-fiber nociceptor function. Sciatic nerve colchicine treatment does not trigger nociceptive fiber collateral sprouting from the adjacent saphenous nerve, nor does it influence the development of hyperalgesia and autotomy behavior after sciatic transection.

Suppression of autotomy by N-methyl- d-aspartate receptor antagonist (MK-801) in the rat

The effects of different doses and time of administration of the N-methyl- d-aspartate (NMDA) receptor antagonist (MK-801) on the development of the autotomy (self-mutilation) were studied in the rats receiving dorsal root ganglionectomy (DRGn). The rats without any treatment and those treated with normal saline immediately after DRGn were the control groups. Three groups of rats were treated with 0.1, 0.5 or 1.0 mg/kg of MK-801 immediately after DRGn, and another three were treated with 1.0 mg/kg of MK-801 2, 4, or 7 days after DRGn. The behavioral observations of these rats were quantified using an autotomy grading scale ranging from 0 to 19, and the scores were compared among these groups. The rats in the control groups manifested autotomy from 5 to 17 days after DRGn and all of them (100%) attained the highest autotomy score. Lower doses (0.1 or 0.5 mg/kg) of MK-801 had no effect on the development of the autotomy. In contrast, higher dose (1.0 mg/kg) of MK-801 administered immediately after DRGn significantly suppressed the autotomy as compared to the control groups ( P<0.01) and only 17% of the rats in this group attained the highest score. The antagonistic effect was retained when the treatment of MK-801 was delayed to 2 days after DRGn, however, it disappeared when the treatment was delayed to 4 or 7 days after DRGn. Thus, the antagonistic effect of MK-801 on the autotomy induced by DRGn was dose-related and time-dependent. The main role of the NMDA receptor in the development of the autotomy was within several days after DRGn.

Gender differences in autotomy following sciatic cryoneurolysis in the rat

Gender differences reported in nociceptive and nerve injury research should be considered before conclusions about basic pathologic mechanisms are drawn. Holtzman male rats are routinely used in the mononeuropathy model produced by a peripheral nerve freeze lesion, sciatic cryoneurolysis (SCN). SCN reproducibly results in abnormal behaviors which include autotomy, the gnawing and scratching of the affected hindpaw. In the present studies, the incidence and severity of autotomy 1 to 21 days following SCN was compared in male and female Holtzman rats. Female Holtzman rats displayed a decreased incidence and severity of autotomy 7 days and beyond following SCN. This disparity was statistically different at 14 days ( p < 0.01) and at 21 days ( p < 0.05) by Newman-Keuls test. Morphometric comparison of the sciatic nerve at the lesion site in male and female rats 14 days post-SCN (time of peak autotomy behavior in this model) displayed differences in the fascicular percentage of edema ( p < 0.01) and remyelinating axons ( p < 0.05) between genders using Student's t-test. However, these percentage values did not correlate with either the incidence or severity of autotomy scores for those animals. Therefore, biochemical differences at and/or proximal to the peripheral nerve freeze lesion may be responsible for mechanisms which generate or relate to autotomy.

Peripheral Nerve Pathology Following Sciatic Cryoneurolysis: Relationship to Neuropathic Behaviors in the Rat

Sciatic cryoneurolysis (SCN) is an experimental rat mononeuropathy model that produces neuropathic behavioral sequelae distinct from other neuropathy models. Following SCN, there is limited autotomy peaking in severity and incidence at 7-14 days and delayed but sustained allodynia appearing at about 21 days, with no evidence of thermal hyperalgesia. This study quantified peripheral nerve pathology at weekly intervals following SCN to determine the relationship of nerve degeneration and regeneration to the resulting abnormal behaviors. Fiber histograms based on axon diameter and grid morphometry were used to quantify the pathologic state of nerve fibers, activated phagocytic cells, vessels, and edema at the lesion site. Approximately 90% of the axons demonstrated Wallerianlike degeneration by 3 days post-SCN. At 14 days, small diameter axons significantly increased in number from earlier times following SCN (P < 0.05) but were not significantly different from normal values. At 21 days, the number of small diameter axons was significantly increased over both 14 days (P < 0.05) and normal values (P < 0.05). At 28 days, intermediate diameter axons significantly increased in number with respect to all earlier time periods (P < 0.05). These increases in regenerating fibers overlapped with the development of peak autotomy at 7-14 days and the onset of allodynia after 21 days. Autotomy scores at 7 days positively correlated with grid morphometry data of regenerating axons (p = 0.7) and activated macrophages and Schwann cells (p = 0.8) and inversely correlated with edema (p= -0.8) using Spearman's rank correlation analysis. These data suggest a macrophage and Schwann cell involvement in the sensitization of first- and second-order neurons to afferent input which leads to neuropathic behaviors. These results are discussed in the context of a hypothesis for the generation of differential neuropathic behaviors associated with the pathological events of degeneration and regeneration following the chronic constriction injury model of neuropathic pain and SNC.