Inflammation-induced GluA1 trafficking and membrane insertion of Ca2+ permeable AMPA receptors in dorsal horn neurons is dependent on spinal tumor necrosis factor, PI3 kinase and protein kinase A.

Peripheral inflammation induces sensitization of nociceptive spinal cord neurons. Both spinal tumor necrosis factor (TNF) and neuronal membrane insertion of Ca2+ permeable AMPA receptor (AMPAr) contribute to spinal sensitization and resultant pain behavior, molecular mechanisms connecting these two events have not been studied in detail. Intrathecal (i.t.) injection of TNF-blockers attenuated paw carrageenan-induced mechanical and thermal hypersensitivity. Levels of GluA1 and GluA4 from dorsal spinal membrane fractions increased in carrageenan-injected rats compared to controls. In the same tissue, GluA2 levels were not altered. Inflammation-induced increases in membrane GluA1 were prevented by i.t. pre-treatment with antagonists to TNF, PI3K, PKA and NMDA. Interestingly, administration of TNF or PI3K inhibitors followed by carrageenan caused a marked reduction in plasma membrane GluA2 levels, despite the fact that membrane GluA2 levels were stable following inhibitor administration in the absence of carrageenan. TNF pre-incubation induced increased numbers of Co2+ labeled dorsal horn neurons, indicating more neurons with Ca2+ permeable AMPAr. In parallel to Western blot results, this increase was blocked by antagonism of PI3K and PKA. In addition, spinal slices from GluA1 transgenic mice, which had a single alanine replacement at GluA1 ser 845 or ser 831 that prevented phosphorylation, were resistant to TNF-induced increases in Co2+ labeling. However, behavioral responses following intraplantar carrageenan and formalin in the mutant mice were no different from littermate controls, suggesting a more complex regulation of nociception. Co-localization of GluA1, GluA2 and GluA4 with synaptophysin on identified spinoparabrachial neurons and their relative ratios were used to assess inflammation-induced trafficking of AMPAr to synapses. Inflammation induced an increase in synaptic GluA1, but not GluA2. Although total GluA4 also increased with inflammation, co-localization of GluA4 with synaptophysin, fell short of significance. Taken together these data suggest that peripheral inflammation induces a PI3K and PKA dependent TNFR1 activated pathway that culminates with trafficking of calcium permeable AMPAr into synapses of nociceptive dorsal horn projection neurons.

Mitotoxicity and bortezomib-induced chronic painful peripheral neuropathy.

Many of the most effective anti-cancer drugs induce a dose-limiting peripheral neuropathy that compromises therapy. Evidence from animal models of chemotherapy-induced painful peripheral neuropathy produced by the taxane agent, paclitaxel, and the platinum-complex agent, oxaliplatin, indicate that they produce neuropathy via a common mechanism-a toxic effect on the mitochondria in primary afferent sensory neurons. Bortezomib is from the proteasome-inhibitor class of chemotherapeutics. It also produces a dose-limiting peripheral neuropathy, but its effects on neuronal mitochondria are unknown. To investigate this, we developed a model of bortezomib-induced painful peripheral neuropathy in the rat and assessed mitochondrial function (respiration and ATP production) in sciatic nerve samples harvested at two time points: day 7, which is three days after treatment and before pain appears, and day 35, which is one month post-treatment and the time of peak pain severity. We found significant deficits in Complex I-mediated and Complex II-mediated respiration, and in ATP production at both time points. Prophylactic treatment with acetyl-L-carnitine, which has previously been shown to prevent paclitaxel- and oxaliplatin-induced mitochondrial dysfunction and pain, completely blocked bortezomib's effects on mitochondria and pain. These results suggest that mitotoxicity may be the core pathology for all chemotherapy-induced peripheral neuropathy and that drugs that protect mitochondrial function may be useful chemotherapy adjuncts.

Characterization of oxaliplatin-induced chronic painful peripheral neuropathy in the rat and comparison with the neuropathy induced by paclitaxel.

Anti-neoplastic agents in the platinum-complex, taxane, vinca alkaloid, and proteasome-inhibitor classes induce a dose-limiting, chronic, distal, symmetrical, sensory peripheral neuropathy that is often accompanied by neuropathic pain. Clinical descriptions suggest that these conditions are very similar, but clinical data are insufficient to determine the degree of similarity and to determine if they share common pathophysiological mechanisms. Animal models do not have the limitations of clinical studies and so we have characterized a rat model of chronic painful peripheral neuropathy induced by a platinum-complex agent, oxaliplatin, in order to compare it with a previously characterized model of chronic painful peripheral neuropathy induced by a taxane agent, paclitaxel. The oxaliplatin model evokes mechano-allodynia, mechano-hyperalgesia, and cold-allodynia that have a delayed onset, gradually increasing severity, a distinct delay to peak severity, and duration of about 2.5 months. There is no effect on heat sensitivity. Electron microscopy (EM) analyses found no evidence for axonal degeneration in peripheral nerve, and there is no upregulation of activating transcription factor-3 in the lumbar dorsal root ganglia. There is a statistically significant loss of intraepidermal nerve fibers in the plantar hind paw skin. Oxaliplatin treatment causes a significant increase in the incidence of swollen and vacuolated mitochondria in peripheral nerve axons, but not in their Schwann cells. Nerve conduction studies found significant slowing of sensory axons, but no change in motor axons. Single fiber recordings found an abnormal incidence of A- and C-fibers with irregular, low-frequency spontaneous discharge. Prophylactic dosing with two drugs that are known to protect mitochondria, acetyl-l-carnitine and olesoxime, significantly reduced the development of pain hypersensitivity. Our results are very similar to those obtained previously with paclitaxel, and support the hypothesis that these two agents, and perhaps other chemotherapeutics, produce very similar conditions because they have a mitotoxic effect on primary afferent neurons.

Mitochondrial abnormality in sensory, but not motor, axons in paclitaxel-evoked painful peripheral neuropathy in the rat.

The dose-limiting side effect of the anti-neoplastic agent, paclitaxel, is a chronic distal symmetrical peripheral neuropathy that produces sensory dysfunction (hypoesthesia and neuropathic pain) but little or no distal motor dysfunction. Similar peripheral neuropathies are seen with chemotherapeutics in the vinca alkaloid, platinum-complex, and proteasome inhibitor classes. Studies in rats suggest that the cause is a mitotoxic effect on axonal mitochondria. If so, then the absence of motor dysfunction may be due to mitotoxicity that affects sensory axons but spares motor axons. To investigate this, paclitaxel exposure levels in the dorsal root, ventral root, dorsal root ganglion, peripheral nerve, and spinal cord were measured, and the ultrastructure and the respiratory function of mitochondria in dorsal roots and ventral roots were compared. Sensory and motor axons in the roots and nerve had comparably low exposure to paclitaxel and exposure in the spinal cord was negligible. However, sensory neurons in the dorsal root ganglion had a very high and remarkably persistent (up to 10 days or more after the last injection) exposure to paclitaxel. Paclitaxel evoked a significant increase in the incidence of swollen and vacuolated mitochondria in the myelinated and unmyelinated sensory axons of the dorsal root (as seen previously in the peripheral nerve) but not in the motor axons of the ventral root. Stimulated mitochondrial respiration in the dorsal root was significantly depressed in paclitaxel-treated animals examined 2-4 weeks after the last injection, whereas respiration in the ventral root was normal. We conclude that the absence of motor dysfunction in paclitaxel-evoked peripheral neuropathy may be due to the absence of a mitotoxic effect in motor neuron axons, whereas the sensory dysfunction may be due to a mitotoxic effect resulting from the primary afferent neuron's cell body being exposed to high and persistent levels of paclitaxel.

The response of spinal microglia to chemotherapy-evoked painful peripheral neuropathies is distinct from that evoked by traumatic nerve injuries.

Painful peripheral neuropathies produced by nerve trauma are accompanied by substantial axonal degeneration and by a response in spinal cord microglia that is characterized by hypertrophy and increased expression of several intracellular and cell-surface markers, including ionizing calcium-binding adapter molecule 1 (Iba1) and Cd11b (a complement receptor 3 antigen recognized by the OX42 antibody). The microglia response has been hypothesized to be essential for the pathogenesis of the neuropathic pain state. In contrast, the painful peripheral neuropathies produced by low doses of cancer chemotherapeutics do not produce degeneration of axons in the peripheral nerve, although they do cause partial degeneration of the sensory axons' distal-most tips, that is the intraepidermal nerve fibers that form the axons' terminal receptor arbors. The question thus arises as to whether the relatively minor and distal axonal injury characterizing the chemotherapy-evoked neuropathies is sufficient to evoke the microglial response that is seen after traumatic nerve injury. We examined the lumbar spinal cord of rats with painful peripheral neuropathies due to the anti-neoplastic agents, paclitaxel, vincristine, and oxaliplatin, and the anti-retroviral agent, 2',3'-dideoxycytidine (ddC), and compared them to rats with a complete sciatic nerve transection and the partial sciatic nerve injury produced in the chronic constriction injury model (CCI). As expected, microglia hypertrophy and increased expression of Iba1 were pronounced in the nerve transection and CCI animals. However, there was no microglia hypertrophy or increased Iba1 staining in the animals treated with paclitaxel, vincristine, oxaliplatin, or ddC. These results suggest that the mechanisms that produce neuropathic pain after exposure to chemotherapeutics may be fundamentally different than those operating after nerve trauma.

Chemotherapy-evoked painful peripheral neuropathy: analgesic effects of gabapentin and effects on expression of the alpha-2-delta type-1 calcium channel subunit.

Chemotherapeutics in the taxane and vinca-alkaloid classes sometimes produce a painful peripheral neuropathy for which there is no validated treatment. Experiments with rat models of paclitaxel- and vincristine-evoked pain suggest that these conditions may not respond to all of the analgesics that have efficacy in other models of painful peripheral neuropathy. We tested gabapentin as a potential analgesic for paclitaxel- and vincristine-evoked pain. We used a repeated dosing paradigm because there are precedents showing that repeated drug exposure may be necessary to demonstrate analgesia in neuropathic pain models. Gabapentin is believed to work via binding to voltage-gated calcium channels that contain the alpha-2-delta type-1 (alpha(2)delta-1) subunit, and the expression of this subunit is known to be increased in some painful peripheral neuropathy models. Thus we also examined whether the paclitaxel-evoked pain syndrome was accompanied by an alpha(2)delta-1 increase, and whether gabapentin had any effect on subunit expression. We found that the paclitaxel- and vincristine-evoked mechano-allodynia and mechano-hyperalgesia were significantly reduced by gabapentin, but only with repeated dosing. Paclitaxel-evoked painful peripheral neuropathy was associated with an increased expression of the alpha(2)delta-1 subunit in the spinal dorsal horn, but not in the dorsal root ganglia. The spinal cord increase was normalized by repeated gabapentin injections. Together, these findings suggest that repeated dosing with gabapentin may be beneficial in patients with chemotherapy-evoked painful peripheral neuropathy and that gabapentin's mechanisms of action may include normalization of the nerve injury-evoked increase in calcium channel alpha(2)delta-1 subunit expression.

Effect of clinical mastitis on the lactation curve: a mixed model estimation using daily milk weights.

The objective of this study was to estimate the milk production losses associated with clinical mastitis using mixed linear models and correlation structures that have not been available previously. Data used included computer-recorded daily milk yields and detailed and accurate recordings of clinical mastitis cases. Two commercial Holstein dairy farms in New York State participated in the study, one with 650 lactating cows and another that began the study with 830 lactating cows and increased to 1120 cows by the end of the study. Cows on both farms were housed in free stall barns and milked 3 times daily in milking parlors. Electrical conductivity was used as a diagnostic aid for clinical mastitis on both farms. Date of clinical onset was recorded for every episode of clinical mastitis as well as for 8 other diseases defined using standardized case definitions (dystocia, milk fever, retained placenta, metritis, ketosis, displaced abomasum, lameness, and cystic ovarian disease) during the study period of October 1, 1999 to July 31, 2001. The mixed linear model for explaining variation in the outcome variable daily milk yield relative to non-mastitic herdmates found the terms for all 9 diseases studied, including clinical mastitis, significant. The model with an autoregressive correlation structure was preferred based on -2 * log likelihood, Akaike's information criterion, and Bayesian information criterion as well as savings in degrees of freedom. Separate analyses were run for first lactation cows and for second-plus lactation cows because their lactation curves were shaped differently. Adjusting for the effects of the other 8 diseases, milk production loss from clinical mastitis during the whole lactation was estimated as approximately 598 kg for second-plus lactation cows. However, cows that contracted mastitis had a daily production advantage of 2.6 kg over their herdmates until they contracted the disease. When compared with this potentially higher milk production, the total loss from clinical mastitis was estimated as 1181 kg.

Use of a craniofacial miniplate for internal fixation in a young child with cervical instability. Case report.

Commercially available anterior cervical internal fixation devices are designed for placement in adults and older children. Use of these systems in preschool-aged children is precluded due to the small size of their cervical vertebral bodies (VBs). The authors describe a 2-year-old boy who suffered a C3-4 injury, resulting in complete ligamentous disruption. Because of the gross cervical instability, they elected to perform surgery via posterior and anterior approaches, supplemented with internal fixation, during the same operation. The purpose of the anterior internal fixation device is to deliver compressive forces onto the interbody graft and keep it in place, thus optimizing the potential for a successful fusion. Because of the discrepancy in size between the VBs and the plate and screws, however, the authors were unable to use any of the standard anterior cervical fixation devices. Instead, they implanted a craniofacial miniplate, and the patient was required to wear an external halo brace. The miniplate provided enough stability to allow for a solid fusion. The authors believe that this technique is a reasonable option in young children who require anterior cervical fixation.

Chemotherapy-evoked painful peripheral neuropathy.

Vincristine and paclitaxel, two of the most effective drugs in the battle against cancer, produce a dose-limiting neurotoxicity that sometimes presents as a painful peripheral neuropathy. For the first time, investigators have been able to produce these chemotherapy-evoked painful peripheral neuropathies in the laboratory rat. These new models have already begun to elucidate the causes of the neuropathic pain associated with these antineoplastic drugs, which will now make it possible to search for effective ways to prevent and treat it.

A neuroimmune interaction in painful peripheral neuropathy.

BACKGROUND: In almost every neuropathic pain state caused by peripheral nerve damage, whether due to trauma or disease, both structural damage and an inflammatory response exist. OBJECTIVE: The goal of this study was to determine the contribution, separate from the effects of the structural lesion, of the inflammatory response to neuropathic pain. METHODS: Two sets of experiments were performed. In the first, an experimental inflammation of the nerve (a neuritis) and an experimental inflammation of the muscle (a myositis control group) were produced in two groups of rats. The pain responses to stimuli applied to the sciatic nerve territory on the plantar hind paw were evaluated through tests of (1) heat hyperalgesia; (2) mechanical allodynia; (3) mechanical hyperalgesia; and (4) cold allodynia. In the second set of experiments, thalidomide or cyclosporin-A was used to block the production of immune modulators in the neuritis model and in a chronic constriction injury model (which involves structural damage and an inflammatory response in the sciatic nerve) to determine the contribution of the immune response to the pain observed in the first set of experiments. RESULTS: In experiment 1, rats with the neuritis but not those with the myositis developed neuropathic pain symptoms. In experiment 2, thalidomide produced a partial but significant reduction in pain in the chronic constriction injury model across all four tests, but there was no effect in the neuritis model in any of the tests. Cyclosporin-A resulted in a dose-related reduction in pain in both models across all four tests. CONCLUSIONS: These data suggest the possibility of an important interaction between the immune system and the nervous system in neuropathic pain and suggest that drugs modulating the immune system may be useful therapies in at least some neuropathic pain states.

Effect of local methylprednisolone on pain in a nerve injury model. A pilot study.

BACKGROUND AND OBJECTIVES: Local injections of corticosteroids are frequently used in the treatment of regional pain. The rationale for this is not very clear, since an inflammatory cause of pain is rarely evident. There are few data on the effect of corticosteroids on nociception in experimental animals. However, corticosteroids have been found to suppress ectopic discharges from experimental neuromas and to have a short-lasting suppressive effect on transmission in normal C-fibers. In this study the influence of a locally applied depot form of a corticosteroid on neuropathic pain was investigated in a rat model. METHODS: Peripheral mononeuropathy was induced with a chronic constriction injury to the left sciatic nerve. This procedure has previously been shown to produce various signs of disturbed sensibility, including heat hyperalgesia, mechanical allodynia, and mechanical hyperalgesia, indicating that a neuropathic pain-like condition has developed. The occurrence of neuropathic pain in these animals was confirmed with behavioral testing after 9 days. The site of injury was then reexposed and treated locally with either a depot form of a corticosteroid (methylprednisolone) or saline. The animals were then tested for another 11 days. RESULTS: The heat hyperalgesia and mechano-allodynia but not the mechano-hyperalgesia were depressed in the animals receiving the corticosteroid but not in those treated with saline. The effect remained during the whole 11-day test period. CONCLUSIONS: It is hypothesized that the corticosteroid acts by suppression of ectopic neural discharges from the injured nerve fibers.

The analgesic effects of R(+)-WIN 55,212-2 mesylate, a high affinity cannabinoid agonist, in a rat model of neuropathic pain.

The effects of a high affinity cannabinoid receptor agonist were evaluated in rats subjected to chronic constriction injury of the sciatic nerve (CCI) or a sham operation. Intraperitoneal (i.p.) injections of the active, but not the inactive enantiomer, alleviated the pain behavior exhibited by CCI animals in a dose dependent manner. Moreover, at doses ranging from 0.43 to 4.3 mg/kg effects on sensitivity to a heat stimulus were observed neither in the paw contralateral to the sciatic ligation, nor in animals subjected to sham surgery. Animals subjected to CCI and treated with 4.3 mg/kg exhibited hypoalgesia in the paw ipsilateral to the ligated sciatic, i.e. heat hypoalgesia was completely reversed. The hypoalgesia is presumed to be the results of unmasking of a sensory deficit reflecting the known loss of C and A delta with CCI. Although side effects were present in some CCI animals subjected to the high dose (4.3 mg/kg), a moderate dose (2.14 mg/kg) completely alleviated the thermal and mechanical hyperalgesia, and mechanical allodynia without side effects. In addition to identifying a potential drug treatment for painful neuropathy, this study suggests that changes in cannabinoid receptors occurs in nerve injured animals.

The sympathetic nervous system contributes to capsaicin-evoked mechanical allodynia but not pinprick hyperalgesia in humans.

The contribution of the sympathetic nervous system (SNS) to pain, mechanical allodynia (MA), and hyperalgesia in humans is controversial. A clearer understanding is crucial to guide therapeutic use of sympatholytic surgery, blocks, and drug treatments. In rats, capsaicin-evoked MA, and to some extent, pinprick hyperalgesia (PPH), can be blocked with alpha-adrenoreceptor antagonists. In this study, we examined the contribution of the SNS to MA and PPH in normal human subjects by blocking alpha-adrenoreceptors with intravenous phentolamine. In a double-blinded, placebo-controlled, crossover study, subjects were given IV saline or phentolamine, 1 mg/kg over 20 min. Ten minutes after the start of the infusion, subjects received 100 micrograms of intradermal capsaicin on the foot dorsum with the temperature of the injected site clamped at 36 degrees C. The temperature of the uninjected foot was used to monitor the degree of alpha-adrenoreceptor blockade produced by phentolamine. Ongoing pain and MA and PPH areas were measured every 5 min for 60 min. A significantly greater increase in temperature on the uninjected foot was seen during the phentolamine infusion compared with the saline infusion, indicating alpha-adrenergic blockade. Significantly less MA was observed with the phentolamine infusion 10-25 min after capsaicin injection than with the saline infusion. No significant differences in ongoing pain or PPH areas were seen between the two infusions at any time. Our results suggest that capsaicin-evoked MA and PPH have different mechanisms, with the SNS having a role in MA but not in PPH or ongoing pain.

Vanilloid receptor loss is independent of the messenger plasticity that follows systemic resiniferatoxin administration.

Resiniferatoxin (RTX) depletes vanilloid (capsaicin) receptors from lumbar dorsal root ganglia (DRG) of the rat. In addition, RTX causes changes in neuropeptide and nitric oxide synthase expression in lumbar DRG neurons, similar to those described following axotomy; this latter phenomenon is referred to as messenger plasticity. These findings suggested that vanilloid receptor loss may be part of the plasticity that follows RTX treatment. Here we show that vanilloid receptor expression, as detected by [3H]RTX autoradiography, is not changed in lumbar DRGs of axotomized rats, nor is it altered in a rat model (chronic constriction injury) of neuropathic pain. Thus, the in vivo expression of vanilloid receptors detected by specific [3H]RTX binding does not require the presence of intraaxonally transported trophic factors such as nerve growth factor. We conclude that messenger plasticity and vanilloid receptor loss are mediated by distinct mechanisms.

Synthetic omega-conopeptides applied to the site of nerve injury suppress neuropathic pains in rats.

In patients and animals with painful peripheral neuropathies, spontaneous ectopic discharge from injured primary afferents is hypothesized to maintain a central state of hyperexcitability that underlies hyperalgesia and allodynia. Temporary suppression of this discharge allows the central state to normalize, such that hyperalgesia and allodynia are absent or reduced until the resumption of the discharge rekindles central hyperexcitability. Previous work suggests that Ca++ channels are involved in the genesis of spontaneous discharge from injured afferents. We applied SNX-111 and SNX-124 (0.1-3.0 micrograms), synthetic homologs of omega-conopeptides (MVIIA and GVIA, respectively) and potent blockers of neuronal N-type voltage-sensitive Ca++ channels, to the site of nerve injury via chronically implanted perineural cannulae in rats with an experimental painful peripheral neuropathy (the chronic constriction injury model). Heat-hyperalgesia and mechano-allodynia were reduced for at least 3 hr. Drug application to a normal nerve had no effect on responses to heat or mechanical stimuli. These results suggest that N-type Ca++ channel blockers may be useful in the treatment of the abnormal pains that occur after nerve injury.

An animal model of neuropathic pain: a review.

Recent work has succeeded in producing models of painful peripheral neuropathies in laboratory animals. There is evidence that the animals experience both abnormal spontaneous pain and abnormal evoked pains (allodynia and hyperalgesia). Experimental analyses of these models have demonstrated potential pathophysiologic mechanisms in both the peripheral and central nervous systems; it is likely that the model neuropathic pain syndromes are due to several different mechanisms. One line of evidence suggests that these pain states gradually become centralized due to an excitotoxic effect on spinal cord dorsal horn inhibitory interneurons. The role of the sympathetic nervous system appears to vary, depending on the type of nerve injury and the temporal evolution of the syndrome. There is evidence indicating that the abnormality of cutaneous temperature regulation that often accompanies painful peripheral neuropathy is not necessarily due to the activity of sympathetic vasomotor efferents.

Biomechanical effects of laminectomy on thoracic spine stability.

Thoracic columns (T1-L1 levels) from 15 fresh human cadavers were used to quantify alterations in the biomechanical response after laminectomy. Eight specimens were tested intact (Group I); the remaining seven preparations were tested after two-level laminectomy (Group II) at the midheight of the column. All specimens were fixed at the proximal and distal ends and loaded until failure. Force and deformation were collected by use of a data acquisition system. Failure of the Group I specimens included compressive fractures with or without posterior element distractions, generally at the midheight of the column. Group II preparations failed at the superior aspect of laminectomy or at a level above laminectomy, suggesting an increased load sharing. Biomechanical responses of the Group II preparations were significantly different (P < 0.05) from those of the Group I specimens at deformations from the physiological to the failure range. In addition, failure forces for Group II preparations were significantly lower (P < 0.001) than for Group I specimens. The stiffness and energy-absorbing capacities of the laminectomized specimens were also significantly different (P < 0.05) from those of the intact columns. In contrast, the deflections at failure for the two groups were not statistically different, suggesting that the human thoracic spine is deformation sensitive. Our data demonstrate that a two-level laminectomy decreases the strength and stability of the thoracic spine throughout the loading range. Although this is not a practical concern with an otherwise intact vertebral column, laminectomy, when other abnormalities such as vertebral fracture, tumor, or infection exist, may require stabilization by fusion and instrumentation.

Autoradiographic analysis of 125I-substance P binding in rat spinal cord following chronic constriction injury of the sciatic nerve.

Using receptor binding and autoradiographic techniques, changes in Bolton-Hunter labeled 125I-substance P (125I-BH-SP) binding were determined in laminae I/II, V and X of rat lumbar spinal cord after chronic constriction injury (CCI) of the sciatic nerve. When compared to the sham-operated side of the control group, SP binding significantly increased ipsilateral to the CCI in laminae I/II at 5, 10 and 20 days after injury and in lamina V at 5 days after injury. Scatchard analysis was performed on the 125I-BH-SP binding to the NK1 receptor in laminae I/II of rats 5 days after generation of the CCI. A significant decrease in the Kd of 125I-BH-SP binding was observed in laminae I/II ipsilateral to CCI when compared with the control side (ipsilateral to sham surgery). There was no significant change in the Bmax in laminae I/II ipsilateral to CCI. The changes in 125I-BH-SP binding in the rat spinal cord that occurred after CCI were found in areas of the spinal cord that receive terminations of nociceptive primary afferent fibers. The increased affinity of the NK1 binding site that we report could result in an increase in SP receptor activation in laminae I/II. Such central changes in SP binding may contribute to the neuropathic pain syndrome observed in rats with the CCI.