Nerve injury-induced tactile allodynia is mediated via ascending spinal dorsal column projections

Peripheral nerve injury produces signs of neuropathic pain including tactile allodynia and thermal hyperalgesia, sensory modalities which may be associated with different neuronal pathways. Studies of spinally-transected, nerve-injured rats have led to suggestions that thermal hyperalgesia may be mediated predominately through local spinal circuitry whereas ascending input to supraspinal sites is critical to the manifestation of tactile allodynia. Here, the nature of ascending spinal input mediating tactile allodynia was explored using selective spinal lesions. Male Sprague-Dawley rats received L(5)/L(6) spinal nerve ligation (SNL) and ipsilateral or contralateral (relative to the SNL side) lesions including spinal hemisections and bilateral and unilateral dorsal column lesions. The rats were maintained in a sling and monitored for tactile allodynia by measuring withdrawal thresholds to probing with von Frey filaments 24 h after the hemisection. Rats receiving dorsal column lesions demonstrated no motor deficits while rats receiving spinal hemisection showed paralysis of the paw which nevertheless responded to strong noxious stimulation. Spinal hemisection ipsilateral, but not contralateral, to SNL completely abolished tactile allodynia while maintaining spinal nocifensive reflexes to noxious pinch. Bilateral and ipsilateral dorsal column lesions blocked tactile allodynia while contralateral dorsal column lesions did not. Administration of lidocaine into the nucleus gracilis ipsilateral to SNL also blocked tactile allodynia, but did not alter thermal hyperalgesia in SNL rats or increase thermal nociceptive responses in sham-operated rats. Lidocaine microinjected into the contralateral nucleus gracilis produced no changes in responses to tactile or thermal stimuli in either group. These results indicate that tactile allodynia after peripheral nerve injury is dependent upon inputs to supraspinal sites. Furthermore, it is apparent that afferent signals interpreted as tactile allodynia course through the ipsilateral dorsal columns and are relayed through the nucleus gracilis. This neuronal pathway is consistent with the interpretation that tactile allodynia pursuant to peripheral nerve injury is transmitted to the central nervous system by means of large diameter, myelinated fibers.     

Tactile allodynia in the absence of C-fiber activation: altered firing properties of DRG neurons following spinal nerve injury

We examined the relation between ectopic afferent firing and tactile allodynia in the Chung model of neuropathic pain. Transection of the L5 spinal nerve in rats triggered a sharp, four- to six-fold increase in the spontaneous ectopic discharge recorded in vivo in sensory axons in the ipsilateral L5 dorsal root (DR). The increase, which was not yet apparent 16 h postoperatively, was complete by 24 h. This indicates rapid modification of the electrical properties of the neurons. Only A-neurons, primarily rapidly conducting A-neurons, contributed to the discharge. No spontaneously active C-neurons were encountered. Tactile allodynia in hindlimb skin emerged during precisely the same time window after spinal nerve section as the ectopia, suggesting that ectopic activity in injured myelinated afferents can trigger central sensitization, the mechanism believed to be responsible for tactile allodynia in the Chung model. Most of the spike activity originated in the somata of axotomized DRG neurons; the spinal nerve end neuroma accounted for only a quarter of the overall ectopic barrage. Intracellular recordings from afferent neuron somata in excised DRGs in vitro revealed changes in excitability that closely paralleled those seen in the DR axon recordings in vivo. Corresponding changes in biophysical characteristics of the axotomized neurons were catalogued. Axotomy carried out at a distance from the DRG, in the mid-portion of the sciatic nerve, also triggered increased afferent excitability. However, this increase occurred at a later time following axotomy, and the relative contribution of DRG neuronal somata, as opposed to neuroma endings, was smaller. Axotomy triggers a wide variety of changes in the neurochemistry and physiology of primary afferent neurons. Investigators studying DRG neurons in culture need to be alert to the rapidity with which axotomy, an inevitable consequence of DRG excision and dissociation, alters key properties of these neurons. Our identification of a specific population of neurons whose firing properties change suddenly and synchronously following axotomy, and whose activity is associated with tactile allodynia, provides a powerful vehicle for defining the specific cascade of cellular and molecular events that underlie neuropathic pain.     

Loose ligation of the rat sciatic nerve elicits early accumulation of Shank1 protein in the post-synaptic density of spinal dorsal horn neurons

Plasticity in the spinal dorsal horn may contribute to the development of pain following peripheral nerve injury. Shank proteins are a constituent family of the post-synaptic density (PSD), and they may play a role in synaptic plasticity through activity-dependent synaptic remodeling and growth. In this study we examined the early consequences of the loose ligation of the sciatic nerve on Shank1 protein and message levels in the PSD of spinal dorsal horn neurons. Four hours after sciatic ligation, the protein levels of Shank1 increased in the ipsilateral PSD of ligated animals. In contrast, no changes were detected in the contralateral PSD of these ligated animals, or either the ipsilateral or contralateral PSD of sham-operated animals. Shank1 was linked to the PSD marker protein PSD-95 and the NR2B subunit of NMDA receptors. The ligated animals also exhibited two early signs of pain behavior, a shift in weight distribution and thermal hyperalgesia. There was no overall change in Shank1 message in either ligated or sham-operated animals. The accumulation of Shank1 in the PSD was abolished by intrathecal pre-treatment with anisomycin or Shank1 siRNA, but not with non-target siRNA. The same pre-treatment prevented both the early signs of pain behavior. Intrathecal pre-treatment with either MK-801 or U0126 similarly prevented the Shank1 accumulation and alleviated both the behavioral signs of pain. The early accumulation of Shank1 in the PSD of dorsal horn neurons may be a necessary step in the injury-associated plasticity that in time leads to the development of persistent pain.     

Nerve growth factor regulates VR-1 mRNA levels in cultures of adult dorsal root ganglion neurons

Nerve growth factor (NGF) regulates the nociceptive properties including sensitivity to capsaicin of a subset of dorsal root ganglion neurons, which express the high-affinity NGF receptor, trkA. Capsaicin sensitivity co-localizes with the expression of a cloned capsaicin receptor, vanilloid receptor type 1 (VR-1), which displays properties similar to the native capsaicin response. To determine whether VR-1 mRNA levels are regulated by NGF, VR-1 mRNA levels and the ability to respond to capsaicin by release of the neuropeptide calcitonin gene related peptide (CGRP) were measured as a function of NGF concentration in cultures of adult dorsal root ganglion neurons. NGF treatment increased both VR-1 mRNA expression and capsaicin evoked release of CGRP. These effects were inhibited by treatment with the trkA inhibitor k252a.     

Mechanical allodynia following contusion injury of the rat spinal cord is associated with loss of GABAergic inhibition in the dorsal horn

The present study investigated whether mechanical allodynia following contusive spinal cord injury (SCI) of the thoracic segments 12 and 13 of the rat was associated with a reduction in gamma-aminobutyric acid (GABA)ergic inhibition adjacent to the site of injury. Five to 7 days following SCI, extracellular recordings were obtained from dorsal horn neurones located 1-2 segments caudal to the injury, in non-allodynic and allodynic halothane anaesthetised rats and from comparable neurones in normal rats. To assess spinal GABAergic inhibition in the three groups of animals, spontaneous and evoked cell firing rates were recorded before, during and after microiontophoretic application of the GABA(A) receptor antagonist bicuculline. Administration of bicuculline to normal animals resulted in significant and reversible increases in the receptive field size, spontaneous firing rate, response to brushing and pinching the skin and afterdischarge activity of dorsal horn neurones, as well as decreasing paired-pulse depression of responses evoked by transcutaneous electrical stimulation. In non-allodynic SCI animals, bicuculline ejection led to significant changes in receptive field size, paired-pulse depression and responses to brush and pinch stimulation that were comparable to those observed in normal animals. By contrast, in allodynic SCI animals, bicuculline ejection had little or no effect on dorsal horn neurone responses to mechanical skin stimuli and paired-pulse depression despite reliably blocking the inhibition of cell firing produced by similarly applied GABA. The demonstration of reduced GABAergic inhibition predominantly in the allodynic SCI rats suggests that such a deficiency contributed to this pain-related behaviour acutely following SCI.     

Differential contribution of TRPV1 to thermal responses and tissue injury-induced sensitization of dorsal horn neurons in laminae I and V in the mouse

Our previous recordings from dorsal root ganglion and spinal lamina V neurons from TRPV1-mutant mice showed dramatic decreases in responses to temperatures near the activation threshold of this channel (43-49 degrees C). Somewhat unexpectedly, we only observed behavioral deficits in these mice at higher temperatures (50-58 degrees C). In the present study, we tested the hypothesis that the noxious heat-evoked pain behavior that persists in TRPV1-mutant mice reflects residual responsiveness of neurons in the superficial, but not deep, dorsal horn. To this end, we performed in vivo extracellular recordings of spinal nociresponsive neurons in laminae I and V in wild type (WT) and TRPV1 mutant mice. Neurons in WT and mutant mice from both laminae did not differ in their spontaneous activity or evoked responses to mechanical or cold stimuli. By contrast, most lamina I neurons from mutant mice responded to noxious heat with significantly higher thresholds than in WT mice. In contrast, lamina V neurons from mutant mice were virtually unresponsive to noxious heat before and after topical mustard oil-induced tissue injury. Interestingly, lamina I neurons in mutant mice displayed thermal sensitization following tissue injury, comparable in magnitude, but of shorter duration, than in WT mice. We conclude that TRPV1 is necessary for noxious heat-evoked responses of lamina V neurons, both before and after tissue injury. It is also an essential contributor to the normal activation threshold of lamina I neurons to noxious heat and for the full duration of thermal sensitization of lamina I neurons following injury. Finally, our results suggest that the processing of noxious thermal messages by neurons in lamina I involves convergent inputs from a heterogeneous population of primary afferent thermal nociceptors.     

Key role of the dorsal root ganglion in neuropathic tactile hypersensibility.

Cutting spinal nerves just distal to the dorsal root ganglion (DRG) triggers, with rapid onset, massive spontaneous ectopic discharge in axotomized afferent A-neurons, and at the same time induces tactile allodynia in the partially denervated hindlimb. We show that secondary transection of the dorsal root (rhizotomy) of the axotomized DRG, or suppression of the ectopia with topically applied local anesthetics, eliminates or attenuates the allodynia. Dorsal rhizotomy alone does not trigger allodynia. These observations support the hypothesis that ectopic firing in DRG A-neurons induces central sensitization which leads to tactile allodynia. The question of how activity in afferent A-neurons, which are not normally nociceptive, might induce allodynia is discussed in light of the current literature.     

Behavioral manifestations of neuropathic pain and mechanical allodynia, and changes in spinal dorsal horn neurons, following L4–L6 dorsal root constriction in rats

We investigated behavioral symptoms of neuropathic pain, and associated changes in dorsal horn neurons, in a rat model involving loose ligation of lumbar dorsal roots. The L4–L6 dorsal roots were exposed unilaterally and loosely constricted central to the respective ganglia with one (1-ligation) or two (2-ligation) silk 7-O ligatures. In control groups the dorsal roots were exposed but not ligated (sham-operated), or sutures were placed lengthwise between the dorsal roots (suture control). There was a significant reduction in mechanical withdrawal threshold on the operated side in both 1- and 2-ligation groups which began at 3 days, peaked at 2–5 week, and gradually recovered. A delayed threshold reduction was also seen on the non-operated side. Immediately post-surgery there was a significant increase (hypoalgesia) in thermal paw withdrawal latency (Hargreaves test) in 1- and 2-ligation groups on the operated (but not non-operated) side that recovered after 1 week. Significantly less weight was borne by the operated limb 1–5 weeks post-operatively in 1- and 2-ligation groups. The force of hind limb withdrawals elicited by graded noxious heat pulses (38–52°C) was significantly lower 1 week post-surgery on the operated side (1-ligation group) followed by recovery. Withdrawal forces were higher 5–9 week post-surgery on the non-operated side in 1- and 2-ligation groups. We found no evidence of cold allodynia. Neither sham-operated nor suture controls showed any signs of allodynia or hyperalgesia. Following behavioral testing, rats were anesthetized with halothane for single-unit recordings from lumbar wide dynamic range-type (WDR) neurons. At 22 week post-surgery, the mean area of mechanosensitive receptive fields was significantly larger for units on the operated side in 1- and 2-ligation groups compared with those on the non-operated side or with those from sham-operated rats. Mean stimulus-response functions to graded noxious heat pulses (38–52°C, 5 s) were not significantly different between operated and non-operated sides for 1- or 2-ligation groups, or compared with the 22-week sham-operated group. At 5 week post-surgery, the mean area of cutaneous receptive fields, and stimulus-response functions to graded noxious heat, were not significantly different between units recorded on operated versus non-operated sides, or compared with units from 5-week sham-operated rats. Spontaneous unit activity was significantly higher on the operated versus non-operated side in the 2-ligation (22-week) and sham (5-week) groups. Enlarged cutaneous receptive fields of dorsal horn neurons may contribute to mechanical allodynia associated with dorsal root constriction. However, the slow (>5 week) development of receptive field enlargement does not match the rapid development of allodynia. The lack of effect of dorsal root constriction on thermal sensitivity of dorsal horn units ipsilaterally corresponds to the lack of marked thermal hyperalgesia observed behaviorally.     

The role of the dorsal column pathway in visceral nociception

Neurosurgeons have successfully used punctate midline myelotomy to relieve visceral cancer pain in human patients. Animal experiments demonstrate a visceral nociceptive pathway in the posterior column that is more effective than the spinothalamic tract in activating thalamic neurons, eliciting behavioral responses and triggering increases in regional cerebral blood flow. This visceral nociceptive pathway involves postsynaptic dorsal column neurons in the central, visceral processing region of the spinal cord. Axons from the sacral cord ascend near the midline and from the thoracic cord at the junction of the gracile and cuneate fasciculi.     

Spinal R-phenyl-isopropyl adenosine inhibits spinal dorsal horn neurons responding to noxious heat stimulation in the absence and presence of sensitization

The effects of spinally administered R(−)N⁶-(2-phenylisopropyl) adenosine (R-PIA) on spinal dorsal horn neurons were investigated in anesthetized rats. Extracellular, single-unit recordings were measured during noxious heating of receptive fields on the hind paw. Three series of experiments were carried out to characterize the effects of R-PIA on spinal dorsal horn neuronal activity. In the first set of experiments, R-PIA dose-dependently suppressed noxiously evoked activity of spinal dorsal horn neurons. In the second set of experiments, R-PIA suppressed noxiously evoked activity in neurons sensitized by the topical application of mustard oil to a region of skin adjacent to their receptive fields. In the third set of experiments, R-PIA prevented mustard oil induced sensitization of dorsal horn neurons. In all cases, the adenosine receptor antagonist theophylline reversed the action of R-PIA. The results of these investigations indicate the involvement of spinal adenosine receptors in spinal pathways of central sensitization and in the modulation of somatically induced noxious pain.     

Spinal nerve injury activates prostaglandin synthesis in the spinal cord that contributes to early maintenance of tactile allodynia

To determine if spinal prostaglandins (PG) contribute to tactile allodynia, male, Sprague-Dawley rats were fitted with either intrathecal (i.t.) microdialysis or drug delivery catheters 3 days before tight ligation of the left lumber 5/6 spinal nerves. Paw withdrawal thresholds (PWT) were determined using von Frey filaments. Ligated rats developed tactile allodynia within 24h, as evidenced by a decrease in PWT in the affected hindpaw (<4 g vs. >15 g control). Sham-operated controls were unchanged from baseline (>15 g). Allodynia was also characterized by a significant increase in the evoked release of PGE(2). Thus, brushing the plantar surface of the affected hindpaw with a cotton-tipped applicator, 5 days postligation, increased the [PGE(2)](dialysate) to 199+/-34% of the prestimulus control period. In contrast, brushing had no detectable effect on release before surgery or in sham-operated animals. Basal release (no brushing) was similar before and after surgery (sham-operated and ligated rats). In a separate group of rats and beginning 2 days after ligation, the acute i.t. injection of S(+)-ibuprofen, SC-51322, SC-236, or SC-560 significantly reversed allodynia (maximum effect=69+/-9, 66+/-6, 57+/-4, 20+/-5%, respectively). R(-)-ibuprofen or vehicle were without effect. The results of this study suggest that: (a). spinal PG synthesis and allodynia-like behaviour are triggered by normally innocuous brushing after spinal nerve ligation; (b). pharmacological disruption of this cascade significantly reverses allodynia; (c). COX-2 is the relevant isozyme; and (d). the PG effect is mediated by spinal EP receptors.     

The effect of spinal GABA receptor agonists on tactile allodynia in a surgically-induced neuropathic pain model in the rat

This study evaluated the effects of spinal gamma-aminobutyric acid (GABA) receptor agonists on the tactile allodynia observed in rats with ligation of the L5/L6 nerve roots (Chung model) and chronic lumbar intrathecal catheters. In these rats, the spinal injection of the GABAb agonist baclofen (BAC; 0.03–0.3 μg) and GABAa agonist muscimol (MUS; 0.1–1.0 μg) resulted in a dose-dependent antagonism of the allodynia at doses which had no detectable effect upon motor function. Intrathecal injection of the GABAb antagonist CGP 35348 (CGP; 30 μg) or the GABAa antagonist bicuculline (BIC; 0.3 μg) prior to injection of each GABA receptor agonist had little effect upon normal or tactile allodynic thresholds, but significantly reversed the anti-allodynic effects produced by the respective receptor agonists. The antagonistic effects were limited to the agonist of the respective receptor. These observations indicate that spinal GABAa and GABAb receptors modulate spinal systems activated by low threshold mechanoreceptors which mediate the allodynia observed following peripheral nerve injury.     

Nerve injury-induced changes in Homer/glutamate receptor signaling contribute to the development and maintenance of neuropathic pain

While group 1 metabotropic glutamate receptors (mGluRs) and ionotropic N-methyl-d-aspartate (NMDA) receptors regulate nociception, the precise molecular mechanism(s) contributing to glutamate signaling in chronic pain remain unclear. Here we not only confirmed the key involvement of Homer proteins in neuropathic pain, but also distinguished between the functional roles for different Homer family members and isoforms. Chronic constriction injury (CCI) of the sciatic nerve induced long-lasting, time-dependent increases in the postsynaptic density expression of the constitutively expressed (CC) isoforms Homer1b/c and/or Homer2a/b in the spinal dorsal horn and supraspinal structures involved in nociception (prefrontal cortex, thalamus), that co-occurred with increases in their associated mGluRs, NR2 subunits of the NMDA receptor, and the activation of downstream kinases. Virus-mediated overexpression of Homer1c and Homer2b after spinal (intrathecal) virus injection exacerbated CCI-induced mechanical and cold hypersensitivity, however, Homer1 and Homer2 gene knockout (KO) mice displayed no changes in their neuropathic phenotype. In contrast, overexpression of the immediate early gene (IEG) Homer1a isoform reduced, while KO of Homer1a gene potentiated neuropathic pain hypersensitivity. Thus, nerve injury-induced increases in CC-Homers expression promote pain in pathological states, but IEG-Homer induction protects against both the development and maintenance of neuropathy. Additionally, exacerbated pain hypersensitivity in transgenic mice with reduced Homer binding to mGluR5 supports also an inhibitory role for Homer interactions with mGluR5 in mediating neuropathy. Such data indicate that nerve injury-induced changes in glutamate receptor/Homer signaling contribute in dynamic but distinct ways to neuropathic pain processing, which has relevance for the etiology of chronic pain symptoms and its treatment.     

Cisplatin-induced apoptosis in rat dorsal root ganglion neurons is associated with attempted entry into the cell cycle.

Platinum compounds induce apoptosis in malignant cells and are used extensively in the treatment of cancer. Total dose is limited by development of a sensory neuropathy. We now demonstrate that when rats are administered cisplatin (2 mg/kg i.p. for 5 d), primary sensory neurons in the dorsal root ganglion die by apoptosis. This was reproduced by exposure of dorsal root ganglion neurons and PC12 cells to cisplatin (3 microg/ml) in vitro. Apoptosis was confirmed by electron microscopy, DNA laddering, and inhibition by the caspase inhibitor z-VAD.fmk (100 microM). Cell death in vitro was preceded by upregulation of cyclin D1, cdk4, and increased phosphorylation of retinoblastoma protein; all are indicators of cell cycle advancement. The level of p16(INK4a), an endogenous inhibitor of the cyclin D1/cdk4 complex decreased. Exposure of PC12 cells and dorsal root ganglion neurons to increased levels of nerve growth factor (100 ng/ ml) prevented both apoptosis and upregulation of the cell cycle markers. Cancer cells without nerve growth factor receptors (gp140TrkA) were not protected by the neurotrophin. This indicated that cisplatin may kill cancer cells and neurons by a similar mechanism. In postmitotic neurons, this involves an attempt to re-enter the cell cycle resulting in apoptosis which is specifically prevented by nerve growth factor.     

Long-lasting enhancement in the intrinsic excitability of deep dorsal horn neurons

Intrinsic excitability (IE) can be defined as an output of action potentials from a given input signal. Changes to the IE of a neuron are an important aspect of the cellular plasticity that underlies learning and memory process. In this study, long-term plastic change in IE of deep dorsal horn neurons (DHNs) was investigated. Associative spike pairing stimulation (PS) induced a long-lasting increase in IE. Buffering intracellular calcium with BAPTA (10mM) prevented the induction of a long-lasting increase in IE. PS failed to induce a long-lasting increase in IE in the presence of either D-APV (50 microM) or cadmium chloride (100 microM). Apamin (100 nM) partially blocked the induction of a long-lasting increase in IE. This intrinsic plasticity requires a rise in postsynaptic Ca(2+) and NMDA receptor activation during the induction period, and this process might be mediated by the down-regulation of small-conductance calcium-dependent potassium (SK) channels. In deep DHNs, PS induced excitatory postsynaptic potential (EPSP)-spike (E-S) potentiation, which increases the firing probability and the number of spikes, by consistent dorsal rootlet stimulation. Under bath application of bicuculline (10 microM) and strychnine (1 microM), PS induced E-S potentiation and long-lasting increases in IE. These results suggest that an increase in IE might underlie E-S potentiation, while a reduction in inhibitory transmission does not contribute to E-S potentiation and long-lasting increases in IE. We conclude that PS enhances the IE of deep DHNs, which may play an important role in spinal processing of nociceptive information.     

Opiate-mediated inhibition of calcium signaling is decreased in dorsal root ganglion neurons from the diabetic BB/W rat.

The effect of diabetes mellitus on opiate-mediated inhibition of calcium current density (I(D Ca) [pA pF-1]) and cytosolic calcium response ([Ca2+]i nM) to depolarization with elevated KCl and capsaicin was assessed. Experiments were performed on isolated, acutely dissociated dorsal root ganglion (DRG) neurons from diabetic, BioBreeding/Worcester (BB/W) rats and age-matched control animals. Sciatic nerve conduction velocity was significantly decreased in diabetic animals compared to controls. Mean I(DCa) and [Ca2+]i responses to capsaicin and elevated KCl recorded in DRGs from diabetic animals were significantly larger than those recorded in DRG neurons from controls. In neurons from diabetic animals, the opiate agonist dynorphin A (Dyn A; 1, 3, and 5 microM) had significantly less inhibitory effect on I(D Ca) and KCl-induced [Ca2+]i responses compared to controls. Omega-conotoxin GVIA (omega-CgTX; 10 microM) and pertussis toxin (PTX; 250 ng ml-1) abolished Dyn A-mediated inhibition of I(DCa) and [Ca2+]i in control and diabetic neurons, suggesting that Dyn A modulated predominantly N-type calcium channels coupled to opiate receptors via PTX-sensitive (Gi/o) inhibitory G proteins. These results suggest that opiate-mediated regulation of PTX-sensitive, G protein-coupled calcium channels is diminished in diabetes and that this correlates with impaired regulation of cytosolic calcium.     

Systemic adenosine infusion reduces the area of tactile allodynia in neuropathic pain following peripheral nerve injury: a multi-centre, placebo-controlled study.

Systemic adenosine has been shown in earlier case reports and a small placebo-controlled study to reduce pathological sensory dysfunction such as tactile allodynia in neuropathic pain. To evaluate this further, the effects of systemic adenosine infusion (50 microg/kg/min for 60 min) on tactile sensory dysfunction and pain was evaluated in 26 patients suffering peripheral neuropathic pain characterized by dynamic tactile allodynia. A randomized, cross-over, double-blind, placebo-controlled technique was used in this multi-centre study.Psychophysical methods were used to evaluate sensory dysfunction and spontaneous pain. The area of dynamic tactile allodynia was significantly reduced by adenosine compared with placebo (p=0.043), but spontaneous pain and tactile pain threshold were not significantly improved compared with the effects of placebo treatment. As a secondary outcome, a higher incidence of positive subjective effects on the clinical pain condition, in a few cases with long duration (several months), following adenosine treatment was found when the global effect of respective treatment was assessed (p=0.028). The results demonstrate involvement of adenosine receptor-sensitive pain mechanisms in some aspects of the sensory dysfunction often found in neuropathic pain.     

细胞外信号调节激酶通路抑制剂对完全弗氏佐剂致痛大鼠背根神经结中谷氨酸转运蛋白表达的影响

目的:观察细胞外信号调节激酶(ERK)通路抑制剂PD98059时完全弗氏佐剂(CFA)致痛大鼠脊髓背根神经结(DRG)中谷氨酸转运蛋白表达的影响.方法:24只大鼠随机分为对照组、单纯致痛组、PD1组和PD10组.疼痛模型采用大鼠足底注射CFA 100μL.对照组及单纯致痛组经椎管内给予二甲基亚砜(DMSO)10μL,每日2次.PD1组和PD10组分别经椎管内给予PD98059 1μg或10μg,每日2次.测定大鼠每日痛阈变化,3 d后RT-PCR法检测大鼠DRG内谷氨酸转运蛋白表达的变化.结果:注射CFA致痛后各组大鼠痛阈均显著降低,PD1组与PD10组大鼠痛阈均较单纯致痛组显著升高,PD1组与PD10组痛阈升高差异无显著性.单纯致痛组DRG中谷氨酸转运体1(GLT-1)和兴奋性氨基酸载体1(EAAC1)表达显著高于对照组、PD1组、PD10组.除PD1组DRG中GLT-1表达高于对照组外,PD1组、PD10组及对照组DRG中GLT-1与EAAC1表达差异无显著性.结论:鞘内给予PD98059可减轻大鼠足底注射CFA引起的疼痛反应并减低致痛侧DRG中谷氨酸转运蛋白表达.     

T cell memory is short-lived in the absence of antigen

Immunological memory has generally been ascribed to the development of long-lived memory cells that can persist for years in the absence of renewed antigenic encounter. In the experiments reported here, we have adoptively transferred memory T cells in the presence and absence of priming antigen and assessed their functional survival. The results indicate that, in contrast to the traditional view, the maintenance of T cell memory requires the presence of antigen, suggesting that memory, like tolerance, is an antigen-dependent process rather than an antigen-independent state.