Nerve growth factor treatment does not prevent dorsal root ganglion cell death induced by target removal in chick embryos

Summary In chick embryos, on the 3rd day of incubation, the developing right wing bud was removed. One group of the operated embryos was treated with a daily dose of 20 g purified nerve growth factor (NGF) from the 5th day of incubation and sacrificed on the 12th day. The other group was sacrificed on the 12th day of incubation and served as control. NGF was also administered to intact, unoperated embryos for comparison. The size of the dorsal root ganglia in segments 13–16 innervating the wings, were estimated and the number of surviving dorsal root ganglion cells counted both on the right (operated) and left (intact) sides. Although NGF brought about an increase in the size of the ganglia and an increase in the number of dorsal root ganglion cells bilaterally, it was not able to prevent excessive cell death of dorsal root ganglion cells on the operated side. The number of surviving neurons in the dorsal root ganglia on the operated side in embryos with or without NGF administration was only about 30–50% of the number of the intact side.These results show that cell death induced by target removal cannot be offset by NGF administration. It is concluded that NGF may act as a growth promoting agent for developing sensory neurons but other peripheral trophic factor/s are also needed for the maintenance and survival of dorsal root ganglion cells.     

TNF-α在CCD模型大鼠背根神经节中的表达及机制

目的:探讨TNF-α和NF-κB在背根神经节慢性压迫(CCD)模型大鼠背根神经节(DRG)中的表达变化及其对疼痛学行为的影响。方法:建立CCD大鼠模型,采用von Frey纤维丝监测机械痛阈的改变;通过Western blotting检测TNF-α和NF-κB在DRG中的表达变化趋势,分析其与疼痛行为之间的相关性;并采用免疫荧光双染技术研究TNF-α在DRG中的表达位置。结果:CCD组的50%机械缩足阈值在术后1 d即开始明显下降(P0.01),7~14 d达到高峰,其后逐渐上升,直至术后35 d仍明显低于术前及sham组(P0.01)。而DRG上的TNF-α及NF-κB于造模后各时点均显著增多(P0.01),且TNF-α的表达趋势与50%机械缩足阈值显著相关(P0.05)。结论:DRG慢性压迫可促进其上的TNF-α和NF-κB的合成和分泌,进而诱发机械痛觉过敏。因此,TNF-α/NF-κB信号通路可能是CCD模型疼痛形成的重要通路之一。     

Peripheral nerve injury decreases the expression of metabolic glutamate receptor 7 in dorsal root ganglion neurons

Group II and III metabolic glutamate receptors (mGluRs) are responsible for the glutamate-mediated postsynaptic excitation of neurons. Previous pharmacological evidences show that activation of mGluR7 could inhibit nociceptive reception. However, the distribution and expression patterns of mGluR7 after peripheral injury remain unclear. Herein we found that mGluR7 was expressed in the rat peptidergic dorsal root ganglion (DRG) neurons and large neurons, but rarely in isolectin B4 positive neurons. Sciatic nerve ligation experiment showed that mGluR7 was anterogradely transported from cell body to the peripheral site. Furthermore, after peripheral nerve injury, mGluR7 expression was down-regulated in both peptidergic and large DRG neurons. Our work suggests that mGluR7 might be involved in the regulation of pathological pain after peripheral nerve injury.     

Curcumin protects the dorsal root ganglion and sciatic nerve after crush in rat

The goal of this study was to quantify the histological changes in the dorsal root ganglion (DRG) and the sciatic nerve in rats subjected to sciatic nerve crush (SNC) following curcumin treatment. The rats were divided into four groups, each including five animals, and underwent the following intervention: group I: control animals which received olive oil; group II: sham-operated animals whose skin of the posterior thigh was opened, sutured, and received the vehicle; group III: SNC animals which received the vehicle; and group IV: SNC plus curcumin (100 mg/kg/day) solved in the vehicle. On the 28th day, the fifth lumbar DRG and sciatic nerve were removed. Volume of the ganglion, mean cell volume, total volume of DRG cells (A- and B-cells), and total surface of DRG cells, total number, diameter, and area of the myelinated nerve fibers were estimated using stereological methods. Except for the volume of the ganglion, all other parameters were decreased after nerve crush. In curcumin-treated rats, these parameters decreased, but to a lesser extent, and the values were significantly higher than in the non-treated SNC group (p < 0.04).It can be concluded that in rats after crush, curcumin has a protective effect on the DRG and sciatic nerve.     

大鼠背根神经节内kv2.1 mRNA和kv4.2 mRNA的表达

目的　了解kv2 1和kv4 2型钾离子通道在背根神经节的表达。方法　应用原位杂交方法观察背根神经节内细胞膜钾离子kv2 1和kv4 2型通道的mRNA阳性神经结构的表达。结果　腰 3～ 5背根神经节内均有kv2 1和kv4 2mRNA阳性神经元的表达 ,kv4 2mRNA阳性神经元的数量和总面积明显多于kv2 1阳性神经元。结论　kv2 1和kv4 2型钾离子通道可能参与了背根神经节对外周传入信息的传递和调制。     

Localization of the neuropeptide manserin in rat dorsal root ganglia: Involvement in nociceptive function

Manserin, a neuropeptide discovered in the rat brain, is distributed in the spiral ganglion of the inner ear and carotid body, suggesting it is also localized in another neuron cluster. In this study, we examined manserin’s localization in the dorsal root ganglion (DRG) and spinal cord of adult Wistar rats using immunohistochemical analyses. The DRG consists of neurofilament (NF) 200-positive large cells and two types of small cells (calcitonin gene-related peptide (CGRP)-positive peptidergic neurons and isolectin B4 (IB4)-positive non-peptidergic neurons). Manserin was localized in some of the small cells. Fluorescence double immunostaining showed that manserin-positive cells corresponded to some of the CGRP-positive cells. The DRG comprises pseudo-unipolar cells that receive sensory information from the skin and viscera and project to each layer of the dorsal horn of the spinal cord. Manserin was localized in the CGRP-positive layer I and II outer, but not in the IB4-positive layer II inner. These results suggest manserin is localized in CGRP-positive cells in the DRG, projects to the dorsal horn of the spinal cord, and is secreted with other neuropeptides, such as CGRP, to participate in nociceptive function.     

Distribution patterns of different P2x receptor phenotypes in acutely dissociated dorsal root ganglion neurons of adult rats

P2x receptors may be used to detect ATP release from tissues during physiological and pathological conditions. We used whole-cell patch clamp recordings to study the expression of P2x receptor phenotypes, their distribution patterns, and their sensitivity to alphabetamATP and suramin in dorsal root ganglion (DRG) neurons acutely dissociated from adult rats. Based on the onset and decay rates of 10 microM ATP-evoked currents, we showed three types of P2x currents: fast, slow, and mixed. Each of these P2x receptor phenotypes had a distinct distribution pattern among DRG neurons. The fast P2x currents were predominantly expressed in small-diameter, isolectin-B4 (IB4)-positive, and capsaicin-sensitive DRG neurons. The slow P2x currents were expressed in both small and medium DRG neurons, and about half of them were IB4 positive. The mixed P2x currents were also expressed in both small and medium-sized DRG neurons, and most of these neurons were IB4-positive neurons. The slow and mixed P2x current groups had both capsaicin-sensitive and -insensitive DRG neurons. All phenotypes revealed with 10 microM ATP could be inhibited by 30 microM suramin. All DRG neurons with fast or mixed P2x currents were also sensitive to 10 microM alphabetamATP, and alphabetamATP evoked currents similar to those induced by ATP. The group expressing slow P2x currents could be further divided into alphabetamATP-sensitive and -insensitive groups. Thus, the relationships among P2x receptor phenotypes, cell sizes, IB4 positivity, and capsaicin sensitivity are more complicated than previously thought, and different P2x receptors may be involved in both nociceptive and non-nociceptive functions.     

Identification of dorsal root ganglion neurons that innervate the common bile duct of rats

Pain originating in the bile duct is common and many patients who have suffered from it report that it is one of the most intense forms of pain that they have experienced. Many uncertainties remain about the mechanisms underlying pain originating in the bile duct. For example, the dorsal root ganglion (DRG) neurons that give rise to the sensory innervation of the common bile duct (CBD) have not been identified and examined in any species. The goal of the present study was to determine the number, distribution, and size of DRG neurons that innervate the CBD in rats. Injections of WGA-HRP or CTB-HRP were restricted to the lumen of the bile duct. Injections of WGA-HRP labeled a mean number of about 500 DRG neurons bilaterally throughout all thoracic and upper lumbar levels. Injections of CTB-HRP labeled smaller numbers of DRG neurons. Application of colchicine onto the surface of the CBD reduced the number of cells labeled following injections of WGA-HRP into the lumen of the CBD by roughly 86%, suggesting that tracer had not spread in large amounts out of the CBD and labeled afferent fibers in other tissues. Approximately 85% of the neurons labeled with WGA-HRP had cell bodies that were classified as small; the remainder were medium in size. Injections of CTB-HRP labeled cell bodies of varying sizes, including a few large diameter cell bodies. These results indicate that a large number of primarily small DRG cells, located bilaterally at many segmental levels, provide a rich innervation of the common bile duct.     

猕猴胸腰段脊神经节nNOS免疫阳性神经元的分布

目的　观察正常猕猴胸腰段脊神经节神经元型一氧化氮合酶 (nNOS)免疫阳性神经元的分布。方法　用ABC免疫细胞化学方法显示nNOS免疫阳性神经元 ,并用体视学方法进行定量分析。结果　胸段和腰段脊神经节nNOS免疫阳性神经元的分布相似 ,均可见较丰富的nNOS免疫阳性神经元分布 ,神经元的大小不等 ,多呈圆形或椭圆形。胞浆着色较深 ,胞核位于细胞中央 ,不着色 ,细胞被神经纤维束分隔成群。nNOS免疫阳性神经元以中型神经元为主 ,其次为小型神经元 ,其胞浆呈强阳性染色 ,细胞直径 <50 μm ,大型神经元较少。胸、腰段脊神经节nNOS免疫阳性神经元的密度无明显差异 (P >0 0 5)。结论　在灵长类动物中 ,NO可能在感觉的传导和调节中发挥重要作用 ,但由于nNOS主要在中、小型神经元中表达 ,提示NO可能主要参与痛觉的调制     

Primary sensory neurons and satellite cells after peripheral axotomy in the adult rat

The timecourse of cell death in adult dorsal root ganglia after peripheral axotomy has not been fully characterised. It is not clear whether neuronal death begins within 1 week of axotomy or continues beyond 2 months after axotomy. Similarly, neither the timecourse of satellite cell death in the adult, nor the effect of nerve repair has been described. L4 and L5 dorsal root ganglia were harvested at 1-14 days, 1-6 months after sciatic nerve division in the adult rat, in accordance with the Animals (Scientific Procedures) Act 1986. In separate groups the nerve was repaired either immediately or following a 1-week delay, and the ganglia were harvested 2 weeks after the initial transection. Microwave permeabilisation and triple staining enabled combined TUNEL staining, morphological examination and neuron counting by the stereological optical dissector technique. TUNEL-positive neurons, exhibiting a range of morphologies, were seen at all timepoints (peak 25 cells/group 2 weeks after axotomy) in axotomised ganglia only. TUNEL-positive satellite cell numbers peaked 2 months after axotomy and were more numerous in axotomised than control ganglia. L4 control ganglia contained 13,983 (SD 568) neurons and L5, 16,285 (SD 1,313). Neuron loss was greater in L5 than L4 axotomised ganglia, began at 1 week (15%, P=0.045) post-axotomy, reached 35% at 2 months ( P<0.001) and was not significantly greater at 4 months or 6 months. Volume of axotomised ganglia fell to 19% of control by 6 months ( P<0.001). In animals that underwent nerve repair, both the number of TUNEL-positive neurons and neuron loss were reduced. Immediate repair was more protective than repair after a 1-week delay. Thus TUNEL positivity precedes actual neuron loss, reflecting the time taken to complete cell death and elimination. Neuronal death begins within 1 day of peripheral axotomy, the majority occurs within the first 2 months, and limited death is still occurring at 6 months. Neuronal death is modulated by peripheral nerve repair and by its timing after axotomy. Secondary satellite cell death also occurs, peaking 2 months after axotomy. These results provide a logical framework for future research into neuronal and satellite cell death within the dorsal root ganglia and provide further insight into the process of axotomy induced neuronal death.     

Acute myocardial ischemia up-regulates nociceptin/orphanin FQ in dorsal root ganglion and spinal cord of rats

Nociceptin/orphanin FQ (N/OFQ) possesses modulatory effects on somatic noxious signals in spinal cord, while the potential role in visceral nociception remains elusive. We designed this study to investigate the hypothesis that cardiac nociceptive signals from acute ischemic myocardium to the spinal cord are transmitted or modulated by mechanisms including N/OFQ. We examined the changes of N/OFQ and its mRNA in the dorsal root ganglia and spinal cord of upper thoracic segments innervating the heart of rats. Thoracic epidural anesthesia was performed to confirm neural mechanism underlying the changes. We observed that selective coronary artery occlusion significantly up-regulated N/OFQ and ppN/OFQ mRNA in the dorsal root ganglia and spinal cord. Thoracic epidural anesthesia abolished the changes in the expression of N/OFQ and its mRNA. The observations indicate that cardiac noxious neural afferent drive is responsible for the up-regulation of N/OFQ in the primary afferent neurons and intrinsic spinal neurons.     

Capsaicin preferentially affects small-diameter acutely isolated rat dorsal root ganglion cell bodies

The effects of capsaicin were tested on 221 acutely isolated dorsal root ganglion neurons of the rat, which ranged in diameter from 15 to 55 m. In a subpopulation of these cells, ranging in diameter from 17.5 to 33 m (n=117), capsaicin (1 M) produced an inward shift in holding current that was associated with an increase in membrane conductance in most cells (114 of 117). These effects of capsaicin were reversible upon washout of the drug. Other cells ranging in diameter from 15 to 52.5 m (n=104) were unaffected in this manner by the 1 m concentration of capsaicin. Capsaicin-sensitive cells had, on average, significantly longer duration action potentials and expressed significantly less I_H than capsaicin-insensitive cells. The relatively long duration action potentials and/or small cell body diameter and paucity of I_H observed in most of the capsaicin-sensitive cells is consistent with their representing C- or A-type sensory neurons.     

Spike potentials and membrane properties of dorsal root ganglion cells in pigeons

Active and passive membrane properties of dorsal root ganglion (DRG)-cells from the intact superfused ganglion of pigeons have been compared with the conduction velocity of their centrifugal axons.About two thirds of the neurones were associated with myelinated axons and classified as A-cells; the remainder were associated with unmyelinated axons and classified as C-cells. Slowly conducting group III A-cells (5–25 m·s^–1) constituted half of the A-cell population. With exception of spike duration, spike parameters and membrane properties did not differ among the A-cells. Spike duration increased with decreasing conduction velocity demonstrating a small plateau (hump) during the fall time in group III neurones. This hump was more distinct in C-cells, resulting in a 2–5 times longer duration of action potentials. Amplitude and duration of afterhyperpolarization (AHP) of C-cells was 2–3 times that of A-cells.Administration of 10 mM CoCl₂ decreased the rate of rise and the overshoot but increased the rate of fall of the action potential in C-cells and group III A-cells, largely abolishing the hump. It is suggested that the hump of the spike potential is largely produced by a Cacurrent and that the resultant increase of intracellular Ca might produce the larger AHP in C-cells, secondary to an increase in K-conductance.     

小鼠背根神经节中痒觉神经元的分布特性

目的观察小鼠背根神经节(DRG)中痒觉特异性Mrgpr A3+神经元的分布特征。方法采用遗传学方法将Mrgpr A3+神经元特异性标记强化绿色荧光蛋白(EGFP)和td Tomato;选取3只纯合Mrgpra3EGFP-Cre;ROSA26td Tomato成年转基因小鼠,分离皮肤和背根神经节组织;采用激光扫描共焦成像技术观察Mrgpr A3+神经元的外周神经纤维在小鼠躯体皮肤的投射分布特征;采用双光子成像技术观察Mrgpr A3+神经元在整体背根神经节中的三维空间分布情况。结果脸颊、背部和脚掌皮肤的Mrgpr A3+神经纤维分布密集,粗且长,分布广泛;颈部和腹部皮肤的Mrgpr A3+神经纤维分布稀疏,短且小,呈散点状分布;Mrgpr A3+神经纤维在皮肤的有毛和无毛区域都有投射分布,且不同部位分布特点不同;几乎所有的Mrgpr A3+神经元都为小直径感觉神经元,且在颈、胸、腰、尾段背根神经节中均有分布;颈段、胸段、腰段和尾段的Z轴成像深度分别为350μm、250μm、400μm和200μm;躯体不同部位背根神经节中的Mrgpr A3+神经元的三维空间分布在不同节段存在明显差异。结论小鼠躯体不同部位皮肤的Mrgpr A3+神经纤维的分布特征和整体背根神经节中Mrgpr A3+神经元的三维空间分布特征都存在较大差异,痒觉神经元和末梢分布的差异可能是不同区域存在痒觉生理反应差异的结构基础。     

Single-channel analysis of two types of Na+currents in rat dorsal root ganglia

The properties of voltage-gated Na⁺ channels were studied in neurones isolated from rat dorsal root ganglia using the outside-out configuration of the patch-clamp technique. Two types of single-channel currents were identified from the difference in unit amplitudes. Neither type was evoked in the medium in which extracellular Na⁺ ions were replaced by an equimolar amount of tetramethylammonium ions. The two types of single-channel currents differed in their sensitivity to tetrodotoxin (TTX). The smaller channel current was insensitive to 1 M TTX (referred to as TTX-I), while the larger channel current was blocked by 1 nM TTX (TTX-S). The unit amplitudes measured during a step depolarization to –30 mV (1.4 mM internal and 250 mM external Na⁺ concentrations) were 1.16 pA for TTX-S and 0.57 pA for TTX-I, respectively. The slope conductance measured at –30 mV was 16.3 pS for TTX-S and 8.5 pS for TTX-I. TTX-S could be activated by step depolarizations positive to –60 mV, while TTX-I could be activated at potentials positive to –40 mV. When the test pulse was preceded by a depolarizing prepulse, the prepulse positive to –50 mV preferentially inactivated TTX-S with a minimal effect on TTX-I. Activation and inactivation time courses of the averaged ensemble currents computed from TTX-S showed remarkable resemblances to the time courses of the macroscopic TTX-sensitive Na⁺ current. Similarly, the ensemble currents of TTX-I mimicked the macroscopic TTX-insensitive Na⁺ current. It was concluded that the two types of Na⁺ channels in rat dorsal root ganglia differ not only in their sensitivity to TTX, but also in their single-channel conductances.     

Dendrotoxin: a selective blocker of a non-inactivating potassium current in guinea-pig dorsal root ganglion neurones

1. The voltage clamp technique was used to study the effects of dendrotoxin (DTX) on outward potassium currents in internally perfused dorsal root ganglion neurones of guinea-pig. Sodium currents were eliminated by tetrodotoxin (TTX, 2 mol/l), calcium currents and calcium-activated potassium conductances were abolished by intracellular perfusion of cells with KF. 2. Depolarizing voltage shifts from a holding potential of –90 mV yielded a fast transient outward current (I _K ^f ) and a delayed non-inactivating outward current (I K/s). These currents could be separated by shifting the membrane potential to –50 mV, whereI _K ^f was almost completely inactivated. 3. DTX, at concentrations of 0.14–1.4 nmol/l selectively reduced a portion of the non-inactivating potassium current, leaving the transient outward current unaffected. Once manifested, the action of DTX could not be reversed by washing. 4. The I–V characteristic of the current blocked by DTX is almost linear and quite different from the one of the DTX-resistant portion ofI _K ^s , which shows a non-linear I–V curve. 5. Tetraethylammonium (TEA, 30 mmol/l) strongly reducedI _K ^f andI _K ^s . However, subsequent application of DTX was still able to further reduceI _K ^s . 6. 3,4-diaminopyridine (3,4-DAP, 500 mol/l) unselectively reducedI _K ^f and a portion ofI _K ^s . The remainder of the latter could not further be reduced by DTX, suggesting a similar action of the two blockers on non-inactivating potassium currents. 7. From the results presented, it is suggested that dendrotoxin selectively blocks a non-inactivating subtype of potassium channel.This is part of the thesis of R.P. to be presented to the Fachbereich Biologie, Justus-Liebig-Universität Gießen     

前列腺酸性磷酸酶在慢性痛大鼠脊髓背角和背根神经节的表达变化

目的:观察前列腺酸性磷酸酶(prostatic acid phosphatase,PAP)在多种慢性痛大鼠脊髓背角(spinaldorsal horn,SDH)和背根神经节(dorsal root ganglion,DRG)内的表达变化。方法:应用免疫组织化学染色法以及免疫荧光多重染色技术在多种慢性痛模型大鼠观察PAP的表达变化。结果:在正常大鼠,PAP阳性反应产物主要位于DRG的中、小型的非肽能神经元,PAP阳性神经元约占DRG神经元总数的64±4.3%;在脊髓背角,PAP阳性纤维和终末主要位于Ⅱ层。在神经病理性痛模型大鼠,术侧脊髓背角Ⅱ层的PAP阳性初级传入终末较对侧减少甚至消失,DRG内PAP阳性神经元较对侧明显减少。在慢性炎性痛模型大鼠,双侧脊髓背角和DRG内PAP的表达未见明显改变。结论:PAP特异地定位于DRG神经元以及脊髓背角Ⅱ层,可能与神经病理性痛信号的传递和加工密切相关。     

Electrophysiological characterization of the tetrodotoxin-resistant Na+ channel, Nav1.9, in mouse dorsal root ganglion neurons

Small dorsal root ganglion neurons express preferentially the Na⁺ channel isoform Na_V1.9 that mediates a tetrodotoxin-resistant (TTX-R) Na⁺ current. We investigated properties of the Na⁺ current mediated by Na_V1.9 (I_NaN) using the whole-cell, patch-clamp recording technique. To isolate I_NaN from heterogeneous TTX-R Na⁺ currents that also contain another type of TTX-R Na⁺ current mediated by Na_V1.8, we used Na_V1.8-null mutant mice. When F^– was used as an internal anion in the patch pipette solution, both the activation and inactivation kinetics for I_NaN shifted in the hyperpolarizing direction with time. Such a time-dependent shift of the kinetics was not observed when Cl^– was used as an internal anion. Functional expression of I_NaN declined with time after cell dissociation and recovered during culture, implying that Na_V1.9 may be regulated dynamically by trophic factors or depend on subtle environmental factors for its survival. During whole-cell recordings, the peak amplitude of I_NaN increased dramatically after a variable delay, as if inactive or silent channels had been kindled. Such an unusual increase of the amplitude could be prevented by adding ATP to the pipette solution or by recording with the nystatin-perforated patch-clamp technique, suggesting that the rupture of patch membrane affected the behaviour of Na_V1.9. These peculiar properties of I_NaN may provide an insight into the plasticity of Na⁺ channels that are related to pathological functions of Na⁺ channels accompanying abnormal pain states.     

坐骨神经分支选择性损伤模型L4～6背根神经节水平不同时间点P2X3mRNA表达变化

目的观察坐骨神经分支选择性损伤(SNI)动物制作型模后不同时间点L4~6背根神经节(DRG)水平P2X3mRNA的表达情况,探讨外周P2X3mRNA在神经病理性痛模型不同阶段中的作用。方法 54只健康雄性SD大鼠完全随机分为空白对照(control)组、假手术(sham surgery)组和手术(surgery)组。通过结扎腓总神经及切断胫神经,保留腓肠神经的方法建立SNI模型。动态观察造模前、造模后1d、3d、7d和14d双侧足跖机械痛阈;Real-time PCR法检测患侧造模后3d、7d和14d L4~6 DRG水平P2X3mRNA表达情况。结果模型制作后各时间点,surgery组大鼠患侧足跖痛阈明显降低(P0.05),sham surgery组大鼠与control组比较差异无显著性(P0.05);各组大鼠健侧足跖痛阈于模型制作后各时间点均无显著变化(P0.05)。模型制作后3d、7d,surgery组大鼠L4、L5、L6 DRG水平P2X3mRNA表达均有不同程度的提高(P0.05);而模型制作后14d,surgery组大鼠L5、L6DRG水平P2X3mRNA表达明显减少(P0.05),L4 DRG水平P2X3mRNA表达仍显著多于sham surgery组(P0.05)。模型制作后各时间点、各DRG水平,sham surgery组和surgery组大鼠P2X3mRNA表达差异均无显著性(P0.05)。结论外周P2X3mRNA参与SNI模型疼痛的产生和维持,且其在不同阶段发挥的作用不同。     

Alteration of dorsal root ganglion P2X3 receptor expression and function following spinal nerve ligation in the rat

One subtype of ATP-gated ion channel, the P2X₃ receptor, is expressed primarily on peripheral sensory neurons. While it is known that P2X₃ receptors can participate in certain forms of nociceptive signaling, their involvement in neuropathic pain transmission is not known. We have examined the expression and function of P2X₃ receptors in a rat spinal nerve ligation model of neuropathic pain. Fourteen days following L5/L6 spinal nerve ligation, the corresponding dorsal root ganglia (DRG) were removed from animals exhibiting mechanical allodynia, and these were studied using immunohistochemical and electrophysiological techniques. Using a polyclonal antibody to label the P2X₃ receptor, a significant reduction in neuronal P2X₃ immunoreactivity was observed in the ipsilateral (injured) L5 and L6 DRG following nerve ligation. In vitro electrophysiological analysis of acutely isolated DRG neurons revealed a similar decrease in functional P2X₃-containing receptors. In small diameter (22–25 μm) neurons, a significant reduction in the number of cells exhibiting a response to α,β-meATP was observed. However, a subset of small diameter neurons retained P2X₃ responses of equal amplitude to those recorded from naive and sham control DRG neurons. Interestingly, P2X₃ immunoreactivity and P2X₃-like responses were also detected in a subset of larger diameter (50 μm) neurons and the number and amplitude of these responses were unchanged after spinal nerve ligation. These results suggest that, while there appears to be a decrease in fast desensitizing P2X₃ receptors following L5/L6 nerve ligation injury, certain subsets of small and large DRG neurons maintain normal P2X₃ receptor expression and function. These remaining receptors may provide a P2X₃ receptor-mediated component to neuropathic pain. Electronic Publication