Laminar distribution and somatotopic organization of primary afferent fibers from hindlimb nerves in the dorsal horn. A study by transganglionic transport of horseradish peroxidase in the rat

Primary afferent nerve fibers to the spinal cord in the adult rat were labeled by applying horseradish peroxidase to the cut end of one of the following hindlimb nerves; the tibial, medial plantar, lateral plantar, common peroneal, saphenous, sural, lateral femoral cutaneous or obturator nerve. Maximal labeling intensity was found in the dorsal horn after 36-72 h survival. Labeling was observed in different dorsal horn laminae at different levels within the L1-S1 spinal cord segments, depending on which nerve horseradish peroxidase had been exposed to, probably reflecting the individual composition of afferent fiber types. Although a certain overlap was found, the central projections of the eight different nerves investigated formed well delineated three dimensional compartments within the medial 2/3 to 3/4 of the dorsal horn. This was most clearly discernible in lamina II. Although interindividual differences were present, bilaterally identical operations gave symmetrical projection patterns in the dorsal horn. The results indicate that dorsal horn projections of hindlimb nerves are organized in a highly ordered somatotopic fashion.     

Effects of spinal and peripheral nerve lesions on the intersegmental synchronization of the spontaneous activity of dorsal horn neurons in the cat lumbosacral spinal cord

In the anesthetized and paralyzed cat, spontaneous negative cord dorsum potentials (nCDPs) appeared synchronously in the L3 to S1 segments, both ipsi- and contralaterally. The acute section of both the intact sural and the superficial peroneal nerve increased the variability of the spontaneous nCDPs without affecting their intersegmental coupling. On the other hand, the synchronization between the spontaneous nCDPs recorded in segments L5-L6 was strongly reduced following an interposed lesion of the left (ipsilateral) dorsolateral spinal quadrant and it was almost completely abolished by an additional lesion of the contralateral dorsolateral quadrant at the same level. Our observations support the existence of a system of spontaneously active dorsal horn neurons that is bilaterally distributed along the lumbosacral segments and affects, in a synchronized and organized manner, impulse transmission along many reflex pathways, including those mediating presynaptic inhibition.     

Spinal cord potentials evoked by cutaneous afferents in the monkey.

1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord.     

Effects of γ-aminobutyrate and bicuculline on primary afferent depolarization of cutaneous fibres in the cat spinal cord

The excitability of single cutaneous primary afferent fibres (sural nerve) was tested by focal stimulation in the dorsal horn of the cat spinal cord, and recording the antidromically conducted action potential in the peripheral nerve. To induce primary afferent depolarization, which is an expression of presynaptic inhibition, the superficial peroneal nerve was stimulated. The primary afferent depolarization was measured as the concomitant excitability change in the antidromically excited sural fibre. This primary afferent depolarization was reduced by 32% during microelectrophoretic release of bicuculline methochloride near the microstimulation electrode in the dorsal horn. Microelectrophoresis of γ-aminobutyrate increased excitability in sural nerve fibres which correlated with the primary afferent depolarization induced by stimulation of the superficial peroneal nerve.The results suggest a possible role for γ-aminobutyrate in presynaptic inhibition of cutaneous afferent fibres in the cat.     

Short latency crossed inhibitory reflex actions evoked from cutaneous afferents

Although stimulation of cutaneous limb afferents has been shown to evoke crossed extension reflexes in unanaesthetised decerebrate or spinalised animals, here we show that stimulation of cutaneous nerves evokes crossed inhibition rather than excitation of contralateral extensor motoneurones in anaesthetised, spinal cord intact cats. Single pulse stimuli delivered to the saphenous, sural or superficial peroneal nerves evoked IPSPs in a high proportion of contralateral motoneurones including those of knee and ankle extensors. These IPSPs had thresholds of less than 1.5 times the threshold of the most excitable fibres and so large myelinated afferents contributed to them. The relative latencies of IPSPs evoked by stimulation of the contralateral superficial peroneal and sural nerves were longer than those evoked via ipsilateral pathways by approximately 1 ms, suggesting that there are at least three synaptic relays in the crossed reflexes. The IPSPs evoked by stimulation of both ipsilateral and contralateral saphenous nerves had minimal latencies suggesting at least three synaptic delays. Like IPSPs evoked by group II afferents, the frequencies of occurrence of crossed IPSPs evoked by stimulation of cutaneous afferents were significantly reduced after spinal transection and the IPSPs recorded after spinalisation were significantly smaller. These findings are consistent with the recent proposal that dorsal horn neurones, which receive input from cutaneous afferents and contact premotor commissural interneurones may mediate the crossed inhibition.     

Differential Akt phosphorylation at Ser473 and Thr308 in cultured neurons after exposure to glutamate in rats

Simultaneous recordings of cortical evoked potentials in the posterior sigmoid gyrus, and spontaneous negative cord dorsum potentials (CDPs) of the L6 lumbar spinal segment, were made in the anaesthetised cat. The electrodes were positioned in cortical and spinal somatosensory regions where the largest spontaneous and evoked negative potentials were detected. Evoked potentials were produced by electrical stimulation to cutaneous nerves or by mechanical stimulation of the hindpaw skin. We found that both electrically and mechanically cortical evoked potentials were facilitated during the spontaneous negative CDPs. The magnitude of such facilitation was proportional to the amplitude of the 'conditioning' spontaneous negative CDPs. This led to a high positive correlation between amplitude fluctuations of spontaneous negative CDPs and fluctuations of the cortical evoked potentials. This observation suggests that transmission of cutaneous sensory information in ascending pathways could be facilitated when dorsal horn spinal neurones are active.     

Dopaminergic control of transmission from group II muscle afferents to spinal neurones in the cat and guinea-pig

The effects of dopamine and its agonists on transmission from muscle afferents to spinal neurones were investigated in the cat and guinea-pig spinal cord, by measuring the drug effects on the amplitude of monosynaptic field potentials evoked by electrical stimulation of group I and group II muscle afferents. Local iontophoretic application of dopamine, the dopamine D1/D5 agonist SKF-38393 and the D2/D3/D4 agonist quinpirole all depressed the group II field potentials evoked at the base of the dorsal horn. Group II field potentials in the intermediate zone were depressed by dopamine to a similar degree as the dorsal horn field potentials, whereas the dopamine agonists were without effect upon them. The intermediate zone field potentials evoked by group I muscle afferents were not depressed by any of the drugs. The dopamine-evoked depression of the group II-evoked field potentials in the dorsal horn in the guinea-pig spinal cord was reduced by the simultaneous application of haloperidol. The results demonstrate that dopamine receptors mediate the depression of transmission from group II muscle afferents to interneurones in the dorsal horn, but not to neurones in the intermediate zone of the spinal cord.     

Electrophysiological changes in adult rat dorsal horn neurons after neonatal peripheral inflammation

Neonatal peripheral inflammation has been shown to produce profound anatomical changes in the dorsal horn of adult rats. In this study, we explored whether parallel physiological changes exist. Neonatal rats were injected with complete Freund's adjuvant (CFA) into the left hind paw. At 8-10 wk of age, single dorsal horn neurons were recorded in response to graded intensities of mechanical stimuli delivered to the receptive field. In addition, cord dorsum potentials, produced by electrical stimuli delivered to the left sciatic nerve at 2.5x threshold, were recorded bilaterally from L2 to S3. There were significant increases in background activity and responses to brush and pinch in neonatal rats that were treated with CFA, as compared with control rats. Further analysis showed similar significant changes when dorsal horn neurons were categorized into wide dynamic range (WDR), high-threshold (HT), and low-threshold (LT) groups. The receptive field was significantly larger in neonatally treated rats as compared with control rats. Additionally, there was a significant increase in the response to a 49 degrees C heat stimulus in neonatally treated rats as compared with control rats. There was also a trend for the amplitudes of N1, N2, and P waves of the cord dorsum potential to increase and latencies to decrease in neonatally treated rats, but no significant differences were detected between different levels of the spinal cord (L2 to S3). These data further support the notion that anatomical and physiological plasticity changes occurred in the spinal cord following early neonatal CFA treatment.     

Depressing effect of electroacupuncture on the spinal non-painful sensory input of the rat

The aim of this study was to explore the effect of electroacupuncture (EA) applied in the Zusanli (ST36) and Sanyinjiao (SP6) points on the N1 component of the cord dorsum potential (CDP) evoked by electrical stimulation of the sural nerve (SU) in the rat. The experiments were performed in 44 Wistar rats (250–300 g) anesthetized with ketamine (100 mg/kg) and xylazine (2 mg/kg). A bilateral laminectomy was performed to expose the L3 to S2 segments of the spinal cord. The SU nerve was exposed and placed on pairs of hook electrodes for electrical stimulation. The N1-CDPs were recorded with three silver-ball electrodes located on the dorsal surface of the L5 to S1 segments. Ipsilateral high and low EA stimulation (100, 2 Hz, 6 mA, 30 min) induced a considerable reduction in the amplitude (45 ± 5.6, 41 ± 6.2 %) of the N1-CDP recorded at the L6 segmental level. Recovery of the N1-CDP amplitude occurred approximately 1–3 s after EA. Sectioning of the saphenous and superficial peroneal nerves reduced the depressing effect provoked by the EA stimulation (18.7 ± 1.3, 27 ± 3.8 %). Similarly, sectioning of the posterior and anterior tibial, deep peroneal and gastrocnemius nerves partially reduced the effect provoked by EA (11 ± 1.5, 9.8 ± 1.1, 12.6 ± 1.9 %). Intravenous picrotoxin (1 mg/kg) also reduced the action of low and high EA (23 ± 4.8, 27 ± 5.2 %). It is suggested that EA stimulation depresses non-painful sensory pathways through the activation of specific inhibitory pathways that receive modulatory actions from other sensory and muscle afferent inputs in the rat spinal cord.     

Projection of a cutaneous nerve to the spinal cord of the pigeon I. Evoked field potentials

Summary Evoked field potentials have been recorded from the spinal cord after electrical stimulation of a cutaneous nerve in the pigeon. Four different postsynaptic negative waves (Nl to N4) could be discerned. These waves were obviously due to monosynaptic activation via the four different afferent fiber groups described for this cutaneous nerve (Necker and Meinecke 1984). Precise localization showed that large fibers project to deeper, medially located areas of the dorsal horn (near lamina IV) whereas smaller fibers project primarily to more laterally located superficial layers. A laterally recorded N-wave which was due to the activation of large fibers had a latency which indicated a disynaptic pathway.     

The innervation of the joints of the foot

The nerve supply of the ankle joint and of the joints of the foot was studied in dissections of fetal and adult feet and in serial sections of fetal feet stained with silver. The ankle joint was supplied by the tibial, sural, deep peroneal, and saphenous nerves, and by the accessory deep peroneal nerve when present. The tarsal joints were supplied on their plantar aspects by the medial or lateral plantar nerves, and on their dorsal aspects chiefly by the deep peroneal nerve. The joint between the lateral and intermediate cuneiform received branches from the intermediate dorsal cutaneous nerve also. The lateral dorsal cutaneous nerve and the accessory deep peroneal nerve when present provided additional branches to the subtalar and calcaneocuboid joints. The tarsometatarsal joints were supplied on their plantar aspects by the medial or lateral plantar nerves. Most of them were supplied on their dorsal aspects by the deep peroneal nerve, but the cuboid-metatarsal joints received their supply from the intermediate dorsal cutaneous nerve. The intermetatarsal joints had a similar but sparser supply. The joint between the fourth and fifth metatarsal received branches from the intermediate dorsal cutaneous nerve. The plantar digital nerves provided the main supply to the metatarsophalangeal joints. The dorsal aspect of the first metatarsophalangeal joint was supplied by the deep peroneal and the medial dorsal cutaneous nerves, of the second metatarsophalangeal joint by the deep peroneal nerve, and of the fourth and fifth metatarsophalangeal joints by the lateral dorsal cutaneous nerve. The interphalangeal joints did not receive articular branches from the dorsal digital nerves, except in the case of the interphalangeal joint of the big toe, which was supplied by the deep peroneal and the medial dorsal cutaneous nerves.     

大鼠蓝斑核区微量注射L—谷氨酸钠对脊髓背表面电位的影响

实验在25只清醒麻痹的大白鼠身上进行。以1s的刺激间隔、C类纤维的最大刺激强度兴奋腓肠神经,用计算机叠加所诱发的脊髓背表面电位(CDP),观察蓝斑(LC)区微量注射L-谷氨酸钠(L-Glut)对CDP的影响。结果显示:大白鼠腓肠神经A+G类纤维诱发的CDP由N_1、N_2、P_1、N_3、P_2波组成。注射L-Glut命中LC区者10例,有9例对CDP产生明显的抑制。所受影响大小依次为p_2、N_3、p_1波,N_1波则完全不受影响。其中2例动物的中缝大核(NRM)被损毁,损毁后仍不改变注射L-Glut于LC区对CDP的影响。注射L-Glut于LC区周围者10例,对GDP各波的波幅、时程和潜伏期均无影响。另外有5例将人工脑脊液注入LC区,对CDP也不发生影响。统计结果表明:L-Glut兴奋LC区神经元,通过其下行的NE能神经纤维,直接抑制由外周纤维诱发的CDP波成分(P_2、N_3波)。本文对兴奋LC神经元影响CDP波成分的相对特异性的意义进行了讨论。     

神经病理性痛大鼠脊髓背角缝隙连接蛋白表达变化及鞘内注射甘珀酸的镇痛作用

目的 研究慢性神经病理性痛大鼠脊髓背角内缝隙连接蛋白家族(Cx)中Cx43和Cx32的表达变化,以及鞘内注射缝隙连接阻断剂甘珀酸（CBX）的镇痛作用。 方法 成年SD大鼠50只,分为正常对照组、假手术组和坐骨神经分支选择性损伤组(SNI)。手术前1d、术后3d、5d、10d、20d和30d,观察大鼠行为并检测机械刺激缩足反射阈值(PWMT)。15只大鼠于术后10d、20d、30d取脊髓腰段进行免疫印迹检测,另15只大鼠于术后10d、20d、30d取脊髓腰段进行免疫荧光染色,检测腰段脊髓背角内Cx43和Cx32表达的变化。有10只大鼠先进行鞘内插管,后行SNI手术,术后20d向鞘内注射生理盐水或CBX,观察大鼠PWMT的变化。 结果 SNI大鼠手术侧PWMT阈值较非手术侧或假手术组明显降低,术后20d达最低值。SNI大鼠手术侧脊髓背角内Cx43、32表达增多,明显高于非手术侧和假手术组背角。鞘内注射CBX 3h后,PWMT平均阈值由(2.5±1.0)g上升到(20.0±3.2)g,有抑制效应, 而生理盐水组则无抑制效应。 结论 脊髓背角内的缝隙连接在因外周神经损伤引起的神经病理性痛中起重要作用。     

PKC在成年大鼠脊髓背角C-纤维诱发电位长时程增强的诱导和维持中的作用

目的：探讨蛋白激酶C (PKC) 在大鼠脊髓背角C-纤维诱发电位长时程增强（LTP）的诱导和维持中的作用。方法： 细胞外记录技术在脊髓腰膨大部记录背角浅层神经元C-纤维诱发电位。 结果：(1) PKC的选择性抑制剂chelerythrine（200 μmol/L）或G 6983（100 μmol/L）对脊髓背角C-纤维诱发电位的基础电位没有影响，但可完全阻断脊髓背角LTP的诱导。(2) Chelerythrine或G 6983呈时间依赖性翻转脊髓背角LTP。在LTP 诱导后15 min，脊髓局部给予chelerythrine（200 μmol/L）后，LTP逐渐降低，于给药后70 min降至对照水平；而G 6983（100 μmol/L）产生同chelerythrine相似的效应，在用药后110 min，LTP降至对照水平。但同样浓度的chelerythrine或G 6983在LTP 诱导后3 h，均不能翻转业已建立的LTP。结论： PKC参与脊髓背角C-纤维诱发电位LTP的诱导和早期维持，而不影响晚期LTP的维持。     

Synaptic actions of cutaneous A delta and C fibers on primate hindlimb alpha-motoneurons

Postsynaptic potentials evoked in hindlimb alpha-motoneurons by stimulation of a cutaneous nerve (sural) with finely graded stimulus strengths were analyzed in the primate, monitoring the spinal cord potentials and afferent nerve volleys in the sural nerve. It was observed that activities in A alpha beta, A delta and C fibers of the cutaneous nerve elicited characteristic excitatory and/or inhibitory postsynaptic potentials (EPSPs and/or IPSPs) with different latencies and durations in extensor and flexor motoneurons. Volleys in A delta fibers of the cutaneous nerve produced EPSPs in 57% of flexor and 31% of extensor motoneurons tested, whereas IPSPs were produced by A delta volleys in 41% of flexor and 62% of extensor motoneurons. EPSPs with longer latencies and longer durations were evoked by cutaneous C fiber volleys in 55% of flexor and 34% of extensor motoneurons, whereas IPSPs due to C volleys were recorded in 9% of flexor and 14% of extensor motoneurons. A alpha beta and A delta volleys caused motoneurons to fire in several instances, and some motoneurons discharged repetitively during the depolarizations evoked by activities in C fibers of the nerve. Central latency for transmission in interneuronal chains in the spinal cord was estimated from the onset of the cord potential (N3 wave) to the onset of the postsynaptic potential evoked by A delta volleys. Ranges of central latencies of the EPSPs and IPSPs evoked by A delta volleys were 2.0-7.0 ms and 3.5-8.5 ms, respectively. It is postulated that there may be at least two interneurons interposed in the excitatory reflex pathway from A delta afferent fibers to motoneurons and the A delta inhibitory pathway may involve longer interneuronal chains. In a few motoneurons, however, sural volleys with strengths sufficient to activate A delta fibers produced EPSPs with a central latency of about 1 ms, suggesting activation of a disynaptic segmental pathway with one interposed interneuron. Stimulation of the sural nerve with strengths sufficient to activate cutaneous C fibers produced slow negative cord dorsum potentials with long latencies. It is proposed that primate motoneurons, which show characteristic postsynaptic potentials evoked by cutaneous A delta and C fiber volleys, may provide a suitable model for analyzing the role of high threshold cutaneous afferent fibers not only in the flexor withdrawal reflex but also in motor control functions.     

Responses in the dorsal accessory olive of the cat to stimulation of hind limb afferents

1. Field potentials and single unit discharges were recorded in the dorsal accessory olive of the cat following stimulation of nerves of the contralateral hind limb.2. The largest field potentials were evoked when nerves were stimulated with brief trains at 200-300/sec. Responses were sometimes evoked from quadriceps nerve by volleys restricted to low threshold group I afferents, but responses were not usually evoked from other muscle nerves unless both group I and II afferents were excited.3. The spatial distributions of the field potentials evoked from different nerves were very similar and individual units were made to discharge by stimulation of each of a wide range of nerves including muscle, skin and joint nerves. Single units were also made to discharge by stimulation of both the ipsilateral and the contralateral quadriceps nerve.4. The latency of the field potentials evoked by stimulation of quadriceps nerve ranged from 14 to 23 msec in different preparations. The latency of responses evoked from various branches of the sciatic nerve was consistently longer and was usually between 20 and 30 msec.5. The activity was conveyed by a tract which, at the upper lumbar level of the spinal cord, lay in the ventral quadrant ipsilateral to the olive. In the upper cervical region the tract lay close to the ventral surface of the cord. Values between 24 and 30 m/sec were found for the conduction velocity of the tract.6. An excitatory response in the dorsal accessory olive was followed by a period of about 100 msec during which the amplitude of a second response was reduced.     

Variations in sural nerve formation pattern and distribution on the dorsum of the foot

The sural nerve, a cutaneous nerve, is clinically important because it is frequently for nerve conduction testing, biopsy, and harvesting for nerve grafts. This nerve exhibits a wide variety of variation in formation, distribution on the dorsum of the foot, and so on, depending on the population observed. In this study, we examined the variation in the sural nerve in 110 Korean cadavers. Of these cadavers, 86.1% of the sural nerves corresponded to type A, where tibial and peroneal components were united to form the sural nerve. These two components most frequently united (65.9%) in the third quarter of the calf, and when the union position was expressed as a ratio to calf length, it corresponded to 0.408 in men and 0.346 in women, with a statistically significant difference. Due to this sexual dimorphism in addition to shorter calf length in females, the length of the sural nerve was shorter in females (male average length: 14.5 ± 4.8 cm; female average length: 11.4 ± 2.9 cm). In terms of distribution of the lateral dorsal cutaneous nerve, the distal continuation of the sural nerve on the dorsum of the foot, it showed variation in association with the superficial peroneal nerve. The innervation of the sural nerve extended most frequently up to the lateral two and a half toes, solely or in conjunction with the superficial peroneal nerve. Obtaining further information regarding sural nerve variation will be useful for various clinical procedures and interpretation of sural nerve conduction results. Clin. Anat. 30:525–532, 2017. © 2017 Wiley Periodicals, Inc.     

Topography and time course of changes in spinal neuropeptide Y immunoreactivity after spared nerve injury

We used a new computer-assisted method to precisely localize and efficiently quantify increases in neuropeptide Y immunoreactivity (NPY-ir) along the mediolateral axis of the L4 dorsal horn (DH) following transection of either the tibial and common peroneal nerves (thus sparing the sural branch, spared nerve injury (SNI)), the tibial nerve, or the common peroneal and sural nerves. Two weeks after SNI, NPY-ir increased within the tibial and peroneal innervation territories; however, NPY-ir in the central-lateral region (innervated by the spared sural nerve) was indistinguishable from that of sham. Conversely, transection of the sural and common peroneal nerves induced an increase in NPY-ir in the central-lateral region, while leaving the medial region (innervated by the tibial nerve) unaffected. All nerve injuries increased NPY-ir in dorsal root ganglia (DRG) and nucleus gracilis (NG). By 24 weeks, both NPY-ir upregulation in the DH and hyper-responsivity to cold and noxious mechanical stimuli had resolved. Conversely, NPY-ir in DRG and NG, and hypersensitivity to non-noxious static mechanical stimuli, did not resolve within 24 weeks. Over this time course, the average cross-sectional area of NPY-immunoreactive DRG neurons increased by 151 μm². We conclude that the upregulation of NPY after SNI is restricted to medial zones of the DH, and therefore cannot act directly upon synapses within the more lateral (sural) zones to control sural nerve hypersensitivity. Instead, we suggest that NPY in the medial DH tonically inhibits hypersensitivity by interrupting mechanisms of central sensitization and integration of sensory signals at the spinal and supraspinal levels.     

Morphine-sensitive late components of the flexion reflex in the neonatal rat

The 8-15-day-old rat spinal cord was isolated together with peripheral nerves innervating a hindlimb. Multiunit neural discharges in response to electrical stimulation of a cutaneous nerve (sural, plantar of superficial peroneal nerve) were recorded from a flexor nerve (deep peroneal nerve or nerve innervating the hamstring muscles). Attempts were made to find relations between the magnitude of the flexion reflex discharges and the sizes of the volleys in the myelinated or unmyelinated afferent fibers. The neonatal flexion reflex discharges due to myelinated fiber volleys were exaggerated when compared with those in the adult rats. Higher stimulus strengths recruited later components of the flexion reflex discharges. The observed increment of the flexion reflex discharges was precisely associated with the recruitment of unmyelinated afferent fibers in the nerve. These late flexion reflex discharges were shown to be depressed by the opiate analgesic morphine in a naloxone-reversible manner.     

ERKⅠ/Ⅱ在脊髓背角LTP的诱导和维持中的作用

目的：探讨胞外信号调节激酶（ERKⅠ/Ⅱ）在大鼠脊髓背角C-纤维诱发电位长时程增强（LTP）的诱导和维持中的作用。 方法： 细胞外记录技术在脊髓腰膨大部记录背角浅层神经元C-纤维诱发电位。 结果： (1) MEK的选择性抑制剂PD98059（100 μmol/L）或SL327 (200 μmol/L) 对脊髓背角C-纤维诱发电位的基础电位没有影响，但可阻断脊髓背角LTP的诱导。(2) PD98059或SL327呈时间依赖性逆转脊髓背角LTP。在LTP 诱导后15 min，脊髓局部给予PD98059（100 μmol/L）或SL327(200 μmol/L)可完全逆转LTP。在LTP 诱导后30 min，单独给予PD98059或SL327，LTP的抑制率分别为62.5％与75.0％。但同样浓度的PD98059或SL327在LTP 诱导后1 h，均不能逆转业已建立的LTP。 结论： 脊髓背角ERKⅠ/Ⅱ的激活参与C-纤维诱发电位LTP的诱导和早期维持。