Capsaicin in adult frogs: Effects on nociceptive responses to cutaneous stimuli and on nervous tissue concentrations of immunoreactive substance P,somatostatin and cholecystokinin

Summary Adult frogs (Rana esculenta) were given subcutaneous injections of 10, 20, 30, 50 and 100 mg/kg capsaicin in sequential order over 5 days, or the vehicle only. The nociceptive thresholds to electrical, thermal and chemical stimuli were measured before, and 1, 5 and 24 h after each injection. Capsaicin was followed by a dose-related reduction of nociceptive responses to all stimuli, but these effects lasted for only 1–5 h after the given injection. Water/acetic extracts of undivided brains and spinal cords were prepared at the corresponding time periods for the radioimmunoassay of peptides. Spinal cord concentrations of immunoreactive substance P were essentially unaffected by capsaicin, while those of immunoreactive somatostatin were significantly increased after the second for fourth injections (20, 30 and 50 mg/kg) of capsaicin. Brain extracts showed an increase of somatostatin and substance P concentrations after the dose of 50 mg/kg. In an additional experiment, immunoreactive substance P, somatostatin and cholecystokinin were measured in tissue samples taken at 2 and 10 min, and 1, 5 and 24 h after a single dose of either 50 mg/kg capsaicin or the vehicle. The only signficant effect of capsaicin was an increase of immunoreactive somatostatin concentration in brain homogenates at 5 h, while the vehicle in itself elicited major variations of all three peptides in spinal cord and/or brain. These results indicate that capsaicin reduces the nociceptive responses to cutaneous stimuli in adult frogs. This effect is transient, and bears no clear relationship to the variations of spinal cord nor of brain concentrations of immunoreactive substance P, somatostatin and cholecystokinin. In the present experimental conditions, the effects of the vehicle injection to neuropeptides far exceeded those of capsaicin itself.     

Antinociceptive effects of serotonergic reuptake inhibitors in mice

The antinociceptive effects of three predominantly serotonergic reuptake inhibitors, alaproclate, citalopram and clomipramine, were examined in mice using the hot-plate, formalin and substance P tests. The effects were compared with those of the noradrenergic reuptake inhibitor, desipramine. Different profiles in the three nociceptive tests were found for all four drugs, using doses of 10 and 40 mg/kg. The selective serotonergic reuptake inhibitor, alaproclate, seemed to have the least antinociceptive effects, and was the only drug that was ineffective in the hot-plate test. The other selective drug, citalopram, had a stronger effect than alaproclate in the substance P test, but in the formalin test, both drugs were approximately equally effective. Clomipramine differed from citalopram by being more effective in the formalin test. These findings thus indicate that selective inhibitors of the uptake of 5-HT have weaker antinociceptive effects than less selective drugs. Desipramine seemed to be no less effective than the serotonergic drugs and was the most potent drug in the hot-plate test.     

Inhibition of ERK phosphorylation by substance P N-terminal fragment decreases capsaicin-induced nociceptive response

Previous research has demonstrated that substance P N-terminal fragments produced by the action of several different enzymes in the spinal cord could reduce nociception when injected intrathecally (i.t.) into mice. The present study examined the possible involvement of spinal extracellular signal-regulated protein kinase (ERK), a mitogen-activated protein kinase (MAPK), in i.t. substance P (1-7)-induced antinociception as assayed by the capsaicin test. The i.t. injection of substance P (1-7) (20-80 nmol) into mice resulted in a dose-dependent attenuation of paw-licking/biting behavior induced by intraplantar injection of capsaicin, which was reversed by co-injection of [d-Pro², d-Phe⁷]substance P (1-7), a d-isomer and antagonist of substance P (1-7). In Western blot analysis, intraplantar injection of capsaicin (400 and 1600 ng/paw) produced an increase of ERK phosphorylation in the dorsal spinal cord, whereas expression of p38 and c-Jun N-terminal kinase (JNK) phosphorylation was unchanged by capsaicin treatment. In parallel to the behavioral results, i.t. substance P (1-7) inhibited capsaicin-induced EKR phosphorylation, which was reversed by [d-Pro², d-Phe⁷]substance P (1-7), a substance P (1-7) antagonist. Both nociceptive behavioral response and spinal ERK activation induced by intraplantar capsaicin were reduced by U0126, an upstream inhibitor of ERK phosphorylation. Taken together, these findings suggest that the activation of ERK, but not p38 and JNK MAPKs in the spinal cord, contributes to intraplantar capsaicin-induced nociception, and that blocking ERK activation via substance P (1-7) binding sites may provide significant antinociception at the spinal cord level.     

大鼠脊髓背角浅层GABA能轴突与SP受体阳性神经元的突触联系(英文)

目的:研究大鼠脊髓背角浅层内GABA能神经元与P物质受体(SPR)阳性神经元之间的相互关系.方法:应用SPR包埋前免疫电镜结合GABA胶体金技术.结果:SPR样免疫阳性神经元主要分布于脊髓背角Ⅰ层和Ⅱ层背侧部的内侧半.电镜下,浅层内SPR样免疫反应阳性产物主要定位于细胞体和树突.免疫反应产物在树突呈片或颗粒状,常常与线粒体外膜表面、粗面内质网、高尔基氏体、树突膜、胞浆膜内面和核膜外表面等相连.双标记显示SPR样免疫反应树突接受GABA样免疫金标记的轴突传入,形成对称性轴-树突触.此外,GABA还可与SPR共存于同一树突中.结论:GABA和P物质受体在脊髓背角神经元的突触联系,为以往GABA调制脊髓伤害感受功能的药理学研究提供了形态学证据.     

The tramadol metabolite O-desmethyl tramadol inhibits substance P-receptor functions expressed in Xenopus oocytes

Tramadol has been widely used as analgesic. O-Desmethyl tramadol (ODT) is one of the main metabolites of tramadol, having much greater analgesic potency than tramadol itself. Substance P receptors (SPR) are well known to modulate nociceptive transmission within the spinal cord. In this study, we investigated the effects of ODT on SPR expressed in Xenopus oocytes by examining SP-induced Ca(2+)-activated Cl(-) currents. ODT inhibited the SPR-induced Cl(-) currents at pharmacologically relevant concentrations. The protein kinase C (PKC) inhibitor bisindolylmaleimide I did not abolish the inhibitory effects of ODT on SP-induced Ca(2+)-activated Cl(-) currents. The results suggest that the tramadol metabolite ODT inhibits the SPR functions, which may be independent of activation of PKC-mediated pathways.     

In vitro release of substance P from spinal cord slices by capsaicin congeners

The in vitro release of immunoreactive substance P (I-SP) by capsaicin and three congeners was studied on slices of rat spinal cord upper dorsal horn. Capsaicin and its congeners were all able to stimulate I-SP release, indicating that they act on chemosensitive primary afferents terminating in this region. A positive correlation was found between the I-SP releasing and pain-producing potencies of these compounds. This is in agreement with the concept that primary afferents containing substance P (SP) are involved in the transmission of nociceptive information.     

鞘内注射P物质拮抗氯胺酮的抗伤害作用

目的观察脊髓P物质对氯胺酮抗伤害作用的影响。方法在小鼠福尔马林实验中,结合行为学和Fos蛋白表达,观察鞘内注射(it)不同剂量的P物质对氯胺酮抗伤害作用的影响。结果氯胺酮20、30mg·kg-1ip可剂量依赖性地减少小鼠舔足时间(P<0.05)。P物质0.25、0.5ngit可增加注射氯胺酮小鼠舔足时间(P<0.05)。小鼠注射福尔马林后,注射侧脊髓背角Fos免疫样(Foslikeimmunoreactive,FLI)阳性神经元数量明显增加(P<0.01),预先给于氯胺酮30mg.kg-1ip可以明显减少脊髓背角FLI阳性神经元数量(P<0.01),而P物质0.5ngit能明显削弱氯胺酮对脊髓背角Fos表达的抑制(P<0.01)。结论鞘内注射P物质能拮抗脊髓水平氯胺酮抗伤害作用。     

Intrathecal substance P (1-7) prevents morphine-evoked spontaneous pain behavior via spinal NMDA-NO cascade

Previous research has shown that injection of high-dose of morphine into the spinal lumbar intrathecal (i.t.) space of rats elicits an excitatory behavioral syndrome indicative of severe vocalization and agitation. Substance P N-terminal fragments are known to inhibit nociceptive responses when injected i.t. into animals. In this study, we investigated the effect of i.t. substance P (1-7) on both the nociceptive response and the extracellular concentrations of glutamate and nitric oxide (NO) metabolites (nitrite/nitrate) evoked by high-dose i.t. morphine (500 nmol). The induced behavioral responses were attenuated dose-dependently by i.t. pretreatment with the substance P N-terminal fragment substance P (1-7) (100-400 pmol). The inhibitory effect of substance P (1-7) was reversed significantly by pretreatment with [d-Pro2, d-Phe7]substance P (1-7) (20 and 40 nmol), a d-isomer and antagonist of substance P (1-7). In vivo microdialysis analysis showed a significant elevation of extracellular glutamate and NO metabolites in the spinal cord after i.t. injection of high-dose morphine (500 nmol). Pretreatment with substance P (1-7) (400 pmol) produced a significant reduction on the elevated concentrations of glutamate and NO metabolites evoked by i.t. morphine. The reduced levels of glutamate and NO metabolites were significantly reversed by the substance P (1-7) antagonist (40 nmol). The present results suggest that i.t. substance P (1-7) may attenuate the excitatory behavior (vocalization and agitation) of high-dose i.t. morphine by inhibiting the presynaptic release of glutamate, and reducing NO production in the dorsal spinal cord.     

Behavioural characterization of substance P-induced nociceptive response in mice

Intrathecal injection of substance P produced a behavioural syndrome, consisting of reciproacal hindlimb scratching and biting or fore- and hind-licking. Pretreatment with either an analogue of substance P, (D-Pro2, D-Trp7,9)-substance P (DPDT-SP) or (D-Arg1, D-Pro2,4, D-Trp7,9, Leu11)-substance P, given intrathecally, reduced the response to substance P in a dose-dependent manner. The behaviour induced by substance P was also inhibited by intrathecal, intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of morphine. Intrathecal or subcutaneous injection of naloxone showed a biphasic effect on substance P response; the substance P-induced nociceptive response was increased by a small dose of naloxone, while it was inversely decreased by a large dose of naloxone. The results with analogues of substance P support the hypothesis that substance P, injected intrathecally, acts directly on substance P receptors in the spinal cord. The nociceptive response induced by substance P appears to be controlled by endogenous opioids in the spinal cord.     

Neuropeptide-mediated transmission of nociceptive information and its regulation. Novel mechanisms of analgesics]

Substance P and somatostatin may be transmitters of nociceptive information, which are involved in the transmission of pressure and heat nociceptive information, respectively, in the spinal dorsal horn. Calcitonin gene-related peptide, which is present in the primary sensory neurons having substance P or somatostatin, may function as a pain-promoting substance and be involved in the production of inflammation-induced hyperalgesia. The descending noradrenergic system plays a role in inhibiting nociceptive transmission in the spinal dorsal horn, and inhibits the release of substance P evoked by noxious mechanical stimulation. Persistent noxious stimuli increase the release of Met-enkephalin from the nucleus reticularis gigantocellularis, which promotes the activity of the descending noradrenergic system. Morphine activates the descending noradrenergic system, acting on the nucleus reticularis gigantocellularis. Morphine also activates the descending serotonergic system, which inhibits the release of somatostatin evoked by thermal noxious stimulation.     

Differential effects of substance P on serotonin-modulated spinal nociceptive reflexes

Recent immunohistochemical studies indicate the presence of a bulbospinal substance P (SP) system, as well as a bulbospinal serotonin (5-HT) system, involved in spinal pain transmission. Although electrophysiological studies indicate that SP may modulate the effects of 5-HT on post-synaptic spinal nociceptive neurons, the functional relationship between SP and 5-HT on “pain behavior” remains obscure. To bridge this gap between mechanism and behavior, the purpose of the present study was to determine specific postsynaptic behavioral effects of SP and 5-HT on local spinal nociceptive reflexes in spinally transected animals. Administration of the 5-HT agonists 5-methoxydi-methyltryptamine (5-MeODMT) (0, 0.5, 1.5, 2.0 mg/kg) and quipazine (0, 5, 10, 20 mg/kg) 2 days after transection significantly expanded the receptive field (RF) areas of three spinal reflexes, as previously reported. Intrathecal administration of SP alone (0, 0.25, 2.5, 7.5 ng) also resulted in hyperalgesia, indicated by a significant expansion of the RF areas of all three nociceptive reflexes. However, administration of SP, in animals pretreated with 5-HT agonists, decreased the 5-HT-induced expansion of RF size. Therefore, SP had opposite effects on spinal nociceptive reflexes depending on whether or not the animal was pretreated with 5-HT agonists, i.e., hyperalgesia in the absence of 5-HT agonists, and analgesia in the presence of 5-HT agonists. The two effects of SP on local spinal reflexes may be related to the anatomical organization of the two spinal SP systems: 1) SP released from primary afferents facilitates nociceptive reflexes, and 2) SP associated with the descending bulbospinal system interacts with the descending bulbospinal 5-HT system and inhibits nociceptive reflexes. The present results help explain contradictory literature regarding the effect of SP on spinal nociceptive reflexes.     

Spantide抑制甲醛炎性痛大鼠脊髓一氧化氮合酶表达和一氧化氮含量的增加(英文)

目的　观察鞘内注射P物质 (SP)拮抗剂spantide { [D Arg1,D Trp7,9,Leu11] substanceP}对炎性痛大鼠L5节段脊髓后角一氧化氮合酶 (NOS)表达和腰膨大一氧化氮 (NO)含量的影响 ,以探讨痛及痛过敏时脊髓NOS表达和NO生成增多的机制。方法　大鼠右后掌足底皮下注射 5 %甲醛 0 .2mL诱发炎性痛及痛过敏 ,NADPH d组化法观察脊髓后角NOS表达的变化 ,硝酸还原酶法测定NO含量的变化。结果　皮下注射甲醛 2 4h后 ,双侧L5节段脊髓后角NOS表达及腰膨大部位NO生成明显增加 ;注射甲醛前 5min鞘内注射spantide (5 μg ,10 μL) ,则明显抑制甲醛所致的NOS表达及NO生成增加。结论　初级传入末梢释放的SP在甲醛炎性痛及痛过敏时脊髓NOS表达及NO生成增多中发挥作用     

Similar behavioural effects of 5-hydroxytryptamine and substance P injected intrathecally in mice

Intrathecal injection of 5-hydroxytryptamine (5-HT) or of substance P in mice elicited a behavioural syndrome consisting of reciprocal hindlimb scratching and biting or licking, directed towards the caudal parts of the body. 5-Hydroxtryptamine elicited more scratching than did substance P, which in turn caused a greater number of biting or licking responses. The 5-HT-induced responses were mimicked by 5,6-dihydroxytryptamine and inhibited by the 5-HT receptor blocker metergoline. The present findings indicate that 5-HT, injected intrathecally, may have similar effects as substance P in stimulating sensory pathways in the spinal cord.     

Acupuncture mechanisms in rabbits studied with microinjection of antibodies against beta-endorphin, enkephalin and substance P

Injection of protein-A purified antibodies against Met-enkephalin and beta-endorphin into the periaqueductal gray matter (PAG) was shown to decrease the analgesic effect of electroacupuncture (EA) in rabbits. Met-enkephalin antibodies were more potent than the beta-endorphin antibodies in causing a statistically-significant effect on electroacupuncture analgesia. Antibodies to Met-enkephalin were also active at the spinal level, whereas antibodies against beta-endorphin were without effect: this is in agreement with a rich enkephalinergic innervation and absence of beta-endorphin-containing fibres in the spinal cord. Substance P, the other neuropeptide of this study, also seems to be important in mediating effects of electroacupuncture. Injection of antibodies into the periaqueductal gray caused decrease of the effect of electroacupuncture whereas intrathecal administration of Fab-fragment substance P antibodies caused a marked potentiation. The demonstration of site specificity of the neuropeptides in mediating analgesia induced by electroacupuncture supports the validity of this experimental approach.     

Intrathecal substance P depresses spinal motor and sensory responses to stimulation of nociceptive afferents — Antagonism by naloxone

Summary The effect of an injection of substance P into the subarachnoid space was studied on a motor and a sensory response elicited by supramaximal stimulation of the sural nerve in spinal rats. Substance P 10 g depressed the reflex activation in the electromyogram recorded from the ipsilateral tibialis anterior muscle; the depression was significant 5 and 10 min after the injection. Substance P 10 g reduced the activity in ascending axons of the spinal cord evoked by stimulation of afferent C fibres; the effect developed slowly, lasted longer than 60 min and was abolished by an i.v. injection of naloxone 0.2 mg/kg. Only half the number of ascending axons tested showed a depression by substance P, and the administration of a higher dose (50 g) did not produce an effect in a greater number of axons. Substance P did not influence the activity evoked in ascending axons by stimulation of afferent A and A fibres. The depression by substance P of ascending nociceptive activity was antagonized by an i.v. injection of naloxone 0.2 mg/kg. When naloxone 0.2 mg/ng i.v. was administered alone, it increased the activity in ascending axons activated by afferent C fibre stimulation. It is concluded that (i) substance P depresses spinal nociceptive activity without the intermediation of endorphinergic neurons, and (ii) naloxone antagonizes tonic inhibition of the spinal nociceptive system mediated by endogenous opioid peptides and, by facilitating excitatory transmission through disinhibition, neutralizes the depression produced by substance P.Supported by the Sonderforschungsbereich 38 Membranforschung     

Streptozotocin-induced diabetes in mice reduces the nociceptive threshold, as recognized after application of noxious mechanical stimuli but not of thermal stimuli.

We report herein that streptozotocin (STZ)-induced diabetes selectively alters the nociceptive threshold with respect to noxious mechanical stimuli. Mice were rendered diabetic by an injection of STZ (200 mg/kg, IV). In the tail-pinch test, the latency of the biting response to forceps was significantly decreased in animals with diabetes of 2 weeks and 8 weeks duration as compared to that in age-matched controls. However, the nociceptive threshold, as determined by the tail-flick test, was not significantly altered. The level of substance P in the spinal cord was significantly increased in mice that has been diabetic for 2 weeks, while, there was a significant decrease, as compared to control levels, in level of substance P in mice diabetic for 8 weeks. However, the level of somatostatin was not significantly altered in mice diabetic for either 2 weeks or 8 weeks. These data suggest that STZ-induced diabetes selectively alters a neuronal system that involves substance P but not somatostatin in the spinal cord.     

Adenosine analogs do not inhibit the potassium-stimulated release of substance P from rat spinal cord slices

Summary Adenosine agonists produce antinociception when injected directly onto the spinal cord of rats and mice. One mechanism to account for this effect could be inhibition of neurotransmitter release from nociceptive sensory neurons. Consequently, we studied whether these agents could inhibit the potassium stimulated release of one such transmitter, substance P, from rat spinal cord slices. A 2 cm section of lumbar spinal cord was dissected from male Sprague-Dawley rats, chopped into 0.5 × 0.5 mm sections and perfused at 37°C with a modified Krebs bicarbonate buffer containing either 3.5 mM, 30 mM, or 50 mM KCl in the presence and absence of various adenosine analogs. Perfusates, collected every 2 min, were assayed for substance P by radioimmunoassay. Exposure of tissue to 50 mM KC1 produced an approximate three-fold increase in the release of substance P over basal release. This increase in release was calcium dependent. Perfusion of spinal cord tissues with either adenosine (10^–3 M), N⁶-cyclohexyladenosine (10^–5 M or 5 × 10^–5 M), 5-N-ethylcarboxamide adenosine (10^–5 M) or L-N⁶-phenylisopropyladenosine (10^–5 M) did not significantly alter basal or potassium-stimulated release of SP when compared to controls. In contrast to the adenosine agonists, exposure of the spinal cord tissue to 10^–5 M morphine significantly reduced the potassium-stimulated release of substance P. Pretreatment of the slices with 10^–5 M theophylline or 8-phenyltheophylline did not significantly attenuate the inhibition of substance P release produced by morphine. Theophylline alone (10^–5 M) had no significant effect on either basal or potassium-stimulated release of SP. These studies demonstrate that adenosine does not inhibit the release of SP from spinal cord slices and does not appear to mediate the morphine-induced inhibition of SP release. The results suggest that the mechanism of the antinociceptive effects of adenosine at the level of the spinal cord is not via inhibition of substance P release. Send offprint requests to M. R. Vasko at the above address     

甲基强地松龙局部浸润对脊神经根炎性损伤后影响的实验研究

目的 观察甲基强地松龙局部浸润对炎性损伤脊神经根的恢复情况，探讨甲基强地松龙对非压迫状态下脊神经根损伤的保护作用。方法 20只家兔全部制成脊神经根炎性损伤的动物模型并饲养3d。分组给予甲基强地松龙或等量生理盐水局部浸润脊神经根。术后1wk测量脊神经根的传导速度，光镜下观察脊神经根的组织学变化及脊髓后角P物质免疫组织化学染色（S－P法）。结果 甲基强地松龙组脊神经根传导速度明显恢复。组织学观察显示脊神经根间质充血，水肿程度显著减轻，范围显著缩小，炎性细胞浸润减少。脊髓灰质后角P物质免疫反应阳性纤维面积及灰度均明显小于对照组。结论 甲基强地松龙局部浸润可以降低脊神经根炎症反应，阻断疼痛传递，促进脊神经根功能恢复。     

Levels of dynorphin peptides, substance P and CGRP in the spinal cord after subchronic administration of morphine in the rat.

Rats were rendered dependent on morphine by repeated injections of morphine, in increasing doses for 14 days and sacrificed. Levels of peptides in the dorsal spinal cord and dorsal root ganglia were analyzed in rats decapitated 2 hr, 24 hr (acute abstinent) or 7 days (late abstinent) respectively, after the last injection of drug. Dynorphin A was significantly decreased in rats abstinent for 24 hr, while dynorphin B remained unaffected. Substance P and CGRP, both putative transmitters in nociceptive primary afferent neurones, and partly existing together in the same neurone, were affected differently. Significantly less substance P but unchanged levels of CGRP were detected in rats abstinent for 24 hr, while on the other hand, CGRP but not levels of substance P, were increased 2 hr after the final injection. In dorsal root ganglia, levels of substance P were lower at 2 hr, while levels of CGRP were unaffected. In late (7 days) abstinence, no effect of opiate on any peptide was detected.     

Tachykinin receptor modulators: novel therapeutics for rheumatoid arthritis

The activation of a cellular immune response in a genetically susceptible individual is widely recognised as a main step in triggering rheumatoid arthritis (RA). The tachykinins, substance P (SP) and neurokinin A (NKA), can play a major role in different immune diseases. In patients with inflammatory joint disease, elevated levels of SP have been demonstrated in the synovial fluid of affected joints. It is well known that SP and, to a lesser extent, NKA are deeply involved in the processing of nociceptive signals and exert many pro-inflammatory actions, which may be elicited by an increased neuronal neurokinin release in arthritis; the mechanism behind this increase remains to be fully elucidated. Different observations suggest that one approach to the treatment of RA might be to inhibit the local effects of neurokinins in the affected joints. This review will summarise the more relevant aspects of this topic.