Hippocampus is involved in 17β-estradiol exacerbating experimental occlusal inter- ference-induced chronic masseter hyperalgesia in ovariectomized rats / 北京大学学报(医学版)

OBJECTIVE@#To investigate the influence of chronic masseter hyperalgesia induced by 17β-estradiol (E2) and experimental occlusal interference (EOI) on underlying mechanism in hippocampus of ovariectomized (OVX) rats.@*METHODS@#In the study, 32 OVX rats were randomly divided into 4 groups (8 rats/group): The control group was OVX group, and 0 μg/d E2 (vehicle) injection was started 7 d after OVX without EOI; in the experimental group (1) OVX + E2 group, 80 μg/d E2 injection was started 7 d after OVX without EOI; in the experimental group (2) OVX + EOI group, vehicle injection was started 7 d after OVX and EOI was applied 17 d after OVX; in the experimental group (3) OVX + E2 + EOI group, 80 μg/d E2 injection was started 7 d after OVX and EOI was applied 17 d after OVX. Bilateral masseter muscle mechanical withdrawal thresholds were measured before OVX, 7 days after OVX (before E2 injection), 17 days after OVX (10 days after E2 injection and before EOI) and 24 days after OVX (7 days after EOI). Immunofluorescence staining was used to reveal phospho-extracellular signal regulated kinase 1/2 (p-ERK1/2)-positive neurons in CA3 of hippocampus. The protein expression of p-ERK1/2 in hippocampus was detected using Western Blot.@*RESULTS@#Compared with the control group [left side: (135.3±8.5) g, right side: (135.4±10.8) g], bilateral masseter muscle mechanical withdrawal thresholds of OVX+E2 group [left side: (113.3±5.6) g, right side: (112.5 ± 5.6) g] and OVX+EOI group [left side: (93.3±5.4) g, right side: 90.8±5.5) g] were decreased (P < 0.01). Bilateral masseter muscle mechanical withdrawal thresholds were significantly lower in OVX+E2+EOI group [left side: (81.2±6.2) g, right side: 79.8±7.7) g] than in the control, OVX+E2 and OVX+EOI groups (P < 0.05). The proportion of p-ERK1/2 positive neurons in the CA3 region of the hippocampus was increased in the control, OVX+E2, OVX+EOI and OVX+E2+EOI groups in turn, and the difference between the groups was statistically significant (P < 0.05). p-ERK1/2 protein expression was increased in the control, OVX+E2 and OVX+EOI groups in turn, but the difference was not statistically significant (P>0.05). p-ERK1/2 expression was significantly higher in OVX+E2+EOI group than in the other three groups (P < 0.05).@*CONCLUSION@#High concentration of E2 could exacerbated EOI-induced chronic masseter hyperalgesia in ovariectomized rats, and its central mechanism may be related to the upregulation of the phosphorylation of ERK1/2 in hippocampus.

Amifostine protects from the peripheral sensory neuropathy induced by oxaliplatin in mice

Sensory neuropathy is a dose-limiting side effect of oxaliplatin-based cancer treatment. This study investigated the antinociceptive effect of amifostine and its potential neuroprotective mechanisms on the oxaliplatin-related peripheral sensory neuropathy in mice. Oxaliplatin (1 mg/kg) was injected intravenously in Swiss albino male mice twice a week (total of nine injections), while amifostine (1, 5, 25, 50, and 100 mg/kg) was administered subcutaneously 30 min before oxaliplatin. Mechanical and thermal nociceptive tests were performed once a week for 49 days. Additionally, c-Fos, nitrotyrosine, and activating transcription factor 3 (ATF3) immunoexpressions were assessed in the dorsal root ganglia. In all doses, amifostine prevented the development of mechanical hyperalgesia and thermal allodynia induced by oxaliplatin (P<0.05). Amifostine at the dose of 25 mg/kg provided the best protection (P<0.05). Moreover, amifostine protected against neuronal hyperactivation, nitrosative stress, and neuronal damage in the dorsal root ganglia, detected by the reduced expression of c-Fos, nitrotyrosine, and ATF3 (P<0.05 vs the oxaliplatin-treated group). In conclusion, amifostine reduced the nociception induced by oxaliplatin in mice, suggesting the possible use of amifostine for the management of oxaliplatin-induced peripheral sensory neuropathy.

Efecto del fentanilo intratecal en hiperlagesia secundaria posoperatoria de cirugía ligamento cruzado anterior de rodilla / Effect of Intrathecal fentanyl on secondary hyperalgesia, in patients undergoing anterior cruciate ligament repair

BACKGROUND AND OBJECTIVES: Fentanyl addition is a common practice when administering spinal anesthesia. Intrathecal fentanyl has been associated to increased postoperative pain and increase morphine consumption, but considered to be related to acute opioid tolerance. This prospective, randomized, blind study evaluates the effect of intrathecal fentanyl in the development of secondary hyperalgesia, measured with Von Frey filaments, in patients undergoing anterior cruciate ligament repair. METHODS: 46 patients having anterior cruciate ligament repair, received intrathecal hyperbaric bupivacaine 13.5 mg with fentanyl 20 mcg or no fentanyl addition. Light touch pain threshold was measured with von Frey filaments before anesthesia, at 6 and 24 hours post anesthesia in the non-operated thigh and in the forearm. Visual analogue pain scores and morphine consumption were also measured at the same time. RESULTS: Baseline thresholds to mechanical stimuli were similar in both groups. In the forearm, analysis showed a decreased threshold for the non-fentanyl group at 24 h p = 0.036. In the lower extremity, control and treatment group showed lower thresholds (secondary hyperalgesia) p = 0.002 but no difference between them p = 0.795. VAS score and morphine consumption did not differ among groups. CONCLUSIONS: Spinal fentanyl added to hyperbaric bupivacaine showed no evidence of an augmented state of hyperalgesia after ACL repair, neither by pain threshold modification nor clinical outcomes. On the contrary, at 24 h, fentanyl may have a protective effect at levels above the spinal block.

ANTECEDENTES Y OBJETIVOS: El uso de fentanilo es una práctica común en la administración de anestesia espinal. Su aplicación se ha asociado a un aumento del dolor post operatorio y a un aumento en el uso de morfina; por otro lado, se ha vinculado a una tolerancia aguda a opioides. El siguiente estudio prospectivo, randomizado y ciego, evalúa los efectos del fentanilo intratecal en la aparición de hiperalgesia secundaria, medida a través de filamentos Von Frey, en pacientes operados de ligamento cruzado anterior. METODOLOGÍA: Se incluyeron a 46 pacientes operados de ligamento cruzado anterior (LCA) con una dosis intratecal de bupivacaína hiperbárica de 13,5 mg; con y sin la adición de fentanilo de 20 mcg. Se midió el umbral del dolor mecánico, a través de filamentos Von Frey, antes de la anestesia, a las 6 y 24 horas postanestesia en el muslo no operado y en el antebrazo. Al mismo tiempo, se midió la puntuación del dolor en la escala verbal numérica (EVN) y el consumo de morfina. RESULTADOS: Los umbrales basales ante la estimulación mecánica resultaron similares en ambos grupos. En el antebrazo, el análisis mostró una disminución del umbral en el grupo de pacientes sin fentanilo, a las 24 h, p = 0,036 comparado con uso de fentanilo. En el muslo, el grupo control y tratamiento mostró umbrales más bajos (hiperalgesia secundaria) p = 0,002; no obstante, no se mostraron diferencias entre ellos. No se mostraron diferencias entre las puntuaciones de la EVN y el consumo de morfina en los dos grupos. CONCLUSIÓN: No hay evidencia que la adición de fentanilo espinal, a la dosis de bupivacaína hiperbárica, haya contribuido a un aumento en la hiperalgesia tras la reparación del LCA, medido por la modificación del umbral del dolor, ni en los resultados clínicos. Al contrario a las 24 h fentanilo puede tener un efecto protector de la hiperalgesia secundaria sobre el nivel del bloqueo espinal.

Interleukin-4 protects from chemotherapy-induced peripheral neuropathy in mice modal via the stimulation of IL-4/STAT6 signaling

Abstract Purpose: To investigate the possible role of IL-4 signaling pathway in vincristine-induced peripheral neuropathy. Methods: The mouse model of vincristine-induced peripheral neuropathy and interleukin (IL)-4 knockout mice were utilized to investigate the possible role of IL-4 signaling pathway in vincristine-induced peripheral neuropathy. Vincristine induced increased sensitivity to mechanical stimulation was measured by von Frey hair test 7 and 14 days after intraperitoneal administration of 0.1 mg/kg vincristine in mice. Relative expression levels of cytokines were detected by quantitative real-time PCR. STAT6 expression following vincristine treatment was assessed with western blotting. Results: We discovered that IL-4/STAT6 signaling was down-regulated in vincristine-treated mice. Deletion of IL-4 in mice increased the sensitivity to mechanical allodynia. IL-4 knockout mice also produced more pro-inflammatory cytokines, including IL-1β and TNF-α. Notably, co-administration of exogenous recombination IL-4 significantly prevented vincristine-induced mechanical allodynia. Conclusion: Anti-inflammatory cytokine IL-4 protects rodent model from vincristine-induced peripheral neuropathy via the stimulation of IL-4/STAT6 signaling and inhibition of the pro-inflammatory cytokines.

Osteoarthritis model induced by intra-articular monosodium iodoacetate in rats knee

ABSTRACT PURPOSE: To evaluate the usefulness of a knee osteoarthritis model through functional, radiological and microscopic changes of the synovial membrane. METHODS: Forty eight rats were divided randomly into two groups. The first received 0.9% saline in the joint and corresponded to the control group. The second was submitted to experimental osteoarthritis of the right knee induced by monosodium iodoacetate and corresponded to the osteoarthritis group. All animals were subjected to comparative tests of forced ambulation and joint movements, inability to articulate and tactile allodynia on day 1 post-experiment by forced ambulation (Roto-rod test), joint assessment of disability (weight bearing test) and assessment of tactile allodynia (Von Frey test). After inflammatory induction they were divided into four sub-groups corresponding to the scheduled death in 7, 14, 21 and 28 days when they were submitted to radiographic examination of the knee, arthrotomy and collection of the synovial membrane. RESULTS: The osteoarthritis group showed significant differences compared to control group on days 7 and 14 in Roto-rod, in weight bearing and Von Frey tests in all days, and in radiological evaluation. Microscopic examination of the synovial membrane showed abnormalities of inflammatory character at all stages. CONCLUSION: The osteoarthritis induced by intra-articular monosodium iodoacetate in rats knee is a good model to be used in related research, because it provides mensurable changes on joint movements, tactile allodynia, progressive radiological degeneration and microscopic inflammation of the synovial membrane, that represent markers for osteoarthritis evaluation

The superoxide anion donor, potassium superoxide, induces pain and inflammation in mice through production of reactive oxygen species and cyclooxygenase-2

It is currently accepted that superoxide anion (O2•−) is an important mediator in pain and inflammation. The role of superoxide anion in pain and inflammation has been mainly determined indirectly by modulating its production and inactivation. Direct evidence using potassium superoxide (KO2), a superoxide anion donor, demonstrated that it induced thermal hyperalgesia, as assessed by the Hargreaves method. However, it remains to be determined whether KO2 is capable of inducing other inflammatory and nociceptive responses attributed to superoxide anion. Therefore, in the present study, we investigated the nociceptive and inflammatory effects of KO2. The KO2-induced inflammatory responses evaluated in mice were: mechanical hyperalgesia (electronic version of von Frey filaments), thermal hyperalgesia (hot plate), edema (caliper rule), myeloperoxidase activity (colorimetric assay), overt pain-like behaviors (flinches, time spent licking and writhing score), leukocyte recruitment, oxidative stress, and cyclooxygenase-2 mRNA expression (quantitative PCR). Administration of KO2 induced mechanical hyperalgesia, thermal hyperalgesia, paw edema, leukocyte recruitment, the writhing response, paw flinching, and paw licking in a dose-dependent manner. KO2 also induced time-dependent cyclooxygenase-2 mRNA expression in the paw skin. The nociceptive, inflammatory, and oxidative stress components of KO2-induced responses were responsive to morphine (analgesic opioid), quercetin (antioxidant flavonoid), and/or celecoxib (anti-inflammatory cyclooxygenase-2 inhibitor) treatment. In conclusion, the well-established superoxide anion donor KO2 is a valuable tool for studying the mechanisms and pharmacological susceptibilities of superoxide anion-triggered nociceptive and inflammatory responses ranging from mechanical and thermal hyperalgesia to overt pain-like behaviors, edema, and leukocyte recruitment.

Analgesic Effects of Dexmedetomidine in Vincristine-Evoked Painful Neuropathic Rats

Dexmedetomidine, which is a selective alpha2-adrenoceptor agonist, was recently introduced into clinical practice for its analgesic properties. The purpose of this study was to evaluate the effects of dexmedetomidine in a vincristine-evoked neuropathic rat models. Sprague-Dawley rats were injected intraperitoneally with vincristine or saline (0.1 mg/kg/day) using a 5-day-on, 2-day-off schedule for 2 weeks. Saline and dexmedetomidine (12.5, 25, 50, and 100 microg/kg) were injected to rats developed allodynia 14 days after vincristine injection, respectively. We evaluated allodynia at before, 15, 30, 60, 90, 120, 180, and 240 min, and 24 hr after intraperitoneal drug (normal saline or dexmedetomidine) injection. Saline treatment did not show any differences for all the allodynia. Maximal paw withdrawal thresholds to mechanical stimuli were 3.0 +/- 0.4, 9.1 +/- 1.9, 13.0 +/- 3.6, 16.6 +/- 2.4, and 24.4 +/- 1.6 g at saline, 12.5, 25, 50, and 100 microg/kg dexmedetomidine injection, respectively. Minimal withdrawal frequency to cold stimuli were 73.3 +/- 4.2, 57.1 +/- 6.8, 34.3 +/- 5.7, 20.0 +/- 6.2, and 14.3 +/- 9.5 g at saline, 12.5, 25, 50, and 100 microg/kg dexmedetomidine injection, respectively. Dexmedetomidine shows a dose-dependent antiallodynic effect on mechanical and cold stimuli in vincristine-evoked neuropathic rat models (P < 0.05).

Analgesic Effects of Dexmedetomidine in Vincristine-Evoked Painful Neuropathic Rats

Dexmedetomidine, which is a selective alpha2-adrenoceptor agonist, was recently introduced into clinical practice for its analgesic properties. The purpose of this study was to evaluate the effects of dexmedetomidine in a vincristine-evoked neuropathic rat models. Sprague-Dawley rats were injected intraperitoneally with vincristine or saline (0.1 mg/kg/day) using a 5-day-on, 2-day-off schedule for 2 weeks. Saline and dexmedetomidine (12.5, 25, 50, and 100 microg/kg) were injected to rats developed allodynia 14 days after vincristine injection, respectively. We evaluated allodynia at before, 15, 30, 60, 90, 120, 180, and 240 min, and 24 hr after intraperitoneal drug (normal saline or dexmedetomidine) injection. Saline treatment did not show any differences for all the allodynia. Maximal paw withdrawal thresholds to mechanical stimuli were 3.0 +/- 0.4, 9.1 +/- 1.9, 13.0 +/- 3.6, 16.6 +/- 2.4, and 24.4 +/- 1.6 g at saline, 12.5, 25, 50, and 100 microg/kg dexmedetomidine injection, respectively. Minimal withdrawal frequency to cold stimuli were 73.3 +/- 4.2, 57.1 +/- 6.8, 34.3 +/- 5.7, 20.0 +/- 6.2, and 14.3 +/- 9.5 g at saline, 12.5, 25, 50, and 100 microg/kg dexmedetomidine injection, respectively. Dexmedetomidine shows a dose-dependent antiallodynic effect on mechanical and cold stimuli in vincristine-evoked neuropathic rat models (P < 0.05).

Pharmacology of Intracisternal or Intrathecal Glycine, Muscimol, and Baclofen in Strychnine-induced Thermal Hyperalgesia of Mice

Glycine and gamma-aminobutyric acid (GABA) are localized and released by the same interneurons in the spinal cord. Although the effects of glycine and GABA on analgesia are well known, little is known about the effect of GABA in strychnine-induced hyperalgesia. To investigate the effect of GABA and the role of the glycine receptor in thermal hyperalgesia, we designed an experiment involving the injection of muscimol (a GABAA receptor agonist), baclofen (a GABAB receptor agonist) or glycine with strychnine (strychnine sensitive glycine receptor antagonist). Glycine, muscimol, or baclofen with strychnine was injected into the cisterna magna or lumbar subarachnoidal spaces of mice. The effects of treatment on strychnine-induced heat hyperalgesia were observed using the pain threshold index via the hot plate test. The dosages of experimental drugs and strychnine we chose had no effects on motor behavior in conscious mice. Intracisternal or intrathecal administration of strychnine produced thermal hyperalgesia in mice. Glycine antagonize the effects of strychnine, whereas, muscimol or baclofen does not. Our results indicate that glycine has anti-thermal hyperalgesic properties in vivo; and GABA receptor agonists may lack the binding abilities of glycine receptor antagonists with their sites in the central nervous system.

Hiperalgesia induzida por opioides (HIO) / Opioid-induced hyperalgesia (OIH) / Hiperalgesia inducida por opioides (HIO)

JUSTIFICATIVA E OBJETIVOS: Opioides são medicamentos frequentemente usados para o controle da dor que, contudo, podem causar hiperalgesia. A circunstância pela qual esse fenômeno pode ocorrer não está inteiramente esclarecida. O objetivo desta revisão foi descrever os mecanismos, os fatores implicados e a modulação por medicamentos. CONTEÚDO: Foram descritos os fatores implicados no desenvolvimento da hiperalgesia induzida por opioides (HIO), como duração de uso, dose e tipo de opioide. Os mecanismos incluem o sistema glutamatérgico e receptores N-metil-D-aspartato (NMDA), ativação de ciclo-oxigenase (COX) espinal, aminoácidos excitatórios, dinorfina, citocinas e quimocinas; prostaglandinas e facilitação descendente. A modulação de hiperalgesia pode ser feita com antagonistas de receptores NMDA, agonistas adrenérgicos-alfa2 e inibidores de COX. CONCLUSÕES: O assunto é bastante complexo, envolvendo uma série de mecanismos fisiopatológicos que podem contribuir para a HIO e o desconforto do paciente, trazendo consequências que podem ser danosas.

BACKGROUND AND OBJECTIVES: Opioids are commonly used for pain control; however, they can cause hyperalgesia. The reason why this can happen is not known. The objective of this review was to describe the mechanisms, factors implicated, and drug modulation. CONTENTS: The factors implicated in the development of opioid-induced hyperalgesia (OIH), such as duration of use, dose, and type of opioids are described. Mechanisms involved include the glutamatergic system and N-methyl-D-aspartate receptors (NMDA), spinal cyclooxygenase (COX) activation, excitatory amino acids, dynorphin, cytokines and chemokines; prostaglandins, and descending facilitation. Modulation of hyperalgesia could be done through: NMDA receptor antagonists, alpha2-adrenergic agonists, and COX inhibitors. CONCLUSIONS: This is a very complex subject, which involves a series of pathophysiological mechanisms that could contribute for OIH and patient discomfort, bringing disastrous consequences.

JUSTIFICATIVA Y OBJETIVOS: Los opioides son medicamentos a menudo usados para el control del dolor y que sin embargo pueden causar hiperalgesia. La circunstancia por la cual ese fenómeno puede ocurrir no está totalmente aclarada. El objetivo de esta revisión es describir los mecanismos, los factores que están involucrados y la modulación por medicamentos. CONTENIDO: Fueron descritos los factores involucrados en el desarrollo de la hiperalgia inducida por opioides (HIO), como la duración en el uso, la dosis y el tipo de opioide. Los mecanismos incluyen los sistemas glutamatérgico y los receptores N-metil-D-aspartato (NMDA), activación de ciclo-oxigenasa (COX) espinal, aminoácidos excitatorios, dinorfina, citocinas y quimocinas; prostaglandinas y facilitación descendiente. La modulación de la hiperalgesia se puede lograr con los antagonistas de receptores NMDA, los agonistas adrenérgicosalfa2 y con los inhibidores de (COX). CONCLUSIONES: El tema es bastante complejo, e involucra una serie de mecanismos fisiopatológicos que pueden contribuir para la HIO y la incomodidad del paciente, con consecuencias dañinas para la salud.

Interference of age and repetition of the same noxious stimulus on hyperalgesia / Interferência da idade e repetição do mesmo estímulo doloroso na hiperalgesia

Pain in animals has been recognized for less than one century. Several authors confirm that animals are capable to process, register and modulate nociceptive stimuli in a very similar way to human kind and there are several evidences registering the impact of pain sensation over vital systems interfering on disease outcome. Nevertheless, despite some evidences that animals, as human beings, can store information from past painful experiences less is known about how this so called pain memory works. The aims of this study were: to evaluate if the response to a painful stimuli differs during different stages of life and if repetition of a same acute stimuli in the same animal interferes with expression of hyperalgesia. Thus, 60 rats were selected and arranged in 3 equal groups: 3 months, 6 months, and 9 months of age. All animals were injected 5 percent formalin solution in the plantar face of hind paw under volatile general anesthesia. Von Frey filaments were applied at 1h, 24h and 48h after sensitization. Injection was repeated twice with a 30-day interval, each time in a different hind paw. Results showed that younger rats express lower hyperalgesia thresholds in the first stimulation compared to elder animals and that repetition of same stimulus diminishes hyperalgesia thresholds when it begins during infant period and augments hyperalgesia thresholds when it begins during elder ages.

A dor nos animais tem sido reconhecida há pouco manos de um século. Vários autores reconhecem que os animais são capazes de processar, registrar e modular estímulos nociceptivos de modo muito similar aos seres humanos e há várias evidências registrando o impacto da sensação dolorosa sobre os sistemas vitais e curso da doença. Entretanto, a despeito das evidências de que os animais, como os seres humanos, podem armazenar informações passadas de experiências dolorosas pouco se sabe sobre como a chamada memoria de dor funciona. Os objetivos deste estudo foram: avaliar se a resposta a um estímulo doloroso difere em diferentes fases da vida e se a repetição de um mesmo estímulo doloroso agudo no mesmo animal interfere na expressão da hiperalgesia. Assim, 60 ratos foram selecionados e agrupados em três grupos iguais: 3 meses, 6 meses e 9 meses. Foi injetada solução de formalina 5 por cento na face plantar de todos os animais durante anestesia. O limiar de hiperalgesia foi testado pelo método de filamentos de Von Frey à 1h, 24h e 48h após a sensibilização. A injecão foi repetida duas vezes com intervalo de 30 dias, uma vez em cada membro. Os resultados demonstraram que animais mais jovens possuem limiares menores de hiperalgesia na primeira estimulação, comparados com os mais velhos e que a repetição de um mesmo estímulo doloroso agudo diminui o limiar de hiperalgesia quando o primeiro estímulo ocorre nas idades mais tenras e aumenta o limiar quando se inicia em idades mais avançadas.

Streptozotocin-induced mechanical hypernociception is not dependent on hyperglycemia

Since streptozotocin (STZ)-induced diabetes is a widely used model of painful diabetic neuropathy, the aim of the present study was to design a rational protocol to investigate whether the development of mechanical hypernociception induced by STZ depends exclusively on hyperglycemia. Male Wistar rats (180-200 g; N = 6-7 per group) received a single intravenous injection of STZ at three different doses (10, 20, or 40 mg/kg). Only the higher dose (40 mg/kg) induced a significant increase in blood glucose levels, glucose tolerance and deficiency in weight gain. However, all STZ-treated rats (hyperglycemic or not) developed persistent (for at least 20 days) and indistinguishable bilateral mechanical hypernociception that was not prevented by daily insulin treatment (2 IU twice a day, sc). Systemic morphine (2 mg/kg) but not local (intraplantar) morphine treatment (8 µg/paw) significantly inhibited the mechanical hypernociception induced by STZ (10 or 40 mg/kg). In addition, intraplantar injection of STZ at doses that did not cause hyperglycemia (30, 100 or 300 µg/paw) induced ipsilateral mechanical hypernociception for at least 8 h that was inhibited by local and systemic morphine treatment (8 µg/paw or 2 mg/kg, respectively), but not by dexamethasone (1 mg/kg, sc). The results of this study demonstrate that systemic administration of STZ induces mechanical hypernociception that does not depend on hyperglycemia and intraplantar STZ induces mechanical sensitization of primary sensory neurons responsive to local morphine treatment.

Effects of captopril and losartan on thermal and chemical induced pain in mice.

Angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers antagonists (ARAs) are widely used compounds in various cardiovascular disorders. ACEIs, but not ARAs, inhibit the enzyme dipeptidyl carboxypeptidase which is involved in the conversion of angiotensin I to II and degradation of kinins like bradykinin and substance P. Bradykinin and substance P are potent mediators of inflammation and pain. Hence the study was undertaken to evaluate the effects of captopril (an ACEI) and losartan (an ARA-AT1 receptor antagonist) on thermal and chemical induced nocioception by employing hot plate and acetic acid induced writhing tests respectively in mice. Inbred albino mice weighing between 25-30 g were used and they were divided into two sets, each set containing 7 groups. Control groups received normal saline and the remaining six groups received three doses (0.5, 1 and 2 mg/kg) of captopril and three doses (0.5, 1 and 2 mg/kg) of losartan. Drugs were administered intraperitoneally fifteen minutes before placing the animal over the hot plate or 30 minutes before injecting 0.6% acetic acid. Both drugs dose dependently reduced the reaction time in hot plate method. In chemical induced writhing test, both the drugs reduced the latency of onset of writhing and in captopril pretreated groups, acetic acid induced sustained abdominal contraction without any intermittent relaxation. However, in losartan pretreated animals acetic acid just increased the number of writhings without sustained abdominal contraction. Thus, our study suggests that both drugs have hyperalgesic effects.

A novel hot-plate test sensitive to hyperalgesic stimuli and non-opioid analgesics

It is widely accepted that the classical constant-temperature hot-plate test is insensitive to cyclooxygenase inhibitors. In the current study, we developed a variant of the hot-plate test procedure (modified hot-plate (MHP) test) to measure inflammatory nociception in freely moving rats and mice. Following left and right hind paw stimulation with a phlogogen and vehicle, respectively, the animals were placed individually on a hot-plate surface at 51°C and the withdrawal latency for each paw was determined simultaneously in measurements performed at 15, 60, 180, and 360 min post-challenge. Plantar stimulation of rats (250 and 500 æg/paw) and mice (125-500 æg/paw) with carrageenan led to a rapid hyperalgesic response of the ipsilateral paw that reached a plateau from 15 to 360 min after challenge. Pretreatment with indomethacin (4 mg/kg, ip) inhibited the phenomenon at all the times analyzed. Similarly, plantar stimulation of rats and mice with prostaglandin E2 (0.5 and 1 æg/paw) also resulted in rapid hyperalgesia which was first detected 15 min post-challenge. Finally, we observed that the MHP test was more sensitive than the classical Hargreaves' test, being able to detect about 4- and 10-fold lower doses of prostaglandin E2 and carrageenan, respectively. In conclusion, the MHP test is a simple and sensitive method for detecting peripheral hyperalgesia and analgesia in rats and mice. This test represents a low-cost alternative for the study of inflammatory pain in freely moving animals.

Role of cyclooxygenase-2 in lipopolysaccharide-induced hyperalgesia in formalin test.

Lipopolysaccharide (LPS)-induced hyperalgesia and the role of cyclooxygenase (COX) isoforms in acute and chronic nociceptive assays have been well established. However, the role of COX isoforms in LPS-induced hyperalgesia in the formalin test is not clear. Thus, the present study was undertaken to characterize the time course of formalin-induced nociceptive response in LPS-pretreated mice and to investigate possible effects of COX inhibitors to address the potential role of COX isoforms in LPS-induced hyperalgesia in the formalin test. All the animals showed typical biphasic response to formalin challenge. At 0 hr (immediately) and 4 hr after LPS pretreatment, animals did not show any alteration in formalin-induced tonic pain. However, 12 and 16 hr after LPS pretreatment, there was a significant increase in the late phase of formalin-induced nocifensive response as compared to control mice. Treatment with intravenously administered ketorolac (a nonselective COX inhibitor) significantly and dose-dependently inhibited the late phase of formalin-induced nociceptive behaviour in saline and LPS-pretreated mice. In contrast, parecoxib (prodrug of valdecoxib, a selective COX-2 inhibitor) or dexamethasone (COX-2 transcription inhibitor), when administered intravenously or intraperitoneally, respectively, did not show antinociceptive effect in the formalin test in saline-pretreated mice. However, both the agents significantly and dose-dependently decreased the late phase nociceptive behaviour of the formalin test in LPS-pretreated mice to the level of the animals that received saline pretreatment. These results suggest that induction of COX-2 by proinflammatory mediators and subsequent release of prostaglandins could be responsible for LPS enhancement of formalin-induced nocifensive behaviour and supports an important role of COX-2 in LPS-induced hyperalgesia in the formalin test.

Cholinergic-NO-cGMP mediation of sildenafil-induced antinociception.

Acetylcholine and cholinomimetic agents with predominant muscarinic action are known to increase the concentration of cGMP by activation of nitric oxide signaling pathway in the nociceptive conditions. The present study was aimed to investigate the NO-cGMP-PDE5 pathway in nociceptive conditions in the experimental animals. Nociceptive threshold was assessed by acetic acid-induced writhing assay (chemonociception) or carrageenan-induced hyperalgesia. Sildenafil [1-5 mg/kg, ip, 50-200 microg/paw, intraplantar (ipl)] produced dose dependent antinociception in both the tested models. Coadministration of acetylcholine (50 mcg/paw, ipl) or cholinomimetic agent, neostigmine (0.1 mcg/kg, ip and 25 ng/paw, ipl) augmented the peripheral antinociceptive effect of sildenafil. This effect was sensitive to blockade by L-NAME (20 mg/kg, ip, 100 microg/paw, ipl), a non-selective NOS inhibitor and methylene blue (1 mg/kg, ip), a guanylate cyclase inhibitor, which per se had little or no effect in both the models of nociception. Further, the per se analgesic effect of acetylcholine and neostigmine was blocked by both L-NAME and methylene blue in the models of nociception, suggesting the activation of NO-cGMP pathway. Also, both L-NAME and methylene blue blocked the per se analgesic effect of sildenafil. These results indicate the peripheral accumulation of cGMP may be responsible for antinociceptive effect, and a possible interaction between cholinergic agents and PDE5 system in models of nociception.

Acute phenobarbital administration induces hyperalgesia: pharmacological evidence for the involvement of supraspinal GABA-A receptors

The aim of the present study was to determine if phenobarbital affects the nociception threshold. Systemic (1-20 mg/kg) phenobarbital administration dose dependently induced hyperalgesia in the tail-flick, hot-plate and formalin tests in rats and in the abdominal constriction test in mice. Formalin and abdominal constriction tests were the most sensitive procedures for the detection of hyperalgesia in response to phenobarbital compared with the tail-flick and hot-plate tests. The hyperalgesia induced by systemic phenobarbital was blocked by previous administration of 1 mg/kg ip picrotoxin or either 1-2 mg/kg sc or 10 ng icv bicuculline. Intracerebroventricular phenobarbital administration (5 æg) induced hyperalgesia in the tail-flick test. In contrast, intrathecal phenobarbital administration (5 æg) induced antinociception and blocked systemic-induced hyperalgesia in this test. We suggest that phenobarbital may mediate hyperalgesia through GABA-A receptors at supraspinal levels and antinociception through the same kind of receptors at spinal levels

Hyperalgesic effect induced by barbiturates, midazolam and ethanol: pharmacological evidence for GABA-A receptor involvement

The involvement of GABA-A receptors in the control of nociception was studied using the tail-flick test in rats. Non-hypnotic doses of the barbiturates phenobarbital (5-50 mg/kg), pentobarbital (17-33 mg/kg), and thiopental (7.5-30 mg/kg), of the benzodiazepine midazolam (10 mg/kg) or of ethanol (0.4-1.6 g/kg) administered by the systemic route reduced the latency for the tail-flick response, thus inducing a 'hyperalgesic' state in the animals. In contrast, non-convulsant doses of the GABA-A antagonist picrotoxin (0.12- 1.0 mg/kg) administered systemically induced an increase in the latency for the tail-flick response, therefore characterizing an 'antinociceptive' state. Previous picrotoxin (0.12 mg/kg) treatment abolished the hyperalgesic state induced by effective doses of the barbiturates, midazolam or ethanol. Since phenobarbital, midazolam and ethanol reproduced the described hyperalgesic effect of GABA-A-specific agonists (muscimol, THIP), which is specifically antagonized by the GABA-A antagonist picrotoxin, our results suggest that GABA-A receptors are tonically involved in the modulation of nociception in the rat central nervous system.

Ranunculus bulbosus: 1ra. parte / Ranunculus bulbosus: 1fts. part

Se resalta el tropismo tisular del medicamento, como así también los principales síntomas característicos y los diversos síndromes para los cuales se adapta. Se hacen resaltar las modalidades de las algias las cuales darán el diagnóstico medicamentoso con exactitud y se traen a consideración cuadros clínicos para los cuales el medicamento es muy útil y poco tenido en cuenta