Vocalization Threshold Research Articles

N-SALICYLOYL AMIDES AND THEIR SALTS: SYNTHESIS, BIOLOGICAL ACTIVITY AND TOXICITY

The Schotten-Baumann reaction was used to synthesize N-salicyloyl derivatives of Morpholine, Glycine and gamma-aminobutyric acid in the process between salicyloyl chloride with morpholine, glycine or gamma-aminobutyric acid with high yield. Sodium and lithium salts of the salicylamides were synthesized by the reaction of an amide with sodium ethylate or lithium hydroxide in inert solvent. The synthesized compounds were charachterized by 1H nuclear magnetic resonance spectra and elemental analysis. Purity was checked by thin layer chromatography. Quantitative analysis of metal ions was done by potentiometry. To select the most promising compounds exhibiting psychotropic (Pa > 0.8) and antiviral (Pa about 0.5) activities, computer analysis was carried out through the PASS program. In the present study, psychotropic (the open-field exploratory test, the forced swim test, the elevated plus-maze test, the passive avoidance test), analgesic (current vocalization threshold) activities and acute toxicity were evaluated. The results of psychotropic activity revealed that amides possess significant psychotropic activity and low acute toxicity. Disodium salicylurate showed a significant antiamnesic action. The results suggested a significant antidepressant activity and antiamnesic action for dilithium salicylurate and sodium salt of salycyloyl morphlide, a psychostimulant action for lithium salt of salicyloyl morphlide. Lithium gamma-(N-salycylamino)butyrate demonstrated psychostimulant and antiamnesic activities. Our present investigation demonstrated that all compounds are very safe for consumption with high LD50 value. All obtained compounds were evaluated for their antiviral activities against a large number of DNA and RNA viruses including herpes simplex viruses 1 and 2, vaccinia virus, vesicular stomatitis virus, HIV-1 and HIV-2. These compounds were evaluated against human cervix carcinoma cells (HeLa) and CEM T-lymphocytes as well as murine leukemia cells (L1210). The antiviral activity studies depicted that none of the tested compounds were active against DNA or RNA viruses.

Mating-induced analgesia is dependent of copulatory male pattern in high- and low- yawning male rats

Mating behavior in rodents can modulate pain sensations in both sexes. In males, the execution of mounts, intromissions, and ejaculations induced a progressive increase in their vocalization thresholds induced by tail shocks and other types of noxious stimuli.We selectively inbred two sublines from Sprague-Dawley (SD) rats that differed in their spontaneous yawning frequency. The high-yawning (HY) subline had a mean of 20 yawns/h and a different pattern of sexual behavior characterized by longer interintromission intervals and more sexual bouts that delayed ejaculation. The low-yawning (LY) subline and SD rats yawned as a mean 2 and 1 yawns/h, respectively.So, we determine mating-induced analgesia in HY, LY, and SD male rats by measuring vocalization thresholds in response to noxious electric tail shocks. Our results showed that the magnitude of mating-induced analgesia was lower in HY and LY rats with respect to SD rats. When the rats performed different components of male sexual pattern, both sublines exhibited a significantly lower increase in their vocalization thresholds with respect to SD rats—being sublines less responsive regarding mating-induced analgesia. Pain modulation mechanisms depend on responses to stress, so the low levels of analgesia obtained in the yawning sublines may be due either to differences in their response to stress in other paradigms, or to atypical performance of male sexual behavior during mating, an event which as a stressful event in rats.Therefore, the yawning sublines are a suitable model for analyzing how a different temporal pattern in the display of male sexual behavior affects analgesia mechanisms. Our results concur with Wistar rats with different endophenotypes that could apply to humans as well.

Behavioral, Cellular and Molecular Responses to Cold and Mechanical Stimuli in Rats with Bilateral Dopamine Depletion in the Mesencephalic Dopaminergic Neurons

Pain is the major non-motor symptom in Parkinson’s disease (PD). Preclinical studies have mostly investigated mechanical pain by considering the decrease in a nociceptive threshold. Only a few studies have focused on thermal pain in animal models of PD. Therefore, the goal of this study was to assess the thermal nociceptive behavior of rats subjected to 6-hydroxydopamine (6-OHDA) administration, which constitutes an animal model of PD. Thermal plate investigation demonstrated significant thermal sensitivity to cold temperatures of 10 °C and 15 °C, and not to higher temperatures, in 6-OHDA-lesioned rats when compared with sham. 6-OHDA-lesioned rats also showed cold allodynia as demonstrated by a significant difference in the number of flinches, latency and reaction time to acetone stimulus. Ropinirole administration, a dopamine receptor 2 (D2R) agonist, blocked the acetone-induced cold allodynia in 6-OHDA-lesioned rats. In addition, mechanical hypersensitivity and static allodynia, as demonstrated by a significant difference in the vocalization threshold and pain score respectively, were noticed in 6-OHDA-lesioned rats. Acetone stimulus induced a significant increase in extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation, a pain process molecular marker, in the spinal dorsal horn (SDH), the insular and cingulate cortices in 6-OHDA-lesioned rats when compared to sham. In 6-OHDA-lesioned rats, there was a significant augmentation in the expression of both protein kinase C gamma (PKCγ) and glutamate decarboxylase 67 (GAD67) in the SDH. This highlighted an increase in excitation and a decrease in inhibition in the SDH. Overall, the present study demonstrated a clear cold thermal hypersensitivity, in addition to a mechanical one, in 6-OHDA-lesioned rats.

Threshold for copulation-induced analgesia varies according to the ejaculatory endophenotypes in rats.

Analgesia may be modulated by multiple internal and external factors. In prior studies, copulatory-induced analgesia was demonstrated using the vocalization threshold to tail shock (VTTS) in male and female rats. Three ejaculatory endophenotypes have been characterized in male Wistar rats based upon their ejaculation latency (EL). Since intromissions and ejaculations produce analgesia, and these copulatory patterns are performed with different frequency depending on the male's ejaculatory endophenotype, we hypothesized that copulation-induced analgesia would vary in relation to these endophenotypes. In the present study, we used three groups according to the EL (medians): rapid ejaculators (236 s; n = 21), intermediate ejaculators (663.2 s; n = 20) and sluggish ejaculators (1582.2 s; n = 8). Our aim was to evaluate whether copulation-induced analgesia is related to the ejaculatory endophenotypes during two consecutive ejaculatory series (EJS). In the first EJS, the VTTS of the rapid ejaculators was significantly higher than that of intermediate and sluggish rats. At the onset of the second EJS, the VTTS of the rapid and intermediate ejaculators was significantly higher than that of the sluggish rats. No differences in VTTS were observed during the first or second post-ejaculatory intervals among the three groups. These findings provide evidence that the more intromissions that occurred per unit time, the higher was the level of analgesia.

Effect of Low Intensity Magnetic Field Stimulation on Calcium-Mediated Cytotoxicity After Mild Spinal Cord Contusion Injury in Rats.

Background:Magnetic field (MF) stimulation has the potential to reduce secondary damage and promote functional recovery after neural tissue injury. The study aimed to observe the effect of very low intensity (17.96µT) MF on general body condition, secondary damage, pain status, and locomotion.Methods:We exposed rats to MF (2 h/day × 3 weeks) after 6.25 mm contusion spinal injury. Locomotor behavior was evaluated by BBB score, pain assessment was done by recording threshold for tail flick, expression of voltage-gated calcium channels and extent of secondary damage in the spinal cord was assessed by immunofluorescence and Cresyl violet staining, respectively.Results:A significant (p ≤ .001) improvement in bladder function as well as BBB score was observed after MF exposure in comparison with sham and SCI over the observation period of 3 weeks. SCI group showed an increase in the threshold for vocalization after discharge, which decreased following MF exposure. Cresyl violet staining showed significantly higher tissue sparing (73%) at the epicenter after MF exposure when compared to SCI group. This was accompanied with a significant decrease in calcium channel expression in MF group as compared to SCI.Conclusion:The results suggest facilitation of sensory-motor recovery after MF exposure, which could be due to attenuation of secondary damage and calcium-mediated excitotoxicity in a mild contusion rat model of SCI.

Study of the Reaction of Hydroxybenzoyl Chlorides and Their Derivatives with Imidazole

The reaction of hydroxybenzoyl chlorides with imidazole was studied on an example of the Schotten-Baumann reaction of salicyloyl and acetylsalicyloyl chlorides with imidazole, which, according to soe published data, can take two different ways. It was shown that the Schotten-Baumann reaction with imidazole involves imidazole ring opening (Bamberger cleavage) to form l,2-bis(salicyloylamino)ethylene and l,2-bis(acetylsalicyloylamino)ethylene rather than N-salicyloylimidazole and N-acetylsalicyloylimidazole. N-Hydroxybenzoylimidazoles were synthesized by the reaction of hydroxybenzoyl chlorides (and derivatives) with a double excess of imidazole in an aprotic solvent (chloroform, benzene, or diethyl ether) at room temperature. The highest yields (about 80%) of N-hydroxybenzoylimidazoles were obtained in chloroform. Some of the newly synthesized compounds were tested for psychotropic (open field and passive avoidance response tests) and analgesic activities (vocalization threshold test). The best results were obtained with N-(2-hydroxybenzoyl)imidazole, which showed an evident analgesic activity, and, therewith, the motor score and oriented exploratory activity parameters were higher than in the control group.

Effects of S 38093, an antagonist/inverse agonist of histamine H3 receptors, in models of neuropathic pain in rats.

Histamine H3 receptors are mainly expressed on CNS neurons, particularly along the nociceptive pathways. The potential involvement of these receptors in pain processing has been suggested using H3 receptor inverse agonists. The antinociceptive effect of S 38093, a novel inverse agonist of H3 receptors, has been evaluated in several neuropathic pain models in rat and compared with those of gabapentin and pregabalin. While S 38093 did not change vocalization thresholds to paw pressure in healthy rats, it exhibited a significant antihyperalgesic effect in the Streptozocin-induced diabetic (STZ) neuropathy model after acute and chronic administration and, in the chronic constriction injury (CCI) model only after chronic administration, submitted to the paw-pressure test. Acute S 38093 administration at all doses tested displayed a significant cold antiallodynic effect in a model of acute or repeated administration of oxaliplatin-induced neuropathy submitted to cold tail immersion, cold allodynia being the main side effect of oxaliplatin in patients. The effect of S 38093 increased following chronic administration (i.e. twice a day during 5days) in the CCI and STZ models except in the oxaliplatin models where its effect was already maximal from the first administration The kinetics and size of effect of S 38093 were similar to gabapentin and/or pregabalin. Finally, the antinociceptive effect of S 38093 could be partially mediated by α2 adrenoreceptors desensitization in the locus coeruleus. These results highlight the interest of S 38093 to relieve neuropathic pain and warrant clinical trials especially in chemotherapeutic agent-induced neuropathic pain. S 38093, a new H3 antagonist/inverse agonist, displays antiallodynic and antihyperalgesic effect in neuropathic pain, especially in oxaliplatin-induced neuropathy after chronic administration. This effect of S 38093 in neuropathic pain could be partly mediated by α2 receptors desensitization in the locus coeruleus.

Динамика ноцицептивной чувствительности крыс после введения мелатонина в норме и при длительном стрессорном воздействии

Цель - изучение динамики ноцицептивной чувствительности крыс в разные временные периоды после внутрибрюшинного введения мелатонина (10 мг/кг) в условиях нормы и при однократной длительной стрессорной нагрузке на модели 24-ч иммобилизации. Результаты. Установлено, что введение мелатонина приводит к усилению перцептуального компонента ноцицепции животных, выраженность которого возрастает на протяжении 8 сут. наблюдений. На 3-и - 5-е сут. у этих особей выявлено возрастание порога вокализации в ответ на электрокожное раздражение, что иллюстрирует ослабление эмоционального компонента болевой чувствительности. Стрессорное воздействие сопровождалось снижением латентного периода реакции отведения хвоста при светотермальном раздражении, что наблюдалось сразу, а также через 1, 2 и 3 сут. после окончания стрессорного воздействия. В этих условиях увеличение порога вокализации крыс при электрокожной стимуляции обнаружено сразу после стрессорной нагрузки. Указанные изменения характеризуют усиление перцептуального компонента ноцицепции - формирование гипералгезии, но подавление эмоционального восприятия болевого раздражения на ранних стадиях постстрессорного периода. Показано, что экзогенный мелатонин не предупреждает развитие гипералгезии после 24-ч иммобилизации, однако подавляет эмоциональный компонент ноцицептивной чувствительности животных в отдаленный период после длительного стрессорного воздействия (4-е и 7-е сут.). Заключение. Применение мелатонина в целях коррекции измененной болевой чувствительности, при отрицательных эмоциогенных нагрузках, необходимо проводить с учетом временной стадии постстрессорного периода, а также принимая во внимание необходимость воздействия на перцептуальный или эмоциональный компонент ноцицепции. The dynamics of nociceptive sensitivity in rats was studied in various periods after intraperitoneal injection of melatonin (10 mg/kg) under normal conditions and during long-term stress exposure on the model of 24-h immobilization. Administration of melatonin was shown to enhance the perceptual component of nociception, whose degree progressively increased over 8 days of observations. The vocalization threshold of these specimens in response to electrocutaneous stimulation was elevated on days 3-5, which illustrates suppression of the emotional component of nociceptive sensitivity. Stress exposure in animals was accompanied by a decrease in the tail-flick latency during light-heat stimulation. It was observed immediately and 1, 2, and 3 days after termination of the stress procedure. An increase in the vocalization threshold of rats was found immediately after stress. These changes illustrate an enhancement of the perceptual component of nociception (hyperalgesia), but suppression of the emotional evaluation of pain stimulation at the early stage of the post-stress period. Exogenous melatonin did not prevent the development of hyperalgesia after 24-h restraint stress. However, melatonin inhibited the emotional component of nociceptive sensitivity in animals during the late period after long-term stress exposure (days 4 and 7). We conclude that the use of melatonin for correction of changes in nociceptive sensitivity due to negative emotiogenic factors should be performed taking into account the stage of the post-stress period and necessity to affect the perceptual or emotional component of nociception.

Analgesic potential of standardized methanol stem bark extract of Ficus platyphylla in mice: Mechanisms of action

Ethnopharmacological relevanceExtracts of the stem bark of Ficus platyphylla (FP) have been used in traditional the Nigerian medicine to treat psychoses, depression, epilepsy, pain and inflammation. Previous studies have revealed the analgesic and anti-inflammatory effects of FP in different assays including acetic acid-induced writhing, formalin-induced nociception, and albumin-induced oedema. Purpose/methodsIn this study, we assessed the effects of the standardised extract of FP on hot plate nociceptive threshold and vocalisation threshold in response to electrical stimulation of the tail root in order to confirm its acclaimed analgesic properties. We also investigated the molecular mechanisms underlying these effects, with the focus on opiate receptor binding and the key enzymes of eicosanoid biosynthesis, namely cyclooxygenase (COX) and 5-lipoxygenase (5-LO). ResultsFP (i) increased the hot plate nociceptive threshold and vocalisation threshold. The increase in hot plate nociceptive threshold was detectable over a period of 30min whereas the increase in vocalisation threshold persisted over a period of 90min. (ii) FP showed an affinity for µ opiate receptors but not for δ or κ opiate receptors, and (iii) FP inhibited the activities of COX-2 and 5-LO but not of COX-1. ConclusionsWe provided evidence supporting the use of FP in Nigerian folk medicine for the treatment of different types of pain, and identified opioid and non-opioid targets. It is interesting to note that the dual inhibition of COX-2 and 5-LO appears favourable in terms of both efficacy and side effect profile.

Intrathecal Transplantation of Embryonic Stem Cell-Derived Spinal GABAergic Neural Precursor Cells Attenuates Neuropathic Pain in a Spinal Cord Injury Rat Model.

Neuropathic pain following spinal cord injury (SCI) is a devastating disease characterized by spontaneous pain such as hyperalgesia and allodynia. In this study, we investigated the therapeutic potential of ESC-derived spinal GABAergic neurons to treat neuropathic pain in a SCI rat model. Mouse embryonic stem cell-derived neural precursor cells (mESC-NPCs) were cultured in media supplemented with sonic hedgehog (SHH) and retinoic acid (RA) and efficiently differentiated into GABAergic neurons. Interestingly, low doses of SHH and RA induced MGE-like progenitors, which expressed low levels of DARPP32 and Nkx2.1 and high levels of Irx3 and Pax6. These cells subsequently generated the majority of the DARPP32(-) GABAergic neurons after in vitro differentiation. The spinal mESC-NPCs were intrathecally transplanted into the lesion area of the spinal cord around T10-T11 at 21 days after SCI. The engrafted spinal GABAergic neurons remarkably increased both the paw withdrawal threshold (PWT) below the level of the lesion and the vocalization threshold (VT) to the level of the lesion (T12, T11, and T10 vertebrae), which indicates attenuation of chronic neuropathic pain by the spinal GABAergic neurons. The transplanted cells were positive for GABA antibody staining in the injured region, and cells migrated to the injured spinal site and survived for more than 7 weeks in L4-L5. The mESC-NPC-derived spinal GABAergic neurons dramatically attenuated the chronic neuropathic pain following SCI, suggesting that the spinal GABAergic mESC-NPCs cultured with low doses of SHH and RA could be alternative cell sources for treatment of SCI neuropathic pain by stem cell-based therapies.

Nociceptive Reactions in Rats during Repeated Stress Exposure.

Changes in nociceptive sensitivity of rats with various behavioral patterns in the open-field test were studied after repeated stress exposure on the model of daily 4-h immobilization for 8 days. The tail-flick latency in response to light-heat stimulation in passive and active specimens decreased most significantly on days 2 and 7, respectively. However, this parameter did not differ from the baseline on day 8 of observations. Vocalization threshold during electrocutaneous stimulation in behaviorally active animals did not change over the first 7 days of repeated stress exposure, but increased significantly on day 8 of the study. The emotional component of nociception in passive animals increased on day 3, but decreased on days 4 and 6 of the experiment. Therefore, repeated stress exposure in rats is mainly accompanied by an increase in the perceptual component of nociception. Variations in the emotional component of nociceptive sensitivity after stress loads are manifested in the initial increase and subsequent decrease in this parameter. The observed changes are more pronounced in behaviorally passive rats than in active animals. These data illustrate the specifics of stress-induced changes in nociception of specimens with various individual and typological characteristics. Our results hold much promise for the development of new individual approaches to modulation of pain sensitivity in humans under conditions of negative emotiogenic exposures.

β2-adrenoceptor agonists as potential therapeutic drugs in diabetic peripheral neuropathy

Objectives: the aim of the current study was to assess the effect of a β2-adrenoceptor agonist; namely salbutamol, on hyperalgesic as well as nerve dysfunction components of diabetic peripheral neuropathy. Material and methods: the present study was conducted on 60 male Wistar albino rats divided into six groups. Groups I and II were normal control rats injected by a single i.p. injection of normal saline and received 2% gum acacia (Group I) or salbutamol (Group II) for six weeks, starting one week following saline injection. Groups III–VI: rats that were rendered diabetic by a single i.p. injection of STZ and received either 2% gum acacia, salbutamol, salbutamol and propranolol or salbutamol and atenolol, respectively daily orally for six weeks, starting one week following STZ injection. Results: vehicle-treated diabetic rats exhibited: significant sciatic nerve dysfunction in the form of significantly prolonged distal latency and significantly decreased maximum peak and peak to peak amplitude of compound muscular action potential, significant thermal and mechanical hyperalgesia evidenced by significant decrease in hot plate latency, tail-flick latency and vocalization threshold, respectively. Salbutamol administration improved nerve dysfunction as well as thermal and mechanical hyperalgesia. These effects of salbutamol are most likely mediated by β2-adrenoceptors evidenced by significant abolishment of salbutamol effects after administration of the non-selective rather than the selective beta blockers; propranolol and atenolol, respectively. Conclusions: chronic administration of salbutamol could ameliorate DPN, an effect which is most likely mediated by β2-adrenoceptors.

Correlation dependencies between nociceptive sensitivity and cytokine level in biological fluids of rats after administration of lipopolysaccharide.

Correlation dependencies between nociceptive sensitivity and cytokine level in biological tissues of rats were studied on days 1 and 7 after antigenic stimulation due to intraperitoneal injection of LPS (30 μg/kg). No correlations were found between the nociceptive thresholds and cytokine contents in the dorsal hippocampus and anterior cingulate cortex of animals. Inverse correlations between the tail-flick latency in response to nociceptive stimulation and concentrations of an anti-inflammatory cytokine IL-10 and pro-inflammatory cytokine TNF-α in the peripheral blood of rats were revealed on day 7 after LPS injection. These animals were characterized by the following inverse correlations between the blood level of proinflammatory cytokines and baseline parameters of nociceptive sensitivity: IL-4 and latency of the tail-flick response; and IL-10 and vocalization threshold. The appearance of significant correlations between immune and nociceptive parameters in rats was shown to coincide with pronounced changes in the perceptual and emotional components of nociception in animals during antigenic stimulation. The formation of close interrelations between nociceptive sensitivity and immune processes in this period probably contributes to the systemic response to antigenic stimulation. Our results complement previous data on the relationship between individual immune reactivity and type of nociceptive reactions in mammals.

Dynamics of changes in nociceptive reactions of rats after peripheral administration of lipopolysaccharide.

The type of changes in nociceptive reactions of rats was studied at various time intervals after intraperitoneal injection of LPS in a dose of 30 μg/kg. The perceptual component of nociception in animals was evaluated from the tail-flick latency in response to light-heat stimulation. The emotional component of nociception in rats was determined from the vocalization threshold during electrocutaneous stimulation of the tail. The tail-flick latency of animals under conditions of light-heat stimulation was shown to decrease 1 day after peripheral administration of LPS, which illustrates an increase in the perceptual component of nociception at the relatively early stage of antigenic stimulation. A significant decrease in the tail-flick latency and vocalization threshold in rats in response to nociceptive stimulation was observed on day 7 after LPS injection. These changes demonstrate an increase in the perceptual and emotional components of nociception at the late period after antigen exposure. Our results indicate that antigenic stimulation due to peripheral administration of LPS is followed by the increase in nociceptive sensitivity of rats. LPS-induced variations in the emotional and perceptual components of nociception in animals suggest the existence of specific mechanisms for systemic regulation of pain. They probably depend on the period of study and type of immune reactions during antigenic stimulation.

Sickle cell disease in mice is associated with sensitization of sensory nerve fibers.

The pain phenotype in sickle cell disease (SCD) patients is highly variable. A small percentage of SCD patients experience many vaso-occlusive crises/year, 5% of patients account for over 30% of pain episodes, while 39% report few episodes of severe pain. Clearly, a better understanding of the pathobiology of SCD is needed to improve its therapy. Humanized sickle cell mice recapitulate several phenotypes of SCD patients and provide a model for the study of SCD pain. Researchers have shown that one strain of humanized SCD mice, the BERK strain, has abnormal pain phenotype. However, the nociception phenotype of another humanized SCD mouse strain, the Townes strain, has not been described. In a large cross-sectional study of BERK and Townes SCD mice, we examined thermosensory response and sensory nerve fiber function using sine-wave electrical stimulation at 2000, 250, and 5 Hz to stimulate preferentially Aβ, Aδ, and C sensory nerve fibers, respectively. We found that BERK and Townes mice, compared to respective controls, had decreases in 2000, 250, and 5 Hz current vocalization thresholds in patterns that suggest sensitization of a broad spectrum of sensory nerve fibers. In addition, the pattern of sensitization of sensory fibers varied according to strain, sex, age, and mouse genotype. In a similarly variable pattern, Townes and BERKs also had significantly altered sensitivity to noxious thermal stimuli in agreement with what has been shown by others. In summary, the analysis of somatosensory function using sine-wave electrical stimulation in humanized sickle cell mice suggests that in SCD, both myelinated and unmyelinated, fibers are sensitized. The pattern of sensory fiber sensitization is distinct from that observed in pain models of neuropathic and inflammatory pain. These findings raise the possibility that sensitization of a broad spectrum of sensory fibers might contribute to the altered and variable nociception phenotype in SCD.

Comparative Effect of Antidepressants (Duloxetine) and NSAID (Dexibuprofen) in a New Rat Model of Chronic Pain Induced Depression Associated with Monosodium Iodo Acetate (MIA) Induced Osteoarthritis in Rats

Objective: To evaluate the role of anti-depressants (Duloxetine) and NSAID (Dexibuprofen) in a new rat model of chronic induced depression. Methods: Twenty four male wistar rats were divided into 4 groups of 6 animals each. Group I to IV served as vehicle control, osteoarthritis (OA) control, duloxetine and dexibuprofen treated groups respectively. Group I received intra-articular Injection of 50 µl of 0.9% normal saline, and Group II to IV received 50 µl MIA, and the treatment of drugs started on the same day. The animals will be monitored for OA parameters and/or depression on pre-dose day (day 0) and on day 1, 3, 5, 7, 11, 14, 18, 21 and 28 th day. Results and Discussion: In MIA treated group, the rise in knee inflammation is maximum on day 3 (12.31±0.85 mm; p<0.001) and reduced near to normal on day 7 (9.26±0.57 mm; p<0.001). Dexibuprofen and duloxetine decreased the inflammation from day 3, and the decrease is comparatively better in dexibuprofen group. Also, dexibuprofen increased vocalization threshold of knee compression force for 7 days and decreased thereafter, whereas duloxetine has no effect for first 7 days and increased thereafter. Duloxetine was significantly (p<0.001) effective on neuropathic pain (Punctate allodynia, mechanical gripstrength, threshold angle of knee extension) and depression (forced swim test and locomotor activity) compared to dexibuprofen. Conclusion: The present study has shown that dexibuprofen has the potential in the initial phase of chronic OA and duloxetine in the later stage, where neuropathic and depressive component dominates.

Glycinamide, a glycine pro-drug, induces antinociception by intraperitoneal or oral ingestion in ovariectomized rats

AimsThe effect of i.p. injection or oral ingestion of glycinamide, a glycine pro-drug, on two tests for nociception was assessed in ovariectomized Sprague Dawley rats. Main methodsTo explore the potential analgesic effect of glycinamide the vocalization threshold to tail shock (VT) and the tail flick latency (TFL) were used. Glycinamide was administered both through the intraperitoneal route (doses 0, 25, 100, 400, 800mg/kg) and through ad libitum oral ingestion of glycinamide solution (40mg/ml) following a 24h period of water deprivation. Key findingsGlycinamide exerted a significant analgesic effect on VT when injected i.p. at doses of 400 or 800mg/kg. Analgesia occurred 10–20min post-injection and persisted approx 45min. At the high dose level, glycinamide exerted a weaker and more delayed effect on TFL than on the VT test. I.p. injection of 800mg/kg glycinamide inhibited vocalizations induced by the application of suprathreshold tail shocks (30% above threshold) with a latency of approx 3min and duration of approx 1h. The volume of a glycinamide solution (40mg/ml) ingested by rats deprived of water for 24h was positively correlated with the degree of analgesia in the VT test. Values between 100 and 200mg glycinamide exerted clear analgesic responses. SignificanceThus, glycinamide, either by systemic or oral routes, exerts a clear analgesic effect in the VT test of nociception and a much weaker action in the TFL test. This effect is probably due to the conversion of glycinamide to glycine in the brain.

Activation of TRPM8 cold receptor triggers allodynia-like behavior in spinally injured rats

AimsPain in response to innocuous cold stimulation (cold allodynia) is a common symptom in patients with neuropathic pain. Cold allodynia is difficult to treat and its mechanisms are poorly understood. Several transient receptor potential (TRP) channels have been shown to be the molecular sensors for cold stimulation in a temperature-dependent manner, but the contribution of various TRP channels in mediating cold allodynia in neuropathic pain is unclear. We have previously shown that spinally injured rats developed neuropathic pain-like behaviors, including marked cold allodynia. We now assessed the role of TRP channels in mediating cold allodynia in rats after ischemic spinal cord injury. MethodsSpinal cord injury was produced using a photochemical method. The mechanical allodynia was assessed by examining the vocalization thresholds to graded mechanical touch/pressure applied with von Frey hairs. Temperature controlled cold stimulation was produced by a Peltier thermode (active surface 25mm×50mm) connected to a MSA Thermal Simulator (Somedic, Sweden) with baseline temperature of 32°C. The rate of temperature change was 0.5°C/s. The temperature required to elicit cold allodynia was examined. The responses of the rats to topical application of icilin or menthol, agonists of transient receptor potential melastain 8 (TRPM8), were also studied. ResultsNormal rats did not exhibit nociceptive responses to cooling stimulation to the trunk and back area (minimal temperature +6°C) and they also did not react aversively to topical application of icilin or menthol. After spinal cord injury, the rats developed mechanical allodynia at the trunk and back just rostral to the dermatome of the injured spinal segments. In the same area, rats exhibited significant nociceptive responses to cooling from day 1 after injury, lasting for at least 70 days which is the longest time of observation. For the first two weeks after injury, the majority of spinally injured rats had a nociceptive response to cooling above 17°C. At day 70, about 50% of rats responded to cooling above 17°C. Topical application of 400μM icilin or 4mM menthol also elicited pain-like responses in spinally injured rats and these two cold mimetics also significantly exacerbated existing mechanical allodynia. ConclusionsOur results showed that activation of the TRPM8 channel by menthol or icilin triggers allodynia in spinally injured rats and increases, rather than decreases, mechanical allodynia. TRPM8 channels which respond to cooling above 17°C may be involved at least in part in mediating cold allodynia in the rat model of neuropathic spinal cord injury pain. ImplicationsThe work introduced a method of quantitative testings of responses of rats to cold stimulation and may contribute to the understanding of mechanisms of cold allodynia after injury to the nervous system.

Quantitative test of responses to thermal stimulation in spinally injured rats using a Peltier thermode: A new approach to study cold allodynia

In this work, we described a method of testing of responses of spinally injured rats to thermal stimulation (heating and cooling) to the flank area using a Peltier thermode. With a baseline holding temperature at 32°C and the temperature change rate of 0.5°C/s, we measured vocalization thresholds of rats to thermal stimulation in the flank area. While normal rats did not vocalize to temperatures changes ranging from 6°C to 50°C, the spinally injured rats exhibited significantly increased response to cooling with average response temperature above 15°C through the 70 day observation period after spinal cord injury. The response temperature to cooling in spinally injured rats is correlated with the magnitude of responses to cold stimulation scored after ethyl chloride spray and with the response threshold to mechanical stimulation. In contrast, we did not observe an increase in response to warm/heat stimuli. The results showed that ischemic spinal cord injury produced cold, but not heat, allodynia in rats. Furthermore, we showed that it is possible to quantitatively measure response of rats to thermal stimulation on the body using temperature as end points which may aid further studies on mechanisms and treatments of thermal stimulation, particularly cold, evoked pain.

NMDA or Non-NMDA Receptor Antagonism Within the Amygdaloid Central Nucleus Suppresses the Affective Dimension of Pain in Rats: Evidence for Hemispheric Synergy

The amygdala contributes to generation of affective behaviors to threats. The prototypical threat to an individual is exposure to a noxious stimulus and the amygdaloid central nucleus (CeA) receives nociceptive input that is mediated by glutamatergic neurotransmission. The present study evaluated the contribution of glutamate receptors in CeA to generation of the affective response to acute pain in rats. Vocalizations that occur following a brief noxious tail shock (vocalization afterdischarges) are a validated rodent model of pain affect, and were preferentially suppressed by bilateral injection into CeA of the NMDA receptor antagonist D-2-amino-5-phosphonovalerate (AP5, 1 μg, 2 μg, or 4 μg) or the non-NMDA receptor antagonist 6-Cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX, .25 μg, .5 μg, 1 μg, or 2 μg). Vocalizations that occur during tail shock were suppressed to a lesser degree, whereas spinal motor reflexes (tail flick and hind limb movements) were unaffected by injection of AP5 or CNQX into CeA. Unilateral administration of AP5 or CNQX into CeA of either hemisphere also selectively elevated vocalization thresholds. Bilateral administration of AP5 or CNQX produced greater increases in vocalization thresholds than the same doses of antagonists administered unilaterality into either hemisphere indicating synergistic hemispheric interactions. PerspectiveThe amygdala contributes to production of emotional responses to environmental threats. Blocking glutamate neurotransmission within the central nucleus of the amygdala suppressed rats’ emotional response to acute painful stimulation. Understanding the neurobiology underlying emotional responses to pain will provide insights into new treatments for pain and its associated affective disorders.