Impacts of morphine addiction on spermatogenesis in rats

Background: There are numerous investigations on wide range of issues that disrupt regulatory spermatogenesis, individuals who are exposed to drug abuse faced infertility and immature spermatogenesis

Objective: The aim of this study was to evaluate the addiction effects of morphine and its derivatives on rats spermatogenesis

Materials and Methods: 40 male Wistar rats were randomly divided into 5 equal groups, which were exposed either with intravenous morphine, naloxone, naloxone and morphine, sham [with normal saline injection] and a control group without infusion. Spermatogenesis was assessed after three months via histological sections with hematoxylin and eosin staining, using a light microscope based on measurement of spermatogonia, spermatocyte, spermatid, and spermatozoa

Results: Those rats that received opioids had changes in spermatogenesis function. The population of spermatogenesis cycle cells at spermatogonia, spermatocyte, spermatid, and spermatozoa stages was significantly decreased in those rats that received opioid in comparison to the control group [p<0.05]. Histological studies revealed that changes in different groups of opioid application might affect sperm formation. Sperm count in morphine group was [0+/-0] and in naloxone group, naloxone+morphine, sham and control were 235+/-3.77, 220+/-3.81, 247.12+/-6.10 and 250+/-6.54, respectively [p<0.001]

Conclusion: Morphine could affect all spermatogenesis stages

Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats / O efeito analgésico de tramadol não é mediado por receptores opioides na dor de ratos no pós-operatório imediato / El efecto analgésico del tramadol no está mediado por receptores opiáceos en el dolor en ratones en el postoperatorio inmediato

BACKGROUND AND OBJECTIVES: Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model. METHODS: Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5 mg, naloxone 200 µg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60 min after incision. RESULTS: Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45 min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period. CONCLUSIONS: Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors. .

JUSTIFICATIVA E OBJETIVOS: Tramadol é conhecido como um fármaco analgésico de ação central, usado para o tratamento de dor moderada a grave. O efeito analgésico local foi demonstrado, em parte devido ao efeito semelhante ao anestésico local, mas outros mecanismos permanecem obscuros. O papel dos receptores opioides periféricos no efeito analgésico local não é conhecido. Neste estudo, examinamos o papel dos receptores opioides periféricos no efeito analgésico local de tramadol em modelo de incisão plantar. MÉTODOS: Ratos Wistar, jovens e machos, foram divididos em sete grupos: controle, tramadol intraplantar, tramadol intravenoso, tramadol intraplantar-naloxona intravenosa, tramadol intraplantar-naloxona intraplantar, tramadol intravenoso-naloxona intravenosa e naloxona intravenosa. Após receber os medicamentos designados (5 mg de tramadol, 200 mg de naloxona ou NaCl a 0,9%, os ratos foram submetidos à incisão plantar e os limiares de retirada após estímulos mecânicos com filamentos de von Frey foram avaliados no início do estudo e nos minutos 10, 15, 30, 45 e 60 após a incisão. RESULTADOS: A incisão plantar levou à hiperalgesia mecânica acentuada durante todo o período de observação no grupo controle; hiperalgesia mecânica não foi observada nos grupos tramadol intraplantar, tramadol intraplantar-naloxona intraplantar e tramadol intraplantar-naloxona intravenosa. No grupo tramadol intravenoso, um aumento tardio do limiar de retirada (após 45 minutos) foi observado. Os grupos tramadol intravenoso-naloxona intravenosa e naloxona intravenosa permaneceram hiperalgésicos durante todo o período. CONCLUSÕES: Tramadol apresentou efeito analgésico local inicial e diminuiu a hiperalgesia mecânica induzida pela incisão plantar. Esse efeito analgésico não foi mediado por receptores opioides periféricos. .

JUSTIFICACIÓN Y OBJETIVOS: Al tramadol se le conoce como un medicamento analgésico de acción central usado para el tratamiento del dolor moderado a intenso. El efecto analgésico local quedó demostrado, en parte, a causa del efecto similar al del anestésico local, pero otros mecanismos permanecen sin clarificar. El rol de los receptores opiáceos periféricos en el efecto analgésico local no se conoce. En este estudio, examinamos el papel de los receptores opiáceos periféricos en el efecto analgésico local del tramadol en un modelo de incisión plantar. MÉTODOS: Ratones Wistar, jóvenes y machos, fueron divididos en 7 grupos: control, tramadol intraplantar, tramadol intravenoso, tramadol intraplantar-naloxona intravenosa, tramadol intraplantar-naloxona intraplantar, tramadol intravenoso-naloxona intravenosa, y naloxona intravenosa. Después de recibir los medicamentos designados (5 mg de tramadol, 200 µg de naloxona o NaCl al 0,9%), los ratones fueron sometidos a la incisión plantar, y los umbrales de retirada de la pata posteriores a los estímulos mecánicos con filamentos de von Frey fueron evaluados al inicio del estudio y en los minutos 10, 15, 30, 45 y 60 después de la incisión. RESULTADOS: La incisión plantar conllevó hiperalgesia mecánica acentuada durante todo el período de observación en el grupo control; la hiperalgesia mecánica no fue observada en los grupos tramadol intraplantar, tramadol intraplantar-naloxona intraplantar, y tramadol intraplantar-naloxona intravenosa. En el grupo tramadol intravenoso, fue observado un aumento tardío del umbral de retirada (después de 45 min); los grupos tramadol intravenoso-naloxona intravenosa y naloxona intravenosa permanecieron hiperalgésicos durante todo el período. CONCLUSIONES: El tramadol presentó un efecto analgésico local inicial, disminuyendo la hiperalgesia mecánica inducida por la incisión plantar. Ese efecto analgésico no fue mediado por receptores opiáceos periféricos. .

Expression of GAP-43 in midbrain ventral tegmental area of morphine withdrawal rats / 法医学杂志

OBJECTIVE@#To observe the protein expression of growth associated protein-43 (GAP-43) in midbrain ventral tegmental area in morphine withdrawal rats at different time, and to evaluate the effect of GAP-43 on morphine withdrawal memory.@*METHODS@#Rat models of morphine dependent 1 week, 2 weeks and 4 weeks were established by morphine hydrochloride intraperitoneal injection with increasing doses to establish natural withdrawal. The protein expression of GAP-43 in midbrain ventral tegmental area was observed by immunohistochemical staining and the results were analyzed by Image-Pro Plus 5.1 image analysis system.@*RESULTS@#With prolongation of dependent time, the expression of GAP-43 was decreased then increased in midbrain ventral tegmental area.@*CONCLUSION@#GAP-43 could play a role in morphine withdrawal memory in midbrain ventral tegmental area.

Effects of terlipressin and naloxone compared with epinephrine in a rat model of asphyxia-induced cardiac arrest

OBJECTIVE: To evaluate the hemodynamic and metabolic effects of terlipressin and naloxone in cardiac arrest. METHODS: Cardiac arrest in rats was induced by asphyxia and maintained for 3.5 minutes. Animals were then resuscitated and randomized into one of six groups: placebo (n = 7), epinephrine (0.02 mg/kg; n = 7), naloxone (1 mg/kg; n = 7) or terlipressin, of which three different doses were tested: 50 µg/kg (TP50; n = 7), 100 µg/kg (TP100; n = 7) and 150 µg/kg (TP150; n = 7). Hemodynamic variables were measured at baseline and at 10 (T10), 20 (T20), 30 (T30), 45 (T45) and 60 (T60) minutes after cardiac arrest. Arterial blood samples were collected at T10, T30 and T60. RESULTS: The mean arterial pressure values in the TP50 group were higher than those in the epinephrine group at T10 (165 vs. 112 mmHg), T20 (160 vs. 82 mmHg), T30 (143 vs. 66 mmHg), T45 (119 vs. 67 mmHg) and T60 (96 vs. 66.8 mmHg). The blood lactate level was lower in the naloxone group than in the epinephrine group at T10 (5.15 vs. 10.5 mmol/L), T30 (2.57 vs. 5.24 mmol/L) and T60 (2.1 vs. 4.1 mmol/L). CONCLUSIONS: In this rat model of asphyxia-induced cardiac arrest, terlipressin and naloxone were effective vasopressors in cardiopulmonary resuscitation and presented better metabolic profiles than epinephrine. Terlipressin provided better hemodynamic stability than epinephrine. .

Suppressive effects of Rosa damascena essential oil on naloxone-precipitated morphine withdrawal signs in male mice

This research was done to test the effect of Rosa damascena essential oil on withdrawal signs of naloxone-precipitated morphine in male mice. Morphine dependence was induced by injection [IP] three times daily at doses of 50, 50 and 75 mg/kg, respectively, for 3 days. On day 4, after the last administration of morphine, Rosa damascena essential oil was administered at different concentrations [5, 2 and 40%, IP] 30 min before administration of naloxone [5 mg/kg, IP]. The following actions were taken as signs of withdrawal and records taken for jumping as a number and scores of 0 to 3 were given for incidences of grooming, teeth chattering, rearing, writing, diarrhea, wet dog shakes and climbing during a 30 min period. Results showed that different concentrations of Rosa damascena essential oil significantly reduced signs of morphine withdrawal compared to the control group in terms of number of jumps [p < 0.05 and p < 0.01], grooming, teeth chattering, rearing, climbing, wet dog shakes and writhing, but not for diarrhea [p < 0.05]. In conclusion it seems that GABAergic activity induced by flavonoids from Rosa damascena essential oil can alleviate signs of morphine withdrawal, but further studies need to be done to better understand this mechanism

Involvement of opioid, adenosine and 5-HT3 receptors in antinociceptive effects of an ayurvedic polyherbal formulation

The present study was undertaken to evaluate the antinociceptive effects of an ayurvedic polyherbal formulation in rats and mice employing the tail immersion test and acetic acid-induced writhing test, respectively. With the tail immersion method, rats received two different doses [270 and 405 mg/kg BW, p.o.] of a formulation, pethidine [5.4 mg/kg BW, p.o.] as a reference standard and the combination of the higher dose of the formulation with naloxone [2 mg/kg, i.p.], an opioid receptor antagonist, and caffeine [16 mg/kg, i.p.], used as an adenosine receptor antagonist. In the acetic acid-induced writhing test, mice received two different doses [390 and 585 mg/kg, BW, p.o.] of formulation, diclofenac sodium [15 mg/kg, BW, p.o.] as a reference standard and the combination of the higher dose of the polyherbal formulation with ondansetron [0.5 mg/kg, i.p.], a serotonin receptor antagonist. The polyherbal formulation [405 mg/kg] exhibited a significant [p < 0.01] antinociceptive effect using the tail immersion method. In the acetic acid-induced writhing test, the formulation showed significant [p < 0.01] dose-dependent activity. The antinociceptive effect of the polyherbal formulation apparently involved an opiate-like mechanism, since its antinociceptive action was attenuated by naloxone pretreatment. In addition, antinociceptive activity was attenuated by caffeine and reversed by ondansetron pretreatment. Our data suggest that the polyherbal formulation possessed centrally and peripherally mediated antinociceptive properties. The activity could be mediated through opioid, adenosine, and serotonin receptors and via inhibition of cyclo-oxygenase- and/or lipoxygenase-dependent pathways

Morphine Postconditioning Attenuates ICAM-1 Expression on Endothelial Cells

The purpose of this study is to determine 1) whether morphine postconditiong (MPostC) can attenuate the intercellular adhesion molecules-1 (ICAM-1) expression after reoxygenation injury and 2) the subtype(s) of the opioid receptors (ORs) that are involved with MPostC. Human umbilical vein endothelial cells (HUVECs) were subjected to 6 hr anoxia followed by 12 hr reoxygenation. Three morphine concentrations (0.3, 3, 30 microM) were used to evaluate the protective effect of MPostC. We also investigated blockading the OR subtypes' effects on MPostC by using three antagonists (a micro-OR antagonist naloxone, a kappa-OR antagonist nor-binaltorphimine, and a delta-OR antagonist naltrindole) and the inhibitor of protein kinase C (PKC) chelerythrine. As results, the ICAM-1 expression was significantly reduced in the MPostC (3, 30 microM) groups compared to the control group at 1, 6, 9, and 12 hours reoxygenation time. As a consequence, neutrophil adhesion was also decreased after MPostC. These effects were abolished by coadministering chelerythrine, nor-binaltorphimine or naltrindole, but not with naloxone. In conclusion, it is assumed that MPostC could attenuate the expression of ICAM-1 on endothelial cells during reoxygenation via the kappa and delta-OR (opioid receptor)-specific pathway, and this also involves a PKC-dependent pathway.

Induction of ovarian growth in Aegla platensis (Crustacea, Aeglidae) by means of neuroregulators incorporated to food

The freshwater crab Aegla platensis was used as a model to induce ovarian growth by adding different neuroregulators to a pellet food formulation. Added compounds were the dopaminergic inhibitor spiperone or the enkephalinergic inhibitor naloxone, both of them at a dose of 10-8 mol/animal. Animals were fed on the enriched pellets twice a week. After 7 wk, the gonadosomatic index (GI) was calculated as (gonad fresh weight / body fresh weight) x 100. GI significantly increased only for those females fed on spiperone pellets, compared to a control group receiving pellets with no compound added. During the assayed period, spiperone would be reverting the arrest exerted by dopamine on the neuroendocrine stimulation of ovarian growth. On the other hand, for both spiperone and naloxone a higher GI was correlated to a higher lipid content of both gonads and/or hepatopancreas, suggesting an increased energetic demand in accordance with an active investment in reproduction. Rev. Biol. Trop. 56 (3): 1201-1207. Epub 2008 September 30.

Se utilizó al anomuro de agua dulce Aegla platensis como modelo para inducir el crecimiento ovárico mediante el agregado de diferentes neuroreguladores a una formulación de alimento pelleteado. Los compuestos agregados fueron el inhibidor dopaminergico spiperona ó el inhibidor encefalinérgico naloxone, ambos a una dosis de 10-8 moles/animal. Los animales fueron alimentados dos veces a la semana con pellets enriquecidos con alguno de los neuroreguladores. Luego de 7 semanas, se calculó el índice gonadomático (IG) como (peso gonadal fresco/ peso corporal fresco) x 100. El IG mostró un incremento significativamente sólo en aquellas hembras alimentadas con pellets enriquecidos con spiperona, en comparación con un grupo control que recibió pellets sin agregado alguno. Durante el período ensayado, la spiperona estaría revirtiendo el arresto ejercido por la dopamina sobre la estimulación neuroendocrina del crecimiento ovárico. Por otro lado, para ambos grupos experimentales (spiperona y naloxone), un mayor valor de IG estuvo correlacionado a un mayor incremento del contenido de lípidos tanto en gonadas como en hepatopáncreas, sugiriendo una demanda energética incrementada en relación con una activa inversión en reproducción.

Opioidergic orofacial antinociception induced by electroacupuncture at acupoint St36

The participation of opioids in the antinociceptive effect of electroacupuncture was evaluated in terms of nociception produced by thermal stimuli applied to the face of male Wistar rats, weighing 180-230 g. Electrical stimulation (bipolar and asymmetric square wave with 0.5 mA intensity for 20 min) of acupoint St36, located in the anterior tibial muscle 10 mm distal to the knee joint, induced antinociception in the present model, which was maintained for 150 min. Acupoint LI4, located in the junction of the first and second metacarpal bones, did not achieve antinociception at any frequency studied (5 Hz: 1.7 ± 0.1; 30 Hz: 1.8 ± 0.1; 100 Hz: 1.7 ± 0.1 vs 1.4 ± 0.2). The antinociception obtained by stimulation of acupoint St36 was only achieved when high frequency 100 Hz (3.0 ± 0.2 vs 1.0 ± 0.1) was used, and not with 5 or 30 Hz (1.2 ± 0.2 and 0.7 ± 0.1 vs 1.0 ± 0.1). The antinociceptive effect of acupuncture occurred by opioid pathway activation, since naloxone (1 and 2 mg/kg, subcutaneously) antagonized it (1.8 ± 0.2 and 1.7 ± 0.2 vs 3.0 ± 0.1).

Effect of withdrawal of diazepam or morphine treatment on gastric motility (charcoal meal test) in mice: possible role of different central and peripheral receptors.

Increased gastrointestinal motility in mice as one of the withdrawal symptoms of commonly abused drugs like diazepam or morphine and its possible mechanism of action was studied. Male Laka mice (20-25 g) were made addict to either diazepam (20 mg/kg, ip for 7 days) or morphine (10 mg/kg, sc for 9 days). Withdrawal symptoms were noted 24 hr after the last injection of diazepam or morphine. The animals were injected with Ro 15-1788 (flumazenil) (1 mg/kg, ip) or naloxone (2 mg/kg, ip) in the respective group to precipitate the withdrawal symptoms. Gastrointestinal motility was assessed by charcoal-meal test. Animals developed tolerance to acute sedative effect of diazepam, and similarly to the acute nociceptive action of morphine. On abrupt cessation of these drugs after chronic treatment the animals showed hyperlocomotion and hyperreactivity in diazepam withdrawal group and hyperalgesia on hot plate in morphine withdrawal groups, respectively. Increase in gastrointestinal motility was observed in all the drug withdrawal groups. Treatment with respective antagonists, Ro 15-1788 (flumazenil) and naloxone precipitated the withdrawal symptoms. The results suggest the involvement of both central and peripheral receptors of benzodiazepines and opioid (mu) receptors in the withdrawal symptoms of the benzodiazepines and morphine, respectively.

A pyrazolyl-thiazole derivative causes antinociception in mice

The present study investigates the antinociceptive effect of the pyrazolyl-thiazole derivative 2-(5-trichloromethyl-5-hydroxy-3-phenyl-4,5-dihydro-1 H-pyrazol-1-yl)-4-(4-bromophenyl)-5-methylthiazole (B50) in mice. Male albino Swiss mice (30-40 g) were used in the acetic acid-induced abdominal writhes and tail-immersion tests. B50 caused dose-dependent antinociception (8, 23 and 80 µmol/kg, sc) in the acetic acid writhing assay (number of writhes: vehicle: 27.69 ± 6.15; B50 (8 µmol/kg): 16.92 ± 3.84; B50 (23 µmol/kg): 13.85 ± 3.84; B50 (80 µmol/kg): 9.54 ± 3.08; data are reported as means ± SEM for 9 animals per group). On the other hand, B50 did not cause antinociception in the tail immersion assay. Naloxone (2.75 µmol/kg, sc) prevented B50-induced antinociception (number of writhes: vehicle-saline: 31.11 ± 3.15; vehicle-naloxone: 27.41 ± 3.70; B50 (80 µmol/kg)-saline: 8.70 ± 3.33; B50 (80 µmol/kg)-naloxone: 31.84 ± 4.26; morphine-saline: 2.04 ± 3.52; morphine-naloxone: 21.11 ± 4.26; 8-9 animals per group). The removal of the methyl group of the thiazole ring of B50 or substitution of the bromo substituent with the methyl at position 4 of the phenyl group, which is attached to the thiazole ring of B50, resulted in loss of activity, suggesting that these substituents are important for antinociceptive activity. B50 had no effect on spontaneous locomotion or rotarod performance, indicating that the antinociceptive effect of B50 is not related to nonspecific motor effects. The antinociceptive profile of B50 seems to be closer to nonsteroidal anti-inflammatory drugs than to classic opioid agents, since it had no analgesic effect in a thermally motivated test.

Antinociceptive activity of Vitex-negundo Linn leaf extract.

Tail flick test in rats and acetic acid induced writhing in mice were employed to study the antinociceptive activity of ethanolic leaf extract of Vitex-negundo (VN) (100, 250 and 500 mg/kg, p.o). The effect was compared with meperidine (40 mg/kg, sc) in tail flick method and aspirin (50 mg/kg, p.o) in writhing test as a standard control respectively. An interaction with naloxone hydrochloride was also studied in tail flick method for its mechanism of central analgesic action. The test drug showed significant analgesic activity in dose dependant manner in both the experimental models. In comparison to standard drug (meperidine), more than ten times dose of VN extract was required to produce comparable significant antinociceptive activity. The sub-effective dose (5 mg/kg, po) of VN potentiated the analgesic activity of meperidine (4 mg/kg, sc) and aspirin (25 mg/kg, po). Naloxone (1 mg/kg, sc) did not reverse the analgesic effect of VN extract. Our observations suggest that VN possesses both central and peripheral analgesic activity. The central analgesic action does not seem to be mediated through opioid receptors. It, may prove to be a useful adjuvant therapy along with standard analgesic drug.

Effect of naloxone on aluminum-induced learning and memory impairment in rats.

BACKGROUND: Uptake of aluminum may disturb the learning and memory of humans or animals. Naloxone (NAL) has been shown to exert beneficial effects on memory deficits. AIMS: We investigated the effects of naloxone on aluminum-induced learning and memory impairment in rats. SETTINGS AND DESIGN: Aluminum-induced learning and memory impairment model was established by gavage of Aluminum chloride (600 mg/kg) for 3 months. Rats were divided into three groups viz. naloxone-treated rats (NAL 0.8 mg/kg, i.p. daily for 7 days), non-treated model rats and normal controls. MATERIALS AND METHODS: The Morris water maze test was performed to study spatial learning and memory. Long-term potentiation (LTP) of the Schaffer collateral-CA1 synapse was recorded. Aluminum and zinc contents in the hippocampus were assayed with atomic absorption spectrophotometry. STATISTICAL ANALYSIS: Parameters of the hidden and visible platform trials and data of LTP were analyzed using two-way repeated measures ANOVA. RESULTS: In the hidden platform trials, escape latencies of the NAL rats were significantly shorter than that of the non-treated rats (P=0.000, 95% confidential interval low bound 14.31, upper bound 22.68). In probe trails, the number of entries in the target area of the NAL rats (6.75+/-1.28 times/min) was more than that of non-treated model rats (4.56+/-2.16 times/min, P=0.004, 95% confidence interval low bound -3.65, upper bound -0.788). The magnitudes of LTP recorded in the CA1 pyramidal neurons of the NAL-treated rats were significantly augmented when compared to the non-treated model rats (P=0.005, 95% confidence interval low bound 0.16, upper bound 0.84). CONCLUSIONS: NAL could facilitate spatial learning and memory and enhance LTP in the CA1 region of the hippocampus in aluminum-induced learning and memory impairment in rats.

The terrestrial Gastropoda Megalobulimus abbreviatus as a useful model for nociceptive experiments: effects of morphine and naloxone on thermal avoidance behavior

We describe the behavior of the snail Megalobulimus abbreviatus upon receiving thermal stimuli and the effects of pretreatment with morphine and naloxone on behavior after a thermal stimulus, in order to establish a useful model for nociceptive experiments. Snails submitted to non-functional (22°C) and non-thermal hot-plate stress (30°C) only displayed exploratory behavior. However, the animals submitted to a thermal stimulus (50°C) displayed biphasic avoidance behavior. Latency was measured from the time the animal was placed on the hot plate to the time when the animal lifted the head-foot complex 1 cm from the substrate, indicating aversive thermal behavior. Other animals were pretreated with morphine (5, 10, 20 mg/kg) or naloxone (2.5, 5.0, 7.5 mg/kg) 15 min prior to receiving a thermal stimulus (50°C; N = 9 in each group). The results (means ± SD) showed an extremely significant difference in response latency between the group treated with 20 mg/kg morphine (63.18 ± 14.47 s) and the other experimental groups (P < 0.001). With 2.5 mg/kg (16.26 ± 3.19 s), 5.0 mg/kg (11.53 ± 1.64 s) and 7.5 mg/kg naloxone (7.38 ± 1.6 s), there was a significant, not dose-dependent decrease in latency compared to the control (33.44 ± 8.53 s) and saline groups (29.1 ± 9.91 s). No statistically significant difference was found between the naloxone-treated groups. With naloxone plus morphine, there was a significant decrease in latency when compared to all other groups (minimum 64 percent in the saline group and maximum 83.2 percent decrease in the morphine group). These results provide evidence of the involvement of endogenous opioid peptides in the control of thermal withdrawal behavior in this snail, and reveal a stereotyped and reproducible avoidance behavior for this snail species, which could be studied in other pharmacological and neurophysiological studies.

Formalin assay parameters differ in confirming the antinociceptive mechanism of domperidone in mice.

Domperidone, a prokinetic drug with minimal extrapyramidal side-effects was investigated for its antinociceptive response in mice using formalin assay procedure. Two parameters namely the pain score and the time spent by the animal in licking/biting the formalin injected paw were considered. Domperidone (1, 2.5 or 5 mg/kg; ip) injected 15 min prior to formalin effectively reduced the pain score bringing it to zero at the 15th minute and was also effective till 30 min but to a lesser degree. This effect of domperidone (2.5 mg/kg) was significantly attenuated in naloxone pretreated mice indicating a partial role for opioid pathways. In the other parameter i.e. time spent in licking/biting, domperidone in all the doses employed failed to modify significantly the same by the animal in the early phase. In contrast, a dose related inhibition of the time spent was recorded in the late phase. Besides, a trend towards the enhancement of the inhibitory effect of domperidone (2.5 mg/kg) in the late phase was noticed in naloxone pretreated mice. Possibly, the peripheral analgesic mechanisms may play a role in this response since the late phase was considered akin to inflammation. The results confirm the antinociceptive effect of domperidone and suggest that caution be exercised while selecting the parameters when formalin assay is employed.

Blocking of enhanced sensitivity to behavioral effects of naloxone induced by narcotic agonists in rats.

The present experiment evaluated whether prior treatment with naloxone could block the sensitization to opiate antagonist induced by single dose administration of pure agonist (morphine) or mixed agonist (buprenorphine). Food deprived male Wistar rats were trained to respond for food on a multiple-trial, fixed-interval 3 min schedule. Reinforcement was contingent upon a response within a 10-s limited hold period following a fixed-interval of 3 min. A trial consisted of three fixed interval of 3 min separated by a 10 min timeout period during which responses were not reinforced. The rate decreasing effects of the opioid antagonist naloxone was determined by cumulative dosing. Pretreatment with morphine (0.3 mg/ kg, SC) and buprenorphine (0.03 mg/kg, SC) resulted in an increase sensitivity to the rate decreasing effect of naloxone compared to saline pretreatment. Administration of naloxone (0.3 mg/kg) 10 min prior to pretreatment doses of buprenorphine (0.03 mg/kg; 1.0 mg/kg) and morphine (0.3 mg/kg) increased sensitization to naloxone. However, greater sensitization was observed at low dose of buprenorphine. The increased sensitivity was partially blocked at high dose of buprenorphine (1.0 mg/ kg) by naloxone pretreatment. These results suggest that the doses of naloxone used to block opioid induced sensitization might be different from those required in animals with normal sensitivity to opioid antagonists. Further agonist-induced sensitization to behavioral effects of opioid antagonist appears to be opioid receptor specific.

Anti-nociceptive effect of synthesized di-hydroxy flavones: possible mechanism.

Renewed interest on the research on the flavonoids is gaining more importance. Earlier literature on flavonoids indicated a significant anti-nociceptive action for flavones and mono-substituted flavones. However, they exhibited a ceiling effect. The present study was undertaken by new synthesizing six disubstituted flavones (DHFs) since poly substituted ones are expected to produce more potent effect. Their anti-nociceptive effect and the role of opioid involvement were studied using acetic acid induced abdominal constriction assay. All the six DHFs administered in elicited a dose related inhibition of abdominal constrictions indicating the presence of the anti-nociceptive response. However, these substances also showed a similar ceiling effect. Like other flavonoid substances, they also utilized opioid pathways. It is suggested that these newly synthesized DHFs can be included along with other flavonoids while attempting clinical trial for analgesic use.

Effect of naloxone on cognitive function in vascular dementia in rats.

BACKGROUND & OBJECTIVES: The endogenous opioid system plays an important role in cognitive functions and may also contribute to the progression of some kind of dementia. Naloxone has been shown to exert beneficial effects on memory deficits in patients with senile dementia and reverse some of the effects induced by endogeneous opioids. We therefore investigated the effects of naloxone on cognitive function in rats with vascular dementia (VD). METHODS: Vascular dementia was established by permanent occlusion of the common carotid arteries. Rats were divided into three groups viz., sham-operated controls, naloxone treated VD rats (naloxone 0.8 mg/kg, i.p. daily for 7 days), and nontreated VD rats. The Morris water maze test was performed to study spatial learning and memory. The extracellular recording technique was used to record long-term potentiation (LTP) of the Schaffer collateral-CA1 synapse in the rat hippocampal slices. RESULTS: In the hidden platform trials, escape latencies of the naloxone treated VD rats were significantly shorter than that of the nontreated VD rats (P < 0.001). In the probe trials, the number of enteries in the target area of the naloxone treated VD rats (8.36 +/- 1.38 times/min) were more than that of the nontreated VD rats (4.64 +/- 1.73 times/min) (P < 0.01). The magnitudes of LTP recorded in the CA1 pyramidal neurons of the naloxone treated VD rats were significantly augmented when compared to the nontreated VD rats (P < 0.05). INTERPRETATION & CONCLUSION: Naloxone could facilitate spatial learning and memory and enhance LTP in the CA1 region of hippocampus in rats with VD. It is postulated that naloxone might exert beneficial effects on cognitive function in VD in rats by modulating the synaptic plasticity in the hippocampal neuronal network.

Influence of GnRH Agonist and Neural Antagonists on Stress-blockade of LH and Prolactin Surges Induced by 17 beta-estradiol in Ovariectomized Rats

In our previous study, we demonstrated that immobilization stress blocked estrogen-induced luteinizing hormone(LH) surge possibly by inhibiting the synthesis and release of gonadotropin-releasing hormone (GnRH) at the hypothalamic level and by blocking estrogen-induced prolactin (PRL) surge by increasing the synthesis of dopamine receptor at the pituitary level in ovariectomized rats. The present study was performed to determine whether immobilization stress affects pituitary LH responsiveness to GnRH, and whether endogenous opioid peptide (EOP) and dopamine systems are involved in blocking LH and PRL surges during immobilization stress. Immobilization stress was found to inhibit basal LH release and to completely abolish LH surge. However, the intravenous application of GnRH agonist completely restored immobilization-blocked LH surge and basal LH release. Treatment with naloxone did not exert any effect on immobilization-blocked LH surge but increased basal LH release during immobilization stress. Pimozide did not affect immobilization-blocked LH surge or basal LH release. Naloxone also decreased immobilization-induced basal PRL release, but had no effect on immobilization-blocked PRL surge. Immobilization-increased basal PRL levels were augmented by pimozide treatment and immobilization-blocked PRL surge was dramatically restored by pimozide. We conclude that immobilization stress does not impair pituitary LH response to GnRH, and that the immobilization stress-induced blockage of LH surge is probably not mediated by either the opioidergic or the dopaminergic system. However, immobilization-blockade of PRL surge may be partly mediated by the dopaminergic system.

Modulation by insulin rather than blood glucose of the pain threshold in acute physiological and flavone induced antinociception in mice.

The present study investigated the cause effect relationship between glycemic and algesic states. The hypo- and hyperglycemic conditions were induced physiologically through exercise (3 min swim at room temperature 28 degrees - 30 degrees C) and external dextrose (2 g/kg, ip) administration respectively in mice. Besides, flavone (50 mg/kg, sc) a known antinociceptive drug was chosen to study such a cause effect relationship. The anti-nociception was assessed by acetic acid assay, blood glucose measured using glucometer (Ames) and serum insulin by radioimmunoassay. The findings revealed that irrespective of the glycemic state whether hypo-, hyper, or euglycemic induced by swim stress, dextrose or flavone per se respectively, significant antinociceptive response was recorded. Pretreatment with flavone (50 mg/kg, sc) always exhibited a tendency to reverse the hyperglycemia, if any, but enhanced the antinociceptive response either after swim stress or after dextrose. These data support the contention that changes in the glycemic state in acute condition is not responsible for antinociceptive response and thereby suggesting dissociation between these two parameters. Extended studies estimating serum insulin level after the above mentioned maneuvers showed a significant rise whenever antinociceptive response was recorded irrespective of the glycemic state. It is suggested that serum insulin level, a hormonal parameter rather than the blood glucose level, which is a metabolic parameter, appears more reliable. It appears that the changes in serum insulin level produced by various treatments may have a relationship with the antinociceptive response. However, this study has the limitation that the results can apply only for acute conditions and extrapolation to clinical conditions is debatable.