Involvement of Opioid Peptides in the Analgesic Effect of Spinal Cord Stimulation in a Rat Model of Neuropathic Pain / 神经科学通报·英文版

Spinal cord stimulation (SCS)-induced analgesia was characterized, and its underlying mechanisms were examined in a spared nerve injury model of neuropathic pain in rats. The analgesic effect of SCS with moderate mechanical hypersensitivity was increased with increasing stimulation intensity between the 20% and 80% motor thresholds. Various frequencies (2, 15, 50, 100, 10000 Hz, and 2/100 Hz dense-dispersed) of SCS were similarly effective. SCS-induced analgesia was maintained without tolerance within 24 h of continuous stimulation. SCS at 2 Hz significantly increased methionine enkephalin content in the cerebrospinal fluid. The analgesic effect of 2 Hz was abolished by μ or κ opioid receptor antagonist. The effect of 100 Hz was prevented by a κ antagonist, and that of 10 kHz was blocked by any of the μ, δ, or κ receptor antagonists, suggesting that the analgesic effect of SCS at different frequencies is mediated by different endorphins and opioid receptors.

Do opioid receptors play a role in the pathogenesis of the inflammatory response in acute pancreatitis? / Os receptores opioides desempenham papel na patogênese da resposta inflamatória na pancreatite aguda?

PURPOSE: To investigate the effect of the opioid blocker naltrexone in the inflammatory response in acute pancreatitis (AP). METHODS: Acute pancreatitis was induced in anesthetized male Wistar rats by retrograde injection of 2.5% sodium taurocholate diluted in 0.5ml saline into the main pancreatic duct. Animals were randomized to the following experimental groups: Control Group (n=9): animals received an intraperitoneal injection of saline solution (0.5ml), 15 minutes before the induction of AP. Naltrexone Group (n=9): animals received an intraperitoneal injection of naltrexone 0.5ml (15 mg/kg), 15 minutes before induction of AP. Peritoneal levels of TNF-α and serum levels of IL-6 and amylase were determined The volume of the ascitic fluid was also evaluated. Myeloperoxidase (MPO) activities were analyzed in homogenates of pulmonary tissue. RESULTS: There were no significant differences in the ascitic fluid volume, nor in TNF-a and IL-6 levels in the naltrexone group compared to controls. Treatment with naltrexone did not affect the lung MPO activity compared to control group. CONCLUSIONS: The opioid receptors don't play an important role in the pathogenesis of the inflammatory response in acute pancreatitis. If opioids affect leukocytes inflammatory signaling, there are no major implications in the pathogenesis of acute pancreatitis.

OBJETIVO: Investigar o efeito do bloqueador opióide naltrexone na resposta inflamatória da pancreatite aguda. METODOS: Pancreatite aguda foi induzida em ratos machos Wistar, através de injeção retrógada de solução de taurocolato de sódio a 2,5% nos ductos pancreáticos. Os animais foram alocados em dois grupos: Grupo controle (n=9) animais receberam 0,5 ml de solução salina intra-peritonial 15 minutos antes da indução da pancreatite aguda e Grupo naltrexone (n=9) animais receberam naltrexone (15mg/kg de peso), em 0,5 ml de volume final por via intraperitoneal, 15 minutos antes da indução da pancreatite aguda. Foram avaliados o volume de ascite, os níveis séricos de amilase e IL-6, assim como TNF-α peritoneal e a atividade da mieloperoxidase (MPO) no tecido pulmonar. RESULTADOS: Não foram encontradas diferenças significantes nos parâmetros analisados entre o grupo que recebeu solução salina e o que recebeu naltrexone . CONCLUSÕES: Os receptores opióides não desempenham papel importante na resposta inflamatória sistêmica associada à pancreatite aguda. Se os opioides alteram a sinalização inflamatória nos leucócitos está ação não se reflete na patogênese da pancreatite aguda.

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.

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).

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.

[Matricaria chamomilla extract infusion in to nucleus paragigantocellularis attenuates most of morphine withdrawal syndrome signs in rats]

Some reports show that co-administration of Matricaria chamomilla [MC] extract with morphine, greatly attenuate the development of morphine dependence and inhibit the expression of abstinence syndrome in morphine-dependent animals. Locus Coeruleus [LC] and nucleus paragigantocellularis [PGi] play an important role in developing symptoms of opiate withdrawal. The objective of this study was to determine the effects of Matricaria chamomilla extract infusion into PGi on morphine withdrawal syndrome signs [MWS] of rats. Thirty male rats [weight: 250-300gr] were surgically implanted with cannula at the PGi and then tested in 2groups: saline [control group] and morphine [twice daily for 7 days]. The dose of morphine on the first and second days was 2.5 mg/kg and was doubled every day. On 7[th] day, the animals received the last injection of morphine [50mg/kg] and divided in 4 subgroups: the morphine group [which only received morphine] and three MC groups [which received 1 micro l of MC extract with the concentrations of 10, 25, 50 micro g/micro l, 5 min before naloxone administration]. In the end of the training day [7[th] day] all groups were received naloxone [5mg/kg IP] 3h after last injection of morphine and then the frequencies of withdrawal behavior [jumping, climbing] were assessed for 30 minute. Our results showed that central administration of MC extract, especially at high doses [25 micro g/micro l], significantly attenuates most signs of the morphine withdrawal syndrome. These results suggest that the injection of MC extract into the PGi may be helpful for morphine withdrawal syndrome treatment

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.

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.

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.

Possible mechanism of anticonvulsant effect of ketamine in mice.

The study was designed to investigate the effect of ketamine on convulsive behaviour using maximal electroshock (MES) test. An attempt was also made to study the possible receptor mechanisms involved. MES seizures were induced in mice via transauricular electrodes (60 mA, 0.2sec). Seizure severity was assessed by the duration of tonic hindlimb extensor phase and mortality due to convulsions. Intraperitoneal administration of ketamine produced a dose-dependent (5-50 mg/kg) protection against hindlimb extensor phase. The anticonvulsant effect of ketamine was antagonized neither by naloxone (low as well as high doses) nor sulpiride, but was attenuated by haloperidol, a dopamine (D2)/sigma receptor antagonist. Co-administration of gamma-aminobutyric acid (GABA)-ergic drugs (GABA, muscimol, diazepam and baclofen) and N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK801) with ketamine facilitated the anticonvulsant action of the latter drug. In contrast, flumazenil, a benzodiazepine (BZD)-GABAA receptor antagonist, reversed the facilitatory effect of diazepam on the anti-MES effect of ketamine. Similarly, delta-aminovaleric acid (DAVA), antagonized the facilitatory effect of baclofen on anti-MES action of ketamine. These BZD-GABAergic antagonists, flumazenil or DAVA per se also attenuated the anti-MES effect of ketamine given alone. The results suggest that besides its known antagonistic effect on NMDA channel, other neurotransmitter systems i.e. sigma, GABAA-BZD-chloride channel complex and GABAB receptors may also be involved in the anti-MES action of ketamine.

Endogenous opiate analgesia induced by tonic immobility in guinea pigs

A function of the endogenous analgesic system is to prevent recuperative behaviors generated by tissue damage, thus preventing the emission of species-specific defensive behaviors. Activation of intrinsic nociception is fundamental for the maintenance of the behavioral strategy adopted. Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. We studied the effect of TI behavior on nociception produced by the formalin and hot-plate tests in guinea pigs. The induction of TI produced a significant decrease in the number of flinches (18 + or - 6 and 2 + or - 1 in phases 1 and 2) and lickings (6 + or - 2 and 1 + or - 1 in phases 1 and 2) in the formalin test when compared with control (75 + or - 13 and 22 + or - 6 flinches in phases 1 and 2; 28 + or - 7 and 17 + or - 7 lickings in phases 1 and 2). In the hot-plate test our results also showed antinociceptive effects of TI, with an increase in the index of analgesia 30 and 45 min after the induction of TI (0.67 0.1 and 0.53 + or - 0.13, respectively) when compared with control (-0.10 + or - 0.08 at 30 min and -0.09 0.09 at 45 min). These effects were reversed by pretreatment with naloxone (1 mg/kg, ip), suggesting that the hypoalgesia observed after induction of TI behavior, as evaluated by the algesimetric formalin and hot-plate tests, is due to activation of endogenous analgesic mechanisms involving opioid synapses

Stereological study of rat spleen following acute ethanol treatment.

To investigate the acute effect of ethanol (4 g/kg, i.p.) on spleen adult female Wistar rats were treated intraperitoneally with: a) ethanol (4 g/kg body wt), b) naltrexone (5 mg/kg body wt) followed 45 minutes later by ethanol (4 g/kg body wt) and c) naltrexone (5 mg/kg body wt) alone. Untreated and saline-treated rats were used as controls. Twenty hours after the ethanol treatment the animals were sacrificed and the spleens were removed. A piece of tissue from the central part of each organ was fixed in Bouin's solution. Paraffin sections were stained with hematoxylin-eosin and analysed using stereological measurements. The volume densities of the following tissue compartments: red pulp, white pulp (divided in follicles, periarterioral lymphatic sheath and marginal zone) and the connective tissue were determined. Stereological analysis also included parameters of follicles: the areal numerical density (the number of follicles per 1 mm2 of tissue section), the numerical density (the number of follicles per mm3 of tissue) and the mean follicle diameter. The immunoarchitecture of the spleen was preserved following acute ethanol treatment. Unlike other parameters that were unaffected, ethanol evoked a decrease in both volume density of follicle and the mean follicle diameter. Naltrexone pretreatment had no influence on ethanol-induced changes. The data obtained indicate that a single dose of ethanol has a profound effect on rat spleen affecting the follicles, but the mechanism of its action remains to be elucidated.

Effect of naloxone on GnRH-induced LH and FSH release in buffalo, Bubalus bubalis.

The effect of naloxone on GnRH-induced LH and FSH release was measured in buffaloes in luteal phase of estrous cycle. Animals were administered intravenously, naloxone/saline (50 mg/injection) every 15 min for 3 hr followed by GnRH (100 micrograms). Peripheral plasma LH and FSH concentrations were measured in blood samples collected at 15 min intervals from 1 hr prior to beginning of naloxone/saline treatment up to 3 hr post GnRH administration and every 30 min for the subsequent 3.5 hr. Between the animals of Group I administered naloxone and those of Group II given saline, GnRH-induced peak LH and FSH concentrations, the total LH and FSH released in response to GnRH, and the time to peak LH and FSH concentrations were not significantly different. The results of the present study suggest the absence of a direct effect of naloxone on pituitary responsiveness to GnRH.

Combined effects of diethylpropion and alcohol on locomotor activity of mice: participation of the dopaminergic and opioid systems

The widespread consumption of anorectics and combined anorectic + alcohol misuse are problems in Brazil. In order to better understand the interactive effects of ethanol (EtOH) and diethylpropion (DEP) we examined the locomotion-activating effects of these drugs given alone or in combination in mice. We also determined whether this response was affected by dopamine (DA) or opioid receptor antagonists. A total of 160 male Swiss mice weighing approximately 30 g were divided into groups of 8 animals per group. The animals were treated daily for 7 consecutive days with combined EtOH + DEP (1.2 g/kg and 5.0 mg/kg, ip), EtOH (1.2 g/kg, ip), DEP (5.0 mg/kg, ip) or the control solution coadministered with the DA antagonist haloperidol (HAL, 0.075 mg/kg, ip), the opioid antagonist naloxone (NAL, 1.0 mg/kg, ip), or vehicle. On days 1, 7 and 10 after the injections, mice were assessed in activity cages at different times (15, 30, 45 and 60 min) for 5 min. The acute combination of EtOH plus DEP induced a significantly higher increase in locomotor activity (day 1: 369.5 + or - 34.41) when compared to either drug alone (day 1: EtOH = 232.5 + or - 23.79 and DEP = 276.0 + or - 12.85) and to control solution (day 1: 153.12 + or - 7.64). However, the repeated administration of EtOH (day 7: 314.63 + or - 26.79 and day 10: 257.62 + or - 29.91) or DEP (day 7: 309.5 + or - 31.65 and day 10: 321.12 + or - 39.24) alone or in combination (day 7: 459.75 + or - 41.28 and day 10: 427.87 + or - 33.0) failed to induce a progressive increase in the locomotor response. These data demonstrate greater locomotion-activating effects of the EtOH + DEP combination, probably involving DA and/or opioid receptor stimulation, since the daily pretreatment with HAL (day 1: EtOH + DEP = 395.62 + or - 11.92 and EtOH + DEP + HAL = 371.5 + or - 6.76; day 7: EtOH + DEP = 502.5 + or - 42.27 and EtOH + DEP + HAL = 281.12 + or - 16.08; day 10: EtOH + DEP = 445.75 + or - 16.64 and EtOH + DEP + HAL = 376.75 + or - 16.4) and NAL (day 1: EtOH + DEP = 553.62 + or - 38.15 and EtOH + DEP + NAL = 445.12 + or - 55.67; day 7: EtOH + DEP = 617.5 + or - 38.89 and EtOH + DEP + NAL = 418.25 + or - 61.18; day 10: EtOH + DEP = 541.37 + or - 32.86 and EtOH + DEP + NAL = 427.12 + or - 51.6) reduced the locomotor response induced by combined administration of EtOH + DEP. These findings also suggest that a major determinant of combined anorectic-alcohol misuse may be the increased stimulating effects produced...

Behavioral changes of Wistar rats with experimentally-induced painful diabetic neuropathy

With the purpose of studying data on spontaneous customary changes in diabetic rats, we induced diabetes in 28 Wistar rats with streptozotocin. The animals were observed for 27 weeks in an attempt to characterize spontaneous customary chages that could suggest signs of chronic pain. Morphine, as a central-acting potent analgesic and its specific antagonist naloxone, were used. Our results evidenced in the animals a clinical syndrome similar to human diabetes. Long-term customary analysis revealed a significant (p<0.05) increase of scratching and resting/sleeping behaviors, but diminished motor, eating and grooming customs. Moreover, the thermal tests revealed hyperalgesia in 43 per cent of the animals, what may corroborate the meaning of scratching as a sign of pain. Pharmacological tests with morphine showed a significant (p<0.05) inhibition of scratch, with concomitant increase of motor and eating activities and diminished rest/sleep capacity. Naloxone antagonized the effects induced by morphine. Such results suggest that these animals exhibit evoked behavior of hyperalgesia and that scratch may possibly be a spontaneous manifestation of chronic pain also in Wistar rats with this experimental model of painful diabetic neuropathy.

Tramadol, a centrally acting opioid: anticonvulsant effect against maximal electroshock seizure in mice.

The present study was designed to investigate the pro- or anticonvulsant effect of tramadol using maximal electroshock (MES) test. An attempt was also made to determine the possible opioid receptor mechanism involved. MES seizures were induced through transauricular electrodes (60 mA, 0.2s) and the seizure severity was assessed by the duration of tonic hindlimb extensor phase. Intraperitoneal (i.p.) administration of tramadol resulted in a dose-dependent anticonvulsant action; the ED50 for the effect was 33 mg/kg. The anti-MES effect of tramadol was antagonized by the low doses (0.05 and 0.1 mg/kg, s.c.) of MR 2266, a selective kappa receptor antagonist and also by the high doses (1.0 and 5.0 mg/kg, i.p.) but not the low doses (0.1 and 0.25 mg/kg) of naloxone. The results suggest that the anti-MES effect of tramadol is mediated by kappa receptors, since MR 2266 and naloxone (in high doses) are known to block these receptors.

Opiatergic participation in the thirst-inhibiting effect of acute third ventricle injections of cadmium (Cd 2+ ) and lead (Pb 2+ )

We have previously demonstrated that acute third ventricle injections of both lead and cadmium prevent the dipsogenic response elicited by dehydration or by central injections of dipsogenic agents such as angiotensin II, carbachol and isoproterenol in rats. We have also shown that the antidipsogenic action of cadmium may be due, at least in part, to activation of thirst-inhibitory central serotonergic pathways. In the present paper we show that in Wistar male rats the antidipsogenic effect of both lead acetate (3.0 nmol/rat) and cadmium chloride (3.0 nmol/rat) may be partially dependent on the activation of brain opiatergic pathways since central injections of naloxone (82.5 nmol/rat), a non-selective opioid antagonist, blunt the thirst-inhibiting effect of these metals. One hundred and twenty minutes after the second third ventricle injections, dehydrated animals (14 h overnight) receiving saline + sodium acetate displayed a high water intake (7.90 ñ 0.47 ml/100 g body weight) whereas animals receiving saline + lead acetate drank 3.24 ñ 0.47 ml/100 g body weight. Animals receiving naloxone + lead acetate drank 6.94 ñ 0.60 ml/100 g body weight. Animals receiving saline + saline drank 8.16 ñ 0.66 ml/100 g body weight whilst animals receiving saline + cadmium chloride drank 1.63 ñ 0.37 ml/100 g body weight. Animals receiving naloxone + cadmium chloride drank 8.01 ñ 0.94 ml/100 g body weight. It is suggested that acute third ventricle injections of both lead and cadmium exert their antidipsogenic effect by activating thirst-inhibiting opioid pathways in the brain