Time course of antagonism of morphine antinociception by intracerebroventricularly administered naloxone in the rat

This kinetic profile and half-life of naloxone were studied for possible use in determination of pA₂ and K_B in vivo. Rats were given morphine subcutaneously and after 15 min naloxone or saline, intracerebroventricularly. A further 15 min later, and at 15 min intervals up to 135 min after morphine, the animals were tested for analgesia in the tail flick test. The dose-response curves of the naloxone group were shifted to the right of those for the saline group. Theamount of displacement decreased with time, indicative of the disappearance of naloxone. The graph of log (dose ratio-1) vs. time was linear with negative slope, in agreement with the time-dependent form of the equation for competitive antagonism. From this slope, the half-life of naloxone was calculated to be 13.3 min. These results demonstrate that the time-dependent method is useful in obtaining the kinetics of centrally acting opiate antagonists.     

Cross tolerance to antinociception elicited by intracerebroventricular administration of mescaline and morphine to rabbits,and EEG correlates

Tolerance and cross tolerance to the antinociceptive effect of equipotent doses of morphine (10 g/kg) and mescaline (100 g/kg) are shown in the rabbit after their repeated intracerebroventricular administration. The recording of the electrical activity of different brain areas indicates that a partial tolerance also develops to the EEG effects in animals undergoing chronic treatment with mescaline.The comparison of certain of the mescaline-induced effects with those of morphine suggests that some biochemical and neural patterns are common to the 2 drugs.     

Selective potentiation of gabapentin-mediated antinociception in the rat formalin test by the nicotinic acetylcholine receptor agonist ABT-594

The treatment of chronic pain is hampered by various issues including multiple underlying mechanisms contributing to disease pathology and treatment-related toxicity concerns. These can be partially circumvented by combining mechanistically distinct drugs with the aim of selectively potentiating analgesia as opposed to side-effects. This approach has been used to assess the antinociceptive efficacy of the nicotinic acetylcholine (nACh) receptor agonist ABT-594 when combined with the antiepileptic drug gabapentin, the μ-opioid receptor agonist morphine or the antidepressant drug duloxetine in the rat formalin test. Alone, ABT-594 (0.01-0.3 mg/kg) dose-dependently attenuated spontaneous flinching behaviour during first (P1) and second (P2) phase. Similarly, P1, interphase and P2 flinching were variously attenuated by gabapentin (25-200 mg/kg), morphine (0.3-3 mg/kg) and duloxetine (3-60 mg/kg). Remarkably, a completely inactive dose of ABT-594 reduced the dose of gabapentin required to produce antinociception during P1 by 4-8 fold and during P2 by 8-16 fold. This striking potentiation was blocked by mecamylamine and indicative of analgesic synergy. Similar, albeit less consistent results (3-10 fold potency increase) were obtained with morphine/ABT-594. Although a 3 fold increase in P2 antinociceptive potency was obtained with duloxetine in the presence of ABT-594, a corresponding increase in efficacy was lacking. Indeed, a mechanistically relevant reduction in antinociceptive efficacy and potency of duloxetine/ABT-594 occurred during interphase. Thus, activation of the nicotinic cholinergic system differentially modulates the antinociceptive actions of distinct mechanism of action compounds, and provides a novel framework for nACh receptor modulators mediating analgesia in the putative absence of adverse events associated with this mechanism of action.     

HPLC法测定双氯芬酸钠凝胶中双氯芬酸钠的含量

目的采用HPLC法测定双氯芬酸钠凝胶中双氯芬酸钠的含量。方法以十八烷基键合硅胶为填充剂;用甲醇-0.005 mol/L磷酸二氢钾溶液(p H=3.8)(70∶30)为流动相;检测波长:280 nm;流速:1.0 m L/min;外标法测峰面积定量。结果双氯芬酸钠在15.90~55.41μg/m L(r=0.999 0)范围内线性关系良好,平均回收率为100.48%,RSD为1.28%。结论本方法简便、快速、准确,可用于双氯芬酸钠凝胶中双氯芬酸钠的含量测定。     

Analgesic effects of lidocaine, morphine and diclofenac on movement-induced nociception, as assessed by the Knee-Bend and CatWalk tests in a rat model of osteoarthritis

Pain is the major symptom of osteoarthritis (OA) and the main reason for patients seeking medical care, but its treatment is not optimal. Animal studies are necessary to elucidate mechanisms underlying OA-induced pain and assess analgesics' efficacy. Previously, we showed that the Knee-Bend test and dynamic weight bearing by the CatWalk test are clinically relevant methods for assessing movement-induced nociception in the mono-iodoacetate (MIA) OA model. Using the same tests, in the present study we investigate the effects of lidocaine (5 mg, 10% solution, intra-articular), morphine (6 mg/kg, subcutaneous) and diclofenac (30 mg/kg per os) on nociceptive behavior in OA animals, on days 3 and 20 of OA evolution.Morphine reduced nociceptive behavior in both tests at both time-points. Lidocaine also decreased nociceptive behavior in both tests on day 3, but on day 20 only reduced the Knee-Bend score. Diclofenac was highly effective in both tests on day 3, while on day 20 it induced a less pronounced decrease in the Knee-Bend score and was ineffective in the CatWalk test.The results showed that the Knee-Bend and CatWalk tests are reliable alternative methods for evaluating movement-induced nociception in OA animals, and measure nociception in a clinically relevant way, since an analgesic profile similar to the one described in humans was observed. Therefore, these tests might be important as good predictors of drug efficacy.     

Blockade of the antinociception induced by diclofenac, but not of indomethacin, by sulfonylureas and biguanides

There is evidence that administration of sulfonylureas, such as glibenclamide and tolbutamide, blocks diclofenac-induced antinociception, suggesting that diclofenac activates ATP-sensitive K⁺ channels. However, there is no evidence for the interaction between diclofenac and other hypoglycemic drugs, such as the biguanides metformin or phenformin. Therefore, this work was undertaken to determine whether two sulfonylureas, glibenclamide and glipizide, as well as two biguanides, metformin and phenformin, have any effect on the systemic antinociception that is induced by diclofenac and indomethacin using the rat formalin test as an animal model. Systemic injections of diclofenac (10 to 30 mg/kg) and indomethacin (10 to 30 mg/kg) produced dose-dependent antinociception during the second phase of the test. Systemic pretreatment with glibenclamide (3 and 10 mg/kg), glipizide (3 and 10 mg/kg), metformin (100 and 180 mg/kg) or phenformin (100 and 180 mg/kg) blocked diclofenac-induced systemic antinociception in the second phase of the test (P < 0.05). In contrast, pretreatment with glibenclamide, glipizide, metformin or phenformin did not block indomethacin-induced systemic antinociception (P > 0.05). These data suggest that diclofenac, but not indomethacin, activated K⁺ channels and metformin and phenformin-dependent mechanisms, which resulted in systemic antinociceptive effects in the rat formalin test.     

Effects of d-amphetamine,morphine, naloxone,and drug combinations on visual discrimination in rats

The effects of d-amphetamine, morphine, and naloxone on visual discrimination were investigated using a two-choice discrete-trial procedure in which rats were trained to discriminate the position of a lightflash. Morphine (0.3–5.6 mg/kg) but not amphetamine (0.1–1.0 mg/kg) caused a significant dose-dependent disruption in discriminative performance. Both amphetamine and morphine increased response latencies. Naloxone (1.0 mg/kg) prevented the disruption of any aspect of performance by up to 100 mg/kg morphine. Performance after naloxone/amphetamine co-administration was not significantly different from that observed after amphetamine alone. Naloxone alone (0.3–10 mg/kg) had no effect on discrimination, spatial bias or response latencies. These results suggest that morphine and amphetamine affect different components of discrimination performance. Offprint requests to: S.G. Holzman     

Increased pain perception and attenuated opioid antinociception in paradoxical sleep-deprived rats are associated with reduced tyrosine hydroxylase staining in the periaqueductal gray matter and are reversed by L-dopa

Paradoxical sleep deprivation (PSD) increases pain sensitivity and reduces morphine antinociception. Because dopaminergic neurons in the periaqueductal gray matter (PAG) participate in pain modulation and opioid-induced antinociception, we evaluated the effects of PSD on thermal pain sensitivity, morphine- and L-DOPA-induced antinociception and dopaminergic functionality in the PAG by assessing tyrosine hydroxylase (TH) immunoreactivity. Rats that were subjected to 96 h of PSD received vehicle, morphine (2.5, 5 or 10 mg/kg), L-DOPA (50 or 100 mg/kg) or L-DOPA (50 mg/kg) + morphine (2.5 and 5 mg/kg) and were tested with a 46 °C hot plate 1 h after. The paw withdrawal latency responses to the hot plate were decreased in PSD rats and were modified by the highest dose of morphine, L-DOPA and L-DOPA + morphine. Analgesic effects were observed in control groups for all of the morphine doses as well as 100 mg/kg of L-DOPA and L-DOPA (50 mg/kg) + morphine (5 mg/kg). The number of cell bodies that were immunopositive for TH in the PAG was reduced in PSD rats. In conclusion, increased thermal sensitivity was reversed by L-DOPA and could be caused by a reduction TH levels in the PAG. Our data also suggest a relationship between central dopaminergic networks and opiate-induced analgesia in rats.     

Morphine-sparing effect of diclofenac in cancer pain

Summary The effectiveness of diclofenac 50 mg t.i.d. as additive treatment to parenteral patient-controlled administration therapy (PCAT) with morphine in cancer pain has been investigated in a double-blind study. In the fifteen patients who completed the study, morphine i.v. was titrated to optimal pain relief over 5 days.The mean total morphine consumption was significantly reduced during diclofenac administration (82.8 mg morphine per day) compared to placebo (95.0 mg morphine per day). The reduction in mean morphine consumption during active treatment with diclofenac was independent of the initial dose of self-titrated morphine.Pain, self-assessed according to VAS, tended to be lower during the diclofenac period, although the difference did not reach statistical significance. No adverse events were recorded among the 15 patients who completed the study.The present findings show that a non-steroidal anti-inflammatory agent, such as diclofenac, has a morphine-sparing effect in morphine-treated patients with cancer pain.J.E. Martinsson, MD, Department of Pulmonary Medicine, Renströmska Hospital, Gothenburg, M. Berndtsson, MD, Department of Pulmonary Medicine, Central Hospital, Bor»s, L. Grettve, MD, Department of Medicine, NÄL Hospital, Vänersborg, and L.G. Carlsson, MD, Department of Medicine, Uddevalla Hospital, Uddevalla, Sweden     

Central administration of prostaglandin E2 facilitates while F2 alpha attenuates acute dependence upon morphine rats

The effects of prostaglandin D2 (PGD2), E2 (PGE2), and F2 alpha (PGF2 alpha) on acute dependence on morphine were investigated. Five mature, male Long-Evans rats were trained to lever press for food reinforcement on a fixed-ratio 30 schedule (FR 30 behavior) and implanted with permanent guide cannulas with the tips of the cannulas in their right lateral brain ventricles. The experimental protocol began with a 45 minute behavioral session and brain infusion (1 microliter/minute of a solution containing 2.3 mM CaCl2 in 0.9% saline, ICV). Fifteen minutes into the session the rats were injected with 7.5 mg morphine/kg (IP). Beginning 2.25 hours later the brain infusion was reinitiated during a second 45 minute behavioral session which was interrupted after 15 minutes to inject 1.0 mg naloxone/kg (IP). In several experiments a dose of PG, which did not in-and-of-itself affect behavior, was added to the infusion medium. Prior to the naloxone injection it was ascertained that the behavioral effects of morphine had dissipated. The injection of naloxone or saline did not alter behavior of the rats while they were being infused with a PG or PG vehicle. Injection of naloxone, 3 hours after the injection of morphine, resulted in a significant suppression of FR 30 behavior (withdrawal). A dose of PGE2, which did not alter the initial suppressant action of morphine, potentiated the naloxone effect. A dose of PGF2 alpha, which likewise did not alter the initial action of morphine, antagonized the naloxone effect. However, a higher dose of PGF2 alpha which enhanced the initial morphine effect, caused an enhanced naloxone effect as well.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of morphine and naloxone on the release of noradrenaline from rat cerebellar cortex slices

Summary In slices of rat cerebellar cortex preincubated with (-)-³H-noradrenaline, the influence of morphine and naloxone on the efflux of tritium was investigated. The spontaneous outflow was not changed by 10^–5 M of either morphine or naloxone. On the other hand, morphine caused a concentration-dependent decrease of the overflow, of tritium evoked by electrical field stimulation. Naloxone did not change the stimulation-induced overflow, but prevented its inhibition by morphine. It is concluded that morphine, through an action on opiate receptors located on cerebellar noradrenergic neurones, inhibits the secretion of the transmitter in response to nerve impulses.     

Central and peripheral tissue distribution of diclofenac after subcutaneous injection in the rat

Nonsteroidal anti-inflammatory drugs (NSAIDs) are viewed as peripherally acting analgesics; however, evidence is accruing that they also act centrally. To help clarify the regional actions of diclofenac, we studied its plasma and tissue concentrations after subcutaneous injection in a model of acute pain, the rat tail ischaemia-reperfusion acute hyperalgesia model. After antinociceptive doses (20 and 40 mg kg^-1), diclofenac plasma C _max occurred at 20 min and neither plasma or tissue concentrations were affected by application of the pain model. Brain, spinal cord, heart, skeletal muscle, (injured) tail cartilaginous tissue, stomach and fat had similar distribution coefficients (0.05-0.2). Distribution coefficients for liver (0.5-1.4) and kidney (0.3-0.5) increased with time, presumably reflecting their roles in the elimination of diclofenac. Subcutaneous injection was found a pharmacokinetically reliable method for administering diclofenac for antinociception studies in the rat. The finding that CNS and peripheral tissue distribution coefficients of diclofenac were similar provides indirect support for a potential central action of NSAIDs.     

Effects of morphine,naloxone and their interaction in the learned-helplessness paradigm in rats

The aim of this study was to investigate the possible involvement of the mu-opioid system on the learned-helplessness paradigm, an experimental model of depression, in rats. In this test, rats were first exposed to inescapable foot-shocks (IS); 48 h later, they were submitted to a daily shuttle-box session (30 trials) for 3 consecutive days. Avoidance responses, escape failures and animal activity during each intertrial interval were recorded. Twice daily injections of morphine (0.25–8 mg/kg per day, SC), a mu-opioid agonist, reduced the increased escape failures induced by IS, as did tricyclic antidepressants. Significantly higher intertrial activity was observed in rats treated with morphine (2–8 mg/kg per day) compared with their associated control groups. Naloxone (1 and 2 mg/kg, IP), a mu-opioid antagonist, injected 10 min before each shuttle-box session impaired escape behavior in non-stressed rats and worsened the escape deficit induced by IS. Morphine-induced improvement of escape behavior and increase in intertrial activity were clearly reversed by a low inactive dose of naloxone (0.5 mg/kg). These results suggest that mu-opioid receptor mediation is involved in the deleterious effects of uncontrollable stress.     

Flupirtine antinociception in the rat orofacial formalin test: an analysis of combination therapies with morphine and tramadol

Combination therapy with two drugs is a straightforward strategy to improve the risk-benefit ratio of analgesic treatments. Flupirtine is a non-opioid analgesic drug acting via the enhancement of so-called M currents, associated to Kv7 potassium channels in the central nervous system. In this study we used the orofacial formalin test as a model of acute inflammatory pain in the rat; putative synergistic interactions between flupirtine and morphine or tramadol, given in various combinations, were investigated. We found that flupirtine exerts antinociception in the second phase of the test, whereas morphine and tramadol induced analgesia both in the first and in the second phase. An isobolographic analysis of data was carried out, showing a synergistic interaction between flupirtine and morphine, as well as between flupirtine and tramadol, in the second phase of the test. Conversely, in the first phase of the test only a single combination of morphine plus flupirtine, but not any of the combinations of tramadol and flupirtine, resulted in a synergistic interaction. Our data clearly indicate that flupirtine enhances in a synergistic manner the acute antinociceptive effects exerted by opioids in this paradigm.     

Hyperglycemic suppression of morphine withdrawal signs in the rat

Male Sprague-Dawley rats maintained under controlled lighting and temperature conditions were used in this experiment. Morphine dependency was induced by giving increasing doses of morphine by intraperitoneal injection (IP group) or by the ingestion of morphine through drinking water (PO group). Animals were injected with 10, 20, 30 and 50 mg/kg morphine sulfate at days 1, 2, 3 and 4, respectively. Another group of animals received increasing concentrations of morphine through drinking water from 0.1, 0.2, 0.3 to 0.4 mg/ml at 48 h intervals. Morphine dependent animals were given naloxone by the intraperitoneal route to precipitate withdrawal. Glucose (3 g/kg or 10 g/kg) was given 10 min prior to the administration of naloxone to the respective groups. Another two groups of animals were made diabetic by the administration of streptozotocin. In one group, animals received increasing concentrations of 10, 20, 30 and 50 mg/kg morphine sulfate by the IP route at days 1, 2, 3 and 4, while the other group was not treated with morphine but was assessed for withdrawal signs to serve as the control. Withdrawal signs were assessed by observing the presence of diarrhea, tremor, piloerection, hunchbacked posture, teeth chattering, salivation, erection, restless activity, territorial exploring, irritability to handling, vocalization and jumping. Results obtained indicate that glucose administration at 10 g/kg abolished most of the withdrawal signs, and we were unable to induce the same degree of morphine dependency in diabetic animals as compared to the non-diabetic groups. It was concluded from this study that hyperglycemia could suppress morphine withdrawal signs.     

长期应用吗啡对雌性大鼠性腺轴功能的影响

目的探讨长期应用吗啡的雌性大鼠,当动情周期发生改变后,其下丘脑-垂体-卵巢轴功能的变化。方法选取30只成年雌性大鼠,采用剂量递增法皮下注射盐酸吗啡,定期进行阴道细胞学观察直至大鼠动情周期紊乱。放射免疫分析测定血清卵泡刺激素(FSH)、黄体生成素(LH)、雌二醇(E2)、孕酮(P),免疫组织化学测下丘脑、垂体、卵巢和子宫雌激素受体(ER)的表达。结果①维持吗啡用药7周时,60%(18/30)大鼠发生动情周期紊乱,用药10周,76.7%(23/30)动情周期被抑制;②长期应用吗啡,造成动情周期紊乱时,FSH、LH、E2、P基础分泌较对照组均显著降低(P<0.05,P<0.05,P<0.01,P<0.05);若长期应用吗啡后未出现动情周期紊乱,各激素水平较对照组有下降趋势;③长期应用吗啡后,无论大鼠动情周期是否被抑制,非动情期及动情期大鼠性腺轴各组织中ER平均吸光度(A)值均显著降低(P<0.01,P<0.001)。结论长期使用吗啡对下丘脑-垂体-卵巢轴有不同程度的损伤。     

TRH对吗啡镇痛作用的影响及其对呼吸、循环和中枢神经系统的作用

本文就TRH与NAL拮抗吗啡类药物的镇痛、成瘾及制动作用作了比较研究,并观察了TRH对呼吸、循环及中枢神经系统的作用。结果发现TRH不能拮抗吗啡类的镇痛、成瘾及制动作用。TRH(10μg icv或5mg/kg iv)可显著升高正常动物平均动脉压,加快心率及呼吸。TRH腹腔注射可缩短戊巴比妥钠的睡眠时间,并呈一定剂量依赖关系。     

Opioids and sexual behavior in the male rat

Naloxone in the doses of 4 or 16 mg/kg failed to effect copulatory behavior of testosterone-treated castrated male rats. Morphine 10 mg/kg, administered 60 min before behavioral observation, reduced the proportion of animals displaying sexual behavior. Doses of 2.5 or 5 mg/kg reduced the latency to the second ejaculation, whereas the few animals still copulating after morphine 10 mg/kg showed a reduced latency to the first ejaculation. The same doses of morphine administered 5 min before behavioral observation produced a dose-dependent reduction of mount, intromission and ejaculation percentages. However, those animals that did copulate showed a normal copulatory behavior. D-Ala²-Met⁵ enkephalinamide (DALA) infused into the left cerebral ventricle in a dose of 5 μg 5 or 60 min before tests had no effect. When the peptide was infused 30 sec after the first intromission, the number of intromissions as well as the latency to ejaculation were reduced. Opioids may facilitate ejaculatory mechanisms, perhaps as a consequence of their rewarding properties. Moreover, in animals treated with DALA after the first intromission, the number of intromissions and the latency to ejaculation were similar for the first and second copulatory series, while these parameters were much reduced upon the second ejaculation for control animals. It is possible that liberation of endogenous opioids is the cause of ejaculation-induced facilitation of subsequent sexual behavior.     

Caerulein and morphine in a model of visceral pain

Summary In pentobarbital-anaesthetized rats (60 mg/kg, i.p.) renal pelvis distension with a pressure of 80 cm H₂O caused a decline in mean arterial blood pressure. This pressure response, which disappeared rapidly after cessation of the distension, was used to study the effects of analgesic drugs known to be effective in renal colic pain in man.Morphine (0.75 and 1 mg/kg, s.c.) and the decapeptide caerulein (1.6, 4 and 8 g/kg, s.c.) abolished the pressure response. The effects of the largest doses lasted for at least 30 min. Ineffective in this respect were (a) desulphated caerulein (40 g/kg, s.c.) and (b) additional doses of pentobarbital (20 and 40 mg/kg, s.c.). This shows (a) the importance of the sulphated tyrosine (known from previous studies on central effects) and (b) the missing influence of the depth of anaesthesia.Naloxone (0.5 mg/kg, s.c.) abolished the effect of morphine (1 mg/kg, s.c.) but failed to influence that of caerulein (8 g/kg, s.c.). Even a fourfold dose of naloxone (2 mg/kg, s.c.) did not weaken the effect of caerulein. Naloxone, per se, was ineffective. These results suggest different mechanisms of the present effects of morphine and caerulein.It appears that renal pelvis distension in the anaesthetized rat can serve as a model of renal colic.     

The development of tolerance to morphine in the rat

Tolerance to various effects of morphine in the rat can be quantified by means of a shift of semilogarithmic dose-response curves. Tolerance to analgesia (hot plate, acetic acid writhing), catalepsy, and the tilted plane develops in a closely similar manner. Also, the stimulating effects of about 1 mg/kg morphine-HCl tested in an open-field procedure are somewhat less pronounced in chronically treated rats than in naive ones. There is no correlation between tolerance development and the acute ED₅₀ of different tests.