Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.     

Ginsenoside Rf potentiates U-50,488H-induced analgesia and inhibits tolerance to its analgesia in mice

In the present study, the effect of ginsenoside Rf (Rf), a trace component of Panax ginseng on U-50,488H (U50), a selective kappa opioid-induced analgesia and its tolerance to analgesia was studied using the mice tail-flick test. In addition, the possible mechanism by which Rf may affect U50-induced analgesia was investigated. Intraperitoneal administration of U50 (40 mg/kg) produced analgesia. Rf (10(-14)-10(-10) mg/kg) on co treatment dose-dependently potentiated the U50 (40 mg/kg)-induced analgesia. Rf (10(-12)-10(-2) mg/ml) did not alter the binding of [3H] naloxone, a opioid ligand and [3H]PN200-110, a dihydropyridine ligand to mice whole brain membrane. Twice daily administration of U50 (40 mg/kg) for six days induced tolerance to its analgesia. Chronic treatment (day 4-day 6) of Rf (10(-14)-10(-10) mg/kg) to U50-tolerant mice, dose-dependently inhibited the tolerance. The inhibition of tolerance to U50-induced analgesia by Rf was not altered by flumazenil (0.1 mg/kg), a benzodiazepine receptor antagonist and picrotoxin (1 mg/kg), a GABA(A)-gated chloride channel blocker on chronic treatment. In conclusion, these findings for the first time demonstrated that ginsenoside Rf potentiates U50-induced analgesia, inhibits tolerance to its analgesia, and suggests that Rf affects U50-induced analgesia via non-opioid, non-dihydropyridine-sensitive Ca(+2) and non-benzodiazepine-GABA(A)ergic mechanisms in mice.     

Comparison of naloxonazine and beta-funaltrexamine antagonism of mu 1 and mu 2 opioid actions.

beta-Funaltrexamine (beta-FNA) irreversibly blocks morphine analgesia, lethality and its inhibition of gastrointestinal transit, confirming that these actions involve mu receptors. In dose-response studies, beta-FNA antagonized all the actions with similar potencies (ID50 values of 12.1, 11.3 and 12.3 mg/kg, respectively). beta-FNA also reduced intra-cerebroventricular and intrathecal DAMGO analgesia equally well (ID50 values of 6.09 and 7.7 mg/kg, respectively). Naloxanazine blocked systemic morphine analgesia (ID50 value 9.5 mg/kg) and supraspinal DAMGO analgesia (ID50 value 6.1 mg/kg) as potently as beta-FNA. However, against spinal DAMGO analgesia, morphine's inhibition of gastro-intestinal transit or lethality, naloxonazine (ID50 values 38.8, 40.7 and 40.9 mg/kg, respectively) was significantly less active than beta-FNA (p less than 0.05). beta-FNA remains a valuable tool in the classification of mu opioid actions. Within the mu category, actions can be defined as either mu 1 (naloxonazine-sensitive) or mu 2 (naloxonazine-insensitive).     

Long-term enhancement of morphine hypalgesia as a result of periodic blockade of opiate receptors using naloxone

A significant enhancement of the analgetic effect of morphine (6 mg/kg, subcutaneously; tail withdrawal reflex at 60 degrees C) was observed in rats 3-4 hours after single naloxone (1 mg/kg) administration. Periodical naloxone injection (0.5 mg/kg, subcutaneously, 3 times per day at 3.5-hour intervals for 3 days) led to a prominent and long-term (testing on the 20th and 105th hour after the last naloxone administration) enhancement of morphine analgesia (2.6 mg/kg subcutaneously) and insignificant inhibition of stress analgesia during two-hour immobilization of animals. These modifications of morphine and stress analgetic effects are considered a result of adaptive changes of opiate receptors after their blockade.     

Cimetidine does not change the effect of Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) on the opiate form of footshock-induced analgesia.

It has been demonstrated that cimetidine blocks the effect of naloxone on footshock-induced analgesia. To study the effect of cimetidine on the antiopiate properties of an endogenous peptide Tyr-MIF-1, the opiate form of intermittent footshock-induced analgesia was elicited in the rat. The nociceptive responses were determined using the hot-plate test (52.5 degrees C). Intraperitoneal pretreatment with cimetidine (100 mg/kg) or chlorpheniramine maleate (20 mg/kg) did not affect the footshock-induced analgesia, and did not change the antagonizing effect of Tyr-MIF-1 (0.2 mg/kg) on this model of antinociception. It is concluded that cimetidine and chlorpheniramine maleate do not change the antagonizing effect of Tyr-MIF-1 on the opiate form of intermittent footshock-induced analgesia.     

Effect of methamphetamine on the development of acute morphine tolerance and dependence in mice

The effect of methamphetamine on morphine analgesia (tail-flick assay) was studied in non-tolerant mice and in mice made acutely tolerant to morphine following a single injection of 100 mg/kg morphine. The analgesic potency of morphine was increased in non-tolerant and tolerant mice to the same extent by 3.2 mg/kg methamphetamine (3.3 and 4.4 fold increases, respectively). In contrast, the ED50's for morphine analgesia and naloxone-precipitated jumping in mice pretreated with either 100 mg/kg morphine or both morphine and 3.2 mg/kg methamphetamine were not significantly different, indicating that methamphetamine had no effect on the development of acute morphine tolerance and dependence. Although methamphetamine had no effect on the development of acute tolerance to morphine, 4-day pretreatment with methamphetamine produced cross-tolerance to morphine analgesia. However, cross-tolerance to morphine was not accompanied by enchanced sensitivity to naloxone.     

The mechanism of the intranasal action of dermorphin in representatives of 2 classes of vertebrates]

It has been shown that endogenous opioid dermorphin induces effective analgesia after intranasal injection to fish (0.02-0.20 mg/kg) and rats (0.005 mg/kg). Maintenance of dermorphin analgesia after olfactory and trigeminal denervation indicates that the analgetic effect is not realized via the olfactory receptors or free terminals of the trigeminal nerve.     

Nicotene-induced analgesia in rats: The role of calcium and the diversity of responders and nonresponders

Following a single dose of nicotine, (NIC, 1 mg/kg s.c.), 60% of tested rats revealed significant anticociception as measured by the tail-flick (TF) test, and were classified as responders, with those in which TF latencies did not change, nonresponders. The following experiments were carried out one week later. In nonresponders, pretreatment with ethylenediaminetetraacetic acid (EDTA, 250 μM/kg s.c. four times every 15 min) followed by 1 mg NIC, produced significant analgesia in 50% of rats, to the same magnitude as did nicotene alone (1 mg) in responders. The other 50% of rats which failed to respond to EDTA pretreatment, all revealed similar analgesia following the higher dose of NIC (1.5 mg/kg s.c.), with similar side effects, as generally observed in responders. In responders, pretreatment with CaCl₂ (1.5 mM/kg s.c.) completely abolished NIC (1 mg/kg s.c.) - induced analgesia in all rats. Our data provide stronger evidence and a further verification that EDTA potentiates, whereas CaCl₂ completely abolishes, nicotene-induced analgesia in rats; supporting our hypothesis of the involvement of calcium ions in this effect.     

Involvement of H2-receptors in the mechanism of analgesic action of Tyr-MIF-1

The antinociceptive effects of H2-agents cimetidine (CIM) and dimaprit (DMP) as well as their effects on the Tyr-MIF-1-evoked analgesia have been studied after intraperitoneal (i.p.) administration in rats. In the paw-pressure (PP) test Tyr-MIF-1 (1 mg/kg), CIM (50 and 100mg/kg) and DMP (5 and 10mg/kg) induced analgesia. Injected before DMP, naloxone (NAL) and CIM diminished or completely prevented the pain-relieving effect of H2-agonist DMP. The antinociceptive effect of Tyr-MIF-1 has been potentiated by DMP dose-dependently. CIM (50mg/kg) decreased the antinociceptive action of the combination Tyr-MIF-1 + DMP, while CIM (100mg/kg) expressed a weaker inhibitory effect on it. The data obtained clearly show that H2-receptor activation is involved in the mechanism of the Tyr-MIF-1 antinociceptive action.     

Non-opioid analgesia of the neuropeptide, neo-kyotorphin and possible mediation by inhibition of GABA release in the mouse brain

The novel neuropeptide, neo-kyotorphin, produced a naloxone-resistant analgesia in the tail pinch test when given (IC) to mice. Pretreatments with implantation of a morphine pellet or with phentolamine (10 micrograms IT) or with reserpine (10 mg/kg SC) did not attenuate this analgesia, yet the analgesia was antagonized by GABA mimetics, such as muscimol (0.1 microgram IC), nipecotic acid (100 mg/kg IP). Neo-kyotorphin inhibited the Ca2+-dependent and depolarization-evoked release of 3H-GABA, from crude synaptosomes of the lower brain stem of rats. These findings suggest that inhibition of GABA in the brain may in part be involved in neo-kyotorphin-induced analgesia.     

Peripheral injection of DNS-RFa, a FMRFa agonist, suppresses morphine-induced analgesia in rats

The present results demonstrate an antagonistic effect of DNS-RFa on morphine-induced analgesia in rats. This confirms previous evidence presented by others on the effects of FMRFa-related peptides when applied centrally. Unlike these peptides, however, it is shown here that DNS-RFa is effective upon peripheral injection. The effects of DNS-RFa on morphine-induced analgesia were dose-dependent (ED50 = 0.5 mg/kg). DNS-RFa alone (5 mg/kg) did not affect the control level of nociception. Peripheral injection of FMRFa (5 mg/kg) did not affect morphine-induced analgesia. DNS-RFa defines the minimal configuration to activate neuronal FMRFa receptors in the pond snail. The present report suggests also that in vertebrates the Arg-Phe-NH2 sequence is essential and that DNS-RFa readily penetrates the blood-brain barrier.     

Acupuncture analgesia in rats and its changes under the effect of morphine and naloxone

It was established in chronic experiments on rats that electric acupuncture of the acupuncture point noticeably decreases pain reaction to electric stimulation of the tail. Morphine given in a subanalgetic dose (5 mg/kg) potentiated acupuncture analgesia, while 5 mg/kg of naloxone completely abolished it. Potential mechanisms of analgesia realization during electric acupuncture are discussed.     

Changes in pain sensitivity under increased atmospheric pressure]

It has been established that augmentation of air pressure from 0.1 to 1.1 MPa (with 0.1 MPa intervals) was accompanied in rats with the development of progressive analgesia which was measured according to the threshold of vocalization in the test of electrical stimulation of the tail. The highest analgesic response arose at 0.7-1.1 MPa. All the animals might be divided into two groups: group 1-72% of the animals with a 200% increase of the threshold, group 2--animals with such an increase by 15%. The augmentation of the pressure of heliox (79.1% of helium, 20.9% of oxygen) also caused analgesia, but not so strong. In patients pain thresholds to the mechanical nociceptive stimulation also increased by about 43-67% and 95-100% under the influence of increased air pressure of 0.4 and 0.7 MPa, respectively. In group 1 patients (67%) pain threshold increased by 50-100%, in group 2 by 15-25%. Pretreatment with naloxone (1 mg/kg), atropine (1 mg/kg), yohimbine (1 mg/kg), parachloramphetamine (5 mg/kg) and prasosin (1 mg/kg) decreased hyperbaric analgesia in rats by 41-56, 41-56, 17-19, 17-19%, respectively. The role of increased partial pressure of nitrogen in hyperbaric analgesia and possible neurochemical mechanisms of its realization are discussed.     

Electroacupuncture analgesia could be mediated by at least two pain-relieving mechanisms; endorphin and non-endorphin systems.

This present paper shows different levels of electroacupuncture analgesia (antinociceptive effect) induced by three different frequencies of stimulation (i.e. 0.2, 4 and 200 Hz); highest analgesia is induced at 200 Hz and lowest at 0.2 Hz. Naloxone (1 mg/kg) completely reverses the electroacupuncture effects at low frequency stimulation (4 Hz) but produces no inhibition at high frequency stimulation (200 Hz). Conversely, parachlorophenylalanine (320 mg/kg) partially blocks the high-frequency (200 Hz) analgesia but produces no effect on the low-frequency (4 Hz) electroacupuncture analgesia. This suggests that electroacupuncture analgesia induced by low frequency stimulation may be mediated by endorphins while high frequency stimulation is not endorphinergic but may be partly due to serotonin.     

Ethanol-induced analgesia

The effect of ethanol (ET) on nociceptive sensitivity was evaluated using a new tail deflection response (TDR) method. The IP injection of ET (0.5-1.5 g/kg) produced rapid dose-dependent analgesia. Near maximal effect (97% decrease in TDR) was produced with the 1.5 g/kg dose of ET ten minutes after injection. At ninety minutes post-injection there was still significant analgesia. Depression of ET-induced nociceptive sensitivity was partially reversed by a 1 mg/kg dose of naloxone. On the other hand, morphine (0.5 or 5.0 mg/kg IP) did not modify ET-induced analgesia, while 3.0 minutes of cold water swim (known to produce non-opioid mediated analgesia) potentiated ET-induced analgesic effect. The 0.5 g/kg dose of ET by itself did not depress motor activity in an open field test, but prevented partially the depression in motor activity produced by cold water swim (CWS). Thus the potentiation by ET of the depression of the TDR produced by CWS cannot be ascribed to the depressant effects of ET on motor activity.     

Comparison of the effects of specific and nonspecific inhibition of nitric oxide synthase on morphine analgesia,tolerance and dependence in mice

The effects of L-Canavanine, a selective inducible nitric oxide synthase (NOS) inhibitor and N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective NOS inhibitor, on pain threshold and morphine induced analgesia, tolerance and dependence in mice were investigated and compared. Morphine was administered by subcutaneous implantation of a pellet containing 40 mg free base and withdrawal was precipitated by intraperitoneal (i.p.) injection of naloxone (2 mg/kg). L-Canavanine (200 mg/kg, i.p.) did not affect the pain threshold, morphine-induced analgesia and the induction and expression phases of morphine tolerance and dependence. L-NAME (20 mg/kg, i.p.) significantly (p < 0.05) enhanced the pain threshold, potentiated morphine-induced analgesia and attenuated the expression phase of morphine dependence which has been characterized by withdrawal signs and body weight loss, but did not modify the induction phase of morphine tolerance and dependence. It is concluded that constitutive NOS isoforms which were inhibited by L-NAME may be involved specifically in the mechanisms of morphine induced analgesia, tolerance and dependence.     

曲马朵与二氢埃托啡协同镇痛并推迟大鼠急性耐受

本文旨在研究曲马朵（tramadol,TRA）和二氢埃托啡（dihydroetorphine,DHE）联合用药是否可产生协同镇痛并延缓耐受的发生。TRA（mg,腹腔注射）与DHE（ng,皮下注射）按固定比率给药（1：6．25,1：12．5,1：25,1：50,l：100,1：200）,用热辐射甩尾法评价镇痛效应,采用等高线法评估药物的协同作用。在急性耐受实验中,连续6次注射TRA（20mg／kg）、DHE（1000ng／kg）或两药的组合（TRA20mg／kg＋DHE250ng／kg）。结果显示：（1）除1mg：6．25ng和1mg：50ng两个比例外,其他所有比例用药均产生显著的协同镇痛效应;（2）TRA与DHE联合用药的疗效在连续给药中持续时间明显延长,提示二者联合使用可延缓耐受。以上结果提示：TRA与DHE在一定剂量比范围内可产生协同镇痛效应,并可推迟耐受的形成。     

Postictal behavioral arrest in the rat: “catalepsy” or “catatonia”?

A period of immobility following chemically (picrotoxin, metrazol) or electrically-activated (maximal electroshock) convulsions was demonstrated to possess features of neuroleptic-type catalepsy. During postictal immobility rats had vivid righting and corneal reflexes and responded t to the tail-oinch. Like haloperidol-pretreated animals they were able to remain on the vertical grid or horizontal bar for 15–60 sec or longer. Ten-fifteen minutes after seizure when catalepsy was minimal or not detectable, animals became totally unresponsive to pressure applied to the tail (“delayed analgesia”). Systematically administered haloperidol (0.25–2 mg/kg) did not affect postictal catalepsy while naloxone (5–10 mg/kg) and apomorphine (10 mg/kg) reduced the duration of the immobility period. Unlike naloxone, apomorphine diminished the intensity of cataleptic behavior. Higher doses of naloxone (20–70 mg/kg) when injected during the postictal period induced violent convulsions. None of the two drugs antagonized delayed analgesia.Daily administration of electroshock caused a build up of postictal rigidity and analgesia, coexisting with symptoms of catalepsy. Naloxone antagonised rigidity but failed to interfere with catalepsy and analgesia.     

Analgesic activity of Piper longum Linn. root

Piper longum root, commonly called Kandantippili, is traditionally used to treat rheumatism, insomnia, palsy and epilepsy. But a scientific study on its central actions is not available. This study screens P. longum root for opioid type analgesia using rat tail-flick method and for NSAID type analgesia using acetic-acid writhing method. Pentazocine (ip) and ibuprofen (oral) are used as respective drug controls. An aqueous suspension of P. longum root powder is given orally to mice and rat in doses of 200, 400 and 800 mg/kg. The delay in reaction time for thermal stimulus in rats and the number of writhings to chemical stimulus in mice are determined in each group. The results are analysed statistically. The 400 and 800 mg/kg doses of P. longum show significant NSAID type of analgesia (P < 0.001). Both Ibuprofen (40 mg/kg) and P. longum (800 mg/kg) show 50% protection against writhing. The delay in reaction time to thermal stimulus was less than 6% for different doses of P. longum as against 100% for pentazocine. This indicates that P. longum root has weak opioid but potent NSAID type of analgesic activity.     

Effects of systemically administered monoamine reuptake blocking agents on patterns of buspirone-induced analgesia in rats

We have recently shown the serotonin 5-HT1A receptor agonist buspirone to produce analgesia in several pain tests in rats. As a 5-HT1A agonist, buspirone may change serotonergic (5-HT) tone to alter the balance of central monoaminergic (MA) systems that function in analgesia. MA-reuptake blocking drugs have been shown to produce analgesia, both when given alone and in combination with a variety of other agents, presumably via their action upon MA neurochemistry. The present study was undertaken to examine the effect of systemic administration of the 5-HT-reuptake blocker amitriptyline (AMI: 10 mg/kg), NE-reuptake blocker desipramine (DMI: 10 mg/kg) or DA-reuptake blocker GBR-12909 (7.5 mg/kg) on patterns of analgesia produced by buspirone (1-5 mg/kg) in thermal and mechanical pain tests in rats. Neither reuptake blocking agents or buspirone, when administered alone or in combination, produced overt changes in motor activity at the doses tested. AMI alone was not analgesic in either thermal or mechanical pain tests. In both assays, AMI reduced the analgesic action of buspirone, with greater effects seen in the thermal test. When administered alone, DMI produced significant analgesia against thermal and mechanical pain. DMI significantly attenuated the analgesic action of all doses of buspirone in both pain tests. Alone, GBR-12909 did not affect nociception in thermal or mechanical tests. GBR-12909 decreased buspirone-induced analgesia at all doses in the thermal test, while having no effect on buspirone-induced analgesia against mechanical pain. These results demonstrate that facilitation of 5-HT, NE and DA function with reuptake blocking drugs did not enhance the analgesic action of buspirone. These data indicate against the adjuvant use of reuptake blocking compounds and buspirone as analgesics. Furthermore, such findings may suggest other possible non-MA substrates of buspirone-induced analgesia.