Effects of electric footshock on barbiturate sensitivity, nociception and body temperature in mice

Crude saponin extracted from Vietnamese ginseng and its major constituent majonoside-R2 attenuate the psychological stress- and foot-shock stress-induced antinociception in mice

Effects of Vietnamese ginseng (VG) crude saponin and majonoside-R2, a major saponin constituent, on the psychological stress- and foot shock stress-induced antinociception in the tail pinch test were examined in mice. VG crude saponin (6.2, 12.5, and 25 mg/kg, P.O.) attenuated psychological stress- but not foot shock stress-induced antinociceptive response, whereas majonoside-R2 (3, 6.2, and 12.5 mg/kg, P.O. and i.p.), as well as naloxone (2 mg/kg, i.p.), suppressed both psychological stress- and foot shock stress-induced antinociception. Pretreatment with the crude saponin (12.5 mg/kg, P.O.) or majonoside-R2 (6.2 mg/kg, P.O.) for 5 days followed by the treatment in combination with stress for next 5 days did not affect the development of adaptation to foot shock stress, but they significantly suppressed the antinociceptive action of the stress measured on the first, second, and third day during the stress exposure period. Majonoside-R2 (6.2 mg/kg, P.O.) but not the crude saponin (12.5 mg/kg, P.O.) significantly blocked the development of adaptation to psychological stress. These results suggest that VG crude saponin has the suppressing effect on psychological stress- and foot shock stress-induced antinociception and that majonoside-R2 is important for the action of the saponin.

Effect of alpha 2-adrenergic drugs on REM sleep deprivation-induced increase in swimming activity

Effects of alpha 2-adrenergic agents on rapid eye movement sleep (REMs) deprivation-induced anti-immobility effect in the forced swimming test (FST) were investigated. Mice were deprived of REMs for 24-72 h by a small pedestal method. Animals that were either group housed or socially isolated during the same period as REMs deprivation were used as the control groups. REMs deprivation for 48 and 72 but not 24 h significantly increased swimming activity without increasing locomotor activity. Clonidine HCl (30-300 micrograms/kg, IP), an alpha 2-adrenoceptor agonist, dose-dependently increased swimming activity in group-housed, isolated, and REMs-deprived mice, but the effective doses of clonidine in REMs-deprived mice were lower than those in group-housed or isolated animals. Yohimbine HCl (5 mg/kg, IP), an alpha 2-adrenoceptor antagonist, blocked the clonidine (300 micrograms/kg)- but not the REMs deprivation-induced increase in swimming activity. These results suggest that REMs deprivation enhances the sensitivity of the alpha 2-adrenoceptor and that the increase in swimming activity by REMs deprivation may be mediated by other neuronal mechanisms rather than the alpha 2-adrenoceptor.

REM sleep deprivation decreases apomorphine-induced stimulation of locomotor activity but not stereotyped behavior in mice

1. Effects of rapid eye movement (REM) sleep deprivation on central dopaminergic system were investigated by testing the behavioral responses to apomorphine and brain dopamine metabolism in mice. 2. REM sleep deprivation for 48 hr significantly suppressed apomorphine.HCl (3.0 and 6.0 mg/kg, i.p.)-stimulated spontaneous locomotor activity without affecting the intensity of stereotyped behavior. 3. Neither the latency of nociceptive response in a hot-plate test nor the duration of pentobarbital-induced sleep was changed by REM sleep deprivation. 4. Dopamine turnover in the striatum and the nucleus accumbens of REM sleep-deprived mice was significantly higher than that of control animals. 5. These results suggest that REM sleep deprivation may decrease the function of postsynaptic dopamine receptor in the mesolimbic but not nigrostriatal dopaminergic system.

Stress in mice increases intrinsic pentobarbitone sensitivity by a predominantly pharmacodynamic mechanism

1. Mice were swum for 3 min at room temperature. 2. After this stress 'sleeping time' in response to pentobarbitone was increased by over 70%. 3. Loss of 'righting reflex' occurred in these stressed animals at brain concentrations of pentobarbitone which were 40% lower than those needed for 'sleep' in the unstressed mice, indicating a true increase in sensitivity to the drug. 'Waking' (the return of the righting reflex) occurred at identical levels in both groups. 4. Kinetic analysis showed that the rates of absorption, elimination and transfer between plasma and brain were slower in the swum than in the unswum mice, probably because of the reduced body temperatures produced by the swimming.

Stress analgesia: the opioid analgesia of long swims suppresses the non-opioid analgesia induced by short swims in mice

In mice, room temperature swimming for as short a period as 15 sec has been found to induce a non-opioid analgesia with a time course of 10-12 min. As the duration of the swim is increased, an opioid analgesia develops with a longer persistence (25-30 min); the development of the opioid analgesia appears to suppress the expression of the non-opioid analgesia so that none of the latter is evident after 3 min swims. The characteristics of the tail-flick nociceptive test are also described.

Effects of forced shaking stress at low temperature on pentobarbital-induced sleeping in mice

1. Effects of a new stressful manipulation, forced shaking stress at low temperature (4 degrees C) (FSLT stress), on sleeping induced by pentobarbital were investigated 70 min following its application. 2. Repeated application (7 times) decreased the duration of sleep induced by pentobarbital-Na (45 mg/kg, i.p.) in mice without affecting that induced by ketamine-HCl and chloral hydrate. This effect of FSLT stress disappeared 3 days after termination of application. 3. The latency of nociceptive response in hot-plate test increased in a naloxone-sensitive manner by single and repeated FSLT stress when tested immediately (2 min) after but not 70 min after the last stress application. 4. Diazepam (0.3 mg/kg, i.p.) significantly prolonged the duration of sleep induced by pentobarbital (45 mg/kg, i.p.) in stressed animals without changing that in unstressed animals. The effect of diazepam was blocked by Ro 15-1788 (10 mg/kg, i.p.), a specific benzodiazepine receptor antagonist. 5. Repeated FSLT stress thus appears to decrease pentobarbital sleep by inducing functional changes in the central nervous system and the GABAergic system may partially participate in FSLT stress-induced decrease in pentobarbital sleep.

Effect of citalopram, amineptine, imipramine and nortriptyline on stress-induced (footshock) analgesia in rats

The influence of the oral administration of different doses of citalopram (5, 15 and 45 mg/kg), imipramine (15, 30, 45 and 60 mg/kg), nortriptyline (15, 45 and 60 mg/kg) and amineptine (45 mg/kg) on stress-induced analgesia has been studied in anaesthetized rats. None of the administered antidepressants seem to have appreciable analgesic activity when analgesia is tested by the tail-immersion method. Citalopram, imipramine and nortriptyline, but not amineptine, increase the analgesia induced by inescapable footshock delivered continuously for 2 min to rats. Citalopram is the most potent drug. Our results support the suggested importance of 5-HT and noradrenaline terminals, but not those of dopamine, in the mediation of the stress-induced analgesia and seem to support the hypothesis that the analgesic activity of antidepressants is partially related to their modulating effects on the endogenously released opioid peptides involved in the endogenous pain inhibitory systems.

Swim stress reduces chronic pain in mice through an opioid mechanism

Chronic nociception has been studied in male mice by means of the formalin test in which forelimb motor behaviour is scored after subcutaneous formalin injection. The rating remained above 2.0 for 30 min after the injection (scale range 0-3). The magnitude of the nociception has been compared with that reported in other animal types. Mice are more sensitive than rats, cats and monkeys. The stress of a swim of 3 min has been found to reduce nociception by up to 25%. This analgesia is wholly opioid in nature, being abolished by a moderate dose of naloxone (1 mg/kg).

Opioid-independent hyperalgesia induced in mice by pentobarbitone at low dosage

The abdominal constriction (writhing) test was used to investigate the effect of pentobarbitone on nociception in mice. At dosages of 10, 20 and 30 mg/kg, pentobarbitone produced marked increases in nociceptive scores. The extent of the enhancement of nociception was uninfluenced by naloxone or swim-stress. The swim-stress induced analgesia but, in contrast to previous results using other tests for nociception, the analgesia was wholly non-opioid with the abdominal constriction test.

Effects of naloxone on dental pain threshold following muscle exercise and low frequency transcutaneous nerve stimulation: a comparative study in man

Previous studies have shown that muscle exercise and low frequency transcutaneous nerve stimulation (TNS) give rise to an analgesic effect in humans and animals. Endorphin has been proposed to mediate this analgesia. In this investigation, the effect of muscle exercise and low frequency TNS, on dental pain thresholds was studied and the possible involvement of endorphinergic mechanisms was investigated using naloxone as an antagonist. Dental pain thresholds were measured in 11 volunteers following leg or arm exercise and after low frequency TNS of the hands or face. After exercise (20 min) or stimulation (30 min) either 0.8 mg naloxone (2 ml) or saline (2 ml) was injected i.v. in a double-blind fashion. Pain thresholds were measured repetitively before and after exercise or stimulation. Both leg and arm exercise increased pain threshold. Stimulation of the hands also increased pain threshold, but less than arm exercise. A marked increase in pain threshold was seen after face stimulation. These changes in pain threshold were unaffected following injections of either naloxone or saline, except for an early and short-lasting reduction when naloxone was injected following arm exercise. The increases in pain threshold following muscle exercise and after low frequency TNS, showed similarities suggesting that a common mechanism might be involved. The pain threshold increase after arm exercise could only be partially mediated by endorphinergic mechanisms.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Diversity of underlying mechanisms in the production of analgesic and pentobarbital-hypnosis prolonging effects of various analgesic drugs and stresses

Stressful stimuli, electric footshock (FS), immobilized-water immersion (IW), and cold-water swimming (CWS), produced analgesia and prolonged the pentobarbital hypnosis as well as morphine and clonidine. Naloxone completely antagonized the analgesic effects of morphine and FS and partially that of IW; however, that of clonidine and CWS were not reversed by naloxone. Naloxone eliminated the hypnosis prolonging effect of morphine and FS, but failed to reverse the effect of clonidine, IW and CWS. Differences in the analgesic and hypnosis prolonging effects and also the respective naloxone sensitivity of each drug and stress suggest the diversity of the underlying mechanisms.