Involvement of the serotonergic system in the prolongation of pentobarbital sleeping time produced by prostaglandin D2

Anxiolytic and hypnotic effects in mice of roasted coffee bean volatile compounds

To clarify the relationship between the volatile compounds present in roasted coffee beans and psychological stress, we investigated the stress-reducing potential of coffee volatiles in mice using a variety of behavioral pharmacology methods. In the elevated plus-maze test, exposure to coffee volatiles increased the time spent in and the number of entries into the open arms without increasing spontaneous locomotor activity. Pentobarbital-induced sleep time was prolonged by volatile exposure. No significant effects were detected in the open-field or forced-swim tests. These results suggest that coffee volatiles lower the arousal level and exert anti-anxiety-like, stress-reducing effects in mice.

Cyclooxygenase-1 Inhibition Shortens the Duration of Diazepam-Induced Loss of Righting Reflex in Mice

Cyclooxygenase-1 (COX-1) inhibition by a selective inhibitor valeryl salicylate, or nonselective inhibitors at 10 mg/kg, including aspirin, ibuprofen, indomethacin, and picroxicam, attenuated by 29%-46% the duration of loss of righting reflex induced by diazepam (20 mg/kg) in mice. On the other hand, arachidonic acid (20 mg/kg) increased the duration of diazepam-induced loss of righting reflex by 48%. This effect of arachidonic acid was abolished by aspirin. However, aspirin at 10 mg/kg also did not alter the effects of diazepam (5 mg/kg) on spontaneous activity and rotarod performance. These findings strongly suggest that one or more COX products, most likely prostaglandins, play a significant role in modulating the hypnotic effect of diazepam. Elucidating the mechanism involved may further our understanding of the pharmacology of benzodiazepines.

Prostaglandin D synthase gene is involved in the regulation of non-rapid eye movement sleep

To examine the function of prostaglandin (PG) D synthase (PGDS) gene, as well as endogenously produced PGD(2) in sleep regulation in vivo, we generated transgenic (TG) mice that overexpress human PGDS gene to study their sleep behavior. Although no difference was observed in the sleep/wake patterns between wild-type and TG mice, a striking time-dependent increase in non-rapid eye movement (NREM), but not in rapid eye movement (REM), sleep was observed in two independent lines of TG mice after stimulation by tail clipping. Concomitantly, the spontaneous locomotor activity of TG animals was drastically decreased in response to the tail clip. Induction of NREM sleep in TG mice was positively correlated with the PGD(2) production in the brain. Sleep, locomotion, and PGD(2) content were essentially unchanged in wild-type mice after tail clipping. The results with TG mice demonstrate the involvement of the PGDS gene in the regulation of NREM sleep.

Microdialysis and EEG in rats reveal cortical PGE2 changes during sleep and wakefulness

Prostaglandin (PG) E2 production was assessed in freely moving rats using the technique of microdialysis in the prefrontal cortex associated with parallel cortical EEG recordings. PGE2 concentrations were 40% higher during wakefulness than during slow wave sleep. PGE2 values varied during wakefulness with a maximal increase in the middle of the stage and a drop towards lower values before the occurrence of slow wave sleep. These variations were similar to those observed previously in the rostromedial hypothalamus, where PGE2 concentration was 2.6 times lower than that in the cortex. These data document a positive correlation between cortical EEG activation and PGE2 levels. Taken together with pharmacological data on the awakening effect of centrally administered PGE2, these observations are in favor of an involvement of PGE2 in the generation of wakefulness.

Zipeprol: preclinical assessment of abuse potential

Zipeprol was evaluated in a number of in vitro and in vivo assays predictive of stimulant, depressant, or opioid abuse potential. Zipeprol had affinity for mu and kappa opioid binding sites as well as sigma binding sites. However, it failed to exert opioid-like agonist actions in rodents, and did not attenuate withdrawal signs in morphine- or pentobarbital-dependent rats. Zipeprol did not substitute for either amphetamine or pentobarbital in drug discrimination assays in rhesus monkeys. On the other hand, it suppressed morphine withdrawal signs in rhesus monkeys in two assays, and it acted as a quadazocine-sensitive reinforcer in monkeys trained to self-inject alfentanil. Zipeprol also acted as a reinforcer in monkeys trained to self-inject methohexital. In a dose range of 10-18 mg/kg, zipeprol induced convulsions in monkeys. Zipeprol appears to have abuse potential and a novel spectrum of action involving both opioid and non-opioid effects.

Decreased hypothalamic prostaglandin D2 and prostaglandin E2 contents during isoflurane anaesthesia in rats

This study was undertaken to evaluate the effect of isoflurane anaesthesia on the hypothalamic contents of both prostaglandin D2 and E2 which affect the sleep-wakefulness cycle. Sixty-three Wistar rats were divided into three equal groups, control, isoflurane and recovery groups. Twenty-one rats of the control did not receive isoflurane. In the other groups 21 rats received isoflurane 2% for 30 min and 21 received isoflurane 2% for 30 min and were allowed to recover their usual behaviours, including righting reflex, spontaneously. The hypothalamus was removed and the contents of PGD2 and PGE2 were measured by enzyme immunoassay. The PGD2 content in the hypothalamus was 397.9 +/- 226.0 pg.g-1 for the control group, 134.2 +/- 41.2 pg.g-1 for the isoflurane group and 269.1 +/- 124.6 pg.g-1 for the recovery group, respectively. The hypothalamic PGE2 contents were 381.4 +/- 139.0 pg.g-1 for the control group, 183.3 +/- 26.4 pg.g-1 for the isoflurane group and 312.2 +/- 96.0 pg.g-1 for the recovery group, respectively. The hypothalamic PGD2 and PGE2 contents in the isoflurane group were lower (P < 0.05) than those in the control and recovery groups, while both the PGD2 and PGE2 contents of the control and the recovery groups were similar. We conclude that decreased hypothalamic PGD2 and PGE2 contents may be related to some manifestations of general anaesthesia with isoflurane.

Changes in hypothalamic prostaglandin E2 may predict the occurrence of sleep or wakefulness as assessed by parallel EEG and microdialysis in the rat

Prostaglandin (PG) E2 is produced by mammalian hypothalamus and when administered exogenously prolongs wakefulness. In order to study the relation of endogenous hypothalamic PGE2 to sleep and wakefulness, we have used microdialysis in freely moving rats associated with EEG recording. Male Wistar rats were implanted with three cortical electrodes and with a guide cannula for microdialysis in the space between the paraventricular nucleus (PVN) and the ventromedial hypothalamus (VMH). PGE2 was measured by RIA in 3- or 6-min dialysates 15 days after surgery, when sleep patterns were normal again and PGE2 production stabilised. PGE2 levels were significantly higher during wakefulness (601 +/- 35 pg/ml, 5 experiments, 35 samples) than during slow-wave sleep (487 +/- 24 pg/ml, 5 experiments, 49 samples). Samples corresponding to paradoxical sleep showed a tendency towards higher PGE2 values compared to slow-wave sleep but lower compared to wakefulness. In epochs of wakefulness or sleep lasting at least 12 min, high PGE2 levels in the middle of wakefulness regularly dropped, thus announcing the occurrence of sleep. During sleep, PGE2 first went on dropping and then reincreased towards the values that characterize early periods of wakefulness. In its turn, this reincrease in PGE2 announced the end of sleep and the imminent occurrence of wakefulness. It is the first study to our knowledge showing that the evolvement in endogenous PG profile may predict the occurrence of sleep or wakefulness.

Serotonin involvement in the inhibition of luteinizing hormone (LH) release induced by prostaglandin D2 (PGD2) in castrated male rats

p-Chlorophenylalanine (PCPA, 320 mg/kg i.p.), an inhibitor of serotonin (5-HT) synthesis, and 5,6-dihydroxy-tryptamine (5,6-DHT, 50 micrograms i.c.v.), a drug toxic to the indoleaminergic system were used to test the involvement of 5-HT in the mediation of the inhibitory effect of prostaglandin D2 (PGD2) on luteinizing hormone (LH) release in castrated male rats. The i.c.v. administration of PGD2 suppressed the episodic LH release characteristic of castrated rats and decreased mean plasma LH levels and mean LH pulse amplitude significantly. Pretreatment with PCPA or 5,6-DHT apparently eliminated the inhibitory effect of PGD2 on LH secretion. These results suggest the possible involvement of a serotonergic mechanism in the mediation of the suppression of LH secretion induced by PGD2 in castrated male rats.

Stimulus properties of 1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDA) analogs

Using a standard two-lever operant procedure, groups of rats were trained to discriminate intraperitoneal doses of the phenylisopropylamines (+)amphetamine (1.0 mg/kg) or racemic 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM; 1.0 mg/kg) from saline using a VI 15-sec schedule of reinforcement for food reward. Once trained, the animals were administered doses of several methylenedioxy analogs (MDAs) of phenylisopropylamine including the N-monomethyl [S(+)MDMA and R(-)MDMA], N-monoethyl [(+/-)MDE, S(+)MDE, and R(-)MDE], and the N-hydroxyl [(+/-)N-OH MDA] derivatives. The DOM-stimulus did not generalize to any of these agents. The amphetamine-stimulus generalized to S(+)MDMA, S(+)N-ethylamphetamine and (+/-)N-hydroxyamphetamine, but not to R(-)MDMA, (+/-)MDE, S(+)MDE, R(-)MDE, or N-OH MDA. The present results are consistent with other reports in the literature suggesting that the psychoactive effects of certain MDA derivatives may be other than simply amphetamine- or DOM-like.