Sleep-wake effects following the selective 5-HT(1A) receptor antagonist p-MPPI in the freely moving rat

Potentiating effect of spinosin, a C-glycoside flavonoid of Semen Ziziphi spinosae, on pentobarbital-induced sleep may be related to postsynaptic 5-HT(1A) receptors

Previous results have suggested that spinosin, a C-glycoside flavonoid of Semen Ziziphi spinosae, potentiates pentobarbital-induced sleep via the serotonergic system. The present study investigated whether spinosin potentiates pentobarbital-induced sleep via serotonin-1A (5-hydroxytryptamine, 5-HT(1A)) receptors. The results demonstrated that spinosin significantly augmented pentobarbital (35 mg/kg, i.p.)-induced sleep in rats, reflected by reduced sleep latency and increased total sleep time, non-rapid eye movement (NREM) sleep time, and REM sleep time. With regard to NREM sleep duration, spinosin mainly increased slow-wave sleep (SWS). Additionally, spinosin (15mg/kg, i.g.) significantly antagonized 5-HT(1A) agonist 8-OH-DPAT (0.1mg/kg, i.p.)-induced reductions in total sleep time, NREM sleep, REM sleep, and SWS in pentobarbital-treated rats. These results suggest that spinosin may be an antagonist at postsynaptic 5-HT(1A) receptors because these effects of 8-OH-DPAT were considered to be mediated via postsynaptic 5-HT(1A) receptors. Moreover, co-administration of spinosin and the 5-HT(1A) antagonist 4-iodo-N-{2-[4-(methoxyphenyl)-1-piperazinyl]ethyl}-N-2-pyridinylbenzamide (p-MPPI), at doses that are ineffective when administered alone (spinosin 5mg/kg, p-MPPI 1mg/kg), had significant augmentative effects on pentobarbital-induced sleep, reflected by reduced sleep latency and increased total sleep time, NREM sleep, and REM sleep. In contrast to the attenuating effects of p-MPPI on REM sleep via presynaptic 5-HT(1A) autoreceptors, 15mg/kg spinosin significantly increased REM sleep. These results suggest that the effect of spinosin on REM sleep in pentobarbital-treated rats may be related to postsynaptic 5-HT(1A) receptors.

Increased extracellular 5-HT but no change in sleep after perfusion of a 5-HT1A antagonist into the dorsal raphe nucleus of rats

AIM

The 5-HT(1A) receptor antagonist 4-Iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPPI) (10 microM) was perfused into the dorsal raphe nucleus (DRN) to study simultaneously the effects of the drug on the DRN and frontal cortex extracellular serotonin (5-hydroxytryptamine, 5-HT) levels and concurring behavioural states.

METHODS

Waking, slow wave sleep and rapid eye movement sleep were determined by polygraphic recordings during microdialysis perfusion and extracellular sample collection. The samples were analysed by microbore high-performance liquid chromatography coupled with electrochemical detection for analysis of 5-HT.

RESULTS

p-MPPI perfusion into the DRN (n = 6) produced a sixfold 5-HT increase in the DRN during all behavioural states. The increased 5-HT level was most likely related to the blockage of 5-HT(1A) receptors in the DRN by p-MPPI. No significant effect was seen on sleep.

CONCLUSION

Despite the dramatic increase in DRN extracellular 5-HT produced by p-MPPI, only a transient and nonsignificant effect on sleep was recorded. It is suggested that the usual coupling between 5-HT level and behavioural state may be lost when an excessive serotonergic output is pharmacologically achieved.

The effect of GABA(A) antagonist bicuculline on dorsal raphe nucleus and frontal cortex extracellular serotonin: a window on SWS and REM sleep modulation

We investigated the effects of the perfusion of gamma-aminobutyric acid(A) antagonist bicuculline in the dorsal raphe nucleus, on brain 5-hydroxytryptamine level and on sleep. Perfusion of 25 and 50 microM bicuculline into the dorsal raphe nucleus dose-dependently increased dorsal raphe nucleus 5-hydroxytryptamine level during sleep and wakefulness. Frontal cortex 5-hydroxytryptamine level was not affected by either 25 or 50 microM perfusion. 25 microM bicuculline produced only minimal effects on sleep. 50 microM decreased rapid eye movement sleep, slow wave sleep 1 and 2 and increased waking. Sleep changes leveled out towards the end of the bicuculline perfusion despite serotonin levels were still elevated. This suggests that an adaptation mechanism may take place in order to counteract the high serotonergic output, producing uncoupling between serotonin level and behavioural state. The results support the notion that gamma-aminobutyric acid is a strong modulator of dorsal raphe nucleus serotonergic neurons, and that this modulation is important in the regulation of slow wave sleep, rapid eye movement sleep and waking.

Sleep organization is unaffected by caffeine in premature infants

We performed 10-hour polysomnographic recordings in 15 neurologically normal and clinically stable 33- to 34-week postmenstrual age (PMA) neonates, 10 of whom had been treated >3 days with once-per-day oral caffeine citrate (5 mg/kg) given at approximately 2 PM. We analyzed (a) the usual sleep-wake variables, including wakefulness, active sleep, quiet sleep, and indeterminate sleep expressed as the number of episodes, duration, and percentage of total sleep time; (b) the duration and order of variable modifications during transitions between the main active sleep and quiet sleep states; and (c) the characteristics of morning data (before caffeine) compared with evening data (after caffeine). We found no significant differences between the controls and the infants receiving maintenance caffeine.

5-HT(1A) receptor antagonist p-MPPI attenuates acute ethanol effects in mice and rats

The effect of a selective 5-HT(1A) antagonist, 4-(2'-methoxy-)phenyl-1-[2'-(N-2"-pyridinyl)-p-iodobenzamino-]ethyl-piperazine (p-MPPI), on acute ethanol-induced hypothermia, sleep and suppression of acoustic startle reflex in C3H/He mice and Wistar rats was studied. Administration of p-MPPI at the doses of 0.4, 0.7 and 1.0 mg/kg reduced in a dose-dependent manner the ethanol-induced hypothermia and the sleep time and attenuated the ethanol-induced decrease of acoustic startle reflex magnitude in mice. Similar p-MPPI (0.4 mg/kg) effects on ethanol-induced sleep and hypothermia were obtained in rats. It was concluded that 5-HT(1A) receptors were involved in the mechanisms of the ethanol-induced hypothermia and sleep, and that 5-HT(1A) antagonist increased acute ethanol tolerance.

Serotonin and sleep

For 50 years, serotonin has been in the centre of the search for the mechanisms and control of sleep. Serotonergic neurotransmission is related to the behavioural state of the animal and plays an important role in modulation of the behavioural state, by interacting with other brain areas modulating circadian rhythm, sleep and waking. Serotonergic activity may be accompanied by waking or sleep depending on the brain area and receptor type involved in the response, on the current behavioural state and on the concomitant agonism/antagonism of other neurotransmitter systems.

The selective 5-HT(1A) receptor antagonist p-MPPI antagonizes sleep--waking and behavioural effects of 8-OH-DPAT in rats

Systemic administration of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) increases waking and reduces slow wave sleep (SWS) and rapid eye movement (REM) sleep in the freely moving rat. The selective 5-HT(1A) antagonist 4-(2'-methoxy-phenyl)-1-[2'-(n-2"-pyridinyl)-p-iodobenzamido]-ethyl-piperazine (p-MPPI) induces a dose-related decrease in REM sleep. The present study examined p-MPPI's potential as an antagonist of the sleep and waking responses elicited by 8-OH-DPAT. Also, the experiments explored the ability of p-MPPI to block behavioural reactions of the 5-HT syndrome induced by 8-OH-DPAT, and whether p-MPPI induced any behavioural effects of its own. This study demonstrated that pre-treatment with p-MPPI (5 mg/kg intraperitoneal (i.p.)) 30 min before 8-OH-DPAT (0.375 mg/kg subcutaneously (s.c.)) reduced the effect of 8-OH-DPAT on waking and REM sleep. Also, p-MPPI (5 and 10 mg/kg i.p.) reduced the effect of 8-OH-DPAT on locomotion and partially or completely antagonized hindlimb abduction and flat body posture. No overt behavioural change was produced by p-MPPI alone. Thus, p-MPPI behaved as a true 5-HT(1A) antagonist.

WAY-100635, a specific 5-HT1A antagonist, can increase the responsiveness of the mammalian circadian pacemaker to photic stimuli

Mammalian circadian rhythms are synchronized daily to light-dark cycles in the environment. The suprachiasmatic nucleus (SCN) is the proposed site of the major circadian pacemaker. Daily entrainment is believed to be influenced by inputs to the SCN, one of these being the dense serotonergic (5-HT) projection from the raphe nuclei. WAY-100635 is a potent and selective 5-HT1A receptor antagonist. In this study, the effects of WAY-100635 on phase-shifts of the hamster circadian pacemaker to light were investigated. Phase-delays after a light pulse administered during the early subjective night (15 min at CT14) were observed to be significantly greater following pre-treatment with WAY-100635 compared to light pulse alone (P < 0.05). However, pre-treatment with WAY-100635 had no effect on the magnitude of phase-shifts to light at CT18, late in the subjective night. Serotonin may influence the responsiveness of the circadian pacemaker to photic stimuli. Specifically, WAY-100635 administered at CT14 can augment phase-shifts to light.

Sleep and waking following microdialysis perfusion of the selective 5-HT1A receptor antagonist p-MPPI into the dorsal raphe nucleus in the freely moving rat

The aim of this study was to examine the involvement of the dorsal raphe nucleus (DRN) presynaptic serotonergic 5-HT1A autoreceptors on sleep and waking parameters, in particular rapid eye movement (REM) sleep. In a previous study, the systemic administration of the selective 5-HT1A receptor antagonist p-MPPI reduced REM sleep in a dose-dependent manner suggesting a blockade of the 5-HT1A autoreceptors. In the present study, a blockade by microdialysis perfusion of 10 microM and 100 microM of p-MPPI for 7 h into the DRN in freely behaving rats influenced vigilance state only to a small extent. The administration of 10 microM of p-MPPI induced a reduction of total REM sleep mainly due to a suppression of REM sleep during the third 2 h period of the recording of sleep and waking. Perfusion of 100 microM of p-MPPI decreased total transition type sleep (TRANS) but the effect on REM sleep did not reach significance. There was no change in waking or slow wave sleep (SWS) following any of the doses. The data suggest that 5-HT1A receptor-mediated mechanisms in the DRN may be only moderately important in the serotonergic modulation of REM sleep.