Variations in extracellular monoamines in the prefrontal cortex and medial hypothalamus after modafinil administration: a microdialysis study in rats.

The role of brain amines in mediating the effects of the wake-promoting agent modafinil, used in the treatment of sleepiness associated with narcolepsy is still uncertain. Therefore we studied the effects of modafinil on extracellular serotonin (5-HT), dopamine (DA) and noradrenaline (NA), in rat prefrontal cortex and in the medial hypothalamus area. Modafinil (128 mg/kg i.p.) significantly increased waking in the first 4 h of EEG sleep recording. This cortical and behavioral activation was associated with an initial increase in extracellular 5-HT, DA and NA during the first 60 min following modafinil administration. In the prefrontal cortex, 5-HT release remained high for 3 h after modafinil administration. In contrast, in the hypothalamus, only NA release was enhanced while DA and 5-HT levels remained low. In a first step, modafinil may generate waking partly via cortical monoamine release, particularly DA and 5-HT, and also hypothalamic NA. In a second step, maintenance of waking might depend on hypothalamic NA.

Extracellular serotonin variations during vigilance states in the preoptic area of rats: a microdialysis study.

Numerous studies have shown that serotonergic transmission decreases from waking (W) to slow wave sleep (SWS) to paradoxical sleep (PS), suggesting an active role of serotonin (5-HT) in W but not in sleep. Conversely, the inhibition of 5-HT activity produces insomnia. This insomnia can be reversed by injections of 5-hydroxytryptophan in the preoptic area (POA), suggesting that 5-HT is necessary in this cerebral structure for sleep. Using microdialysis, we studied, 5-HT variations in the POA of rats in relation to vigilance states. 5-HT levels were higher during W than during during SWS and PS. 5-HT increased just before the rats fell asleep and then decreased during sleep. A decreased 5-HT transmission was also observed from SWS to PS. These data document a positive correlation between 5-HT levels in POA and wakefulness. Moreover, these observations are in favour of a permissive role of 5-HT in the POA during PS. A comparison between the POA and the prefrontal cortex in the sleep-wake cycle is discussed.

Neuromodulation of the prefrontal cortex during sleep: a microdialysis study in rats.

To test the hypothesis that biogenic amines of the prefrontal cortex are involved in state-dependent cortical and behavioural activation, changes in extracellular levels of serotonin (5-HT), dopamine (DA), and noradrenaline (NA) were determined during the sleep-wake cycle in freely moving rats using microdialysis probes with parallel EEG recording. Serotonin gradually increased up to 450% during wakefulness (W) as compared to slow wave sleep (SWS), before decreasing toward stable levels during the next episode of SWS. Dopamine and its metabolite homovanillic acid (HVA) were reduced during W as compared to SWS. Although contradictory with the generally admitted enhancement of DA activity related to vigilance, this may be due to the particular role of DA neurons in the prefrontal cortex. However, DA and HVA showed dramatic changes announcing the transition between SWS and W. During paradoxical sleep (PS), DA and 5-HT showed complex changes, the direction of which depended on whether PS was followed by SWS or W. Biogenic amines of the prefrontal cortex are probably involved in cortical and behavioural activation.

Psychogenetically selected (Roman high- and low-avoidance) rats differ in 24-hour sleep organization.

A comparison of sleep organization in Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats, which differ in the way they respond to environmental stimuli and in several neuroendocrine and neurochemical parameters, was carried out. EEG-sleep recordings were obtained from adult males over 12:12 light-dark periods to determine how these two psychogenetically selected rat lines might also differ in their sleep-wake cycle. There was no significant difference in total sleep time between the two lines. However, the (hypoemotional) RHA/Verh rats showed an overall increase (percentage of total sleep) in paradoxical sleep (PS) duration, with a concomitant decrease in slow-wave sleep (SWS). During the dark phase, RHA/Verh rats showed a shorter PS latency and a larger number of PS episodes. Hourly sleep scoring also revealed a more discontinuous pattern (total sleep and PS vs. SWS) during the dark phase in RHA/Verh rats. In relation to recognized neurochemical and neuroendocrine differences between them, these rat lines may prove useful in investigations of the neurobiological mechanisms underlying sleep regulation.

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.

Effects of nisoxetine, a selective noradrenaline transporter blocker, on sleep in rats.

Nisoxetine has been shown to block specifically noradrenaline (NA) reuptake. Therefore, this potential antidepressant is a valuable tool for investigating the involvement of the NA system in sleep regulation. This study aimed to investigate the effects of different doses of nisoxetine on sleep parameters in rats. The main effects were observed with the highest dose and concern paradoxical sleep (PS). Indeed, although total sleep time was not modified, PS appeared later and its amount and the number of its episodes were reduced. These changes suggest a critical involvement of NA in the induction of PS.

Active immunization of rats against insulin beta subunits: effects on sleep and feeding.

The effects of active immunization against peripheral insulin beta subunits on different sleep variables and food consumption were studied in rats. Insulin subunits beta coupled to thyroglobulin was used as immunogen and rats immunized with thyroglobulin alone served as controls. Active immunization against insulin beta subunits affects sleep variables, particularly slow-wave sleep during the dark period, increasing significantly this stage of sleep and decreasing waking. Feeding behavior and body weight remained unchanged. These results are compatible with previous studies showing a positive correlation between decrease of insulin secretion and sleep disturbances. A possible relationship between peripheral alpha and or beta subunits of insulin, sleep, and feeding is suggested.

Differential effects of an alpha-2 agonist on wakefulness and paradoxical sleep in the rat: A polygraphic and biochemical approach.

The purpose of this experiment was to determine the sensitivity of wakefulness and paradoxical sleep to the α2-agonist, c1onidine. The drug inhibited both wakefulness and paradoxical sleep but the smallest dose necessary to inhibit wakefulness was 64 times larger than the smallest dose inhibiting paradoxical sleep. The effect on paradoxical sleep was inhibitory for all the clonidine doses but wakefulness was enhanced transiently after the four largest doses used. The time between injection and maximum wakefulness enhancement was highly correlated with the dose of c1onidine. The brain level measured after these four different doses at the moment of maximum wakefulness enhancement was the same, suggesting that this effect occurred only when a critical concentration of the drug was attained in the brain and not when the concentration was higher or lower. These data suggest that different α2-adrenoceptors are involved in these two states of vigilance or, alternatively, that their sensitivity is modulated physiologically. In addition, a sensitivity imbalance between different α2-adrenoceptors may exist in wakefulness but not in paradoxical sleep.

Effects of a D2 receptor agonist RO 41-9067 alone and with clonidine on sleep parameters in the rat.

The effects of RO 41-9067, a D2 dopamine receptors agonist, on different sleep parameters were studied in the rat. RO 41-9067 dose dependently decreased paradoxical sleep, and only at the higher dose increased waking during the light period. In contrast, the higher dose of RO 41-9067 increased paradoxical sleep and decreased waking during the dark period. Finally, the combination of RO 41-9067 and clonidine significantly prevent the decrease of total sleep time and paradoxical sleep found after clonidine alone. These results, compared with those of classical D2 dopamine receptors agonists, suggest an action for RO 41-9067 on D2 dopamine receptors depending on the cerebral structure, a different action particularly on the striatum and/or on the structures responsible for paradoxical sleep. An active role for D2 dopamine receptors and an interaction between noradrenergic and dopaminergic systems in the regulation of sleep is proposed.

Possible involvement of alpha 2-adrenoceptor on the hypnotic action of flunitrazepam.

This study examined whether the pharmacologic manipulation of catecholaminergic systems would affect the hypnotic action of flunitrazepam in rats. Flunitrazepam, a potent hypnotic, was used alone or in combination with alpha-methyl paratyrosine (alpha MPT), an inhibitor of the synthesis of catecholamines, and clonidine (CLN), an alpha 2-adrenoceptor agonist. Flunitrazepam significantly increased the amount of slow-wave sleep and the latency of paradoxical sleep (PS) and decreased the amount of PS. Administration of flunitrazepam to alpha MPT-treated rats significantly increased the number of sleep cycles and PS episodes as compared with flunitrazepam alone. Clonidine decreased total sleep time and significantly decreased PS. The association of flunitrazepam with CLN induced a decrease in PS and waking as compared with flunitrazepam alone. The possible involvement of noradrenergic mechanisms in modulating the effect of flunitrazepam on the rat sleep-waking cycle is proposed.

Effect of a new cognitive drug-enhancer S-12024-2 on EEG sleep recordings in rats.

A newly synthesized agent S-12024-2 was shown to improve some aspects of cognitive processes such as memory consolidation. The relationships between sleep and memory lead us to investigate the effects of the intraperitoneal administration of three different doses (1, 3, and 10 mg/kg) of S-12024-2 on sleep variables in the rat. The results showed that S-12024-2 (10 mg/kg) increased slow wave sleep (SWS) and decreased wakefulness during the light period of the first 24 h of sleep recording. During day 1 of sleep recording, S-12024-2 tended to increase paradoxical sleep (PS) with a maximal effect observed with 3 mg/kg. Four days after administration of S-12024-2 (3 mg/kg), PS remained significantly high. These data suggest an active role for S-12024-2 on SWS and PS, compatible with its favourable effects on memory.

Effects of WIN 35,428 a potent antagonist of dopamine transporter on sleep and locomotor activity in rats.

The new cocaine derivative CFT naphthalene sulphonate (WIN 35,428), has been shown to have a considerably longer duration of action and greater potency than cocaine as a central stimulant and it appears to have a similar mode of action on dopamine (DA) systems. The purpose of the present study was first to investigate the effects of low doses of WIM 35,428 with particular reference to the involvement of dopaminergic system in paradoxical sleep (PS), other sleep parameters and locomotor activity in the rat. WIN 35,428 a potent ligand of dopamine transporter showed biphasic effects upon PS and locomotor activity with low doses increasing and high doses decreasing PS. These changes reflect a functional involvement probably relevant to the action of Win 35,428 on DA transporters.

Dynamic changes in hypothalamic monoamines during sleep/wake cycles assessed by parallel EEG and microdialysis in the rat.

Monoaminergic changes during sleep/wake cycles were investigated in the rostral hypothalamic areas since feeding, metabolism and sleep were shown to be causally related. Thus, the microdialysis probe was located stereotaxically in the ventromedial and paraventricular nuclei and cemented together with cortical electrodes for EEG sleep recordings. The monoaminergic changes were extensively investigated. Sampling of dialysates over six minutes in freely behaving rats showed an increase in 5-HT and its metabolite 5-HIAA during wakefulness. DOPAC rose during PS. The two other monoamines, DA and NA, remained unchanged. It appears that this method of investigation, extended in the future to other candidate areas and other dialysable substances, may provide us with a dynamic picture that characterizes the sleep/wake cycle.

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.

Active immunization against insulin affects sleep and feeding in rats.

The effects of active immunization against peripheral insulin on different sleep parameters and food consumption were studied in rats. Insulin coupled to thyroglobulin was used as immunogen and rats immunized with thyroglobulin alone served as controls. Active immunization against insulin is summarized as follows: (a) the number of arousals was reduced; (b) waking time decreased by about 20%; (c) slow wave sleep was increased; (d) The amount of sleep increased during the light and dark period; (e) feeding was decreased; (f) body weight was reduced; and (g) the blood glucose level rised. These results are compatible with previous studies showing positive correlation between decrease of insulin secretion, sleep disturbances and decrease of feeding. A possible association between peripheral insulin and brain noradrenergic system, sleep and feeding is suggested.

Nonamphetamine awakening agent modafinil induces feeding changes in the rat.

In rats, modafinil, an alpha1 adrenergic receptor dependent, that has been shown to increase wakefulness without subsequent rebound effect, decreases feeding and reduces body weight. However, modafinil does not show a monotonic dose-related decrease in food intake. The dose-response curve for modafinil is U-shaped; feeding decreases after doses of 20 and 40 mg/kg, but no effects were seen after doses of 10 and 80 mg/kg. When feeding is resumed, no compensatory effect is seen, and body weight remains lower during the 24-h session. The drinking-to-feeding ratio remains unchanged, showing that modafinil has no effect on water intake. These results are discussed with reference to the possible mechanisms underlying the relation between sleep, feeding, and metabolism.

Enhancement of slow wave sleep parallel to the satiating effect of acidic fibroblast growth factor in rats.

Male Wistar rats bearing both chronic cortical electrodes and ICV guide cannula were used. Acidic fibroblast growth factor (aFGF) or vehicle was injected in the lateral ventricle (20, 40, and 80 ng) while EEG and feeding patterns (via microbalance and a computerized monitor) were recorded. Forty and 80, but not 20, ng of aFGF brought about a significant reduction of feeding during 3 h and a dramatic increase of slow wave sleep during 6 h postinjection. Paradoxical sleep remained unchanged. Rectal temperature did not change. These concomitant effects of a single injection of aFGF on feeding and particularly on sleep are similar to the effect of a large meal on the same behavioral parameters.

Peripheral administration of bombesin increases metabolism in the rat.

Bombesin has been shown to decrease food intake and increase the duration of slow wave sleep, as well as to increase blood glucose and glucagon. A suspected mechanism of bombesin's anorexigenic and hypnogenic action could be via its possible effect on the enhancement of metabolism itself. Therefore, the effect of bombesin on rat metabolism was investigated in an open circuit computerized respirometer. This device was specifically conceived to extract the fraction of metabolism which is not due to the energy cost of muscular effort. This fraction of metabolism was designed background metabolism. In the absence of food, peripheral administration of bombesin increased the background metabolism at all doses. The higher dose of bombesin (32 micrograms/kg IP) elicited a four-hour enhancement of background metabolism, the magnitude of which was equivalent to that induced by a meal of about 1.5 grams. Therefore, it is suggested that the effect of bombesin on feeding and sleep could be achieved, at least partly, by its effect on the background metabolism, which ultimately may modulate the behavioral responses.

Effect of a highly selective central CCK-B receptor agonist: BC-264 on rat sleep.

The possible involvement of the CCK-B receptor type in the atypical somnolence and EEG changes induced by low doses of CCK-B was investigated by intraperitoneal administration of three different doses (8, 16 and 32 micrograms/kg) of the new highly potent and selective CCK-B agonist, BC-264, on sleep parameters in the fasted rat. At the dose of 8 micrograms/kg BC-264 induced a significant increase in waking in the second 120 min of recording without effect on slow wave sleep (SWS). BC-264 did not modify the others sleep parameters. Taken all together these results suggest that CCK-B type receptors are probably not critically involved in satiety and sleep.

Intraperitoneal cholecystokinin-8 induces atypical somnolence and EEG changes.

EEG sleep recordings were performed in rats after administration of CCK-8. Mildly food-deprived rats were given IP CCK-8 (8 and 16 micrograms/kg body weight) and behavioural as well as EEG changes were examined. With 16 micrograms/kg of CCK-8, there was a significant increase of slow wave sleep in the 30 min of recording. Paradoxical sleep was unchanged or slightly decreased. The low dose of CCK-8 did not promote sleep. In addition both doses of CCK-8 induced EEG alterations including the presence of unusual acute spikes and slowing of EEG rhythm concomitant with awake immobility in rats. The computerized spectral analysis showed that CCK-8 slowed the EEG-wave frequency without modifying the total power energy in comparison with control wakefulness. In contrast, there was no effect in alcuronium-immobilized rats after 8 to 32 micrograms/kg IP of CCK-8. These observations do not support the idea that CCK-8, as a satiating factor like food, would promote sleep.