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Sleep Regulation After Reduction of Brain Serotonin: Effect of p-Chlorophenylalanine Combined with Sleep Deprivation in the Rat
Abstract and Figures
Sleep was recorded in the rat after combined treatment with p-chlorophenylalanine (PCPA; 300 mg/kg) and 24-h sleep deprivation (SD) and then compared with sleep recorded after either treatment alone. PCPA alone reduced total sleep (TS), rapid eye movement sleep (REMS) per TS, as well as the power density of the EEG delta band (1.25-4.00 Hz) of non-REM sleep (NREMS). SD enhanced these sleep parameters and reduced the frequency of wake episodes. The combined treatment with PCPA and SD reduced TS and REMS/TS to a level similar to that induced by PCPA alone, and it increased delta activity to a level similar to that induced by SD alone. The frequency of wake episodes was reduced. It is concluded that essential aspects of sleep regulation are still functional during PCPA-induced insomnia. The sleep-inhibiting action of PCPA may be related to the hyperresponsiveness to stimuli rather than to the impairment of sleep regulation itself.
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... Serotonin (5HT), for example, has long been implicated in sleep drive [29], as its brain concentrations are highest in wakefulness and low in sleep, pharmacological blockade of 5HT2 receptors increases NREM SWA, and embryonic KO of the 5HT2c receptor increases the compensatory response to SDep [30]. On the other hand, it is not clear that 5HT is necessary and sufficient for sleep homeostasis because while brain depletion of 5HT (using p-chlorophenylalanine) combined with SDep reduces compensatory changes in sleep time [31], this has no effect on NREM SWA [32]. A relatively stronger case can be made for NA. ...
Astrocytes influence sleep expression and regulation, but the cellular signaling pathways involved in these processes are poorly defined. We proposed that astrocytes detect and integrate a neuronal signal that accumulates during wakefulness, thereby leading to increased sleep drive. Noradrenaline (NA) satisfies several criteria for a waking signal integrated by astrocytes. We therefore investigated the role of NA signaling in astrocytes in mammalian sleep. We conditionally knocked out (cKO) β2-adrenergic receptors (β2-AR) selectively in astrocytes in mice and recorded electroencephalographic and electromyographic activity under baseline conditions and in response to sleep deprivation (SDep). cKO of astroglial β2-ARs increased active phase siesta duration under baseline conditions and reduced homeostatic compensatory changes in sleep consolidation and non-rapid eye movement slow-wave activity (SWA) after SDep. Overall, astroglial NA β2-ARs influence mammalian sleep homeostasis in a manner consistent with our proposed model of neuronal–astroglial interactions.
... 14 Moreover, in rats subjected to combined treatment with PCPA and sleep deprivation, delta activity reached the same high levels as after deprivation alone, which tends to indicate that SWS-regulating mechanisms are not disrupted in PCPA-treated rats. 15 With regard to an alternative hypothesis, 16 there is no firm evidence to support the proposal that 5-HT released during W might act as a neurohormone and induce the synthesis and/or release of hypnogenic factors secondarily responsible for SWS and REM (rapid eye movement) sleep (REMS) occurrence. ...
... When sleep deprivation is combined with serotonin depletion in the cat, compensatory increases in deeper SWS states (where SWA is maximal) are diminished (Sallanon and others 1983). However, these results were not replicated in the rat (Tobler and Borbely 1982). ...
Electroencephalographic slow-wave activity (EEG SWA) is an electrophysiological signature of slow (0.5 to 4.0 Hz), synchronized, oscillatory neocortical activity. In healthy individuals, EEG SWA is maximally expressed during non-rapid-eye-movement (non-REM) sleep, and intensifies as a function of prior wake duration. Many of the cellular and network mechanisms generating EEG SWA have been identified, but a number of questions remain unanswered. For example, although EEG SWA is a marker of sleep need, its precise relationship with sleep homeostasis and its roles in the brain are unknown. In this review, the authors discuss their current understanding of the neural mechanisms and possible functions of EEG SWA.
Sleep is considered a naturally occurring reversible state of rest, which is accompanied by reduced voluntary activity and sensory perceptions. It is involved in the regulation of body physiology and cognitive functions. Earlier it was thought that sleep is generated as a consequence of a mechanical blockage in nerve conduction. This popular concept of that era was disregarded only in the late 1950s after the endorsement of von Economo’s findings of 1927 that insomnia and hypersomnia are caused in individuals with lesions in the anterior and posterior hypothalamus. Around the same time, “rapid eye movement sleep” was also discovered, which attracted several ingenious researchers toward the sleep field. Several studies between the early 1960s and late 1970s demonstrated that sleep was generated exclusively by sleep-associated neural circuits. We now know that the wake centers are located in the brainstem, midbrain, and basal forebrain; non-rapid eye movement (NREM) sleep centers are located in the anterior hypothalamus and rapid eye movement (REM) sleep centers are located in the brainstem. We now have a clear understanding of a large part of brain sleep–wake machinery, but, surprisingly, it took a long time to come to this point. Although our ancient traditional science had described some of the modern concepts of sleep, it somehow remained obscured before contemporary researchers provided scientific evidence. This chapter highlights the conceptual and historical aspects of sleep research and the events that led sleep researchers to believe that sleep is not a consequence but a vital physiological state.
Depression is often associated with disruption of the normal sleep cycle. In particular, though patients frequently show disturbances in sleep continuity and a reduction in slow wave sleep, the most commonly observed effects are a shortened latency to the first episode of rapid eye movement (REM) sleep after sleep onset (i.e., a reduced REM latency), and an increase in REM density in the first REM periods during the night (Kupfer, 1982). The administration of antidepressant drugs typically suppresses most measures of REM sleep (see Kupfer, 1982), and it is an issue of general interest whether there is a connection between the pharmacologies of REM suppression and of antidepressant treatment. Several of the antidepressants in past, current, and experimental use are active at serotonin (5HT) synapses. The antidepressant action of such drugs is commonly thought to be associated with their ability to enhance transmission across 5HT synapses (see Willner, 1985). If this is the case and if there is a connection between a drug’s effects on sleep and depression, then these agents should have predictable actions on sleep, as should other drugs that affect 5HT synaptic function. The purpose of this review is to evaluate this latter proposition. To this end, a discussion is presented of the effects that each of several classes of agents that modify 5HT transmission has on sleep in mammals. These are broadly classed as agents that decrease or increase synaptic transmission.
In an attempt to examine chronic effects of toluene on sleep, spontaneous locomotor activity and drinking behavior, rats were repeatedly administered toluene i.p. at doses of 100 and 200 mg/kg body weight for 14 consecutive days. The 200-mg/kg injections induced a decrease in total sleep on Day 1, an increase in locomotor activity on Days 1 through 4 and an increase in drinking activity on Days 0 through 6 after discontinuation of the daily injections. Both the reduced sleep and the increased locomotor activity appeared during the light period, whereas the drinking activity increased during the dark period. In order to find neurochemical correlates of the toluene-induced changes in behavior, regional concentrations of brain monoamines and their metabolites were determined. The toluene-induced partial insomnia and hyperactivity were associated with lowered concentrations of serotonin in frontal cortex, hippocampus and midbrain and 5-hydroxyindoleacetic acid in midbrain and hypothalamus. The increased drinking activity was associated with increased concentrations of striatal 3,4-dihydroxy-phenylacetic acid and homovanillic acid and hypothalamic noradrenaline and 3-methoxy-4-hydroxyphenylethyleneglycol. Central monoaminergic mechanisms were implicated in the toluene-induced partial insomnia, hyperactivity and hyperdipsia.
There are two main problems related to the neuropharmacology of sleep: Is it possible to induce physiological sleep, at will, and for a predetermined duration, with a drug in a normal intact animal? The answer to this question is still negative. Neither in animals nor in man do we have yet the right hypnogenic drug or the combination of drugs which will induce at any time and for any duration the delicate and harmonious succession of the different stages and states of sleep. However, neuropharmacology has allowed us to dissect some of the intimate mechanisms underlying the sleep-waking cycle since some drugs may suppress both states of sleep, or suppress paradoxical sleep (ps) selectively, or restore physiological sleep in an insomniac cat.
A rapid and sensitive method for measuring 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, using o-phthalaldehyde and L-cysteine, is presented, enabling both compounds to be measured in small areas of rat brain.
In general, many of the behavioral changes seen in animals injected with serotonin neurotoxic drugs are similar to those observed after other surgical, pharmacologic, or dietary manipulations of brain serotonergic neurotransmission. However, some of the behavioral alterations associated with these neurotoxins are not easily understood in light of other data, even though similar experimental protocols have often been employed. For example, even a cursory review of the literature reveals that the behavioral changes observed after chemical lesions of brain serotonin-containing neurons often differ from those associated with electrolytic lesions of these cells. Moreover, the behavior of animals injected with one of the serotonin neurotoxic drugs is frequently different from that of animals treated with other drugs in this group. To fully understand why these discrepancies occur, future studies will have to determine to what extent the neuroanatomic and neurochemical changes that follow treatment with neurotoxic drugs are similar to, or different from, those induced by other manipulations of brain serotonergic neurotransmission. For example, it no longer seems clear that electrolytic lesions of the median or dorsal raphe nuclei most likely damage ascending serotonergic nerves but leave serotonin-containing neurons that send axons and terminals into the spinal cord relatively intact. In contrast, intraventricular injections of the dihydroxytryptamine neurotoxins produce relatively greater damage to serotonin nerves that descend in the spinal cord rather than to those that ascend into forebrain regions. The authors know relatively little about the neurotoxic effects of the halogenated amphetamines (p-CA or fenfluramine), although some evidence indicates that these drugs may destroy a set of serotonergic nerves different from those that originate in the median or dorsal raphe nuclei. Thus, it is not terribly suprising to find that the behavioral effects of the various neurotoxic drugs are sometimes different from one another and often different from the changes in behavior observed after electrolytic brain lesions.
1.
The vigilance states (waking, rapid eye movement (REM) sleep, and non-REM (NREM) sleep), motor activity, food intake and water intake were continuously recorded by telemetry in unrestrained rats. In addition, an amplitude measure and a frequency measure (number of zero-crossings (ZCR) per 10 s) of the telemetered EEG-signal was obtained. The animals were recorded during a control day, then subjected to 12-h or 24-h sleep-deprivation (SD) by means of a slowly rotating cylinder, and subsequently recorded for further 1–2 days. The EEG-parameters were recorded also during SD.
2.
On the control day, the EEG-amplitude of NREM-sleep exhibited a decreasing trend in the 12-h light-phase (Figs. 3, 4). The occurence of slow wave sleep (SWS; defined as the NREM-sleep fraction with less than 40 ZCR/10 s) was practically limited to the first part of the light-phase (Figs. 2, 4). Cumulative plots of the zero-crossing bands (Fig. 2) revealed a prominent daily rhythm in the EEG-frequency distributionwithin NREM-sleep.
3.
The percentage of NREM-sleep and REM-sleep was little affected by the 12-h SD, but the amount of SWS and the EEG-amplitude of NREM-sleep were increased (Figs. 4, 6). After a 24-h SD period terminating before light-onset, NREM-sleep was reduced and REM-sleep was markedly enhanced (Figs. 4, 6; Table 1). Both the duration and frequency of REM-sleep episodes were increased, and episodes of total sleep prolonged (Table 2). The amount of SWS was significantly more increased after 24-h SD than after 12-h SD, whereas the EEG-amplitude of NREM-sleep was enhanced to a similar extent after both SD-schedules (Tables 1, 3 Fig. 6).
4.
After a 24-h SD period terminating before dark-onset, sleep (particularly REM-sleep) was enhanced in the first hours of the dark-phase, yet the usual high activity bouts prevailed in the later part of the dark-phase (Figs. 7, 8; Table 1). The extent and time-course of REM-sleep rebound was similar after the two 24-SD schedules, whereas SWS-rebound was different: SWS exhibited a one-stage rebound when recovery started in the light-phase, and a two-stage rebound when recovery started in the dark-phase (Fig. 9).
5.
A comparison of the effects of 12-h SD performed with the usual and with the double cylinder rotation rate, showed only small differences, indicating that forced locomotion was a minor factor in comparison to sleep-deprivation (Fig. 10; Table 1).
6.
The daily pattern of SWS on control days, and the marked increase of SWS after SD correspond to the results from other animal and human studies. It is proposed that due to the existence of an intensity dimension, NREM-sleep is finely regulated around its baseline level, and thus may be readily and accurately adjusted to current needs, whereas REM-sleep, lacking an apparent intensity gradient, is regulated around a level which is considerably below baseline. Thus, in contrast to NREM-sleep, REM-sleep compensation can occur only by an increase in the time devoted to this state, thereby curtailing the time available for other activities.
1.
The vigilance states (waking, slow wave sleep (SWS) and paradoxical sleep (PS)), motor activity, food intake and water consumption were continuously recorded by telemetry in unrestrained rats. The animals were maintained for 2 days under 12-h light–12-h dark conditions (LD 1212). Subsequently, the photoperiod was gradually extended by 1 h/day from 12 to 20 h, and restored to the original length for the last 2 days. In one group of animals the extension of the photoperiod was obtained by phase-advancing light-onset (La-group), in the other by phase-delaying dark-onset (Dd-group).
2.
During the LD 1212 control period, sleep, motor activity and food intake exhibited an asymmetric daily distribution. The percentages (Fig. 2) and episode durations (Fig. 4) of total sleep (TS) and slow wave sleep (SWS) were highest at the beginning of the light-phase and then exhibited a decreasing trend. The corresponding values for PS showed a slight increasing trend during the light-phase. A marked increasing trend during the light-phase was seen for PS expressed as the percentage of TS. Motor activity (Fig. 3) was minimal and food intake (Fig. 6) absent during the first half of the light-phase, increasing gradually during the second half. The daily minimum of sleep and the daily maximum of motor activity were situated at the end of the dark-phase.
3.
During the extension of the photoperiod the daily period of high activity and waking was shortened and remained largely restricted to the dark-phase (Figs. 7–9). Motor activity and food intake were more restricted to the dark-phase in the La-group than in the Dd-group. Throughout the experiment, the percentage of PS relative to TS remained lower at the beginning of the light-phase than towards its end, whereas the values for TS and SWS tended to show an inverse relationship (Figs. 9–11). After restoration of the original LD 1212 condition, the altered daily patterns of sleep and motor activity tended to persist.
4.
The daily pattern of sleep in the rat with the predominance of SWS in the early part of the rest period, and of PS in the late part, is strikingly similar to the distribution of sleep states in man. The difference in the daily rhythms of SWS and PS may reflect a phase-difference of two separate, and partly independent, circadian oscillators.
An identification system for the vigilance states of the rat is described which uses as inputs the cortical EEG, neck muscle EMG and motor activity, and which allows concomitant monitoring of feeding and drinking behaviour. State identification and data recording are performed in an on-line and an off-line stage which are designed to accommodate a large number of data for computer processing.
The article describes a miniature 2-channel FM-AM transmitter for recording EEG and EMG in unrestrained, small animals. Field changes during head movements yield a signal which can serve as a measure of motor activity.
The effect of p-chlorophenylalanine (PCPA) on the specific binding of 3H-serotonin (5-HT) was investigated in crude membrane preparations of the rat forebrain. The level of cerebral 5-HT and 5-hydroxyindoleacetic acid were concomitantly determined. A single dose of PCPA (300 mg/kg i.p.) increased specific binding at a low concentration of 3H-5-HT within 24 h by more than 100%. The timecourse of the elevation of specific binding was mirrored by the reduction in the 5-HT level. However, 8–10 days after drug administration, specific binding was close to the control level, while 5-HT was still significantly reduced. A Scatchard analysis revealed that the apparent affinity was significantly increased (k
D reduced) during the initial period after PCPA administration, whereas the number of binding sites (B
Max) was little changed. In contrast, after repeated injections of PCPA (3 injections of 300 mg/kg at 6–8 day intervals, or 100 mg/kg/day for up to 12 days) leading to a prolonged 5-HT depletion, B
Max was significantly increased, while k
D tended to be restored towards the baseline level. Daily injections of PCPA (100 mg/kg) for 12 days resulted in a transitory increase in day-time motor activity with a maximum on drug day 3, and in a persistent reduction of night-time activity. It is concluded that the initial PCPA-induced decrease in k
D was due to a reduced competition for binding sites by the endogenous 5-HT, whereas the increase of B
Max after a prolonged 5-HT depletion may reflect a 5-HT receptor supersensitivity.
Sleep parameters were monitored following (1) a single 2 g/kg oral dose of ethanol, (2) an oral dose of L-tryptophan (600 mg/kg), and (3) administration of both drugs simultaneously. Ethanol reduced REM and increased slow wave significantly. The effects of L-tryptophan were apparent only in the case of one parameter, REM latency. Administration of both drugs resulted in a significantly shorter REM latency than that observed for ethanol alone. Results are discussed in terms of possible changes in the biosynthesis of 5-HT.