NREM sleep with low-voltage EEG in the rat

On-line detection of sleep-wake states and application to produce intermittent hypoxia only in sleep in rats

Sleep-disordered breathing is associated with adverse clinical consequences such as daytime sleepiness and hypertension. The mechanisms behind these associations have been studied in animal models, especially rats, but intermittent stimuli such as hypoxia have been applied without reference to sleep-wake states. To determine mechanisms underlying the adverse physiological consequences of stimuli associated with sleep-disordered breathing requires criteria for detection of sleep-wake states on-line to trigger stimuli only in sleep. This study aimed to develop such a system for freely behaving rats. Twelve rats with implanted electroencephalogram and neck electromyogram electrodes were studied in the light and dark phases. Electroencephalogram frequencies in the high (20–30 Hz) and low (2–4 Hz) frequency bands distinguished non-rapid eye movement (REM) sleep, whereas neck electromyogram distinguished REM. Using these parameters in a simple algorithm led to detection accuracies of 94.5 ± 1.0 (SE) % for wakefulness, 96.2 ± 0.8% for non-REM sleep, and 92.3 ± 1.6% for REM compared with blinded human judgment. The algorithm was then used to trigger hypoxic stimuli only in sleep. Because frequency and amplitude analysis is readily performed using a variety of commercial systems, incorporation of these parameters into such an algorithm will facilitate studies investigating mechanisms underlying the physiological consequences of sleep-related respiratory stimuli in a fashion that more effectively models clinical disorders.

Rat sleep and eye movement density as biological markers of demyelinating disease

Myelin mutants provide an opportunity to study neurophysiological and behavioral effects of demyelination. The taiep rats are myelin mutants with progressive demyelination of the central nervous system (CNS), resulting in five neurological symptoms: tremor, ataxia, immobility, epilepsy, and paralysis. The demyelination affects the brainstem, an important area in the control of sleep. This study compared eye movement density (EMD) in taiep vs. normal control rats during paradoxical sleep (PS). It was hypothesized that taiep rats would have significantly reduced EMD during PS in comparison to normal controls due to their demyelinating disease. In addition, demyelination of brainstem structures would suggest possible changes in sleep-wake structure. Hence, we compared sleep-wake stages in taiep vs. normal, control rats. The results confirmed significantly reduced EMD during PS in taiep rats compared to normal rats during the 12-h (light) recording period. In addition, analysis of EMD values across the 12-h light period revealed significant differences in EMD values as a function of time of day in the taeip rats only. Comparison of waking and sleep values across the 12-h light phase revealed an "immobility episode" in three taiep rats, which was not present in normal controls. In addition, PS percentage was significantly lower and low-voltage sleep was significantly higher in taiep rats. These results suggest that EMD, immobility episodes, and sleep architecture may be useful as measurable biological events in the study of demyelinating disease. The results were discussed in terms of possible mechanisms underlying these differences, as well as possible implications for future studies.

Are neocortical gamma waves related to consciousness?

Previous research has shown that neocortical gamma waves (approximately 30-80 Hz) are continuously present during low voltage fast neocortical activity (LVFA) occurring during waking or active sleep. Gamma waves occur in a burst-suppression pattern in association with large amplitude slow waves during quiet sleep or anesthesia. The present experiments show that continuous gamma activity is also present in rats during LVFA occurring during surgical anesthesia (with ether, isoflurane or urethane) and that a burst-suppression pattern of gamma activity occurs during large amplitude slow waves occurring in the waking state either spontaneously in undrugged rats or as a result of treatment with parachlorophenylalanine and scopolamine. The amplitude of gamma activity occurring during anesthesia is variable but is often greater than it is in the normal waking state. It is concluded that the pattern of neocortical gamma wave activity is strongly related to the presence or absence of large amplitude slow waves but is quite independent of the state of behavioral arousal. Whether or not gamma wave activity is related to subjective awareness is a very difficult question which cannot be answered with certainty at the present time.

Diurnal variations and sleep deprivation-induced changes in rat hypothalamic GHRH and somatostatin contents

Previous reports indicate that hypothalamic growth hormone-releasing hormone (GHRH) promotes sleep and is involved in sleep regulation. The aim of our experiments was to determine whether the GHRH and somatostatin contents of the rat hypothalamus have diurnal variations and whether they are altered by sleep deprivation (SD). Hypothalamic samples were collected at 10 time points during the 24-h light-dark cycle. SD started at light onset. Hypothalamic samples were obtained after 4 and 8 h of SD and after 1 and 2 h of recovery following 8 h of SD. The peptides were determined by means of radioimmunoassay. GHRH displayed significant diurnal variations with low levels in the morning (a transient rise occurred at 1 h after light onset), gradual increases in the afternoon (peak at the end of the light period and beginning of the dark period), and decreases at night. SD induced significant GHRH depletion, which persisted during recovery. The afternoon rise was delayed, and the nocturnal decline of somatostatin was more rapid than the changes in GHRH. Although the patterns of the diurnal variations in GHRH and somatostatin were similar, there was no significant correlation between them. SD did not alter somatostatin significantly. Comparisons of the present results with previously reported changes in hypothalamic GHRH mRNA suggest that periods of deep nonrapid eye movement sleep (first portion of the light period and recovery sleep after SD) are associated with intense hypothalamic GHRH release.

EEG delta power during sleep in young and old rats

Delta EEG power density, which has been viewed as a measure of intensity of NREM sleep, declines across the lifetime in humans, cats, and hamsters, but data in rats have been unclear. It is also uncertain whether older rats differ from younger animals in the degree of change in delta power during recovery sleep following short-term sleep deprivation. We have examined delta power density in NREM sleep under baseline conditions and following 48 h of sleep deprivation in young (3 months), middle-aged (12 months), and older (24 months) rats. The presence or absence of age effects was highly dependent on the method of normalizing the data. When expressed as a fraction of total NREM EEG power, there was no age effect on baseline delta power density, or on the change from baseline to recovery conditions. When expressed as a multiple of delta power in REM under the same condition, the younger rats had higher delta power density than the middle-aged and older rats. For all the ages combined, there was an increase in delta power density in the recovery condition. When examined by age, the younger rats (which started from a higher level of delta power density than the other groups) did not have an increase in delta during recovery; the middle-aged rats tended to, and the older rats (which started from lower baseline levels) significantly increased delta power density in the recovery condition. This suggests that the lower delta power seen during baseline in older rats is not due to decreased ability to generate delta activity.

No evidence of brain cell degeneration after long-term sleep deprivation in rats

Sleep deprivation leads to cognitive impairments in humans and, if sustained for 2-3 weeks in rats, it is invariably fatal. It has been suggested that neural activity associated with waking, if it is not interrupted by periods of sleep, may damage brain cells through excitotoxic or oxidative mechanisms and eventually lead to cell death. To determine whether sustained waking causes brain cell degeneration, three parallel strategies were used. The presence and extent of DNA fragmentation was analyzed with the TUNEL technique on brain sections from rats sleep deprived for various periods of time (from 8 h to 14 days) and from their respective controls. Adjacent sections from the same animals were stained with a newly developed fluorochrome (Fluoro-Jade) specific for degenerating neurons. Finally, total RNA from the cerebral cortex of the same animals was used to determine whether the expression of several stress response genes and apoptosis-related genes is modified after sustained waking. In most long-term sleep deprived rats only a few scattered TUNEL positive nuclei (1-3) were found in any given brain section. The overall number, distribution, and morphology of TUNEL positive cells in long-term sleep deprived rats did not differ significantly from yoked controls, short-term sleep deprived rats, and sleep controls. No evidence of degenerating neurons as detected by Fluoro-Jade was found in any experimental group. mRNA levels of all the stress response genes and apoptosis-related genes tested did not differ between long-term sleep deprived rats and their yoked controls. These results argue against the hypothesis that sustained waking can significantly damage brain cells through excitotoxic or oxidative mechanisms and that massive cell death may explain the fatal consequences of sleep deprivation.

Automated sleep staging systems in rats

One of the major inconveniences encountered in sleep studies is the time consuming labor involved in equating visual analysis of physiological recordings (EEG, EMG, EOG, ...) to an appropriate state of vigilance. The explosion of computer technology is responsible for the emergence of several automated sleep-wake staging systems to supplement human analysis. Conversely to human sleep analysis, rat sleep is characterized by the absence of consensus about numerous elements constituting the sleep-wake staging systems used to build a hypnogram (recording position, length of epoch, number and definition of the vigilance state discriminated, ...). If justified, the choices of the parameters involved by each system generally result from various viewpoints (physiology, mathematics, electronics, ...). The diversity generated by the liberty offered the investigator in building a system excludes any rigorous comparison between systems. Nevertheless, this variety can also be viewed as a representative of the effervescence of research in the field of sleep, and as a catalyst for new ideas.

Physiological properties of raphe magnus neurons during sleep and waking

Neurons in the medullary raphe magnus (RM) that are important in the descending modulation of nociceptive transmission are classified by their response to noxious tail heat as ON, OFF, or NEUTRAL cells. Experiments in anesthetized animals demonstrate that RM ON cells facilitate and OFF cells inhibit nociceptive transmission. Yet little is known of the physiology of these cells in the unanesthetized animal. The first aim of the present experiments was to determine whether cells with ON- and OFF-like responses to noxious heat exist in the unanesthetized rat. Second, to determine if RM cells have state-dependent discharge, the activity of RM neurons was recorded during waking and sleeping states. Noxious heat applied during waking and slow wave sleep excited one group of cells (ON-U) in unanesthetized rats. Other cells were inhibited by noxious heat (OFF-U) applied during waking and slow wave sleep states in unanesthetized rats. NEUTRAL-U cells did not respond to noxious thermal stimulation applied during either slow wave sleep or waking. ON-U and OFF-U cells were more likely to respond to noxious heat during slow wave sleep than during waking and were least likely to respond when the animal was eating or drinking. Although RM cells rarely respond to innocuous stimulation applied during anesthesia, ON-U and OFF-U cells were excited and inhibited, respectively, by innocuous somatosensory stimulation in the unanesthetized rat. The spontaneous activity of >90% of the RM neurons recorded in the unanesthetized rat was influenced by behavioral state. OFF-U cells discharged sporadically during waking but were continuously active during slow wave sleep. By contrast, ON-U and NEUTRAL-U cells discharged in bursts during waking and either ceased to discharge entirely or discharged at a low rate during slow wave sleep. We suggest that OFF cell discharge functions to suppress pain-evoked reactions during sleep, whereas ON cell discharge facilitates pain-evoked responses during waking.

Changes in sleep and wakefulness following 5-HT1A ligands given systemically and locally in different brain regions

Serotonin (5-HT) has been implicated in the regulation of vigilance, but whether 5-HT is important for sleep or waking processes remains controversial. This review addresses the role of 5-HT1A receptors in sleep and wakefulness. Systemic administration of 5-HT1A agonists consistently increases wakefulness, whereas slow wave sleep (SWS) and REM (rapid-eye movement) sleep are reduced. However, systemic 5-HT1A agonists also produce a delayed increase in deep slow wave sleep, or an increase in slow wave activity. Intrathecal administration of a selective 5-HT1A agonist produces an increase in SWS, whereas wakefulness is reduced, presumably by stimulating 5-HT1A receptors located presynaptically on primary afferents in the spinal cord. Microinjection of serotonin into the region of the cholinergic basalis neurons produces an increase in slow wave activity, presumably by stimulating 5-HT1A receptors. Microdialysis perfusion of a selective 5-HT1A agonist into the dorsal Raphe nucleus causes an increase in REM sleep, whereas the other sleep/wake stages are unaltered. The REM sleep increase is likely due to a decrease in 5-HT neuronal activity, and thereby reduced 5-HT neurotransmission in projection areas, e.g. the laterodorsal and pedunculopontine tegmental nuclei. Direct injection of a selective 5-HT1A agonist into the pedunculopontine tegmental nuclei reduces REM sleep, consistent with such a hypothesis. These complex sleep/wake data of 5-HT1A ligands suggest that 5-HT1A receptor activation may increase waking, increase slow wave sleep or increase REM sleep depending on where the 5-HT1A receptors are located within the central nervous system.

The superior colliculus-pretectum mediates the direct effects of light on sleep

Light and dark have immediate effects on sleep and wakefulness in mammals, but the neural mechanisms underlying these effects are poorly understood. Lesions of the visual cortex or the superior colliculus-pretectal area were performed in albino rats to determine retinorecipient areas that mediate the effects of light on behavior, including rapid eye movement sleep triggering by lights-off and redistribution of non-rapid eye movement sleep in short light-dark cycles. Acute responses to changes in light conditions were virtually eliminated by superior colliculus-pretectal area lesions but not by visual cortex lesions. Circadian entrainment was evident in both groups with lesions and in normal controls. Thus, acute light-dark effects on sleep and wakefulness appear to be mediated independently from cortical vision or circadian rhythms.

Enhancement of behavioral and electroencephalographic indices of waking following stimulation of noradrenergic beta-receptors within the medial septal region of the basal forebrain

Previous studies in halothane-anesthetized rat documented potent electroencephalographic (EEG) modulatory actions of the locus coeruleus (LC) noradrenergic system, with LC neuronal activity causally related to the maintenance of EEG activity patterns associated with enhanced arousal/alertness. Recent studies, also in halothane-anesthetized rat, demonstrated that the region of the basal forebrain encompassing the medial septum/vertical limb of the diagonal band of Broca (MS) is a site at which noradrenergic efferents act to influence EEG state via actions at beta-receptors. These and other observations are consistent with the hypothesis that the LC noradrenergic system participates in the modulation of behavioral state. However, the degree to which this system modulates EEG state in the absence of anesthesia and to what extent such actions are accompanied by behavioral modulatory actions remain to be determined. The current studies examined whether small infusions of isoproterenol (ISO), a beta-adrenergic agonist, into MS alter behavioral, EEG, and electromyographic (EMG) measures of sleep and waking in the resting, undisturbed rat. These infusions resulted in a significant increase in time spent awake, defined by both behavioral and EEG/EMG measures, and in the nearly complete suppression of REM sleep. EEG/EMG responses either coincided with or preceded behavioral responses by 10-320 sec. The pattern of behavioral responses observed following MS-ISO infusions was qualitatively similar to that associated with normal waking. Infusions of vehicle into MS or ISO into sites adjacent to MS did not elicit consistent alterations in behavioral state. These results suggest that the LC noradrenergic system exerts potent behavioral and EEG-activating effects via actions of norepinephrine at beta-receptors located within MS.

Effects of neonatally administered iprindole on adult behaviors of rats

In past studies, administration of the antidepressant drugs clorimipramine, zimeldine, or desipramine to neonatal rats produced abnormalities in adult rats that modeled some behavioral and/or REM sleep features of human endogenous depression. Although these three drugs affected different neurotransmitter systems, all caused REM sleep deprivation (RSD). This suggested the hypothesis that RSD of neonatal rats caused their adult depression. One prediction of this hypothesis is that neonatally administered iprindole, an antidepressant drug that does not produce RSD, will not produce adult rats that model depression. The present study tested this hypothesis. Iprindole was administered to neonatal experimental rats and saline was administered to neonatal control rats. When the rats matured, compared with control rats, experimental rats were not significantly different in aggressive behavior (shock induced fighting), sexual behaviors, open field locomotion, and REM sleep. In our previous studies on rats, all these adult behaviors were affected in a depressive-like way by neonatally administered clorimipramine. Because iprindole does not decrease REM sleep, the present results support the hypothesis that in rats neonatal RSD causes adult depression.

Sleep deprivation in rats with preoptic/anterior hypothalamic lesions

Chronic total sleep deprivation (TSD) of rats by the disk-over-water method reliably produces initial increases and subsequent decreases in waking intraperitoneal (Tip) and hypothalamic (Thy) temperatures, progressive increases in energy expenditure, skin lesions on the tail and plantar surfaces, debilitated appearance, and eventual death. We investigated the possible role of the preoptic/anterior hypothalamus (POAH) in the mediation of the TSD effects by comparing these effects in POAH-lesioned and unlesioned rats. Bilateral POAH lesions sufficient in size to impair homeothermic responses to changes in ambient temperature did not produce TSD-like temperature changes under baseline ambient temperatures of 28-29 degrees C, implying that the thermoregulatory changes produced by TSD do not result from impairment of the lesioned area. However, the possibility remains that the TSD effects are mediated by damage to POAH areas that were not lesioned. During TSD, lesioned and unlesioned rats showed similar progressive increases in energy expenditure, but the lesioned rats showed earlier, steeper, and eventually greater declines in Tip and Thy. This result suggests that in unlesioned rats the POAH may counter-regulate against, and thereby attenuate, the reduction in heat retention caused by TSD. This failure of regulation in lesioned rats is consistent with their impaired response to ambient temperature change and implies that, in unlesioned rats, some POAH thermoregulatory mechanisms continue to function normally during TSD. Lesioned rats did not show the characteristic TSD-induced early increases in Tip and Thy. This result could imply either that heat retention was so compromised that body temperatures did not rise in spite of a TSD-induced increases in thermoregulatory setpoint, or that the setpoint increase in unlesioned rats is POAH-mediated. Notwithstanding the greater Tip and Thy declines in lesioned rats, they survived the TSD procedure longer than the unlesioned rats, thus supporting previous indications that death did not result from hypothermia.

Brain temperature- and behavior-related changes in the dentate gyrus field potential during sleep, cold water immersion, radiant heating, and urethane anesthesia

The field potential evoked in the dentate gyrus (DG) by stimulation of the perforant path (PP) is known to vary with ongoing behavior and with brain temperature. To further study these phenomena chronic stimulating and recording electrodes were implanted into the PP and DG of rats, and a thermistor was implanted into the contralateral homotopic DG. Field potentials and brain temperature records were made during (1) slow wave sleep (SWS), (2) radiant heating, (3) immersion in cool water, (4) a control session during which no manipulations were made, and (5) under urethane anesthesia. In another group of rats field potentials were recorded during (1) baseline immobile wakefulness, (2) SWS, (3) before SWS or after gentle awakening from SWS (eyes open and presence of intermittent slow waves in the EEG), (4) immobile wakefulness, and (5) 24 h later. Findings were that field EPSP slope decreased and population spike (PS) amplitude increased by up to 60% of baseline values during conditions in which brain temperature was reduced (SWS, immersion in cool water, urethane anesthesia). Conversely, EPSP slope increased and PS amplitude decreased by up to 100% of baseline values during conditions in which brain temperature increased (awakening from SWS, radiant heating, and warming after immersion in cool water or urethane anesthesia). Product moment correlations between brain temperature and field potential measures confirmed the statistical reliability of these findings and accounted for up to 77% of the variance. These findings confirm the robust effect on hippocampal field potentials of brain temperature changes due to exogenous heating and cooling, and extend this effect to anesthetic- and sleep-induced brain temperature changes. They also identify a state that behaviorally resembles quiet wakefulness but resembles SWS in terms of neocortical EEG, brain temperature, and hippocampal field potential measures. The findings indicate the need to control for brain temperature-mediated changes in hippocampal research that uses the dentate gyrus field potential as a dependent measure.

Administration of human chorionic gonadotropin affects sleep-wake phases and other associated behaviors in cycling female rats

We investigated the possible effects of human chorionic gonadotropin (hCG) on sleep-wake phases and other associated behaviors controlled by the medial preoptic area, cerebral cortex and hippocampus. Chronic epidural electroencephalographic (EEG) and temporal muscle electromyographic (EMG) electrodes were placed in cycling female rats. After a week of recovery, rats were injected intraperitoneally at 3.00 pm on the day of proestrus with either saline or highly purified hCG or indomethacin or hCG plus indomethacin. Three hours after injection, EEG, EMG and behavioral activities were recorded for 3.5 h. The administration of hCG increased high and low amplitude sleep, resting phase and decreased active awake phase, walking, sniffing and chewing as compared to the controls. While the administration of indomethacin alone had no effect, coadministration inhibited hCG effects. Medial preoptic area, cerebral cortex and hippocampus contain immunostaining for LH/hCG receptors. The administration of hCG resulted in an increase of immunoreactive PGD2 and a decrease of PGE2 in median preoptic area, cerebral cortex and hippocampus as compared to the controls. In summary, hCG administration affects sleep-wake phases and other associated behaviors in rats which can collectively be described as decreased activity. These effects are probably mediated by increasing PGD2 and decreasing PGE2 in areas of brain which control these activities. The above findings may be relevant to pregnant women who experience decreased activity when hCG is present in the circulation and cerebrospinal fluid.

Effects of chronic sleep deprivation on central cholinergic receptors in rat brain

Rats subjected to chronic total sleep deprivation (TSD) by the disk-over-water method have shown very large, sustained rebounds in paradoxical sleep (PS) (also known as REM sleep). Other studies have indicated that cholinergic mechanisms are involved in the instigation and maintenance of PS. Hypothetically, the large PS rebounds could be mediated by an upregulation of cholinergic receptors during TSD. To evaluate this hypothesis, regional brain cholinergic receptors were compared in rats subjected to 10-day TSD by the disk-over-water method (TSD rats), yoked control (TSC) rats which received the same physical stimulation but with much smaller reductions in sleep, and home cage control (HCC) rats. L-[3H]nicotine and [3H]quinuclidinyl benzilate were used as specific cholinergic radioligands for nicotinic and muscarinic receptor binding assays, respectively. Nicotinic receptor binding was not significantly different among groups for any of the brain regions assayed, including frontal cortex, parietal cortex, thalamus, amygdala, hippocampus, anterior hypothalamus, posterior hypothalamus, caudate, limbic system (including septal area, olfactory tubercle, and nucleus accumbens), midbrain, pons, and medulla. Thus, there was no evidence that changes in nicotinic receptors mediate the PS rebounds. For muscarinic receptor binding, TSD rats differed significantly from control rats only in showing a higher binding affinity than TSC rats in the limbic system and a lower binding density than HCC rats in the hippocampus. On the other hand, significant differences in muscarinic receptor binding sites between rats selectively deprived of PS and their yoked controls were found only for the septal area.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure to induce rapid eye movement sleep by dark pulses in pigmented inbred rat strains

Studies of albino Lewis rats, pigmented Brown Norway rats, and their F2 backcross progeny have demonstrated that the ability to trigger rapid eye movement (REM) sleep by turning off cage lights (dark pulses) is associated with albinism in these rat strains. Other studies have shown that pigmented inbred rats show REM sleep induction in the dark portion of short light:dark cycles or skin temperature changes. In the present study, these same pigmented breeds, Dark Agouti and hooded Long-Evans rats, were subjected to 5-min dark pulses and failed to show any evidence of REM sleep triggering. In fact, they showed trends towards REM sleep suppression during dark pulses. These results extend the finding that dark pulse triggering of REM sleep, readily evoked in albino rats, does not appear in pigmented rat strains.

Effects of chronic total sleep deprivation on central noradrenergic receptors in rat brain

The effect of chronic total sleep deprivation (TSD) on the regulation of central noradrenergic receptors was evaluated. Rats were subjected to 10 days of TSD by the disk-over-water method. As in previous TSD studies, these rats showed greater increases in food intake and energy expenditure and greater eventual declines in waking body temperature than their yoked-control (TSC) rats. After sacrifice, alpha 1-, alpha 2-, and beta-adrenoceptors were determined in 11 brain regions using radioligand binding assays with [3H]prazosin, [3H]rauwolscine, and 125I-iodocyanopindolol, respectively. Adrenoceptor density and affinity values were significantly different among TSD, TSC, and normally caged control rat groups only for the cerebellum, which showed higher alpha 2-binding density concomitant with lower affinity and lower beta-binding density than cage control rats. Such changes are attributable to apparatus or stimulus effects common to TSD and TSC rats. Given the absence of firm evidence for a TSD-induced downregulation of central noradrenergic receptors, the present results offer no support for the hypothesis of Siegel and Rogawski that a major function of paradoxical sleep is to upregulate these receptors.

Sleep deficits in rats after NMDA receptor blockade

N-Methyl-D-aspartate (NMDA) receptor blockade disrupts a variety of functions associated with neural plasticity, including acquisition of learned responses and long-term potentiation. Deficits in memory are significantly correlated with deficits in measures of paradoxical sleep in several amnesic populations. The present experiment therefore assessed whether NPC 12626, a competitive NMDA receptor antagonist, also disrupts sleep. NPC 12626 (1, 10, 50, and 100 mg/kg) or saline was administered to Sprague-Dawley rats 30 min prior to 3-h daytime recording periods. Paradoxical sleep was selectively impaired at all but the highest dose, which prevented all sleep during the recording period. Some deficits in nonparadoxical sleep first appeared at the 10 mg/kg dose but did not became prominent until the 50 mg/kg dose. The results thus show that NPC 12626 impairs sleep states in rats and demonstrate that paradoxical sleep is particularly susceptible to the effects of NMDA receptor blockade. These findings, along with previous evidence that NMDA antagonists impair waking measures of arousal, provide evidence that all sleep-wake states are impaired by NMDA receptor blockade. More generally, the results suggest that some brain mechanisms underlying sleep and memory may share common elements.

Heritability of dark pulse triggering of paradoxical sleep in rats

A previous study showed that albino Lewis (L) rats could be triggered into paradoxical sleep (PS) by dark pulse stimulation, i.e., turning off cage lights, whereas brown Norway (BN) rats showed no evidence of PS triggering by dark pulses (2). The transmission of the PS triggering behavior was studied in L x [L x BN]F1 hybrid backcross (BC) animals. Albino BC rats increased PS% during 5-minute dark pulses to three times the average PS% for the preceding 5 minutes of lights-on. In contrast, no significant PS triggering was observed in pigmented BC rats. These data support the hypothesis that PS triggering by dark pulse stimulation is related to albinism in these rat strains. The absence of a connection between PS triggering and total daily amounts of PS suggests independent genetic transmission of these two parameters.

The electrocorticogram in relation to physiology and behavior: a new analysis

Recent research in animals indicates that the generalized regulation of cortical activity that is represented by activation of the electrocorticogram is dependent on ascending cholinergic and serotonergic projections. The effect of the activity of these systems is correlated with concurrent motor activity in a detailed and specific manner. Combined blockade of central cholinergic and serotonergic function results in impaired cerebral control of behavior, i.e., a dementia-like syndrome. Previous concepts, which held that electrocortical activation is mediated via a reticulo-thalamo-cortical pathway and that it is related primarily to arousal, vigilance, and the sleep-waking cycle appear to be incomplete or erroneous.

Diurnal variation in continuous measures of the rat EEG power spectra

EEG measures that vary on a continuous scale, without separating behavior into discrete states, may complement sleep staging as a means of characterizing diurnal variation in level of arousal. The object of the present study was to evaluate diurnal variation in the EEG power spectrum averaged independently of sleep state, and to determine which parameters best reflect this variation. The EEG from rats maintained with chronic cortical electrodes was continuously digitized at 256 Hz, and power spectra computed by fast Fourier transformation every four seconds. Artifact-free spectra occurring over one-hour periods were averaged. Spectral edge, calculated from 66 percent of the area of spectra, and relative power in delta and theta band-widths derived from averaged spectra vary in a consistent and highly significant diurnal pattern. The trend of relative delta power over the daytime, inactive period (when sleep occurs in nocturnal rodents) resembles that seen in human subjects during sleep, with peak levels occurring at the onset, followed by a steady decline during remaining hours of the daytime rest period.

Rat strain differences in response to dark pulse triggering of paradoxical sleep

Previous studies of inbred rats have shown that Brown Norway (BN) rats had more daily paradoxical sleep (PS) than Lewis (L) rats, while F1 progeny had intermediate amounts, suggesting codominant or polygenic transmission. Amount of PS and the induction of PS episodes may be under separate genetic control. Earlier work had shown that five-minute exposures to cage lights-off every half-hour can trigger PS in outbred albino strains. To explore the genetic controls for PS induction, PS triggering by dark pulse stimulation was examined in L and BN rats. L rats showed a five-fold increase in PS during dark pulse stimulation. Although, as in the earlier study, BN rats had more total daily PS than L rats, they exhibited no dark pulse triggering of PS. Thus L and BN rats show significant strain differences in two independent parameters of PS, and may be a useful model for studying genetic and neurologic factors which regulate PS.

Sensitivity of EEG in young rats to toluene exposure

Effects of toluene on the electroencephalogram (EEG) and its power spectra were measured during a 2-hr exposure in a dynamic inhalational chamber in young rats (30-53 days old) and compared to those in adult rats (63-77 days old). Rats were exposed to one of the three concentrations [low (108-111 ppm), medium (160-163 ppm), and high (407-432 ppm)] of toluene on different days. In tests on sleep-wake cycle, in the young animals the duration of the wake stage (W) was increased with decreases of rapid eye movement (REM) and non-REM (NREM) sleep during hr 1 and hr 2 of exposure to the low concentration. These effects were marked at the medium and the high concentrations. In adult rats, at the low concentration the increase of W and the decrease of REM were observed only at hr 1; however, at medium and high concentrations these changes of W and REM sleep were marked along with a decrease of NREM. Comparison of the changes of duration of different states in rats of two age groups showed that there was a significant difference in the increase of W and the decrease of NREM sleep in young rats at hr 2 of exposure to low concentrations only compared to those in adult rats. Tested on power spectrum in young rats during REM sleep recorded from the visual cortex, the power of delta waves increased at the medium and high concentrations and that of theta wave decreased at the high concentration during hr 2 of exposure compared to the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

REM sleep abnormalities in a new animal model of endogenous depression

Endogenous depression has reliable REM sleep abnormalities. These include a short REM latency, frequent sleep onset REM periods, and after REM sleep deprivation (RSD), an abnormal temporal course of REM rebound in the presence of a normal total REM rebound. The reliability of these abnormalities suggests that they ought to be present in an animal model of endogenous depression. In 1982, we proposed a new animal model of endogenous depression. Our hypothesis is that in rats neonatal clomipramine (CLI) will produce adult animals that model endogenous depression. In this study we tested the prediction that after neonatal treatment with CLI, adult rats will show the above three REM sleep abnormalities of human endogenous depression. We found that neonatal treatment with CLI produced rats that at age 6 months had shorter REM latency, more sleep onset REM periods than control rats, and after RSD, had an abnormal temporal course of REM rebound in the presence of a normal total REM rebound. The finding of these REM sleep abnormalities supported the validity of the animal model of endogenous depression.

A large scale, high resolution, automated system for rat sleep staging. I. Methodology and technical aspects

An automatic rat sleep classification system is described which records and analyses bioelectrical signals from 32 rats over extended periods of time. At present this system is used routinely for the screening of drug effects on sleep. The analysis is based on 3 signals, the parieto-occipital EEG, nuchal EMG and a movement indicator signal. The on-line analysis is done per epoch of 2 sec and involves power spectral analysis of the EEG and rectification and integration of the EMG and movement signals. The automatic sleep staging into 6 stages (active and quiet waking; quiet, deep, pre-REM and REM sleep) is performed off-line. Parameters derived from a discriminant analysis of visually scored tracings of individual rats constitute the basis for the automatic scoring procedure. The movement index is used to discriminate between active and quiet waking, while the use of the EMG level improves the separation of waking and REM sleep. After the construction of hypnograms from these computer scorings a set of parameters can be extracted which characterizes the sleep-waking behavior of each individual rat. These parameters are then used to compare statistically the 2-4 treatment groups which make up each experiment of 32 rats. Experimental validation of the system is reported in an accompanying paper.

Distributed computer system for capture, analysis and display of biological data

A distributed real-time computer system has been developed to automate the collection, analysis and display of biological (pharmacological) data. It comprises a series of laboratory interface devices (CED 1401/1609) connected to a micro-VAX II via multiple IEEE-488 buses. The micro-VAX II is integrated to the main site computers using Ethernet running DECnet. The micro-VAX II system supports a multi-user, multipreparation and multitasking environment and it provides rapid transfer, storage, analysis and display of data. The system saves the pharmacologists from the manual analysis of their data, typically saving them four days of analysis per experiment and has improved both the quality of data detected and their subsequent analysis. Also, the development of a standard data capture procedure on common hardware along with the modular design of application software has almost quartered project development times.

Differential effects of acetylsalicylic acid and acetaminophen on sleep abnormalities in a rat chronic pain model

We studied the effects of two non-steroidal anti-inflammatory analgesics (NSAIAs), acetylsalicylic acid (ASA) and acetaminophen, on sleep patterns in rats with adjuvant-induced arthritis. We found that in the normal rat both NSAIAs reduced non-rapid eye movement (NREM) sleep. In arthritic rats ASA and acetaminophen had opposite effects on sleep. ASA increased wakefulness and decreased all sleep stages and acetaminophen decreased wakefulness and increased NREM sleep and paradoxical sleep during the light hours (the hours of maximal sleep in the normal rat). When the effects of severity of arthritis were factored out, both drugs still had large and significant effects on sleep and wakefulness. Thus, two prostaglandin synthetase inhibitors showed differential effects on sleep and wakefulness in the normal rat and in rats experiencing chronic pain. Although ASA is important in the treatment of pain in rheumatic diseases, it may contribute to abnormal sleep patterns.

Variations in period-analysed EEG asymmetry in REM and NREM sleep

Monopolar EEG was recorded from lateral frontal and parietal sites with linked ear reference during sleep in 24 adults. Electrode placement followed the 10-20 International system. EEG was quantified using digital period analyses. The absolute difference in interhemispheric EEG parameters was compared for Stage 2, REM, and a slow wave sleep measure. The absolute difference measures reflect the degree of symmetry or asymmetry, regardless of the hemisphere of origin. Theta and delta activity in slow wave sleep was more asymmetrical than in either Stage 2 or REM. REM sleep was associated with the smallest asymmetries. These results do not support a right hemisphere REM, left hemisphere NREM relationship. Rather they suggest that REM sleep is associated with relative hemispheric symmetry whereas asymmetries are most prominent in slow wave sleep. Stage 2 sleep was significantly less asymmetrical than slow wave on a number of theta and delta measures. The significant differences between slow wave and Stage 2 sleep may denote functional differences within NREM sleep stages.

Effects of toluene exposure on the spontaneous cortical activity in rats

Effects of toluene on the electroencephalogram (EEG) and its power spectra were measured during a 2-hr exposure in a dynamic inhalational chamber in rats. Rats were exposed to one of six graded concentrations (110.6, 162.5, 432, 676, 1558, 2730 ppm) of toluene on different days. It was found that the duration of waking (W) was increased with a decrease in duration of rapid eye movement (REM) sleep even at 110.6 ppm. Duration of nonrapid eye movement (NREM) sleep was decreased with an increase of W and a decrease of REM sleep at 162.5 ppm. Dose-related effects were noted in higher concentrations. The power of delta frequency band was increased with a decrease of theta frequency band power at hr 1 of exposure to 676 ppm during REM sleep recorded from the visual cortex. The power of theta frequency band was also decreased at hr 2 of exposure at 432 ppm. During W and NREM sleep power spectra were not changed significantly. Results indicate that the changes of EEG are a sensitive measure of the effects of toluene on the central nervous system (CNS).

Sleep fragmentation in the arthritic rat

We examined the diurnal sleep-wake patterns in the adjuvant arthritic rat. In contrast to control rats, arthritic rats lacked a normal diurnal variation in sleep and wakefulness. Thus, arthritic rats exhibited no differences in the mean number or duration of bouts of sleep and episodes of wakefulness between light and dark hours. Arthritic rats also had a marked increase in the fragmentation of their sleep manifested by an increased number of sleep bouts and episodes of wakefulness and a decrease in the duration of episodes of deep sleep recorded both during the time of maximal sleep (08.00-11.00 h) and of maximal wakefulness (20.00-23.00 h). The possibility that the experience of chronic pain causes these marked changes in sleep patterns in the arthritic rat is discussed.