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A meta-analysis was conducted to review the prevalence and associated moderators of depression or depressive symptoms in patients with narcolepsy. An extensive search of the literature yielded 1104 articles and abstracts, of which 31 studies were included in the meta-analysis. Meta-analysis revealed that the overall pooled prevalence of depression or depressive symptoms in patients with narcolepsy was 32% (95% Confidence Interval, 28–36%) with high between-study heterogeneity (Q = 249.77, df = 30, p

Fear conditioning associated with inescapable shock training (ST) and fearful context re-exposure (CR) alone can produce significant behavioral fear, a stress response and alterations in subsequent REM sleep. These alterations may vary among animals and are mediated by the basolateral nucleus of the amygdala (BLA). Here, we used the GABAA agonist, muscimol (Mus), to inactivate BLA prior to CR and examined the effects on sleep, freezing and stress-induced hyperthermia (SIH). Wistar rats (n=28) were implanted with electrodes for recording sleep, data loggers for recording core body temperature, and with cannulae aimed bilaterally into BLA. After recovery, the animals were habituated to the injection procedure and baseline sleep was recorded. On experimental day 1, rats received ST (20 footshocks, 0.8mA, 0.5s duration, 60s interstimulus interval). On experimental day 7, the rats received microinjections (0.5ul) into BLA of either Mus (1.0uM; n = 13) or vehicle (Veh; n = 15) prior to CR (CR1). On experimental day 21, the animals experienced a second CR (CR2) without Mus. For analysis, the rats were separated into 4 groups: (Veh-vulnerable (Veh-Vul; n=8), Veh-resilient (Veh-Res; n=7), Mus-vulnerable (Mus-Vul; n=7), and Mus-resilient (Mus-Res; n=6)) based on whether or not REM was decreased, compared to baseline, during the first 4 h following ST. Pre-CR1 inactivation of BLA did not alter freezing or SIH, but did block the reduction in REM in the Mus-Vul group compared to the Veh-Vul group. These data indicate that BLA is an important region for mediating the effects of fearful memories on sleep.

Intense stress has the potential to produce traumatic memories that are core features of chronic mental disorders. However, encountering even intense stress most often does not have a persisting negative impact on health. Stress outcomes appear to involve complex interactions of sleep, learning, stressor qualities, and individual differences in resilience and vulnerability. This chapter will discuss how these interactions can impact the formation of traumatic memories, with a focus on factors that can differentially lead to normal and pathological stress outcomes. It will discuss the potential roles of different types of learning, stress resilience and vulnerability, and the neurobiological substrates that regulate interactions of stress, sleep, and the formation of traumatic memories. A case will be made that, given its role in learning and the processing of emotion, sleep may be key to fully understanding normal and pathological outcomes of intense stress.

Study objectives To examine the REM sleep response to stress and fearful memories as a potential marker of stress resilience and vulnerability and to assess the role of the basolateral amygdala (BLA) in mediating the effects of fear memory on sleep. Methods Outbred Wistar rats were surgically implanted with electrodes for recording EEG and EMG and with bilateral guide cannulae directed at the BLA. Data loggers were placed intraperitoneally to record core body temperature. After recovery from surgery, the rats received shock training (ST: 20 footshocks, 0.8 mA, 0.5-s duration, 60-s interstimulus interval) and afterwards received microinjections of the GABAA agonist muscimol (MUS; 1.0 μM) to inactivate BLA or microinjections of vehicle (VEH) alone. Subsequently, the rats were separated into 4 groups (VEH-vulnerable (VEH-Vul; n = 14), VEH-resilient (VEH-Res; n = 13), MUS-vulnerable (MUS-Vul; n = 8), and MUS-resilient (MUS-Res; n = 11) based on whether or not REM was decreased, compared to baseline, during the first 4 h following ST. We then compared sleep, freezing, and the stress response (stress-induced hyperthermia, SIH) across groups to determine the effects of ST and fearful context re-exposure alone (CTX). Results REM was significantly reduced on the ST day in both VEH-Vul and MUS-Vul rats; however, post-ST MUS blocked the reduction in REM on the CTX day in the MUS-Vul group. The VEH-Res and MUS-Res rats showed similar levels of REM on both ST and CTX days. The effects of post-ST inactivation of BLA on freezing and SIH were minimal. Conclusions Outbred Wistar rats can show significant individual differences in the effects of stress on REM that are mediated by BLA. These differences in REM can be independent of behavioral fear and the peripheral stress response, and may be an important biomarker of stress resilience and vulnerability.

Fear conditioning alters sleep, with the most consistent effect being significant reductions in rapid eye movement sleep (REM). DBA/2 (D2) mice show behavioral signs of anxiety, respond greater to shock training, and potentially behave differently in cued and contextual fear, raising the question of how fear conditioning would affect their sleep. D2 mice were implanted to record sleep via telemetry. After baseline sleep recording, groups of D2 mice were trained in cued (15 tone–shock pairings) and contextual (15 non-cued shocks) fear on 4 consecutive days. Cue and context control mice were given identical training but were never presented with shock. Sleep was recorded after shock training and after presentation of cue or context alone. Shock training produced selective suppression of REM. On the day after shock training was completed, light period sleep was significantly altered in mice in the cued fear group, but not in the contextual fear group. Subsequent presentation of fearful cues and re-exposure to the fearful contexts also produced significant reductions in REM. The effects of fear conditioning on sleep in D2 mice and other mouse strains and the differential effects of cued and contextual fear on sleep are discussed.

Study objectives Contextual fear is followed by significant reductions in rapid eye movement sleep (REM) that are regulated by the central nucleus of the amygdala (CNA). Corticotropin-releasing factor (CRF) plays a major role in regulating the stress response as well as arousal, and CRF in CNA is implicated in stress-related behavior. To test the hypothesis that CRF regulation of CNA is involved in fear-induced alterations in REM, we determined the effects of microinjections into CNA of the CRF1 antagonist, antalarmin (ANT) on fear-induced reductions in REM. We also evaluated c-Fos activation in the hypothalamic paraventricular nucleus (PVN), locus coeruleus (LC), and dorsal raphe nucleus (DRN) to determine whether activation of these regions was consistent with their roles in regulating stress and in the control of REM. Design On separate days, rats were subjected to baseline and 2 shock training sessions (S1 and S2). Five days later, the rats received bilateral microinjections of ANT (4.8 mM) or vehicle (VEH) prior to exposure to the fearful context. Sleep was recorded for 20 h in each condition. Freezing was assessed during S1, S2, and context. Separate groups of rats received identical training and microinjections or handling control (HC) only, but were sacrificed 2 h after context exposure to assess c-Fos expression. Setting NA. Patients or participants NA. Interventions NA. Measurements and results Compared to baseline, S1 and S2 significantly reduced REM. Exposure to the fearful context reduced REM in VEH treated rats, whereas REM in ANT treated rats did not differ from baseline. ANT did not significantly alter freezing. Fear-induced c-Fos expression was decreased in PVN and LC after ANT compared to VEH. Conclusions The results demonstrate that CRF receptors in CNA are involved in fear-induced reductions in REM and neural activation (as indicated by c-Fos) in stress and REM regulatory regions, but not in fear-induced freezing.

Contextual fear significantly reduces rapid eye movement sleep (REM) during post-exposure sleep in mice and rats. Corticotropin releasing factor (CRF) plays a major role in CNS responses to stressors. We examined the influence of CRF and astressin (AST), a non-specific CRF antagonist, on sleep after contextual fear in BALB/c mice. Male mice were implanted with transmitters for recording sleep via telemetry and with a guide cannula aimed into the lateral ventricle. Recordings for vehicle and handling control were obtained after ICV microinjection of saline (SAL) followed by exposure to a novel chamber. Afterwards, the mice were subjected to shock training (20 trials, 0.5 mA, 0.5 s duration) for 2 sessions. After training, separate groups of mice received ICV microinjections of SAL (0.2 microl, n=9), CRF (0.4 microg, n=8), or AST (1.0 microg, n=8) prior to exposure to the shock context alone. Sleep was then recorded for 20 hours (8-hour light and 12-hour dark period). Compared to handling control, contextual fear significantly decreased REM during the 8-h light period in mice receiving SAL and in mice receiving CRF, but not in the mice receiving AST. Mice receiving CRF exhibited reductions in REM during the 12-h dark period after contextual fear, whereas mice receiving SAL or AST did not. CRF also reduced non-REM (NREM) delta (slow wave) amplitude in the EEG. Only mice receiving SAL prior to contextual fear exhibited significant reductions in NREM and total sleep. These findings demonstrate a role for the central CRF system in regulating alterations in sleep induced by contextual fear.

Learning and memory play an important role in morphine addiction. Status epilepticus (SE) can impair the spatial and emotional learning and memory. However, little is known about the effects of SE on morphine-induced conditioned place preference (CPP). The present study was designed to investigate the effects of SE on morphine CPP, with food CPP being used as a control. The effects of SE on spatial memory in the Morris water maze (MWM) and Y-maze were investigated. SE was induced in adult mice using intraperitoneal injection of pentylenetetrazole; control mice received saline. The data indicated that SE had no effects on the formation of morphine CPP; however, the formation of food CPP was blocked by SE. Meanwhile, spatial memory assayed in the MWM and Y-maze was impaired by SE. In addition, the data demonstrated that SE did not cause a lasting disturbance of motor activity nor a change in the mice's appetite. These results suggested that although SE had no effects on morphine CPP, there was impaired food CPP and spatial memory in both the MWM and the Y-maze. The mechanisms underlying memory process of morphine CPP may be different from other types of memory.

Sleep mechanisms and synaptic plasticity are thought to interact to regulate homeostasis and memory formation. However, the influences of molecules that mediate synaptic plasticity on sleep are not well understood. In this study we demonstrate that mice lacking Rab3 interacting molecule 1 alpha (RIM1 alpha) (Rim1 alpha KO), a protein of the synaptic active zone required for certain types of synaptic plasticity and learning, had 53+/-5% less baseline rapid eye movement (REM) sleep compared with their wild type littermates. Also, compared with wild type littermates, exposure of the mice to an open field or to a novel object induced more robust and longer lasting locomotion suggesting altered habituation. This difference in exploratory behavior correlated with genotype specific changes in REM and deregulated release of norepinephrine in the cortex and basal amygdala of the Rim1 alpha KO mice. Also, moderate sleep deprivation (4 h), a test of the homeostatic sleep response, induced REM sleep rebound with different time course in Rim1 alpha KO and their wild type littermates. As norepinephrine plays an important role in regulating arousal and REM sleep, our data suggest that noradrenergic deficiency in Rim1 alpha KO animals impacts exploratory behavior and sleep regulation and contributes to impairments in learning.

Corticotropin releasing hormone (CRH) plays a major role in central nervous system responses to stressors and has been implicated in stress-induced alterations in sleep. In the absence of stressors, CRH contributes to the regulation of spontaneous waking. We examined the effects of CRH and astressin (AST), a non-specific CRH antagonist, on wakefulness and sleep in two mouse strains with differential responsiveness to stress to determine whether CRH might also differentially affect undisturbed sleep and activity. Less reactive C57BL/6J (n=7) and high reactive BALB/cJ (n=7) male mice were implanted with a transmitter for determining sleep via telemetry and with a guide cannula aimed into a lateral ventricle. After recovery from surgery and habituation to handling, ICV microinjections of CRH (0.04, 0.2, and 0.4 microg), AST (0.1, 0.4, and 1.0 microg) or vehicle alone (pyrogen-free saline, 0.2 microl) were administered during the fourth hour after lights on and sleep was recorded for the subsequent 8 h. Comparisons of wakefulness and sleep were conducted across conditions and across strains. In C57BL/6J mice, REM was significantly decreased after microinjections of CRH (0.2 microg) and CRH (0.4 microg), and NREM and total sleep were decreased after microinjections of CRH (0.4 microg). CRH (0.04 microg) and AST did not significantly change wakefulness or sleep. In BALB/cJ mice, CRH (0.4 microg) increased wakefulness and decreased NREM, REM and total sleep. AST decreased active wakefulness and significantly increased REM at the low and high dosages. These findings demonstrate that CRH produces changes in arousal when given to otherwise undisturbed mice. Strain differences in the effects of CRH and AST may be linked to the relative responsiveness of C57BL/6J and BALB/cJ mice to stressors and to underlying differences in the CRH system.

Study objective To determine sleep and EEG spectra in rats during surgical recovery. Design Sleep, activity, and EEG spectral power were examined in rats via telemetry on days 1, 2, 3, 7, 14, and 15 after implantation surgery. Results NREM sleep and total sleep were increased on days 1 and 2 compared to later days. REM sleep was decreased on days 2 and 3 compared to days 14 and 15, and activity was decreased on days 1 and 2 compared to later days. EEG power (0.5-5 Hz for NREM and wakefulness, and 5.5-10 Hz for REM and wakefulness) was increased on days 1-3 compared to days 7, 14, and 15. Conclusion The results are discussed in terms of their implications for post-surgery stabilization of sleep and potential relevance for sleep after injury.

We examined individual differences in sleep and motor activity across two consecutive days in rats. EEG and motor activity were recorded via telemetry in Wistar rats (n=29) for 48 h under well-habituated conditions. Rats were grouped based on sleep amounts and stability across days (short [SS, n=7], intermediate [IS, n=15] and long [LS, n=7] sleep) and comparisons were conducted to determine group differences for measures of sleep and motor activity. We found that correlations across recording days were significant for all selected sleep measures and motor activity counts. Rankings for 24 h total sleep time and non-rapid eye movement sleep (NREM) were SS < IS < LS rats whereas amounts of rapid eye movement sleep did not differ among groups. Further analyses of NREM episode parameters found significant differences in mean episode length (SS < IS < LS) but not in the number of episodes. Total and average motor activity counts (per waking min) were greater (32-38%) in SS compared to LS rats on both recording days. The results indicate that individual differences in sleep and motor activity in Wistar rats are stable across days. Differences between SS and LS rats have parallels to those reported for short and long sleep humans.

Corticotropin releasing factor (CRF) is a major mediator of central nervous system responses to stressors, including alterations in wakefulness and sleep. However, its role in mediating stress-induced alterations in sleep has not been fully delineated. In this study, we assessed the role of CRF and the non-specific CRF antagonist, astressin (AST), in regulating changes in sleep produced by signaled, escapable shock (SES) and signaled inescapable shock (SIS), two stressors that can increase or decrease sleep, respectively. Male BALB/cJ mice were surgically implanted with transmitters (DataSciences ETA10-F20) for recording EEG, activity and core body temperature by telemetry and a cannula for intracerebroventricular (ICV) microinjections. After baseline (Base) sleep recording, mice were presented tones (90 dB, 2 kHz) that started 5.0 s prior to and co-terminated with footshock (0.5 mA; 5.0 s maximum duration). SES mice (n = 9) always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. Yoked SIS mice (n = 9) were treated identically, but could not alter shock duration. Training with SES or SIS was conducted over 2 days to stabilize responses. Afterwards, the mice received saline, CRF [0.4 μg (0.42 mM) or AST (1.0 μg (1.4 mM)] prior to SES or SIS. Sleep was analyzed over 20 h post-stress recordings. After administration of saline, REM was significantly greater in SES mice than in SIS mice whereas after CRF or AST, REM was similar in both groups. Total 20 h NREM did not vary across condition or group. However, after administration of saline and CRF, NREM episode duration was significantly decreased, and NREM episode number significantly increased, in SIS mice compared to SES animals. SES and SIS mice showed similar stress induced hyperthermia (SIH) across all conditions. These data demonstrate that CRF can mediate stress-induced changes in sleep independently of SIH, an index of hypothalamic-pituitary-adrenal axis activation.

Change in the sleeping environment can produce significant alterations in sleep. To determine how these alterations may vary with the amount of change and the relative reactivity of the sleeper, we examined the influences of environmental novelty on sleep in two mouse strains that differ in behavioral anxiety. Mice [BALB/cJ (n=7) and C57BL/6J (n=8)] were implanted for recording EEG and activity via telemetry. Following baseline data collection, activity and sleep were examined over 46 h after routine cage change, after placing a simple novel object (PVC Tee) in the home cage, and after handling controls. Mice of both strains showed immediate increases in activity and decreases in rapid eye movement sleep (REM) and non-REM (NREM) after cage change and novel object. Within strain, changes in activity and sleep were greater after cage change than after novel object. Changes in activity and sleep time were significantly correlated in each strain. Compared to C57BL/6J mice, BALB/cJ mice exhibited greater and longer duration initial reductions in sleep time, and greater increases in EEG slow wave activity power after cage change and novel object, but these changes were not followed with subsequent increases in sleep time. In contrast, C57BL/6J mice showed significantly greater subsequent increases in sleep time following the initial reductions induced by both manipulations. The results suggest that initial decreases and subsequent increases in sleep time are related to putative differences in the intensity of environmental novelty (cage change>novel object) and to previously described strain differences in anxiety (BALB/cJ>C57BL/6J).

The open field (OF) is thought to induce anxiety in rodents. It also allows an opportunity for exploration in a novel environment. Less activity in the OF is thought to indicate greater anxiety whereas more activity may reflect greater exploration, and possibly greater exploratory learning. Anxiety and learning have poorly understood relationships to sleep. In order to determine how anxiety and exploration in the OF could influence sleep, we recorded sleep in mouse strains (C57BL/6J (B6), BALB/cJ (C), DBA/2J (D2), and CB6F1/J (CB6)) with different levels of anxiety and exploration after 30 min in an OF. In all strains, OF exposure induced immediate decreases in rapid eye movement sleep (REM) followed by longer latency increases in REM. The time course and amount of REM decreases and increases varied among strains. Compared to less anxious B6, D2 and CB6 mice, C mice had greater and longer lasting immediate decreases in REM. C mice also displayed longer periods of decreases REM and a smaller, longer latency increase in REM. OF exploratory activity was positively correlated to percentage of REM increases from 6 to 10 h after OF exposure. The results suggest that the anxiogenic component of the OF produced an immediate decrease in REM that was greater in more “anxious” mice. In contrast, exploration in the OF was associated with increased REM, with the increase greater in less anxious mice. The results are discussed with respect to the potential influences of anxiety and learning on sleep.

Serotonin [5-hydroxytryptamine (5-HT)] plays an inhibitory role in rapid-eye-movement (REM) sleep although the exact mechanism(s) and site(s) of action are not known. It is commonly assumed that 5-HT exerts its influence on REM sleep via input from the dorsal raphe nucleus (DRN) directly onto cholinergic neurons involved in the generation of REM sleep. 5-HT 2 receptor sites have been found on cholinergic neurons in the laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT). We locally microinjected the 5-HT 2 agonist DOI ((±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl) and the 5-HT 2 antagonist, ketanserin, in LDT in rats to determine whether these receptor sites are involved in the regulation of behavioral states. DOI and ketanserin primarily affected REM sleep, by significantly decreasing or increasing, respectively, the number, but not the duration, of REM sleep episodes. DOI specifically decreased the occurrence of clusters of REM sleep episodes appearing at intervals less than or equal to 3 min (sequential episodes) without affecting single episodes separated by more than 3 min. An opposite effect of ketanserin on REM sleep clusters, although not statistically significant, was observed.

In fear conditioning, shock training (ST) and shock-associated fearful cues (FC) produce relatively selective decreases in rapid eye movement sleep (REM) in mice that vary with strain, and can last for an extended period. We examined sleep in BALB/cJ mice over 6 h after ST and FC, and in handling and tone control conditions. In separate groups of mice, we used immunohistochemical techniques to examine Fos expression in limbic and brainstem regions involved in fear conditioning and in the regulation of REM in 2-h intervals over this period. Significant reductions in REM were observed at 2 and 4 h after ST. Fos expression in the brainstem was significantly elevated at 2 h after ST in the laterodorsal and peduculopontine tegmentum, up to 4 h in the dorsal raphe nucleus (DRN) and up to 6 h in the locus coeruleus (LC). Significant elevations in Fos expression were observed in several regions of the amygdala up to 4 and 6 h after ST. Decreases in REM after FC were significant at 2 h. Increased Fos expression was observed in LC at 2 h and in DRN up to 6 h after FC. Increased Fos expression in the amygdala was observed in several regions of the amygdala at 2 h after FC, but not longer. Significant changes in Fos expression in the central nucleus of the amygdala were not observed at any time point examined or in any condition. The data are discussed with respect to the putative role of brainstem nuclei in regulating REM and the role of the amygdala in conditioned fear.

Study Objectives: This study assessed the influence of contextual fear on sleep in inbred and hybrid mouse strains. Design: Uninterrupted baseline recordings of sleep were obtained for 3 days in 3 mouse strains. After baseline sleep recording sessions, fear-conditioned mice were presented 15 shock presentations on 4 consecutive days. Control mice were subjected to the same procedures except that they never received shock. Sleep was examined after shock training and after exposure to the shock context alone. Settings: N/A Participants: The subjects were mice of 2 inbred (C57BL16J [B6], N=15; BALB/cJ [C], N=19) strains and 1 hybrid (CB6F1/J [CB6: C x B6], N=17) strain. Interventions: Electroencephalograms (EEG) and activity were recorded by telemetry, and behavioral states were visually scored based on EEG and motor activity records. Measurements and Results: Shock training selectively reduced rapid eye movement (REM) sleep in mice compared to time-matched baseline recordings. The reduction of REM sleep was significantly greater in the reactive C and the F1 hybrid strain compared to the less reactive B6 strain. Posttraining exposure to the context alone reduced REM sleep in much the same manner as exposure to the footshock, with the CB6 hybrid mice exhibiting greater alterations in sleep and a greater reduction of REM sleep. In contrast, mice that did not receive shock training showed increased REM sleep after being returned to the chamber. Conclusion: Aversive events and the fearful contexts that become associated with them can alter sleep in much the same way. Sleep disruptions after an aversive event or its reminders vary with genetic background.

Fear conditioning is thought to model anticipatory anxiety. Inbred mouse strains exhibit different levels of reactivity to aversive environmental stimuli, which may reflect anxiety. We examined the effects of fear conditioning on sleep in mouse strains that differ on behavioral measures of anxiety. Mice (BALB/cJ [C], C57BL/6J [B6], CB6F1/J [CB6], n = 7-10 per strain) were implanted with transmitters for recording sleep by telemetry. Baseline sleep was recorded, and the mice were trained to associate a cue (tone) with footshock (15 cue-shock pairings on 4 consecutive days). Sleep was recorded after shock training and again 4 to 5 days later after presentation of the cue alone. Shock training produced a relatively selective suppression of rapid eye movement sleep (REM) that was greater in the C strain compared to the B6 and CB6 mice. Post-training exposure to the cue alone suppressed REM in all strains. The C strain exhibited a relatively greater immediate suppression of REM, and the CB6 hybrid mice showed the greatest overall suppression of REM. These data demonstrate that stimuli associated with an aversive event can alter sleep and suppress REM in much the same way as exposure to the event itself. Fear conditioning may provide a model for examining genetic and neural mechanisms underlying the influence of anxiety on sleep.

Locomotor activity is a key component in many behavioral tests, suggesting that genetic differences in activity levels may be a critical consideration when comparing mouse strains. In order to assess the relationship between activity and performance, we recorded home cage activity, and locomotion and defecation, a non-activity-linked behavior, in tests of anxiety in inbred (C57BL/6J (B6), n = 25; BALB/cJ (C), n = 24; DBA/2J (D2), n = 28) and hybrid (CB6F1/6J (CB6: B6 x C) n = 19) mice. Under our test conditions, the strains showed significant differences in home cage activity levels: C > B6 > D2. The CB6 mice were similar to the B6 mice in horizontal activity and were intermediate between the parental strains in vertical movement. Based on measures of locomotion and defecation in the open field, emergence and novel object tests, and the elevated zero maze, the C mice appeared to be the most anxious and the B6 were the least anxious. The D2 mice were intermediate on some measures but more similar to B6 mice on others, making ranking them more difficult. In addition, the CB6 mice displayed characteristics of both parental strains. They had greater similarity to B6 mice in measures of horizontal movement in the home cage and locomotion in the open field and emergence tests, but exhibited defecation responses similar to those of C mice in the novel object test and elevated zero maze. The results suggest that strain differences in spontaneous locomotion should be considered when interpreting strain differences in behavioral tests, and that home cage activity may be a useful interpretive aid.

Study objectives This study assessed differences in spontaneous sleep and locomotor activity in inbred and hybrid mouse strains and evaluated telemetry for recording sleep in mice. Design Uninterrupted recordings of sleep and home cage activity were obtained in four mouse strains. Pre-operative and post-operative home cage activity was obtained in two strains. Settings N/A PARTICIPANTS: The subjects were mice of three inbred (C57BL/6J (B6), n=25; BALB/cJ (C), n=24; DBA/2J (D2), n=30) strains and one hybrid (CB6F1/J (CB6: C x B6), n=19) strain. Interventions Electroencephalogram (EEG) and activity were recorded by telemetry, and behavioral states were visually scored based on EEG and activity records. Home cage activity was determined utilizing photobeam interruptions. Measurements and results 1) Among the three inbred strains: C mice had the least sleep and the greatest amount of activity; D2 mice exhibited the least non-rapid-eye-movement (NREM) sleep, the longest average NREM-bout length, and the greatest diurnal ratio of sleep and were the most inactive; B6 mice had the most sleep and an intermediate activity level; no differences among inbred strains were observed in total REM. The CB6 mice exhibited intermediate levels of total sleep and activity and had greater amounts of REM compared to its parental strains. 2) Total operative mortality was 9.3%, with all deaths occurring within 3 to 9 days after the operation; significant reductions in activity were observed after the operation. Conclusion Differences in spontaneous sleep and activity exist among inbred and hybrid mouse strains. Accurate determination of sleep states in mice can be achieved with telemetrically recorded EEG and activity.

Modafinil, a novel non-amphetamine stimulant recently approved for the treatment of narcolepsy, has been shown to increase waking in both animals and humans. However, its mechanism of action is currently unknown. Earlier research into the brain structures responsible for the wake-producing actions of modafinil implicated the central nucleus of the amygdala (ACe) as a possible site of action [Neuroscience 87 (1998) 905-911; Neurosci. Lett. 241 (1998) 95-98]. The present experiments were designed to test the hypothesis that the ACe is, at least in part, involved in the wake-producing actions of modafinil. In the first experiment, rats with lesions of the ACe were injected systemically with varying doses of modafinil and sleep was recorded. At the highest dose, modafinil significantly increased waking and decreased sleep. However, there was no interaction between the lesion and the effect of the drug. In the second experiment, varying doses of modafinil were injected directly into the ACe and sleep was recorded. Injection of modafinil into the ACe did not affect sleep architecture. Thus, ACe does not play a simple role in modafinil's wake-promoting action. We suggest that more complex testing will be required to elucidate its role.

Significant differences in many aspects of sleep/wake activity among inbred strains of mice suggest genetic influences on the control of sleep. A number of genetic techniques, including transgenesis, random and targeted mutagenesis, and analysis of quantitative trait loci may be used to identify genetic loci. To take full advantage of these genetic approaches in mice, a com- prehensive and robust description of behavioral states has been developed. An existing automated sleep scoring algorithm, designed for sleep analysis in rats, has been examined for acceptability in the analysis of baseline sleep structure and the response to sleep deprivation in mice. This algorithm was validated in three inbred strains (C57BL/6J, C3HeB/FeJ, 129X1/SvJ) and one hybrid line (C57BL/6J X C3HeB/FeJ). Overall accuracy rates for behavioral state detection (mean±SE) using this system in mice were: waking, 98.8%±0.4; NREM sleep, 97.1%±0.5; and REM sleep, 89.7%±1.4. Characterization of sleep has been extended to include measurements of sleep consolidation and fragmentation, REM sleep latency, and delta density decline with sleep. An exper- imental protocol is suggested for acquiring baseline sleep data for genetic studies. This sleep recording protocol, scoring, and anal- ysis system is designed to facilitate the understanding of genetic basis of sleep structure.

Background: Hyperarousal in posttraumatic stress disorder (PTSD) is manifested during sleep as well as waking. Elevated rapid eye movement sleep (REMS) phasic activity, likely signifying central nervous system alerting, has been identified in PTSD. The authors reasoned that PTSD compared to control subjects would show particularly increased REMS phasic activity on the first night of polysomnography, with adaptation to a novel environment. Methods: First-night polysomnograms of 17 veterans with PTSD were compared with those of 11 control subjects. Sleep was also studied in subsets of both groups over two nights. Results: On the first night, the PTSD subjects had a higher density of rapid eye movements in the first REMS period. This measure was increased on the first compared to the second night, but there was no interaction effect between night and group. Conclusions: REMS changes are again demonstrated in veterans with PTSD. Introduction to a novel environment activated a REMS phasic process, but not differentially in PTSD compared to control subjects.

In contrast to the many neural studies into the mechanisms of sleep onset and maintenance, few studies have focused specifically on awakening from sleep. However, the abrupt electrographic changes and large brief cardio-respiratory activation at awakening suggest that a distinct, transiently aroused, awake state may exist compared to later wakefulness. To test this hypothesis we utilized the acoustic startle reflex, a standard un-conditioned reflex elicited by a sudden loud noise. This reflex is modulated under specific conditions, one being a diminution of startle when a quieter pre-stimulus is presented immediately before the loud stimulus. This pre-pulse inhibition (PPI) is used as a measure of sensorimotor gating, with smaller PPI indicating less filtering of sensory inputs and increased responsiveness to external stimuli. Eight rats with electrodes for recording sleep-wake state were studied. An accelerometer measured startle responses. The startle reflex was elicited by 115 dB, 40 ms tones. PPI was produced by 74 dB, 20 ms tones preceding the 115 dB tone by 100 ms. Responses within 100 ms were measured. Stimuli were applied either 3-10 s after spontaneous awakenings, or in established wakefulness (30 s). Responses to the startle stimuli alone were similar in the different awake states (P = 0.821). However, PPI was smaller at awakening from non-REM sleep compared to established wakefulness (45.4 +/- 7.5% vs. 74.3 +/- 6.1%, P = 0.0002). PPI after awakening from REM sleep (52.8 +/- 17.9%) was not significantly different than established wakefulness (P = 0.297). Reduced PPI of the startle reflex at awakening from non-REM sleep supports the hypothesis that wakefulness immediately after spontaneous sleep episodes is neurophysiologically distinct from later wakefulness and associated with reduced gating of motor responses to sensory inputs. Spontaneous activation of this distinct, transiently aroused, state upon awakening may serve a protective function, preparing an animal to respond immediately to potentially threatening stimuli.

Fear conditioning [inescapable shock training (ST)] and fearful context re-exposure (CR) alone can produce significant fear indicated by increased freezing and reductions in subsequent rapid eye movement (REM) sleep. Damage to or inactivation of the basolateral nucleus of the amygdala (BLA) prior to or after ST or prior to CR generally has been found to attenuate freezing in the shock training context. However, no one has examined the impact of BLA inactivation on fear-induced changes in sleep. Here, we used the GABAA agonist, muscimol (MUS), to inactivate BLA prior to ST, the period when fear is learned, and assessed sleep after ST and sleep and freezing after two CR sessions. Wistar rats (n = 14) were implanted with electrodes for recording sleep and with cannulae aimed bilaterally into BLA. After recovery, the animals were habituated to the injection procedure (handling) over 2 consecutive days and baseline sleep following handling was recorded. On experimental day 1, the rats were injected (0.5 μl) into BLA with either MUS (1.0 μM; n = 7) or vehicle (distilled water, n = 7) 30 min prior to ST (20 footshocks, 0.8 mA, 0.5-s duration, 60-s interstimulus interval). On experimental days 7 and 21, the animals experienced CR (CR1 and CR2, respectively) alone. Electroencephalogram and electromyogram were recorded for 8 h on each day, and the recording was scored for non-rapid eye movement sleep, REM sleep, and wakefulness. Freezing was examined during CR1 and CR2. MUS microinjections into BLA prior to ST blocked the post-training reduction in REM sleep seen in vehicle-treated rats. Furthermore, in MUS-treated rats, REM sleep after CR1 and CR2 was at baseline levels and freezing was significantly attenuated. Thus, BLA inactivation prior to ST blocks the effects of footshock stress on sleep and reduces fear memory, as indicated by the lack of freezing and changes in sleep after CR. These data indicate that BLA is an important regulator of stress-induced alterations in sleep and an important site for forming fear memories that can alter sleep.

Study objective To determine whether corticotropin-releasing factor (CRF) in the basolateral amygdala (BLA) modulated sleep and fear-conditioned alterations in sleep. Design After 2 days of habituation to recording procedures, baseline sleep recordings were obtained. The animals were then habituated to the handling procedure necessary for microinjections over 2 consecutive days. In experiment 1, rats received microinjections of 0.5 μL antalarmin (1.61 or 4.82 mM), a CRF receptor 1 antagonist, or distilled water once a week for 3 wk. In experiment 2, rats received a microinjection of either antalarmin or vehicle prior to inescapable shock training (ST; 20 shocks; 0.8 mA, 0.5 sec; 1 min interstimulus interval). The animals were placed back in the context 7 days later for 30 min without shock (CR; context re-exposure). Sleep was recorded for 8 h after each manipulation. Setting NA. Subjects Outbred Wistar rats. Interventions The rats were surgically implanted with electrodes for recording the electroencephalogram and electromyogram for determining arousal state and with bilateral guide cannulae directed at BLA. Measurements and results Antalarmin microinjected into BLA did not significantly alter sleep under undisturbed conditions. However, antalarmin microinjected bilaterally into BLA prior to ST blocked reductions in rapid eye movement sleep that ST normally produces. Further, the single microinjection prior to ST blocked the reduction in rapid eye movement typically seen after subsequent CR. Behavioral freezing, an indicator of fear memory, was not altered. Conclusions CRF in BLA is involved in regulating stress-induced alterations in sleep and it plays a role in modulating how stressful memories influence sleep.

Study Objectives: Controllable stress, modeled by escapable shock (ES), can produce significant alterations in post-stress sleep, including increased rapid eye movement (REM) sleep. Recent work has demonstrated that post-stress sleep may be influenced by stressor predictability, modeled by predictive auditory cues. In this study, we trained mice with ES, either signaled (SES) or unsignaled (UES) by auditory cues, and investigated the effects of predictability on escape learning and sleep associated with ES. Design: Adult male BALB/cJ mice were implanted for recording electroencephalography and activity via telemetry. After the mice recovered from surgery, baseline sleep recordings were obtained. The mice were then randomly assigned to SES and UES conditions. Both groups had control over the duration of footshocks (0.5 mA; 5.0 sec maximum duration) by moving to the non-occupied chamber in a shuttlebox. SES mice were presented tones (90 dB, 2 kHz, 10 sec maximum duration) that started 5.0 sec prior to and co-terminated with footshocks. UES mice were presented identical tones that were not synchronized to shock presentation. ES training continued for 2 consecutive days (EST1 and EST2) with 20 footshock presentations (1 min inter-stimulus intervals). Seven days after EST2, the animals were re-exposed to the training chamber (context) alone for 30 min. Measurements and Results: Escape latency was used to determine successful or unsuccessful escape learning. Sleep was scored for 20 h for baseline and on each treatment day. Freezing in the training context was scored as a behavioral index of fear. Nine of 14 SES mice successfully learned escape (SESl), and 5 failed to learn escape (SESf). Compared with baseline, SESl mice, but not SESf mice, showed significantly increased post-shock REM. All UES mice learned escape and showed enhanced post-shock REM. Freezing and sleep did not differ among groups on the context re-exposure day. Conclusions: The results indicate that information available in a stressful situation can affect an animal's ability to learn an appropriate response and post-stress sleep.

The acute administration of drugs that block norepinephrine (NE) reuptake suppresses rapid eye movement (REM) sleep in cats and other mammals. The mechanism is presumed to involve NE acting on cells in a pontine REM sleep-generator region. Postsynaptic noradrenergic receptor mechanisms have not been identified. In the present experiments, we tested the ability of the alpha-1 antagonist prazosin and the beta antagonist propranolol to reverse the REM sleep suppression produced by the NE reuptake blocker desipramine (DMI) in the cat. DMI reduced the number of REM sleep episodes, the REM percentage (REM sleep time/total sleep time), and the average REM sleep episode duration. The co-administration of prazosin, but not propranolol, increased the REM percentage and the average REM sleep episode duration toward the placebo level. The co-administration of the peripherally-acting, anti-hypertensive agent hydralazine did not reverse the DMI-induced REM sleep suppression. While the identity of the brain region(s) involved in mediating the alpha-1 noradrenergic suppression of REM sleep by DMI remains unclear, there is reason to consider forebrain structures including the amygdala as well as the pontine areas that generally have been implicated in REM sleep control.

Stress can have a significant negative impact on health and stress-induced alterations in sleep are implicated in both human sleep disorders and in psychiatric disorders in which sleep is affected. We have demonstrated that the amygdala, a region critical for regulating emotion, is a key modulator of sleep. Our current research is focused on understanding how the amygdala and stressful emotion affect sleep and on the role sleep plays in recovery from stress. We have implemented animal models to examine the how stress and stress-related memories impact sleep. Experiencing uncontrollable stress and reminders of uncontrollable stress can produce significant reductions in sleep, in particular rapid eye movement sleep. We are using these models to explore the neurobiology linking stress-related emotion and sleep. This research is relevant for sleep disorders such as insomnia and into mental disorders in which sleep is affected such as post-traumatic stress disorder (PTSD), which is typically characterized by a prominent sleep disturbance in the aftermath of exposure to a psychologically traumatic event.

Study Objectives: Predictability and controllability are important factors in the persisting effects of stress. We trained mice with signaled, escapable shock (SES) and with signaled, inescapable shock (SIS) to determine whether shock predictability can be a significant factor in the effects of stress on sleep. Design: Male BALB/cJ mice were implanted with transmitters for recording EEG, activity, and temperature via telemetry. After recovery from surgery, baseline sleep recordings were obtained for 2 days. The mice were then randomly assigned to SES (n = 9) and yoked SIS (n = 9) conditions. The mice were presented cues (90 dB, 2 kHz tones) that started 5.0 sec prior to and co-terminated with footshocks (0.5 mA; 5.0 sec maximum duration). SES mice always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. SIS mice received identical tones and shocks, but could not alter shock duration. Twenty cue-shock pairings (1.0-min interstimulus intervals) were presented on 2 days (ST1 and ST2). Seven days after ST2, SES and SIS mice, in their home cages, were presented with cues identical to those presented during ST1 and ST2. Setting: NA. Patients or Participants: NA. Interventions: NA. Measurements and Results: On each training and test day, EEG, activity and temperature were recorded for 20 hours. Freezing was scored in response to the cue alone. Compared to SIS mice, SES mice showed significantly increased REM after ST1 and ST2. Compared to SES mice, SIS mice showed significantly increased NREM after ST1 and ST2. Both groups showed reduced REM in response to cue presentation alone. Both groups showed similar stress-induced increases in temperature and freezing in response to the cue alone. Conclusions: These findings indicate that predictability (modeled by signaled shock) can play a significant role in the effects of stress on sleep.

Ponto-geniculo-occipital (PGO) waves spontaneously occur in the pons, lateral geniculate body (LGB), and occipital cortex during rapid eye movement sleep (REM), and PGO-like waves (PGOE) may be elicited in LGB during sleep and waking. Because REM has been hypothesized to be a state of continual "orienting" or "hyper-alertness," we tested whether the amplitudes of PGOE in "alerting" situations (the abrupt onset of a loud sound or presentation of a novel stimulus within a series of stimuli) that evoke orienting responses (OR) would be greater than those following stimuli without OR. We also compared PGOE accompanying OR to PGOE during REM and NREM when OR are absent. The amplitudes of PGOE in W were greatest when OR were observed, and the amplitudes of PGOE accompanying OR were not significantly different from PGOE amplitudes in REM. Likewise, the amplitudes of PGOE during REM were not significantly different from those of the highest amplitude spontaneous PGO waves. We propose that the presence of PGOE signals registration of stimuli and that stimuli of sufficient significance to induce behavioral OR in waking also elicit PGOE of significantly greater amplitudes in all behavioral states. These findings support the hypothesis that the presence of high-amplitude PGO waves in REM indicates that the brain is in a state of more-or-less continual orienting.

STRESS CAN HAVE A SIGNIFICANT, LONG-LASTING NEGATIVE IMPACT ON HEALTH INCLUDING CHANGES IN BEHAVIOR AND SLEEP. HOWEVER, STRESSORS are often encountered without producing permanent or pathological changes. The difference between successful and unsuccessful coping with stress may involve the resilience of the organism1 as well as characteristics of the stressor. Stressor controllability, along with intensity and predictability, have been found to be important factors in the effects of stress.2 For example, lack of stressor controllability has been suggested to be a factor in the development of posttraumatic stress disorder (PTSD).3,4 Conditioned fear training is conducted with a fear-inducing stressor (usually inescapable shock, [IS])5,6 presented in an experimental paradigm in which the animal receiving training has no control over the stressor. Through association to IS, initially neutral environmental cues and contexts acquire the capacity to elicit behavioral and physiological responses indicative of fear and anxiety, including behavioral freezing,7–9 autonomic responses,10–12 and fear-potentiated startle.5,6 Disturbances in sleep often follow a stressful or traumatic event,13 and we and others have demonstrated that IS and IS-associated fearful cues and contexts produce similar alterations in sleep, including a prominent reduction in rapid eye movement sleep (REM).14,15 By comparison, training with avoidable, signaled shock (a controllable stressor) in a shuttlebox is followed by significant increases in REM,15–18 even though the same stressor (footshock) is initially experienced before the avoidance response is acquired. The results of these studies have typically been focused on demonstrating a correlation between REM and acquisition of the avoidance response.15–18 It is possible to train animals with escapable shock (ES) as a controllable stressor using a shuttlebox paradigm. In this paradigm, the stressor is always experienced but can be terminated by the animal's action. The effects of ES and IS have not been directly compared with respect to post-stress alterations in sleep. Therefore, in this study, we used a yoked design to examine the effects of ES and IS training and of contextual reminders of ES and IS on sleep in BALB/cJ mice, a “behaviorally reactive” strain that shows greater post-stress reductions in REM and alterations in sleep in response to IS compared to C57BL/6J mice.19–21 We also compared mice in the ES and IS conditions for potential differences in gross motor activity and we examined freezing, a common behavioral index of fear,7,22,23 during exposure to the fearful context. Examining freezing enabled us to compare immediate emotional reactivity across conditions and to determine the relationship of initial emotionality to subsequent changes in arousal and sleep.

FEARFUL EXPERIENCES CAN LEAD TO ENDURING ALTERATIONS IN EMOTION AND BEHAVIOR IN HUMANS1 AND ANIMALS.2–5 FEAR CONDITIONING ASSOCIATED with these experiences is thought to be important in the development of pathophysiology underlying anxiety disorders and posttraumatic stress disorder (PTSD).9–11 Moreover, disturbances in sleep often follow a stressful or traumatic event,6 and the persistence of sleep disturbances may be predictive for future psychiatric and physical pathology.6–8 In animals, fear conditioning associated with stressful footshock training also produces marked changes in subsequent sleep.10,12,13 Specifically, the original shock training is followed by a significant decrease in subsequent REM sleep.10,14,15 Conditioned “reminders” of the shock training also decrease subsequent REM.10,14 Experimental conditioned fear involves the use of specific cues such as tone or light that presage the occurrence of footshock or less specific contextual stimuli which become associated with shock. Through pairings of cue or contextual stimuli with the occurrence of shock, these previously neutral stimuli acquire the ability to elicit a conditioned fear response (behavioral and physiological responses indicative of fear and anxiety such as behavioral freezing) when presented alone. Interestingly, though, the conditioned fear response produced by fearful cues and contexts can typically be blocked through extended presentations of either type of stimuli without the reoccurrence of footshock. This fear “extinction” is considered a type of new learning that inhibits subsequent fear without erasing the original memory for fear conditioning.16 The failure of extinction is thought to be a significant factor in persisting fear responses and anxiety.17 However, even though disturbed sleep has been associated with the continuing effects of stress, and several studies have demonstrated the effects of conditioned fear on sleep, the effects of fear extinction on subsequent sleep have yet to be examined. Therefore, the goal of this study was to determine whether fear extinction was followed by different patterns of sleep compared to those after continued fear. We trained 2 groups of rats in contextual fear using a footshock stressor and then re-exposed both groups to the fearful context alone. One group was removed from the context before extinction occurred and the other was allowed to remain in the fearful context until behavioral signs of fear (freezing) had completely subsided. Lastly, we recorded sleep in both groups after a second exposure to the fearful context without readministering footshock. This allowed us to compare the sleep of rats with extinguished fear behavior to that of rats which continued to show fear. We also examined both groups for similarities and differences in freezing during shock training and on reexposure to the context. These data demonstrate that fear extinction is associated with significantly improved sleep compared to continued fear, and may have implications for understanding the role of persisting sleep disruptions in the long-term effects of stress and trauma.

Serotonin (5-HT) is implicated in the regulation of both behavioral arousal and a brainstem alerting system that operates in wakefulness and in rapid eye movement sleep (REM). Activation of the brainstem alerting system is marked by the presence of ponto-geniculooccipital (PGO) waves that occur in association with orienting in wakefulness and spontaneously in REM. Local application of serotonergic agents into REM and PGO wave regulatory regions can alter REM, but there is conflicting evidence as to whether 5-HT in the brainstem can independently influence PGO wave generation. A potential site of action of 5-HT outside the brainstem is the amygdala, which can influence arousal as well as neurobiological responses to novel and significant stimuli. The amygdala also modulates the occurrence and amplitude of PGO waves. We discuss the linkages between arousal and alerting systems and the role 5-HT may play in their regulation at brainstem and amygdalar sites.

Monkeys have strong abilities to remember the visual properties of potential food sources for survival in the nature. The present study demonstrated the first observations of rhesus monkeys learning to solve complex spatial mazes in which routes were guided by visual cues. Three monkeys were trained in a maze (6 m x 6 m) included of four different mazes. We recorded the cue and cup errors, latencies, and pathway for each trial. The data showed that monkeys learned the target place after three days in the first maze and spent a shorter time in learning the following mazes. The maze was an efficient method to measure the ability and proceeding of spatial memory in monkeys. Moreover, working memory can also be tested by using the maze. MK-801 at 0.02 mg/kg but not at 0.005 mg/kg impaired monkeys' retrieval of spatial memory after they learned all four mazes. The present maze may provide an efficient method to help bridging the gap in cognition between nonhuman primates and humans, and in particular to gain insight into human cognitive function and dysfunction.

Presentation of a tonal cue that previously had been associated with a fearful experience (footshock) produces alterations in arousal and sleep that occur after the fearful cue is no longer presented. To begin investigating neurochemical mechanisms that may underlie the effects of fearful cue presentation, we measured release of [ 3 H]-norepinephrine ([ 3 H]-NE]) and [ 14 C]-γ-amino-butyric acid ([ 14 C]-GABA) from brain regions known to regulate arousal states and REM sleep. Depolarization-evoked release of [ 3 H]-NE from amygdalar slices of mice, which were trained to recognize a tone as a fearful cue, was suppressed at 2–3 h after exposure of animals to the fearful cue, but recovered after 4–5 h. Interestingly, depolarization-evoked release of [ 14 C]-GABA was significantly increased in the amygdala, and also showed a tendency for enhancement in the hippocampus, NPO, and DRN at 2–3 h after cue presentation. The changes in [ 14 C]-GABA release were also transient; 4–5 h after cue presentation no significant differences were detected between samples derived from experimental groups which experienced fearful or neutral cues. The similar time course of fearful cue-induced changes in neurotransmitter release and changes in arousal and REM sleep suggests that alterations in amygdalar neurotransmission may be involved in the changes in arousal and sleep that occur after fear.

Study objectives To determine the effects of temporary functional inactivation of the central nucleus of the amygdala on sleep and on activity in an arousing environment, an open field. Design Rats were implanted with electrodes for recording the electroencephalogram (EEG) and electromyogram (EMG), and with guide cannulae aimed into CNA. Sleep was recorded for 22 h (10 h light, 12 h dark) following microinjections of tetrodotoxin (TTX: 5.0 ng/0.2 microl given unilaterally [TTXUH] or bilaterally [TTXBH], and 2.5 ng/0.1 microl given bilaterally [TTXBL]) or saline (SAL) alone on separate days. Activity during 1 h in an OF was recorded after microinjections of TTXBH and SAL. Setting NA. Patients or participants Three-month-old Wistar rats (n=12). Interventions Functional inactivation of the central nucleus of the amygdala with TTX. Measurements and results Compared to SAL, all TTX microinjections significantly shortened NREM latency, but did not alter total NREM during either light or dark periods. During the light period, TTXBH significantly reduced total REM and REM episode number, and TTXBL decreased REM episode number. All TTX microinjections increased EEG slow wave activity (0.5-4 Hz, SWA) during wakefulness, NREM and REM. Activity in OF was decreased after TTXBH compared to SAL. Conclusions Functional lesions of the amygdala, including the central nucleus of the amygdala, decreased REM sleep and reduced arousal, as indicated by shortened NREM latency and decreased activity in an arousing environment. These findings suggest that the amygdala plays a broad role in modulating spontaneous sleep and wakefulness and in modulating responsiveness in arousing situations.

The amygdala has been implicated in emotional arousal and in the regulation of sleep. Previously, we demonstrated that tetrodotoxin (TTX), a sodium channel blocker that temporarily inactivates neurons and tracts, microinjected into the central nucleus of the amygdala (CNA) during the light period significantly reduced REM, shortened sleep latency, and increased EEG delta power in rats. TTX inactivation of CNA also reduced activity in the open field. These findings suggest that the amygdala modulates arousal in a variety of situations. To test the hypothesis that the amygdala may influence spontaneous arousal, we examined the effects of TTX inactivation of CNA on sleep and activity during the dark period when rats show higher arousal and less sleep. EEG and activity were recorded via telemetry in Wistar rats (n = 8). Bilateral microinjections of TTX (L: 2.5 ng/0.1; H: 5.0 ng/0.2 microl) or SAL (saline, 0.2 microl) were administered before lights off followed by recording throughout the 12-h dark period and following 12-h light period. Microinjections were given at 5-day intervals and were counterbalanced across condition. TTX significantly shortened sleep latency, increased NREM time, decreased REM time, and decreased activity. TTX increased NREM episode duration, whereas the number and duration of REM episodes were decreased. The present results indicate that TTX inactivation of CNA can increase NREM time when spontaneous arousal is high, suggesting a broad role for the amygdala in regulating arousal. The results suggest that understanding the ways in which the amygdala modulates arousal may provide insight into the mechanisms underlying altered sleep in mood and anxiety disorders.

Genetic and physiological diversity amongst rodent strains provide the potential for developing models that may give insight into factors that regulate sleep in response to environmental challenges. We examined home cage activity, behavioral performance in the open field and sleep after a number of mild stressors (cage change [CC], open field [OF]) and after 1 and 4h of sleep deprivation (1hSD and 4hSD) in rat strains (Fischer 344 [F344], Lewis [LEW], Wistar [WST] and Sprague-Dawley [Sp-D], n=16 per strain) that differ in behavior and sleep. F344 and WST rats had greater home cage locomotion than LEW and Sp-D rats, but F344 rats exhibited the least relative locomotion in OF. In 24h baseline recordings of sleep, strain rankings were LEW=WST=Sp-D>F344 in rapid eye movement sleep (REM), and LEW=Sp-D>F344 and LEW>WST in non-REM (NREM). Compared to baseline, total sleep was reduced in all four strains after CC, OF and 1hSD, but not after 4hSD, in the first hour after treatment. Afterwards, increases in REM and NREM were seen after all treatments with the amount and time course varying across treatments and strains. CC induced the weakest and 4hSD the largest effects on sleep, whereas OF and 1hSD had intermediate effects. Among strains, the more anxious F344 rats exhibited the greatest sleep increases during the light period after OF, 1hSD and 4hSD. The results are discussed with respect to the relationship between behavioral and sleep responses to stressors, and to potential mechanisms underlying the strain differences.

Shock training and auditory cues associated with shock produce alterations in sleep that can be long-lasting in BALB/cJ (C) mice. We examined sleep in C mice after different amounts of shock training, and after cues with different strength cue-shock associations. Mice were implanted with transmitters for determining sleep via telemetry. After baseline sleep recording, the mice were trained (between 08:00 and 09:00 h) to associate a cue (tone) with footshock in either single shock training (SST: a single tone-shock pairing) or multiple shock training (MST: 15 tone-shock pairings) conditions. For testing, the mice were presented 15 cues (tone only) in their home cage between 10:45 and 11:00 h on post-training days 6, 13, 20, 27, and 34 (Cue 1 to Cue 5) following shock training. Sleep was recorded for two days after shock training or cue presentation. A separate group of mice received 15 tone-shock pairings and had their sleep recorded for 10 consecutive uninterrupted days. Both SST and MST mice showed decreases in rapid eye movement sleep (REM) after shock training, with the larger effect in the MST mice. Only MST mice showed significant reductions in REM in response to the fearful cues, and longer-term alterations in sleep could be observed even on the day after cue presentation. These results indicate that reminders of an aversive event can impact sleep for prolonged periods, and that the degree of the impact varies with amount of training.

Lesions of the dorsal pontine tegmentum release muscle tone and motor behaviour, much of it similar to orienting during wakefulness, into rapid eye movement sleep (REM), a state normally characterized by paralysis. Sleep after pontine lesions may be altered, with more REM-A episodes of shorter duration compared to normal REM. We examined behaviour, ponto-geniculo-occipital (PGO) waves (which may be central markers of orienting) and sleep in lesioned cats: (i) to characterize the relationship of PGO waves to behaviour in REM-A; (ii) to determine whether post-lesion changes in the timing and duration of REM-A episodes were due to activity-related awakenings: and (iii) to determine whether alterations in sleep changed the circadian sleep/wake cycle in cats. Behavioural release in REM-A was generally related to episode length, but episode length was not necessarily shorter than normal REM in cats capable of full locomotion in REM-A. PGO wave frequency was reduced overall during REM-A, but was higher during REM-A with behaviour than during quiet REM-A without overt behaviour. Pontine lesions did not significantly alter the circadian sleep/wake cycle: REM-A had approximately the same Light/Dark distribution as normal REM. Differences in the patterning of normal REM and REM-A within sleep involve more than mere movement-induced awakenings. Brainstem lesions that eliminate the atonia of REM may damage neural circuitry involved in REM initiation and maintenance; this circuitry is separate from circadian control mechanisms.

SUMMARY Ponto-geniculo-occipital (PGO) waves are spontaneously-occurring macropotential waveforms recorded in the pons, lateral geniculate body (LGB) and occipital cortex. PGO waves mark the onset and course of rapid eye movement sleep (REM). PGO-like waves can be recorded in several brain areas including the thalamic central lateral nucleus (CL). Alerting stimuli elicit PGO waves (PGOE) from LGB and waves from CL (CLE) in all behavioural states. We compared spontaneous activity in LGB and CL across behavioral states to examine the relationship of CL waves to PGO waves. Spontaneous waves in LGB and CL may occur concurrently or separately in all states. Although REM is marked by a high level of LGB PGO activity, CL waves are rare. Frequencies of CL and LGB waves are similar in non-REM (NREM) although the waves do not necessarily occur at the same time. These findings suggest that the widespread phasic activity recorded throughout the brain in sleep cannot be assumed to be a non-specific unitary phenomenon propagated from a single brainstem generator.

Dreaming in sleep must depend on the activity of the brain as does cognition and memory in wakefulness. Yet our understanding of the physiological subtleties of state differences may still be too primitive to guide theories adequately in these areas. One can state nonetheless unequivocally that the brain in REM is poorly equipped to practice for eventualities of wakefulness through dreaming, or for consolidating into memory the complex experiences of that state.[Hobson et al., Nielsen, Solms, Vertes & Eastman, Revonsuo]

Waves similar to ponto-geniculo-occipital (PGO) waves occurring spontaneously in the lateral geniculate body (LGB), pons, and occipital cortex during rapid eye movement (REM) sleep can be elicited in the LGB and the cortex by tones in waking (W), non-rapid eye movement sleep (NREM), and REM. In W, the elicited waves (PGOE) sometimes accompany orienting responses (OR). We have hypothesized that REM is a state resembling exaggerated "orienting" in part because spontaneous PGO waves similar to PGOE accompanying OR are constantly observed in REM. The present experiment tested whether: (1) PGOE and OR were strongly correlated in W across a large number of tone presentations as might be predicted if PGOE were central wave form markers for a state of orienting; and (2) recovery of responsiveness of PGOE to tones would then be greater in REM than NREM, as might be expected if REM but not NREM were a state in which central mechanisms of orienting were highly active. Tones were presented in W and then in REM and NREM to six cats in order to measure the degree of habituation of OR and PGOE simultaneously. PGOE and OR exhibited a degree of independence: the former were readily produced in W despite the rapid decline in OR across trials. Recovery in the amplitude of PGOE occurred in both NREM and REM. The recovery tended to be greater in REM than NREM, although this was not statistically significant. Refinements of the theory that REM represents a state of exaggerated internal orienting are discussed.

Waves similar to spontaneous ponto-geniculo-occipital (PGO) waves of paradoxical sleep (PS) in cats are elicited by tones and can be considered a form of evoked potential termed PGOE. The aims of the present experiment were to determine: (1) the effects of tone intensity on the probability of producing PGOE; (2) the effects of intensity on the amplitude and latency of PGOE across slow-wave sleep (SWS) and PS; (3) whether the effects of intensity on PGOE are similar to those on a particular form of auditory evoked potential known as the mid-latency response (MLR). Increasing the intensity of the stimulus from 60 to 100 in 10 dB increments resulted in increased probability, increased amplitude, and decreased latency of PGOE in both SWS and PS. This pattern was similar to published findings with MLR, and latencies of PGOE (roughly 60-100 msec) fell within the range of 'C wave' type of MLR recorded in intralaminar nuclei of the thalamus of cats. The possibility that PGOE and MLR share underlying mechanisms and represent the same phenomenon is discussed with particular attention to the function of the mechanisms during alerting and orienting.