Elissa H. Patterson

Activation of Phasic Pontine-Wave Generator Prevents Rapid Eye Movement Sleep Deprivation-Induced Learning Impairment in the Rat: A Mechanism for Sleep-Dependent Plasticity

Animal and human studies of sleep and learning have demonstrated that training on various tasks increases subsequent rapid eye movement (REM) sleep and phasic pontine-wave (P-wave) activity, followed by improvement in performance on the learned task. It is well documented that REM sleep deprivation after learning trials blocks the expected improvement in performance on subsequent retesting. Our aim was to test whether experimentally induced P-wave generator activation could eliminate the learning impairment produced by post-training REM sleep deprivation. Rats were trained on a two-way active avoidance-learning task. Immediately thereafter, two groups of those rats received a control vehicle (100 nl saline) microinjection and one group received a carbachol (50 ng in 100 nl saline) microinjection into the P-wave generator. The carbachol-injected group and one of the two control saline microinjected groups were selectively deprived of REM sleep during a 6 hr polygraphic recording session. All rats were then tested on the avoidance-learning task. The rats that received both the control saline injection and REM sleep deprivation showed learning deficits compared with the control saline-injected rats that were allowed to sleep normally. In contrast, the rats that received the carbachol microinjection and REM sleep deprivation demonstrated normal learning. These results demonstrate, for the first time, that carbachol-induced activation of the P-wave generator prevents the memory-impairing effects of post-training REM sleep deprivation. This evidence supports our hypothesis that the activation of the P-wave generator during REM sleep deprivation enhances a physiological process of memory, which occurs naturally during post-training REM sleep.

Endogenous and exogenous nitric oxide in the pedunculopontine tegmentum induces sleep

Mesopontine cholinergic cells in the pedunculopontine tegmental (PPT) nuclei modulate the control of the wake‐sleep cycle by releasing acetylcholine to their target structures. These cells also synthesize nitric oxide (NO) which diffuses into the extracellular space and acts as a neuronal messenger. The present study is based on the hypothesis that NO synthesis and its presence in the extracellular space in the PPT play a functional role in regulating the behavioral states of waking and sleep. This hypothesis was tested by microinjecting a control vehicle, NO donor, S‐Nitroso‐N‐acetyl‐penicillamine (SNAP) and a competitive inhibitor of NO synthase enzyme (NOS), NG‐Nitro‐L‐arginine methylester hydrochloride (L‐NAME) into the PPT while quantifying the effects on wakefulness and sleep. Six cats were implanted with bilateral guide tubes for PPT microinjection and with standard electrodes to measure waking, slow‐wave sleep (SWS), and rapid eye movement (REM) sleep. Five‐hour free‐moving polygraphic recordings were made following each microinjection (0.25 μl) of control saline, SNAP or L‐NAME.

Excitation of the pedunculopontine tegmental NMDA receptors induces wakefulness and cortical activation in the rat

Microinjection of the excitatory amino acid, L‐glutamate into the brainstem pedunculo pontine tegmentum (PPT) has been shown to induce wakefulness, however, it has been unclear that receptors mediate this effect. The aim of this study was to test the hypothesis that in the PPT, L‐glutamate induces cortical activation and wakefulness via activation of NMDA receptors. To test this hypothesis, three sets of micro‐injections into the PPT were carried out on two different groups of rats that were then allowed to move freely although chronic instrumentation recorded sleep/wake states. Three days after the initial control injections of saline, in a contra‐lateral site, Group I was micro‐injected with saline + glutamate (saline first, and glutamate 15 min later); after another 3 days, the same rats were micro‐injected with the NMDA‐receptor‐specific antagonist, 2‐amino‐5‐phosphonopentanoic acid, (AP5) + glutamate. Group II received the same initial control injections (saline only), then AP5 + glutamate and the saline + glutamate micro‐injections last. In rats that were not pretreated with AP5, microinjection of a 90 ng dose of L‐glutamate (0.48 nmol in a volume of 0.1 μl vehicle) kept animals awake for 2–3 hr by eliminating both slow‐wave sleep (SWS) and rapid eye movement (REM) sleep. These behavioral state changes were accompanied by concomitant increase in the power of gamma (γ) frequency (20–60 Hz) waves in the cortical EEG. Pretreatment of L‐glutamate injection sites with 0.48 nmol of AP5 blocked L‐glutamate‐induced‐wakefulness and preserved a normal amount of wakefulness and sleep. Pretreatment with AP5 decreased the power of γ‐wave activity below its control level. These results support the hypothesis that the glutamate‐induced‐wakefulness and cortical activation effects are mediated via the NMDA receptors. J. Neurosci. Res. 66:109–116, 2001.

A novel role of pedunculopontine tegmental kainate receptors: a mechanism of rapid eye movement sleep generation in the rat

Considerable evidence suggests that pedunculopontine tegmental cholinergic cells are critically involved in normal regulation of rapid eye movement sleep. The major excitatory input to the cholinergic cell compartment of the pedunculopontine tegmentum arises from glutamatergic neurons in the pontine reticular formation. Immunohistochemical studies reveal that both ionotropic and metabotropic receptors are expressed in pedunculopontine tegmental cells. This study aimed to identify the role of endogenous glutamate and its specific receptors in the pedunculopontine tegmentum in the regulation of physiological rapid eye movement sleep. To identify this physiological rapid eye movement sleep-inducing glutamate receptor(s) in the pedunculopontine tegmental cholinergic cell compartment, specific receptors were blocked differentially by local microinjection of selective glutamate receptor antagonists into the pedunculopontine tegmental cholinergic cell compartment while quantifying the effects on rapid eye movement sleep in freely moving chronically instrumented rats. By comparing the alterations in the patterns of rapid eye movement sleep following injections of control vehicle and selective glutamate receptor antagonists, contributions made by each receptor subtype in rapid eye movement sleep were evaluated. The results demonstrate that when kainate receptors were blocked by local microinjection of a kainate receptor selective antagonist, spontaneous rapid eye movement sleep was completely absent for the first 2 h, and for the next 2 h the total percentage of rapid eye movement sleep was significantly less compared to the control values. In contrast, when N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid, groups I, II, and III metabotropic receptors were blocked, total percentages of rapid eye movement sleep did not change compared to the control values. These findings suggest, for the first time, that the activation of kainate receptors within the cholinergic cell compartment of the pedunculopontine tegmentum is a critical step for the regulation of normal rapid eye movement sleep in the freely moving rat. The results also suggest that the different types of glutamate receptors within a small part of the brainstem may be involved in different types of physiological functions.

Prenatal protein malnourished rats show changes in sleep/wake behavior as adults.

Prenatal protein malnutrition significantly elevates brain levels of serotonin in rats, and these levels remain elevated throughout their lives. This biogenic amine is involved in the regulation of many physiological functions, including the normal sleep/wake cycle. The present study examined the effects of prenatal protein malnutrition on the sleep/wake cycle of freely moving adult rats. Six prenatally protein malnourished (6% casein) and 10 well‐nourished (25% casein) male rats (90–120‐day‐old) were chronically implanted with a standard set of electrodes (to record cortical electroencephalogram, neck muscle electromyogram, electrooculogram, and hippocampal theta wave) to objectively measure states of sleep and wakefulness. Six‐hour polygraphic recordings were made between 10.00 and 16.00 h; a time when the rats normally sleep. Prenatally malnourished rats spent 20% more time in slow wave sleep (SWS) compared to the well‐nourished rats. The total percentage of time spent in rapid eye movement (REM) sleep was 61% less in prenatally malnourished rats compared to well‐nourished control rats. These findings demonstrate the adverse consequences of prenatal protein malnutrition on the quality and quantity of adult sleep in rats. These sleep changes are potentially detrimental to normal social behavior and cognitive functions. Prenatally malnourished rats are an excellent animal model to study the role of endogenous serotonin in the regulation of the normal sleep/wake cycle.

Concealment and fabrication by experienced research subjects

Background Subjects who enroll in multiple studies have been found to use deception at times to overcome restrictive screening criteria. Deception undermines subject safety as well as study integrity. Little is known about the extent to which experienced research subjects use deception and what type of information is concealed, withheld, or distorted. Purpose This study examined the prevalence of deception and types of deception used by subjects enrolling in multiple studies. Methods Self-report of deceptive behavior used to gain entry into clinical trials was measured among a sample of 100 subjects who had participated in at least two studies in the past year. Results Three quarters of subjects reported concealing some health information from researchers in their lifetime to avoid exclusion from enrollment in a study. Health problems were concealed by 32% of the sample, use of prescribed medications by 28%, and recreational drug use by 20% of the sample. One quarter of subjects reported exaggerating symptoms in order to qualify for a study and 14% reported pretending to have a health condition in order to qualify. Limitations Although this study finds high rates of lifetime deceptive behavior, the frequency and context of this behavior is unknown. Understanding the context and frequency of deception will inform the extent to which it jeopardizes study integrity and safety. Conclusion The use of deception threatens both participant safety and the integrity of research findings. Deception may be fueled in part by undue inducements, overly restrictive criteria for entry, and increased demand for healthy controls. Screening measures designed to detect deception among study subjects would aid in both protecting subjects and ensuring the quality of research findings.

Calcium/Calmodulin Kinase II in the Pedunculopontine Tegmental Nucleus Modulates the Initiation and Maintenance of Wakefulness

The pedunculopontine tegmentum nucleus (PPT) is critically involved in the regulation of wakefulness (W) and rapid eye movement (REM) sleep, but our understanding of the mechanisms of this regulation remains incomplete. The present study was designed to determine the role of PPT intracellular calcium/calmodulin kinase (CaMKII) signaling in the regulation of W and sleep. To achieve this aim, three different concentrations (0.5, 1.0, and 2.0 nmol) of the CaMKII activation inhibitor, KN-93, were microinjected bilaterally (100 nl/site) into the PPT of freely moving rats, and the effects on W, slow-wave sleep (SWS), REM sleep, and levels of phosphorylated CaMKII (pCaMKII) expression in the PPT were quantified. These effects, which were concentration-dependent and affected wake–sleep variables for 3 h, resulted in decreased W, due to reductions in the number and duration of W episodes; increased SWS and REM sleep, due to increases in episode duration; and decreased levels of pCaMKII expression in the PPT. Regression analyses revealed that PPT levels of pCaMKII were positively related with the total percentage of time spent in W (R2 = 0.864; n = 28 rats; p < 0.001) and negatively related with the total percentage of time spent in sleep (R2 = 0.863; p < 0.001). These data provide the first direct evidence that activation of intracellular CaMKII signaling in the PPT promotes W and suppresses sleep. These findings are relevant for designing a drug that could treat excessive sleepiness by promoting alertness.

Effects of passive-avoidance training on sleep-wake state-specific activity in the basolateral and central nuclei of the amygdala.

This study examined the effects of intense emotional learning on the sleep-wake state-specific electroencephalographic (EEG) activities of the basolateral (BLA) and central (CeA) nuclei of the amygdala. Rats were trained on a passive-avoidance learning (PAL) protocol that was followed by 6 hr of undisturbed polygraphic recording and a PAL test. After PAL training, the total amount of REM sleep decreased: high-frequency EEG power decreased in the CeA during REM sleep and increased in the BLA during all sleep-wake stages. These results suggest that there is no homeostatic demand for REM sleep after intense emotional learning. However, the PAL-specific changes in the local EEG suggest that some form of memory processing may occur within the amygdala during REM sleep.