Behavioral phenotyping based on physical inactivity can predict sleep in female rats before, during, and after sleep disruption

BACKGROUND

A noninvasive method that can accurately quantify sleep before, during, and after sleep disruption (SD) has not been validated in female rats across their estrous cycle. In female rats, we hypothesized that the duration of physical inactivity (PIA) required to predict sleep would 1) change with the differences in baseline sleep between the circadian and estrous cycle phases and 2) predict sleep and the change in sleep (Δsleep) before, during, and after SD independent of circadian and estrous cycle phase.

NEW METHODS

EEG, EMG, physical activity and estrous cycle phase were measured in female Sprague-Dawley rats before, during, and after SD. Sleep was determined by two methods [EEG/EMG and a duration of continuous PIA (i.e., PIA criterion)]. Reliability between the methods was tested with a previously validated criterion (40 s). Sensitivity analyses and criterion-related validity analyses for sleep during SD and recovery were conducted across multiple PIA criteria (10 s-120 s). Predictability between the two methods and Δsleep was calculated.

RESULTS/COMPARISON WITH EXISTING METHODS

Three criteria (10 s, 20 s, 30 s) predicted baseline sleep independent of circadian and estrous cycle phase. Sleep during SD and recovery were predicted by two criteria (30 s and 10 s). Δsleep between study periods was not reliably predicted by a single PIA criterion.

CONCLUSION

PIA predicted sleep independent of estrous cycle phase in female rats. However, the specific criterion was dependent upon the study period (before, during, and after SD) and circadian phase. Thus, prior work validating a PIA criterion in male rodents is not applicable to the female rat.

Sleep loss in male rats contributes more to weight gain during sleep disruption than stress assessed by corticosterone

Sleep disruption (SD) promotes stress which may mediate the effect of SD induced by noise on bodyweight gain and food intake. We determined if the change in bodyweight during SD caused by noise was driven by stress (assessed by corticosterone) and whether the effects of noise on SD, stress and bodyweight were specific to the method of SD or a consequence of SD per se. We isolated stress from SD due to noise by exposing rats to noise during the darkphase to test whether darkphase noise stimulated weight gain, stress and food intake. Male Sprague-Dawley rats slept undisturbed, were exposed to noise during both circadian phases (lightphase vs darkphase) and lightphase gentle handling. Bodyweight, food intake, physical activity, vigilance states, and plasma corticosterone were determined. Darkphase noise did not affect vigilance states. Unlike lightphase noise, darkphase noise and lightphase gentle handling did not stimulate weight gain or food intake. Only gentle handling significantly increased corticosterone levels. Noise during the lightphase increasesed weight gain and food intake by causing SD and these effects were not driven by stress as assessed by corticosterone. These results may have significant implications for developing translational models of insomnia-induced obesity in humans.

Role of orexin-A in the ventrolateral preoptic area on components of total energy expenditure

BACKGROUND

Identifying whether components of total energy expenditure (EE) are affected by orexin receptor (OXR1 and OXR2) stimulation or antagonism with dual orexin receptor antagonists (DORAs) has relevance for obesity treatment. Orexin receptor stimulation reduces weight gain by increasing total EE and EE during spontaneous physical activity (SPA).

OBJECTIVE

The purpose of this study was to determine if a DORA (TCS-1102) in the ventrolateral preoptic area (VLPO) reduced orexin-A-induced arousal, SPA, total EE and EE during sleep, rest, wake and SPA and whether the DORA alone reduced total EE and its components. We hypothesized that: (1) a DORA would reduce orexin-A induced increases in arousal, SPA, components of total EE, reductions in sleep and the EE during sleep and (2) the DORA alone would reduce baseline (non-stimulated) SPA and total EE.

SUBJECTS/METHODS

Sleep, wakefulness, SPA and EE were determined after microinjection of the DORA (TCS-1102) and orexin-A in the VLPO of male Sprague-Dawley rats with a unilateral cannula targeted towards the VLPO. Individual components of total EE were determined based on time-stamped data.

RESULTS

The DORA reduced orexin-A-induced increases in arousal, SPA, total EE and EE during SPA, wake, rest and sleep 1 h post injection (P<0.05). Orexin-A significantly reduced sleep and significantly increased EE during sleep 1 h post injection (P<0.05). Furthermore, the DORA alone significantly reduced total EE, EE during sleep (NREM and REM) and resting EE 2 h post injection (P<0.05).

CONCLUSIONS

These data suggest that orexin-A reduces weight gain by stimulating total EE through increases in EE during SPA, rest and sleep. Residual effects of the DORA alone include decreases in total EE and EE during sleep and rest, which may promote weight gain.

Promotion of Wakefulness and Energy Expenditure by Orexin-A in the Ventrolateral Preoptic Area

STUDY OBJECTIVES

The ventrolateral preoptic area (VLPO) and the orexin/hypocretin neuronal system are key regulators of sleep onset, transitions between vigilance states, and energy homeostasis. Reciprocal projections exist between the VLPO and orexin/hypocretin neurons. Although the importance of the VLPO to sleep regulation is clear, it is unknown whether VLPO neurons are involved in energy balance. The purpose of these studies was to determine if the VLPO is a site of action for orexin-A, and which orexin receptor subtype(s) would mediate these effects of orexin-A. We hypothesized that orexin-A in the VLPO modulates behaviors (sleep and wakefulness, feeding, spontaneous physical activity [SPA]) to increase energy expenditure.

DESIGN AND MEASUREMENTS

Sleep, wakefulness, SPA, feeding, and energy expenditure were determined after orexin-A microinjection in the VLPO of male Sprague-Dawley rats with unilateral cannulae targeting the VLPO. We also tested whether pretreatment with a dual orexin receptor antagonist (DORA, TCS-1102) or an OX2R antagonist (JNJ-10397049) blocked the effects of orexin-A on the sleep/wake cycle or SPA, respectively.

RESULTS

Orexin-A injected into the VLPO significantly increased wakefulness, SPA, and energy expenditure (SPA-induced and total) and reduced NREM sleep and REM sleep with no effect on food intake. Pretreatment with DORA blocked the increase in wakefulness and the reduction in NREM sleep elicited by orexin-A, and the OX2R antagonist reduced SPA stimulated by orexin-A.

CONCLUSIONS

These data show the ventrolateral preoptic area is a site of action for orexin-A, which may promote negative energy balance by modulating sleep/wakefulness and stimulating spontaneous physical activity and energy expenditure.

Glut1 deficiency (G1D): epilepsy and metabolic dysfunction in a mouse model of the most common human phenotype

Brain glucose supplies most of the carbon required for acetyl-coenzyme A (acetyl-CoA) generation (an important step for myelin synthesis) and for neurotransmitter production via further metabolism of acetyl-CoA in the tricarboxylic acid (TCA) cycle. However, it is not known whether reduced brain glucose transporter type I (GLUT-1) activity, the hallmark of the GLUT-1 deficiency (G1D) syndrome, leads to acetyl-CoA, TCA or neurotransmitter depletion. This question is relevant because, in its most common form in man, G1D is associated with cerebral hypomyelination (manifested as microcephaly) and epilepsy, suggestive of acetyl-CoA depletion and neurotransmitter dysfunction, respectively. Yet, brain metabolism in G1D remains underexplored both theoretically and experimentally, partly because computational models of limited brain glucose transport are subordinate to metabolic assumptions and partly because current hemizygous G1D mouse models manifest a mild phenotype not easily amenable to investigation. In contrast, adult antisense G1D mice replicate the human phenotype of spontaneous epilepsy associated with robust thalamocortical electrical oscillations. Additionally, and in consonance with human metabolic imaging observations, thalamus and cerebral cortex display the lowest GLUT-1 expression and glucose uptake in the mutant mouse. This depletion of brain glucose is associated with diminished plasma fatty acids and elevated ketone body levels, and with decreased brain acetyl-CoA and fatty acid contents, consistent with brain ketone body consumption and with stimulation of brain beta-oxidation and/or diminished cerebral lipid synthesis. In contrast with other epilepsies, astrocyte glutamine synthetase expression, cerebral TCA cycle intermediates, amino acid and amine neurotransmitter contents are also intact in G1D. The data suggest that the TCA cycle is preserved in G1D because reduced glycolysis and acetyl-CoA formation can be balanced by enhanced ketone body utilization. These results are incompatible with global cerebral energy failure or with neurotransmitter depletion as responsible for epilepsy in G1D and point to an unknown mechanism by which glycolysis critically regulates cortical excitability.

Orexin/hypocretin plays a role in the response to physiological disequilibrium

In the decade since the discovery that pathology of the orexin/hypocretin system is causative for the sleep disorder narcolepsy, considerable progress has been made in understanding the functional role of the neuropeptide. Two, apparently separate functions of orexin have emerged as a consensus from studies to date. The first is the effect on vigilance state boundaries, as exemplified by narcolepsy. Thus the absence of orexin severely limits the ability to maintain prolonged periods of wakefulness or sleep and also allows the unregulated appearance of cataplexy as sudden muscle weakness during wakefulness. The second function is that orexin acts as a signaling molecule in transferring information about physiological disequilibrium to the central nervous system. Orexin activates the central arousal and motor systems during such disequilibrium and so may facilitate the necessary response and adaptation to restore equilibrium. A feasible relationship between these two functions is therefore that the maintenance of prolonged and active wakefulness is an integral part of this adaptive process. Furthermore, the limit placed on the onset of sleep by orexin suggests that these adaptive processes then continue during sleep to become integrated into the development of a coping strategy for the longer term.

Validation of a novel method to interrupt sleep in the mouse

Interrupted sleep, fragmented sleep or restricted sleep is a corollary of many psychiatric, neurological and respiratory disorders and also results from disruptive environments such as that of the intensive care unit (ICU). Recent rodent studies have revealed that sleep interruption (SI) can have more significant consequences for cognitive and neurophysiological variables than were expected and may even be equivalent to those of total sleep deprivation. Results from this research are therefore being increasingly recognized for their implications, which may include delayed recovery from critical illness in the ICU. Here we describe in detail a method for interrupting sleep in a murine model, which we had previously adopted to show an increase in mortality after septic insult. Interrupting sleep for 30s every 2 min over 48 h significantly decreased rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. The technique, which is based on using a standard laboratory orbital shaker to oscillate the cage containing the mouse, can easily be adapted to use different parameters for SI. During recovery, mice exhibited a rebound in REM sleep time and an increase in the depth of NREM sleep as measured by delta (1-4 Hz) power in the electroencephalogram. The changes in sleep both during and after SI showed some differences from those previously observed in the rat using the same SI parameters. In conclusion, the mouse may provide a useful alternative model for studying the effects of SI.

Regulation of hippocampal and behavioral excitability by cyclin-dependent kinase 5

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase that has been implicated in learning, synaptic plasticity, neurotransmission, and numerous neurological disorders. We previously showed that conditional loss of Cdk5 in adult mice enhanced hippocampal learning and plasticity via modulation of calpain-mediated N-methyl-D-aspartic acid receptor (NMDAR) degradation. In the present study, we characterize the enhanced synaptic plasticity and examine the effects of long-term Cdk5 loss on hippocampal excitability in adult mice. Field excitatory post-synaptic potentials (fEPSPs) from the Schaffer collateral CA1 subregion of the hippocampus (SC/CA1) reveal that loss of Cdk5 altered theta burst topography and enhanced post-tetanic potentiation. Since Cdk5 governs NMDAR NR2B subunit levels, we investigated the effects of long-term Cdk5 knockout on hippocampal neuronal excitability by measuring NMDAR-mediated fEPSP magnitudes and population-spike thresholds. Long-term loss of Cdk5 led to increased Mg²⁺-sensitive potentials and a lower threshold for epileptiform activity and seizures. Biochemical analyses were performed to better understand the role of Cdk5 in seizures. Induced-seizures in wild-type animals led to elevated amounts of p25, the Cdk5-activating cofactor. Long-term, but not acute, loss of Cdk5 led to decreased p25 levels, suggesting that Cdk5/p25 may be activated as a homeostatic mechanism to attenuate epileptiform activity. These findings indicate that Cdk5 regulates synaptic plasticity, controls neuronal and behavioral stimulus-induced excitability and may be a novel pharmacological target for cognitive and anticonvulsant therapies.

Abnormal response of melanin-concentrating hormone deficient mice to fasting: hyperactivity and rapid eye movement sleep suppression

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that has been implicated in energy homeostasis. Pharmacological studies with MCH and its receptor antagonists have suggested additional behavioral roles for the neuropeptide in the control of mood and vigilance states. These suggestions have been supported by a report of modified sleep in the MCH-1 receptor knockout mouse. Here we found that MCH knockout (MCH(-)(/)(-)) mice slept less during both the light and dark phases under baseline conditions. In response to fasting, MCH(-)(/)(-) mice exhibited marked hyperactivity, accelerated weight loss and an exaggerated decrease in rapid eye movement (REM) sleep. Following a 6-h period of sleep deprivation, however, the sleep rebound in MCH(-)(/)(-) mice was normal. Thus MCH(-)(/)(-) mice adapt poorly to fasting, and their loss of bodyweight under this condition is associated with behavioral hyperactivity and abnormal expression of REM sleep. These results support a role for MCH in vigilance state regulation in response to changes in energy homeostasis and may relate to a recent report of initial clinical trials with a novel MCH-1 receptor antagonist. When combined with caloric restriction, the treatment of healthy, obese subjects with this compound resulted in some subjects experiencing vivid dreams and sleep disturbances.

A seizure-prone phenotype is associated with altered free-running rhythm in Pten mutant mice

Conditional deletion of Pten (phosphatase and tensin homolog on chromosome ten) in differentiated cortical and hippocampal neurons in the mouse results in seizures, macrocephaly, social interaction deficits and anxiety, reminiscent of human autism spectrum disorder. Here we extended our previous examination of these mice using electroencephalogram/electromyogram (EEG/EMG) monitoring and found age-related increases in spontaneous seizures, which were correlated with cellular dispersion in the hippocampal dentate gyrus. Increased spontaneous locomotor activity in the open field on the first and the second day of a 3-day continuous study suggested heightened anxiety in Pten mutant mice. In contrast, the mutants exhibited decreased wheel running activity, which may reflect reduced adaptability to a novel environment. Synchronization to the light-dark cycle was normal, but for up to 28 days under constant darkness, the Pten mutants maintained a significantly lengthened and remarkably constant free-running period of almost exactly 24 h. This result implies the involvement of Pten in the maintenance of circadian rhythms, which we interpret as being due to an effect on the phosphatidylinositol 3-kinase (PI3K) signaling cascade.

Epigenetic modulation of seizure-induced neurogenesis and cognitive decline

The conceptual understanding of hippocampal function has been challenged recently by the finding that new granule cells are born throughout life in the mammalian dentate gyrus (DG). The number of newborn neurons is dynamically regulated by a variety of factors. Kainic acid-induced seizures, a rodent model of human temporal lobe epilepsy, strongly induce the proliferation of DG neurogenic progenitor cells and are also associated with long-term cognitive impairment. We show here that the antiepileptic drug valproic acid (VPA) potently blocked seizure-induced neurogenesis, an effect that appeared to be mainly mediated by inhibiting histone deacetylases (HDAC) and normalizing HDAC-dependent gene expression within the epileptic dentate area. Strikingly, the inhibition of aberrant neurogenesis protected the animals from seizure-induced cognitive impairment in a hippocampus-dependent learning task. We propose that seizure-generated granule cells have the potential to interfere with hippocampal function and contribute to cognitive impairment caused by epileptic activity within the hippocampal circuitry. Furthermore, our data indicate that the effectiveness of VPA as an antiepileptic drug may be partially explained by the HDAC-dependent inhibition of aberrant neurogenesis induced by seizure activity within the adult hippocampus.

Neuropeptide B-deficient mice demonstrate hyperalgesia in response to inflammatory pain

Neuropeptide B (NPB) and neuropeptide W (NPW) have been recently identified as ligands for the G protein-coupled receptor (GPR) 7 and GPR8. The precise in vivo role of this neuropeptide-receptor pathway has not been fully demonstrated. In this paper, we report that NPB-deficient mice manifest a mild adult-onset obesity, similar to that reported in GPR7-null mice. NPB-deficient mice also exhibit hyperalgesia in response to inflammatory pain. Hyperalgesia was not observed in response to chemical pain, thermal pain, or electrical stimulation. NPB-deficient mice demonstrated intact behavioral responses to pain, and learning from the negative reinforcement of electrical stimulation was unaltered. Baseline anxiety was also unchanged as measured in both the elevated plus maze and time spent immobile in a novel environment. These data support the idea that NPB is a factor in the modulation of responses to inflammatory pain and body weight homeostasis.

Orexin neurons function in an efferent pathway of a food-entrainable circadian oscillator in eliciting food-anticipatory activity and wakefulness

Temporal restriction of feeding can entrain circadian behavioral and physiological rhythms in mammals. Considering the critical functions of the hypothalamic orexin (hypocretin) neuropeptides in promoting wakefulness and locomotor activity, we examined the role of orexin neurons in the adaptation to restricted feeding. In orexin neuron-ablated transgenic mice, the food-entrained rhythmicity of mPer2 expression in the brain and liver, the reversal of the sleep-wake cycle, and the recovery of daily food intake were unaltered compared with wild-type littermates. In contrast, orexin neuron-ablated mice had a severe deficit in displaying the normal food-anticipatory increases in wakefulness and locomotor activity under restricted feeding. Moreover, activity of orexin neurons markedly increased during the food-anticipatory period under restricted feeding in wild-type mice. Orexin neurons thus convey an efferent signal from putative food-entrainable oscillator or oscillators to increase wakefulness and locomotor activity.

Modafinil more effectively induces wakefulness in orexin-null mice than in wild-type littermates

Narcolepsy-cataplexy, a disorder of excessive sleepiness and abnormalities of rapid eye movement (REM) sleep, results from deficiency of the hypothalamic orexin (hypocretin) neuropeptides. Modafinil, an atypical wakefulness-promoting agent with an unknown mechanism of action, is used to treat hypersomnolence in these patients. Fos protein immunohistochemistry has previously demonstrated that orexin neurons are activated after modafinil administration, and it has been hypothesized that the wakefulness-promoting properties of modafinil might therefore be mediated by the neuropeptide. Here we tested this hypothesis by immunohistochemical, electroencephalographic, and behavioral methods using modafinil at doses of 0, 10, 30 and 100 mg/kg i.p. in orexin-/- mice and their wild-type littermates. We found that modafinil produced similar patterns of neuronal activation, as indicated by Fos immunohistochemistry, in both genotypes. Surprisingly, modafinil more effectively increased wakefulness time in orexin-/- mice than in the wild-type mice. This may reflect compensatory facilitation of components of central arousal in the absence of orexin in the null mice. In contrast, the compound did not suppress direct transitions from wakefulness to REM sleep, a sign of narcolepsy-cataplexy in mice. Spectral analysis of the electroencephalogram in awake orexin-/- mice under baseline conditions revealed reduced power in the theta; band frequencies (8-9 Hz), an index of alertness or attention during wakefulness in the rodent. Modafinil administration only partly compensated for this attention deficit in the orexin null mice. We conclude that the presence of orexin is not required for the wakefulness-prolonging action of modafinil, but orexin may mediate some of the alerting effects of the compound.

Neurophysiological mechanisms of sleep and wakefulness: a question of balance

Following a summary of the stages of sleep and wakefulness as monitored with the electroencephalogram and electromyogram, important aspects of the neurophysiology and neuroanatomy of the circuits of vigilance state control are reviewed. A homeostatic drive for sleep and a circadian influence work in concert to determine sleepiness. These processes influence sleep-promoting and central arousing neuronal systems, the former dependent on a group of neurons in the hypothalamic ventrolateral preoptic area and the latter governed by neurons in the pons and basal forebrain. The interactive neuronal circuit that is formed by these cell groups ensures the balance between sleep and wakefulness and the rapid transition to and from sleep. As sleep deepens, the switch to rapid eye movement (REM) sleep occurs. This transition can also be viewed as a balance between one group of pontine neurons that discharge only during REM sleep and another group that cease to discharge during REM sleep. This article concludes with future perspectives based on the recent discovery of the orexin cell group. Orexinergic neurons may be critical both for promoting wakefulness at certain times in the daily cycle and for controlling the switch into REM sleep.

Expression of a poly-glutamine-ataxin-3 transgene in orexin neurons induces narcolepsy-cataplexy in the rat

The sleep disorder narcolepsy has been linked to loss of hypothalamic neurons producing the orexin (hypocretin) neuropeptides. Here, we report the generation of transgenic rats expressing a human ataxin-3 fragment with an elongated polyglutamyl stretch under control of the human prepro-orexin promoter (orexin/ataxin-3 rats). At 17 weeks of age, the transgenic rats exhibited postnatal loss of orexin-positive neurons in the lateral hypothalamus, and orexin-containing projections were essentially undetectable. The loss of orexin production resulted in the expression of a phenotype with fragmented vigilance states, a decreased latency to rapid eye movement (REM) sleep and increased REM sleep time during the dark active phase. Wakefulness time was also reduced during the dark phase, and this effect was concentrated at the photoperiod boundaries. Direct transitions from wakefulness to REM sleep, a defining characteristic of narcolepsy, occurred frequently. Brief episodes of muscle atonia and postural collapse resembling cataplexy were also noted while rats maintained the electroencephalographic characteristics of wakefulness. These findings indicate that the orexin/ataxin-3 transgenic rat could provide a useful model of human narcolepsy.

Orexin peptides prevent cataplexy and improve wakefulness in an orexin neuron-ablated model of narcolepsy in mice

Narcolepsy-cataplexy is a neurological disorder associated with the inability to maintain wakefulness and abnormal intrusions of rapid eye movement sleep-related phenomena into wakefulness such as cataplexy. The vast majority of narcoleptic-cataplectic individuals have low or undetectable levels of orexin (hypocretin) neuropeptides in the cerebrospinal fluid, likely due to specific loss of the hypothalamic orexin-producing neurons. Currently available treatments for narcolepsy are only palliative, symptom-oriented pharmacotherapies. Here, we demonstrate rescue of the narcolepsy-cataplexy phenotype of orexin neuron-ablated mice by genetic and pharmacological means. Ectopic expression of a prepro-orexin transgene in the brain completely prevented cataplectic arrests and other abnormalities of rapid eye movement sleep in the absence of endogenous orexin neurons. Central administration of orexin-A acutely suppressed cataplectic behavioral arrests and increased wakefulness for 3 h. These results indicate that orexin neuron-ablated mice retain the ability to respond to orexin neuropeptides and that a temporally regulated and spatially targeted secretion of orexins is not necessary to prevent narcoleptic symptoms. Orexin receptor agonists would be of potential value for treating human narcolepsy.

N-type calcium channel alpha1B subunit (Cav2.2) knock-out mice display hyperactivity and vigilance state differences

Differential properties of voltage-dependent Ca2+ channels have been primarily ascribed to the alpha1 subunit, of which 10 different subtypes are currently known. For example, channels that conduct the N-type Ca2+ current possess the alpha1B subunit (Cav2.2), which has been localized, inter alia, to the piriform cortex, hippocampus, hypothalamus, locus coeruleus, dorsal raphe, thalamic nuclei, and granular layer of the cortex. Some of these regions have been previously implicated in metabolic and vigilance state control, and selective block of the N-type Ca2+ channel causes circadian rhythm disruption. In this study of Cav2.2-/- knock-out mice, we examined potential differences in feeding behavior, spontaneous locomotion, and the sleep-wake cycle. Cav2.2-/- mice did not display an overt metabolic phenotype but were hyperactive, demonstrating a 20% increase in activity under novel conditions and a 95% increase in activity under habituated conditions during the dark phase, compared with wild-type littermates. Cav2.2-/- mice also displayed vigilance state differences during the light phase, including increased consolidation of rapid-eye movement (REM) sleep and increased intervals between non-REM (NREM) and wakefulness episodes. EEG spectral power was increased during wakefulness and REM sleep and was decreased during NREM sleep in Cav2.2-/- mice. These results indicate a role of the N-type Ca2+ channel in activity and vigilance state control, which we interpret in terms of effects on neurotransmitter release.

Distinct narcolepsy syndromes in Orexin receptor-2 and Orexin null mice: molecular genetic dissection of Non-REM and REM sleep regulatory processes

Narcolepsy-cataplexy, a neurological disorder associated with the absence of hypothalamic orexin (hypocretin) neuropeptides, consists of two underlying problems: inability to maintain wakefulness and intrusion of rapid eye movement (REM) sleep into wakefulness. Here we document, using behavioral, electrophysiological, and pharmacological criteria, two distinct classes of behavioral arrests exhibited by mice deficient in orexin-mediated signaling. Both OX2R(-/-) and orexin(-/-) mice are similarly affected with behaviorally abnormal attacks of non-REM sleep ("sleep attacks") and show similar degrees of disrupted wakefulness. In contrast, OX2R(-/-) mice are only mildly affected with cataplexy-like attacks of REM sleep, whereas orexin(-/-) mice are severely affected. Absence of OX2Rs eliminates orexin-evoked excitation of histaminergic neurons in the hypothalamus, which gate non-REM sleep onset. While normal regulation of wake/non-REM sleep transitions depends critically upon OX2R activation, the profound dysregulation of REM sleep control unique to the narcolepsy-cataplexy syndrome emerges from loss of signaling through both OX2R-dependent and OX2R-independent pathways.

Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats

During rapid eye movement (REM) sleep, activity of non-retinal origin is propagated into central visual-system pathways in a manner similar, in pattern and intensity, to central visual-system activity that is exogenously generated in waking. It has been hypothesized that REM sleep, which is more abundantly represented early in life than later, functions to provide adjunct 'afferent' input for shaping synaptic connectivity during brain maturation. Here we present data that support this proposal. Recent studies have described a developmentally regulated form of in vitro long-term potentiation (LTP) in the visual cortex that is experience- and age-dependent. In immature rats, suppression of retinal activation of the visual system by removal of visual experience (dark rearing) extends the age when the developmentally regulated form of LTP can be produced. This study tests whether suppression of REM-state activation of the visual system also lengthens the developmental period in which this specific form of LTP can be elicited. Young rats were deprived of REM sleep by the multiple-small-platforms-over-water method during the typically latest week for induction of such LTP in slices of visual cortex. After this week, we could still induce LTP in slices from nearly all the REM-sleep-deprived rats (8/9) but not from age-matched rats that had not lost REM sleep (0/5). The control rats had been housed on large platforms that allow the animals to obtain REM sleep. Only body weights and the concentration of thyrotrophin-releasing hormone in the hypothalamus distinguished home-caged, normal-sleeping controls from both groups of platform animals. On all measures, stress levels were not dissimilar in the two platforms groups. After 7 days of behavioral suppression of REM sleep in immature rats, and consequent reduction of the intense, extra-retinal activity endogenously generated during this sleep state, we found that the period was extended in which developmentally regulated synaptic plasticity (LTP) could be elicited in slices of visual neocortex. These studies support the role of REM sleep and its associated neuronal activity in brain maturation.

To eat or to sleep? Orexin in the regulation of feeding and wakefulness

Orexin-A and orexin-B are neuropeptides originally identified as endogenous ligands for two orphan G-protein-coupled receptors. Orexin neuropeptides (also known as hypocretins) are produced by a small group of neurons in the lateral hypothalamic and perifornical areas, a region classically implicated in the control of mammalian feeding behavior. Orexin neurons project throughout the central nervous system (CNS) to nuclei known to be important in the control of feeding, sleep-wakefulness, neuroendocrine homeostasis, and autonomic regulation. orexin mRNA expression is upregulated by fasting and insulin-induced hypoglycemia. C-fos expression in orexin neurons, an indicator of neuronal activation, is positively correlated with wakefulness and negatively correlated with rapid eye movement (REM) and non-REM sleep states. Intracerebroventricular administration of orexins has been shown to significantly increase food consumption, wakefulness, and locomotor activity in rodent models. Conversely, an orexin receptor antagonist inhibits food consumption. Targeted disruption of the orexin gene in mice produces a syndrome remarkably similar to human and canine narcolepsy, a sleep disorder characterized by excessive daytime sleepiness, cataplexy, and other pathological manifestations of the intrusion of REM sleep-related features into wakefulness. Furthermore, orexin knockout mice are hypophagic compared with weight and age-matched littermates, suggesting a role in modulating energy metabolism. These findings suggest that the orexin neuropeptide system plays a significant role in feeding and sleep-wakefulness regulation, possibly by coordinating the complex behavioral and physiologic responses of these complementary homeostatic functions.

Gene therapy to prevent organophosphate intoxication

The specific hydrolytic activity of PON1 paraoxonase/arylesterase enzymes in liver and blood provides a natural barrier against the entry of organophosphate toxins into the central and peripheral nervous systems. Inherited differences in PON1 enzyme concentrations may determine levels of susceptibility to organophosphate injury in humans. To test whether boosting serum levels of PON1 enzymes by gene therapy might provide increased protection, we compared the degree of inactivation of whole brain acetylcholinesterase of mice exposed to chlorpyrifos 4 days after intravenous injection of recombinant adenoviruses containing PON1-LQ or PON1-LR genes or no PON1 gene. Both recombinant viruses containing PON1 genes boosted serum arylesterase concentrations by approximately 60% and significantly prevented the inactivation of brain acetylcholinesterase. Some mice were completely protected. These findings indicate that boosting serum levels of PON1 enzymes by a gene delivery vector raises the threshold for organophosphate toxicity by hydrolytic destruction before the chemical can enter the brain.

Genetic ablation of orexin neurons in mice results in narcolepsy, hypophagia, and obesity

Orexins (hypocretins) are a pair of neuropeptides implicated in energy homeostasis and arousal. Recent reports suggest that loss of orexin-containing neurons occurs in human patients with narcolepsy. We generated transgenic mice in which orexin-containing neurons are ablated by orexinergic-specific expression of a truncated Machado-Joseph disease gene product (ataxin-3) with an expanded polyglutamine stretch. These mice showed a phenotype strikingly similar to human narcolepsy, including behavioral arrests, premature entry into rapid eye movement (REM) sleep, poorly consolidated sleep patterns, and a late-onset obesity, despite eating less than nontransgenic littermates. These results provide evidence that orexin-containing neurons play important roles in regulating vigilance states and energy homeostasis. Orexin/ataxin-3 mice provide a valuable model for studying the pathophysiology and treatment of narcolepsy.

Stressful manipulations that elevate corticosterone reduce blood-brain barrier permeability to pyridostigmine in the Rat

Pyridostigmine bromide (PB), a reversible inhibitor of acetylcholinesterase (AChE), is used for the treatment of myasthenia gravis. PB has also been provided to military personnel for preexposure protection against potential soman release. The entry of PB into the brain is typically minimal, but recently published data in mice suggest that a brief forced swim stress increases the permeability of the blood-brain barrier to PB. From these results, PB administered under stressful conditions was proposed to induce long-lasting central cholinergic deficits, potentially explaining the neurological and neuropsychological symptoms presented by some Gulf War veterans. In undertaking to replicate these results in the Long-Evans rat, no evidence of a stress-potentiated central effect of PB, administered at doses up 5.0 mg/kg ip, was found. Three stress protocols were used: restraint, forced swim, or a combined restraint/forced swim. Wistar rats were also tested in some of the protocols to ensure that the results were generalizable across rat strains, and plasma corticosterone levels were measured to test the effectiveness of the stressors employed. In contrast to the previously reported findings in the mouse, stress significantly reduced the entry of PB into rat brain, as measured by reduced inhibition of AChE activity: a 12.5% reduction in whole brain AChE activity after treatment with 5.0 mg/kg PB under control conditions declined to 9% after stress exposure. It is apparent, therefore, that the interaction between stress and PB requires further study, and previous data should be reassessed before they are used as a basis for interpreting symptoms presented by veterans.

Upregulation of estrogen receptors in the forebrain of aromatase knockout (ArKO) mice

Estrogens have numerous reproductive and nonreproductive functions in brain. The actions of estrogens are mediated by estrogen receptors (ERs), and estrogens are believed to down-regulate their own receptors in many tissues. Assuming this to be true, if estrogens are removed there should be an upregulation of ERs. We have developed a mouse model in which estrogen synthesis is completely eliminated by homologous recombination to delete the gene encoding aromatase cytochrome P450 (P450(arom)). The P450(arom) enzyme catalyzes the synthesis of estrogens from androgens in the brain. The localization and density of ERs was studied in the brains of aromatase knockout (ArKO) and wild type male mice by using immunohistochemistry with a peptide antibody to ERalpha (ER-21) and computer imaging. In the wild-type animals a high density of ERalpha was found in a small number of hypothalamic cells; in the medial preoptic area, periventricular, arcuate, and ventromedial nuclei. A low and medium density of ERalpha was observed in cells of the lateral preoptic area, supraoptic, bed nucleus of the stria terminalis, and in central, medial and anterior cortical amygdaloid nuclei. The number of cells containing ERalpha-immunoreactivity was significantly increased (244%) in the medial preoptic area of the ArKO mice. In neither wild type nor ArKO animals was immunoreactivity observed in the cerebral cortex or striatum. There was intense ER-immunostaining in the nucleus of neurons in both wild type and ArKO mice. These data indicate that in the absence of estrogens there is as much as a 2-fold increase in the number of cells with ERalpha-immunoreactivity in certain hypothalamic and limbic regions. Thus, estrogens can down-regulate ERalpha in brain.

Neuroanatomical and neurophysiological aspects of sleep: basic science and clinical relevance

This is an exciting period for basic sleep research, because we are now beginning to understand some of the mechanisms controlling the changes in consciousness associated with sleep and wakefulness. Witness the recent discoveries of a probable genetic involvement in narcolepsy, the identification of hypothalamic structures promoting sleep, and the mounting evidence that adenosine is an endogenous sleep factor. We review these and other recent developments that help us understand the neuroanatomical and neurophysiological basis of some sleep disorders. For a detailed discussion of specific sleep disorders and clinical issues, the reader is referred to other sources. Overviews are also available covering rapid eye movement (REM) and non-REM sleep physiology, the role of humoral factors in sleep, and the relationship between the immune system and sleep. In fact, where appropriate, here we draw directly on material from our earlier summaries of work in the field. We begin with a brief review of the organization of sleep and wakefulness to provide the background for the subsequent discussions of the anatomy and neurophysiology of the neural control of different vigilance states and associated sleep disorders. For example, a brief description of the neural mechanisms of REM sleep will be followed by an outline of selected sleep disorders related to REM sleep. In summary, we make no attempt here to include all sleep disorders and only review a few selected examples, those in which there is an understanding based on knowledge of central nervous system physiology. Unfortunately we are not now able to include sleep apnea, because the discovery of sleep apnea not only was a defining moment for clinical sleep research, but to this day remains the principal presenting complaint at some sleep disorder clinics.

Evidence for a deficit in cholinergic interneurons in the striatum in schizophrenia

Neurochemical and functional abnormalities of the striatum have been reported in schizophrenic brains, but the cellular substrates of these changes are not known. We hypothesized that schizophrenia may involve an abnormality in one of the key modulators of striatal output, the cholinergic interneuron. We measured the densities of cholinergic neurons in the striatum in schizophrenic and control brains in a blind analysis, using as a marker of this cell population immunoreactivity for choline acetyltransferase, the synthetic enzyme of acetylcholine. As an independent marker, we used immunoreactivity for calretinin, a protein which is co-localized with choline acetyltransferase in virtually all of the cholinergic interneurons of the striatum. A significant decrease in choline acetyltransferase-positive and calretinin-positive cell densities was found in the schizophrenic cases compared with controls in the striatum as a whole [for the choline acetyltransferase-positive cells: controls: 3.21 +/- 0.48 cells/mm2 (mean +/- S.D.), schizophrenics: 2.43 +/- 0.68 cells(mm2; P < 0.02]. The decrease was patchy in nature and most prominent in the ventral striatum (for the choline acetyltransferase-positive cells: controls: 3.47 +/- 0.59 cells/mm2, schizophrenics: 2.52 +/- 0.64 cells/ mm2; P < 0.005) which included the ventral caudate nucleus and nucleus accumbens region. Three of the schizophrenic cases with the lowest densities of cholinergic neurons had not been treated with neuroleptics for periods from more than a month to more than 20 years. A decrease in the number or function of the cholinergic interneurons of the striatum may disrupt activity in the ventral striatal-pallidal-thalamic-prefrontal cortex pathway and thereby contribute to abnormalities in function of the prefrontal cortex in schizophrenia.

The effects of leptin on REM sleep and slow wave delta in rats are reversed by food deprivation

Leptin (ob protein) is an adipose tissue derived circulating hormone that acts at specific receptors in the hypothalamus to reduce food intake. The protein is also critically involved in energy balance and metabolic status. Here the effect of leptin on sleep architecture in rats was evaluated because food consumption and metabolic status are known to influence sleep. Sprague-Dawley rats were chronically implanted with electrodes for EEG and EMG recording and diurnal sleep parameters were quantified over 9-h periods following leptin administration. Murine recombinant leptin (rMuLep) was administered systemically to rats that either had undergone 18 h of prior food deprivation or had received food ad libitum. In the normally fed rats, leptin significantly decreased the duration of rapid eye movement sleep (REMS) by about 30% and increased the duration of slow wave sleep (SWS) by about 13%, the latter effect reflecting enhanced power in the delta frequency band. These results are consistent with studies that have linked changes in metabolic rate with effects on sleep. Leptin administration has previously been shown to alter neuroendocrine parameters that could have mediated these changes in sleep architecture. Unexpectedly, prior food deprivation negated the effect of leptin on both REMS and SWS, a result that emphasizes the significance of the apparent coupling between sleep parameters and energy status.

Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation

Neurons containing the neuropeptide orexin (hypocretin) are located exclusively in the lateral hypothalamus and send axons to numerous regions throughout the central nervous system, including the major nuclei implicated in sleep regulation. Here, we report that, by behavioral and electroencephalographic criteria, orexin knockout mice exhibit a phenotype strikingly similar to human narcolepsy patients, as well as canarc-1 mutant dogs, the only known monogenic model of narcolepsy. Moreover, modafinil, an anti-narcoleptic drug with ill-defined mechanisms of action, activates orexin-containing neurons. We propose that orexin regulates sleep/wakefulness states, and that orexin knockout mice are a model of human narcolepsy, a disorder characterized primarily by rapid eye movement (REM) sleep dysregulation.

Inhibition of striatal energy metabolism produces cell loss in the ipsilateral substantia nigra

This study examined whether damage to dopamine (DA) nerve terminals via inhibition of energy metabolism in the striatum would result in the retrograde loss of cell bodies in the substantia nigra. Infusion of 2 micromol malonate into the left striatum of rats resulted in a 67% loss of striatal DA and a 40% loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra. No change in the number of Nissl-positive-TH-negative neurons was observed. These findings demonstrate the retrograde destruction of DA cell bodies in the substantia nigra resulting from energy impairment at their terminal projection site.

The neurotoxin MPTP causes degeneration of specific nucleus A8, A9 and A10 dopaminergic neurons in the mouse

The neurotoxin MPTP has been used to create an animal model of Parkinson's disease in the mouse, in part, because it causes a significant loss of dopaminergic neurons in the substantia nigra (nucleus A9). The purpose of the present study was to determine whether MPTP also causes degeneration of midbrain dopaminergic neurons in nuclei A8 and A10 in the mouse, as occurs in humans with Parkinson's disease. Two commonly used strains of mice were used: FVB/N and C57BL/6. MPTP was administered in cumulative doses of 50-300 mg/kg. Seven days later, dopamine concentrations were measured in the striatum using high performance liquid chromatography, and midbrain dopaminergic neurons were identified using an antibody against tyrosine hydroxylase. The cell locations were mapped with a computer imaging system. In the FVB/N strain, there was a dose-dependent decrease in striatal dopamine concentrations. Although the highest dose (300 mg/kg) caused an 86% reduction in striatal dopamine concentrations, there was only a moderate and non-significant loss of midbrain dopaminergic neurons. In the C57BL/6 strain, however, a high dose of MPTP (240 mg/kg) caused a significant reduction in both striatal dopamine concentrations (95%), and midbrain dopaminergic cells; 69% loss of nucleus A8 cells, 75% loss of nucleus A9 cells, and in nucleus A10 subnuclei there was 42% loss of ventral tegmental area cells, 55% loss of interfascicular nucleus cells, and no loss of cells in the central linear nucleus. These data (1) provide further evidence for differential susceptibility to MPTP toxicity among different mouse strains, (2) indicate that a significant depletion of striatal dopamine is not necessarily due to degeneration of midbrain dopaminergic neurons, (3) provide the precise locations of midbrain dopaminergic cells that are vulnerable to MPTP, which will aid future studies that seek to determine the mechanism/s by which-MPTP selectively destroys only certain midbrain dopaminergic neurons, and (4) indicate that MPTP produces midbrain dopaminergic neuronal degeneration in the same nuclei in the C57BL16 mouse that degenerate in humans with Parkinson's disease.

Midbrain dopaminergic neurons in the mouse that contain calbindin-D28k exhibit reduced vulnerability to MPTP-induced neurodegeneration

The calcium-binding protein calbindin-D28k (CB) is located in midbrain dopaminergic (DA) neurons that are less vulnerable to degeneration in Parkinson's disease and in an animal model of the disorder, the MPTP-treated monkey. The present study sought to determine whether CB-containing DA neurons are also less vulnerable to degeneration in the MPTP-treated mouse. Double-labelling immunocytochemical staining and computer imaging techniques were employed to map and quantify the tyrosine hydroxylase-, CB- and CB-containing tyrosine hydroxylase neurons in portions of nucleus A9 and nucleus A10 (ventral tegmental area and central linear nucleus) following MPTP treatment in the C57BL/6 mouse. A cumulative dose of 140 mg/kg MPTP produced a significantly greater loss of DA neurons that lack CB in both nucleus A9 (71 +/- 4%) and the ventral tegmental area (70 +/- 4%), compared to the loss of DA neurons that contain CB (44 +/- 6% and 25 +/- 14%, respectively). In the central linear nucleus there was no loss of CB-containing DA neurons. These data demonstrate that the presence of CB in midbrain DA neurons identifies a population of cells in the mouse that are less vulnerable to MPTP-induced degeneration. The mouse, therefore, can serve as a useful model in which to investigate the putative neuroprotective effects of CB in an animal model of Parkinson's disease.

Midbrain dopaminergic neurons in the mouse: co-localization with Calbindin-D28K and calretinin

The calcium-binding proteins Calbindin-D28k and calretinin are co-localized with dopamine in some of the midbrain dopaminergic neurons in the rat and monkey; the present study sought to examine the pattern of co-localization in the mouse. Double immunofluorescence staining procedures were used for tyrosine hydroxylase (a dopaminergic cell marker) and Calbindin-D28k or calretinin. Midbrain dopaminergic neurons were examined at four rostrocaudal levels, and the percentage of cells that contained both tyrosine hydroxylase and either of the two calcium-binding proteins was determined in nucleus A8 (retrorubral field), nucleus A9 (substantia nigra pars compacta, pars reticulata and pars lateralis) and nucleus A10 (nucleus paranigralis, ventral tegmental area, interfascicular nucleus, central linear nucleus). The two calcium-binding proteins were distributed similarly in midbrain dopaminergic neurons in the several nuclear groups that comprise nuclei A8, A9 and A10. The calcium-binding proteins were found in the majority (50-100%) of nucleus A10 neurons, whereas in nuclei A8 and A9 (except for the substantia nigra pars lateralis) less than 40% of the cells contained either calcium-binding protein. The pattern of co-localization in the mouse is similar to that reported for the rat and monkey. The calcium-binding proteins mark the population of midbrain dopaminergic neurons that are less vulnerable to degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease.

Midbrain dopaminergic neurons in the mouse: computer-assisted mapping

The dopaminergic (DA) neurons in the midbrain play a role in cognition, affect and movement. The purpose of the present study was to map and quantify the number of DA neurons in the midbrain, within the nuclei that constitute cell groups A8, A9 and A10, in the mouse. Two strains of mice were used; the C57BL/6 strain was chosen because it is commonly used in neurobiological studies, and the FVB/N strain was chosen because it is used frequently in transgenic studies. DA neurons were identified, in every fifth 20-microns-thick coronal section, using an antibody against tyrosine hydroxylase. Cell locations were entered into a computer imaging system. The FVB/N strain has 42% more midbrain DA neurons than the C57BL/6 strain; on one side of the brain there were 15,135 +/- 356 neurons (mean +/- S.E.M.) in the FVB/N strain, and 10,645 +/- 315 neurons in the C57BL/6 strain. In both strains, approximately 11% of the neurons were located in nucleus A8 (the DA neurons in the retrorubral field), 38% in nucleus A9 (the DA neurons in the substantia nigra pars compacta, pars reticulata, and pars lateralis), and 51% in nucleus A10 (the DA neurons in midline regions such as the ventral tegmental area, central linear nucleus, and interfascicular nucleus). The number of midbrain DA cells, and their distribution within the three nuclear groups, is discussed with respect to findings in other species.

Preliminary indications that functional effects of fetal caffeine exposure can be expressed in a second generation

Caffeine, added to the drinking water of males used for impregnation and gestant BALB/c mice such that their daily caffeine intake was 60 mg/kg, modified the passive avoidance behavior of the offspring when tested as adults. Caffeine-treated and control mice of the F1 generation were then cross-mated. The F2 generation was not exposed to caffeine but, when tested as adults, there were significant differences in passive avoidance latencies among the F2 mice. These data are a preliminary indication that effects resulting from fetal caffeine exposure in the F1 mice can be expressed in a second generation. Some cross-fostered groups of mice were tested in both the F1 and F2 generations as an initial control for postnatal maternal effects. F1 caffeine-treated mice also carried significantly smaller litters, implying that prenatal caffeine exposure could have affected the reproductive ability of these mice. It is tentatively concluded that a changed uterine environment, possibly interacting with an effect on the germ line, may be reflected in neurobehavioral effects in the second generation.

The effectiveness of different isomers of octanol as blockers of harmaline-induced tremor

Intracellular recording in the guinea-pig brainstem slice has demonstrated that high molecular weight alcohols block the low threshold calcium channel (LTCC) in the inferior olive (IO). These alcohols thus provide a tool for understanding the function of the pacemaking cellular networks of the olivo-cerebellar system, since the LTCC has been implicated in the oscillatory behavior of these neurons. Aspects of normal and pathological tremor are also believed to be mediated by these circuits, and thus development of effective ways of blocking the LTCC in vivo may eventually lead to novel treatments for essential tremor. The present experiments evaluated the effectiveness of the isomers of octanol in decreasing harmaline-induced tremor in vivo in the rat. Harmaline was used in this study because its tremorgenic action is mediated at the level of IO; octanol was found to be a potent antagonist of harmaline-induced tremor. Significant differences between the isomers further suggested conformational differences. This, taken in conjunction with the lack of effect of octanol in both IO lesioned rats and oxotremorine-induced tremor, implied that the action of the alcohol may be mediated at a specific binding site. These findings thus support the conclusions that the antagonism of harmaline-induced tremor by octanol occurs in the IO, and, in view of the previously reported in vitro data, that octanol may be an effective blocker of the LTCC in vivo.

The influence of chronic caffeine administration on sleep parameters in the cat

Caffeine (20 mg/kg/day) was administered per os to 5 cats for 21 days and sleep parameters were measured both during drug administration and over the withdrawal phase. The initial effect of caffeine was a marked increase in waking. As the animal habituated to the stimulant action of the methylxanthine, however, total sleep time normalized, although time spent in Stage II slow wave sleep (S2) remained below, and Stage I slow wave sleep (S1) above, control levels throughout the period of drug administration. In contrast, a significant increase in the S2/S1 ratio was recorded as soon as caffeine treatment ended, and this parameter remained elevated for about 30 days. Chronic caffeine administration has been previously shown to increase the number of central adenosine receptors, and it has also been reported that adenosine agonists increase S2 at the expense of S1. The present data were thus interpreted as indicating that the action of caffeine on sleep may be mediated at a central adenosine receptor site. Results also imply that changes induced in this receptor population by chronic caffeine administration last for at least 30 days after the drug is withdrawn.

Cholecystokinin modulates neurotransmission through the dentate gyrus

The sulfated and unsulfated cholecystokinin (CCK) octapeptide sequences and the pancreatic CCK antagonists, CR 1409 and benzotript, were administered iontophoretically while dentate gyrus granule cell activity was recorded in the anesthetized rat. During application of the compounds, the peri-stimulus time histogram (PSTH) was constructed of granule cell activity coupled to stimulation of the sciatic nerve. CCK and CR 1409, but not benzotript, were found to change significantly the PSTH by enhancing and prolonging the response to sensory stimulation. These results are interpreted as indicating that CCK can modulate impulse flow through the dentate gyrus.

Electrophysiological evidence for a functional differentiation between subtypes of the 5-HT1 receptor

Serotonin (5-HT) neurons in the dorsal (DRN) and median (MRN) raphe nuclei, and dopamine (DA) neurons in the substantia nigra (SN) were recorded extracellularly in the anesthetized rat. Compounds which have a relatively high affinity for the 5-HT1A or 5-HT1B subtypes of the 5-HT1 receptor were administered and their effect on the firing rate of the monoamine cells was determined. 5-HT1A ligands were more potent in inhibiting impulse activity in the DRN than in the MRN, but had little effect in the SN. In contrast, 5-HT1B ligands increased the firing rate of MRN 5-HT units at low doses, and were also effective inhibitors of DA cell firing in the SN. These results could be correlated with recently described differences in the distribution of the 5-HT1A and 5-HT1B receptor subtypes, and were interpreted as indicating possible functional differentiation between these subtypes. In particular, agonist activity at the 5-HT1B autoreceptor site may decrease 5-HT release, suggesting a presynaptic locus for this receptor in the somatodendritic region. The site also appears to be implicated in 5-HT modulation of nigral DA impulse flow.

Partial reversal of barbiturate anesthesia by dopamine antagonism: an electroencephalographic study

The D-1 dopamine antagonist, SCH 23390, was administered to rats under barbiturate anesthesia. Recording of the power frequency spectrum of the electroencephalogram (EEG) showed that the D-1 antagonist shifted the relative power in the EEG to higher frequencies. In contrast, a relatively selective D-2 antagonist, haloperidol, administered under the same conditions, had no effect. These results suggest that SCH 23390 can partially reverse barbiturate anesthesia, and imply that central dopamine, acting at the D-1 site, might modulate this type of anesthetic.

Cholecystokinin and cholecystokinin antagonists enhance postsynaptic excitability in the dentate gyrus

The sulfated and unsulfated octapeptide cholecystokinin (CCK) sequences and the pancreatic CCK antagonists, CR 1409 and benzotript, were applied iontophoretically in the rat dentate gyrus granular layer while the response evoked by single pulse stimulation of the perforant path was recorded. The stimulating current was varied and the resulting relationship between the slope of the response (input) against the population spike amplitude (output) was used as a measure of excitability at the granule cell synapse. All four test compounds shifted the input/output curve to the left indicating an increase in postsynaptic excitability. These results thus imply that endogenous CCK acts at the central type of CCK receptor to modulate cortical input to granule cells by reducing the threshold for synaptic excitation.

Cholecystokinin and an evoked response in the dentate gyrus

Cholecystokinin (CCK) as the sulfated (CCK-8S) and unsulfated (CCK-8U) octapeptide sequences, and CR 1409 were administered intraventricularly while the action potential (EAP) in the granular cell layer of the hippocampal dentate gyrus evoked by perforant path stimulation was recorded. No consistent effect of the test substances on the amplitude of the EAP was found at doses corresponding to those previously reported to cause an increase in the EAP when administered systemically. Similarly, no effect of CCK on the EAP could be found when the peptide was administered iontophoretically in the granular cell layer. In contrast, iontophoretically applied CCK-8S, CCK-8U and CR 1409 slightly but consistently reduced the slope of the evoked response recorded in the dentate gyrus molecular layer. These results are interpreted as indicating that the CCK receptor on granular cell dendrites is likely to be the central type that is activated by both CCK-8S and CCK-8U, but that any effects of systemically administered CCK on the EAP are probably mediated in the periphery.

CGS 19755, a selective and competitive N-methyl-D-aspartate-type excitatory amino acid receptor antagonist

CGS 19755 (cis-4-phosphonomethyl-2-piperidine carboxylic acid) was found to be a potent, stereospecific inhibitor of N-methyl-D-aspartate (NMDA)-evoked, but not KCl-evoked, [3H] acetylcholine release from slices of the rat striatum. The concentration-response curve to NMDA was shifted to the right by CGS 19755 (pA2 = 5.94), suggesting a competitive interaction with NMDA-type receptors. CGS 19755 inhibited the binding of [3H]-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid to NMDA-type receptors with an IC50 of 50 nM, making it the most potent NMDA-type receptor antagonist reported to date. CGS 19755 failed to interact with 23 other receptor types as assessed by receptor binding, including the quisqualate- and kainate-type excitatory amino acid receptors. In crude P2 fractions, no evidence was obtained to suggest that CGS 19755 is taken up by an active transport system. Furthermore, CGS 19755 failed to affect the uptake of L-[3H]glutamate, or to interact with aconitine-induced inhibition of L-[3H]glutamate uptake, the latter finding suggesting a lack of membrane-stabilizing or local anesthetic properties. CGS 19755 selectively antagonized the excitatory effect of iontophoretically applied NMDA in the red nucleus of the rat without affecting the excitatory effects of quisqualate. CGS 19755 blocked the harmaline-induced increase in cerebellar cyclic GMP levels at a dose of 4 mg/kg i.p. with a duration of action exceeding 2 hr. CGS 19755 inhibited convulsions elicited by maximal electroshock in rat (ED50 = 3.8 mg/kg i.p. 1 hr after administration) and in mouse (ED50 = 2.0 mg/kg i.p. 0.5 hr after administration). Likewise, convulsions elicited by picrotoxin were inhibited by CGS 19755, whereas the compound was relatively weak in protecting against convulsions elicited by pentylenetetrazole or strychnine. CGS 19755 produced retention performance deficits in a dark avoidance task. However, CGS 19755 did not show a unique propensity for learning and memory disruption compared to other anticonvulsants.

Biochemical and pharmacological characterization of CGS 12066B, a selective serotonin-1B agonist

CGS 12066B is a novel pyrroloquinoxaline with selectivity for the serotonin-1B (5HT1B) recognition site as assessed by binding, biochemical and electrophysiological studies. The compound had an IC50 value of 51 nM at the 5HT1B recognition site as determined using the binding of [3H]5HT in the presence of 1 microM spiperone. At the 5HT1A receptor the compound had an IC50 value of 876 nM, providing a 5HT1A/5HT1B ratio of 17 in contrast to the putative 5HT1B selective agent trifluoromethylphenylpiperazine (TFMPP) which had a corresponding ratio of 3.6. The compound had minimal affinity for alpha 1-, alpha 2- and beta-adrenoceptors and for dopamine D-1 and D-2 receptors. CGS 12066B, in contrast to TFMPP, which was inactive, was found to inhibit dorsal raphe cell firing with an ED50 value of 358 nmol/kg i.v. The corresponding values for the 5HT1A selective agonists 8-OH-DPAT and ipsapirone were 1.3 and 33 nmol/kg. CGS 12066B was also effective in decreasing rat brain 5-HTP concentrations and inhibiting in vitro 5HT release. The data obtained indicate that CGS 12066B is a reasonably active 5HT1B site agonist, which due to its selectivity as compared to compounds such as TFMPP, will be a useful tool for evaluating the physiological role of such receptors in the mammalian CNS.

Modulation of auditory evoked magnetic fields by benzodiazepines

The N1 and P2 components of the auditory evoked magnetic field were shown to be modified by the benzodiazepines diazepam and triazolam. Previous studies indicate that the electrical sources of these components are located in the auditory cortex, implying that benzodiazepines have a direct or indirect effect on neuronal activity at this level. The recorded changes were comparable to those previously reported using auditory evoked potential measurements. These results suggest that magnetic recordings may eventually be used as a sensitive, supplementary and location-specific measure of the central action of psychoactive substances.

Anaesthetic and forebrain modulation of raphe-coerulean interactions

Variations in tyrosine hydroxylase (TH) activity and serotonin (5-HT) content in the rat locus coeruleus were measured four days after lesion of the nucleus raphe centralis superior. Lesions were made under either ether or pentobarbital anaesthesia and, in addition, (under ether) in rats pretreated with atropine or with lesions of the medial septum. Results showed a dissociation between 5-HT reduction and TH induction, differences due to the anaesthetic used, and a possible influence from limbic centres on 5-HT in the LC. These findings are discussed in terms of the apparent complexity of raphe-coerulean interactions.

Paradoxical sleep and coping with environmental change

Long-term sleep recordings of mice from 3 inbred strains showed that the amount of time spent in sleep over successive 24-h periods varied as the subjects adapted to experimental conditions. A sinusoidal type variation, with a period of about 15 days, modulating the basic trends in sleep times is described; but the principal finding of this study relates to a monotonic decrease in Paradoxical Sleep (PS) as recording continued. Age, stimulus deprivation and fatigue effects do not appear to be causative factors for this decrement, indicating that the changes in PS might reflect a habituation process. On this basis it is hypothesized that an increase in PS time in the mouse is a specific response to a significant environmental stimulus and could, therefore, form part of the coping strategy. This hypothesis is generalized and discussed in terms of its implications, both for experimentation concerned with measuring PS times and with the possible functional significance of PS.

Increased sleep time in the offspring of caffeine-treated dams from two inbred strains of mice

Dams from two inbred strains of mice (C57BR and BALB/c) were treated with caffeine in solution in their drinking water during gestation. Doses of caffeine used corresponded to about 60, 80 or 100 mg/kg/day; controls received tap water. The offspring (as adults) revealed a significantly increased sleep time following caffeine treatment, but primarily as slow wave sleep in the males of the BALB/c strain and paradoxical sleep in the females of the C57BR strain. BALB/c females and C57BR males were relatively unaffected. These results, and in particular the sex differences, are discussed in terms of a possible central site of action of caffeine.