Insufficient sleep impairs cognitive functions in humans and animals. However, whether long-term synaptic plasticity, a cellular substrate of learning and memory, is compromised by sleep loss per se remains unclear because of confounding factors related to sleep deprivation (SD) procedures in rodents. Using an ex vivo approach in C57BL/6J mice, we show that sleep loss rapidly and reversibly alters bidirectional synaptic plasticity in the CA1 area of the hippocampus. A brief (ϳ4 h) total SD, respecting the temporal parameters of sleep regulation and maintaining unaltered low corticosterone levels, shifted the modification threshold for long-term depression/long-term potentiation (LTP) along the stimulation frequency axis (1-100 Hz) toward the right. Reducing exposure to sensory stimuli by whisker trimming did not affect the SD-induced changes in synaptic plasticity. Recovery sleep reversed the effects induced by SD. When SD was combined with moderate stress, LTP induction was not only impaired but also occluded. Both electrophysiological analysis and immunoblotting of purified synaptosomes revealed that an alteration in the molecular composition of synaptically activated NMDA receptors toward a greater NR2A/NR2B ratio accompanied the effects of SD. This change was reversed after recovery sleep. By using an unparalleled, particularly mild form of SD, this study describes a novel approach toward dissociating the consequences of insufficient sleep on synaptic plasticity from nonspecific effects accompanying SD in rodents. We establish a framework for cellular models of cognitive impairment related to sleep loss, a major problem in modern society.

Ligands acting at the benzodiazepine (BZ) site of ␥-aminobutyric acid type A (GABAA) receptors currently are the most widely used hypnotics. BZs such as diazepam (Dz) potentiate GABAA receptor activation. To determine the GABAA receptor subtypes that mediate the hypnotic action of Dz wild-type mice and mice that harbor Dz-insensitive ␣1 GABAA receptors [␣1 (H101R) mice] were compared. Sleep latency and the amount of sleep after Dz treatment were not affected by the point mutation. An initial reduction of rapid eye movement (REM) sleep also occurred equally in both genotypes. Furthermore, the Dz-induced changes in the sleep and waking electroencephalogram (EEG) spectra, the increase in power density above 21 Hz in non-REM sleep and waking, and the suppression of slow-wave activity (SWA; EEG power in the 0.75-to 4.0-Hz band) in non-REM sleep were present in both genotypes. Surprisingly, these effects were even more pronounced in ␣1(H101R) mice and sleep continuity was enhanced by Dz only in the mutants. Interestingly, Dz did not affect the initial surge of SWA at the transitions to sleep, indicating that the SWA-generating mechanisms are not impaired by the BZ. We conclude that the REM sleep inhibiting action of Dz and its effect on the EEG spectra in sleep and waking are mediated by GABAA receptors other than ␣1, i.e., ␣2, ␣3, or ␣5 GABAA receptors. Because ␣1 GABAA receptors mediate the sedative action of Dz, our results provide evidence that the hypnotic effect of Dz and its EEG ''fingerprint'' can be dissociated from its sedative action.F ast synaptic inhibition in the mammalian central nervous system is largely mediated by activation of ␥-aminobutyric acid type A (GABA A ) receptors. GABA A receptors are heteromeric membrane proteins that operate as GABA-gated ion channels. Most GABA A receptors are composed of ␣, ␤, and ␥ 2 subunits with a pentameric stoichiometry (1). GABA A receptor function can be enhanced by allosteric modulators, e.g., benzodiazepines (BZ), barbiturates, and neurosteroids. This enhancement of neuronal inhibition by GABA is one of the most powerful therapeutic strategies for treatment of central nervous system diseases such as sleep disturbances, anxiety disorders, muscle spasms, and seizure disorders (2). Classical BZ like diazepam (Dz) bind to GABA A receptors that contain the ␣ subunits ␣1, ␣2, ␣3 or ␣5, hereafter called ␣1, ␣2, ␣3, or ␣5 GABA A receptors, respectively (3). GABA A receptors containing the ␣4 or ␣6 subunits are insensitive to Dz. The ␣ subunits show distinct patterns of distribution in the brain (4).The ␣1 GABA A receptors represent Ϸ60% of all Dz-sensitive GABA A receptors in the brain and are found mainly in the cerebral and cerebellar cortex, thalamus, and pallidum (4). To assess the functions of this most prevalent receptor subtype in the pharmacological spectrum of Dz, a point-mutated knock-in mouse line, [␣1(H101R)], in which the ␣1 GABA A receptors are insensitive to Dz, has been developed (5, 6). These mice represent a useful tool to distinguish between Dz acti...

No abstract

The inhibitory neurotransmitter ␥-aminobutyric acid (GABA) is involved in the generation of various brain rhythmic activities that can be modulated by benzodiazepines. Here, we assessed the contribution of ␣2GABA type A (GABAA) receptors to the effects of benzodiazepines on sleep and waking oscillatory patterns by combining pharmacological and genetic tools. The effects of diazepam on the electroencephalogram were compared between ␣2(H101R) knock-in mice in which the ␣2GABAA receptor was rendered diazepam-insensitive, and their wild-type controls. The suppression of delta activity typically induced by diazepam in non-rapid eye movement (REM) sleep was significantly stronger in wild-type control mice than in ␣2(H101R) mice. Moreover, electroencephalogram frequency activity above 16 -18 Hz was enhanced in wild-type mice both in non-REM sleep and waking. This effect was absent in ␣2(H101R) mice. Theta activity was enhanced after diazepam both in REM sleep and in waking in wild-type mice. In ␣2(H101R) mice, this effect was markedly reduced in REM sleep whereas it persisted in waking. These findings suggest that ␣2GABAA receptors, which are expressed in hypothalamic and pontine nuclei and in the hippocampus, are localized in distinct neural circuits relevant for the modulation of rhythmic brain activities by benzodiazepines.T he main inhibitory neurotransmitter ␥-aminobutyric acid (GABA) is involved in the generation of various rhythmic activities in the brain (1-3). By potentiating the GABAergic neurotransmission through an allosteric modulation of GABA type A (GABA A ) receptors, benzodiazepines and analogs modify sleep and waking electroencephalogram (EEG) patterns. In humans and rodents, these compounds typically reduce EEG delta activity in non-rapid eye movement (NREM) sleep (4-14). In addition, in humans, benzodiazepines enhance NREM sleep EEG power in the spindle frequency range (7). In rodents, EEG activity was increased in a broader band encompassing frequencies above the spindle range both in NREM sleep and in waking (9)(10)(11)13). Recently, an increase of theta activity in rapid eye movement (REM) sleep and waking was reported in mice injected with diazepam (9, 13).The mechanisms underlying the effects of benzodiazepines on the sleep EEG have not yet been identified. Benzodiazepines potentiate the GABA-induced chloride influx by increasing the affinity of GABA to its binding site on GABA A receptors containing ␣ 1 , ␣ 2 , ␣ 3 or ␣ 5 subunits, hereafter called ␣ 1 -, ␣ 2 -, ␣ 3 -, and ␣ 5 GABA A receptors (15). These receptor subtypes are differentially distributed in the brain (16, 17) and mediate selective psycho-pharmacological properties of benzodiazepines (18-24).The ␣ 1 -and ␣ 3 GABA A receptor subtypes are predominant in the corticothalamic network (16, 25), which is responsible for the generation of delta oscillations and spindle activity in NREM sleep (1,(26)(27)(28)(29). Surprisingly, the typical suppression of delta activity in NREM sleep after diazepam was largely present in point-mutated mice...

Somatostatin (SRIF) controls many physiological and pathological processes in the central nervous system but the respective roles of the five receptor isotypes (sst1–5) that mediate its effects are yet to be defined. In the present study, we attempted to identify functions of the sst2 receptor using mice with no functional copy of this gene (sst2 KO mice). In contrast with control 129Sv/C57Bl6 mice, sst2 mRNA was no longer detectable in the brain of sst2 KO mice; 125I‐labeled Tyr0DTrp8‐SRIF14 binding was also greatly reduced in almost all brain structures except for the hippocampal CA1 area, demonstrating that sst2 accounts for most SRIF binding in mouse brain. Invalidation of this subtype generated an increased anxiety‐related behaviour in a number of behavioural paradigms, while locomotor and exploratory activity was decreased in stress‐inducing situations. No major motor defects could be detected. sst2 KO mice also displayed increased release of pituitary ACTH, a main regulator of the stress response. Thus, somatostatin, via sst2 receptor isotype pathways, appears involved in the modulation of locomotor, exploratory and emotional reactivity in mice.