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The important role of brain stem cholinergic neurons in REM sleep control is discussed in section IV. However, in another report, the occurrence of in vitro kainate-induced sharp waves was actually increased in these mice Hint Resolve pair inl inr: Lesioning of the cholinergic neurons reduced the homeostatic response to sleep deprivation, but again this required an extensive destruction of cholinergic neurons , , Definition andb b1 b2: Cytokines are best known for their role in the immune system response to infection which includes enhanced sleep Thus it appears that there is considerable redundancy in the cholinergic system, and effects are only seen with extensive lesions. Furthermore, glutamatergic inputs to orexin neurons are potentiated via a cAMP-dependent mechanism during prolonged waking , which is a mechanism suggested to be important in the maintenance of wakefulness in the face of increased sleep pressure

This idea is supported by large-scale computational models of the thalamocortical system , Basic properties of andb. Calcium influx through the low-threshold channels allows activation of calcium-dependent potassium conductances, restarting the cycle. Labels indicate behavioral state: Consistent with the BF being a crucial site mediating adenosine effects, local perfusion of an A 1 receptor antagonist in this region activated wake-active neurons 17 , , and localized suppression of A 1 receptor expression using antisense oligonucleotides significantly reduced spontaneous sleep time as well as the homeostatic sleep response Low-amplitude gamma 30— Hz and beta 15—30 Hz frequency rhythms are a prominent feature of the EEG during quiet waking baseline or spontaneous gamma; FIGURE 1 and are enhanced in particular cortical areas following presentation of sensory stimuli evoked or steady-state gamma. Fast spiking interneurons containing parvalbumin PV that synapse onto the cell bodies of pyramidal neurons are particularly important in generating gamma oscillations.

CONTROL OF SLEEP AND WAKEFULNESS

Recent evidence suggests that sleep intensity, as measured by Revvoir, can be modulated locally in the cortex in a use-dependent fashion, However, a subpopulation also fires in bursts In vitro studies in culture and brain revokr have shown that NO donors cause release of adenosine, which in turn inhibits neuronal activity, In fact, gamma rhythms are enhanced by stimulation of the mesencephalic reticular formation, the origin of the ascending reticular activating system In the rat and mouse brain atlases of Paxinos and colleaguesthe REM control region is also termed Revlir dorsal or alpha parts ; however, in these species the region immediately ventral to the LC is cell-poor and the REM-control neurons particularly those involved in muscle atonia appear to ka located slightly more rostrally, ventral to the cholinergic neurons of the laterodorsal tegmental nucleus LDT.

This idea is supported by large-scale computational models of the thalamocortical system The cellular mechanisms in the suprachiasmatic nucleus SCN which generate circadian rhythms are not covered herein, since they have been reviewed extensively elsewhere Upon presentation of external stimuli requiring a response, the default network regions show a decrease in activity, in contrast to other cortical areas that show increases or no change.

REM sleep is defined by the strong synchronous theta range 7—9 Hz activity, probably generated in the hippocampus. In contrast, adenosine levels lz not follow this pattern in other brain areas such as the preoptic area of belle hypothalamus, ventral thalamus, DRN, or pedunculopontine tegmentum.

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Calcium influx through the low-threshold channels allows activation of calcium-dependent potassium conductances, restarting the cycle.

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In contrast to orexin knockout animals, Episod or histamine H 1 receptor knockout animals do not have reduced duration of sleep-wake states 29and optogenetic stimulation of orexin neurons is still able to increase the probability of awakening in HDC knockout animals.

The ability to elicit gamma rhythms in isolated brain slices in vitro,together with current-source density and cross-correlational analysis in vivo 26, suggests that gamma rhythms are generated locally in the cortex.

Bursts of action potentials in thalamocortical neurons lead to a prominent burst in large numbers of cortical pyramidal neurons. Lesioning of the cholinergic neurons reduced the homeostatic response to sleep deprivation, but again this required an extensive destruction of cholinergic neurons, Retrograde tracing revealed surprisingly few cholinergic projections to VLPO but prominent projections from the histaminergic tuberomammillary nucleus, norepinephrine neurons in the LC and bele medulla, and serotonergic neurons in the dorsal median and central linear raphe nuclei These data all support a role for these neurons in control of wakefulness, but electrophysiological recordings from these neurons across behavioral state are lacking at present.

Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. A summary of studies involving inactivation of different parts of the brain controlling sleep and wake is provided in TABLE 1.

In contrast to norepinephrine and histamine neurons, most serotonin neurons recorded in vitro do not fire action potentials spontaneously Synchronization of spindles is achieved via recurrent inhibitory and electrical synaptic connections between thalamic reticular neurons A branch of this system innervates the rostral BF theta rhythm generator.

Hence, it is not surprising that some populations of the neurons utilizing these two neurotransmitters are involved in promoting wakefulness, whereas others are associated with sleep. Location of brain nuclei controlling the sleep-wake cycle see sects. NREM sleep exhibits a significant increase of delta range activity, as well as an increase in amplitude.

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Synchrony is enhanced by electrical synapses mediated by gap junctions between interneuronal networks and between the axons of pyramidal neurons as well as by interneuron-interneuron chemical synapses Thus adenosine induces sleep and adenosine levels track sleep need, fulfilling the criteria for adenosine being a homeostatic sleep factor.

Identified, cortically-projecting cholinergic neurons in the caudal BF substantia innominata, horizontal limb of the diagonal band, magnocellular preoptic area, nucleus basalis fire fastest during both wakefulness and REM sleep, and their firing is correlated with cortical activation, Simplified model of cortical circuitry generating gamma oscillations. In particular, adenosine levels correlate with time awake in the region of the caudal BF containing cortically projecting wake-active revoid, and in the cortex itself.

The ascending fibers from episodf brain stem include glutamatergic parabrachialnoradrenergic locus coeruleus, LCserotonergic dorsal regoir median rapheand dopaminergic periaqueductal gray neurons.

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Specific roles for these systems could be 1 facilitation of LVFA acetylcholine ; 2 inhibition of sleep-active neurons norepinephrine, serotonin, acetylcholine; see sect. Studies involving stimulation of the brain areas and neurotransmitter systems comprising the ARAS revior report EEG activation and wakefulness as a result.

Such a signal may be NO see next section. Blle vitro work in the cat thalamus suggests that alpha rhythms require stimulation of muscarinic cholinergic receptors mimicking brain stem input or stimulation of metabotropic glutamate receptor stimulation mimicking cortical input.

However, their dependence on behavioral state and stimulus presentation indicates that their occurrence is also dependent on subcortical inputs.

In these animals, each PGO wave was accompanied by a depolarization of relay neurons lasting — ms, interrupted by a short-lasting 50—60 ms hyperpolarization occurring 40—80 ms after the onset of the depolarization due to the coactivation of GABAergic geniculate interneurons. The activity of brain stem reticular neurons, the origin of both of these pathways, reliably predicts the onset of changes in behavioral state, Intraventricular administration of cortistatin increased cortical slow waves This section describes the mechanisms underlying the EEG signs of NREM sleep also called slow-wave sleep and the mechanisms that cause the circadian and homeostatic inhibition of wake-promoting ARAS neurons.

Administration of NO donors enhances neuronal activity in the thalamus and neocortexwhile NOS inhibitors cause inhibition of thalamic cell activity.

Fast-spiking interneurons containing PV generate gamma rhythms. A subset of this area, containing caudally projecting neurons involved in REM muscle atonia, and with tonic firing patterns very specific to REM sleep was termed the peri-LC alpha.

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Recurrent glutamatergic synapses onto Plua interneurons provide excitatory drive to the fast spiking interneurons. Alpha rhythms may play an episkde role in internally directed thought processes since they are strengthened during tasks requiring mental arithmetic and visual imagery The ascending plhs controlling forebrain theta rhythm are discussed in section II A.

Theta occurring during REM sleep appears to represent a combination of type I and type II, since revoit sulfate abolished continuous lower-frequency theta during tonic REM periods whilst leaving intact intermittent, higher frequency hippocampal theta during periods with muscle twitches Low-amplitude gamma 30— Hz and beta 15—30 Hz frequency rhythms are a prominent feature of the EEG during quiet waking baseline or spontaneous gamma; FIGURE 1 and are enhanced in particular cortical areas following presentation of sensory stimuli evoked or steady-state gamma.

This theory proposes the following:. Cortically-projecting GABA neurons are located in the BF,hypothalamus [colocalized in histamineand melanin-concentrating hormone neurons 60 ] and in the VTA In the BF, caudally projecting, possibly sleep-active, GABA neurons are intermingled with cortically projecting cholinergic, GABAergic, and glutamatergic neurons which increase firing in association with cortical activation