A key role for the caudoventral pontine tegmentum in the simultaneous generation of eye saccades in bursts and associated ponto-geniculo-occipital waves during paradoxical sleep in the cat.

Ponto-geniculo-occipital waves and rapid eye movements (eye saccades) are two prominent phasic events of paradoxical sleep which occur in conjunction. Although they have been studied intensively, the neuronal link between these two events is still poorly understood. On the basis of our previous results, combining brainstem transections and carbachol microinjections, we postulated that the oculomotor and ponto-geniculo-occipital systems do not work in series, but in parallel, and that the caudoventral pontine tegmentum might represent a structure controlling and/or co-ordinating the simultaneous production of the two phenomena. This hypothesis was further supported by the demonstration that, during paradoxical sleep, the instantaneous velocity of eye saccades in bursts is higher than that of isolated ones which, in turn, are more rapid than waking saccades. This acceleration of eye saccades in bursts also seems to be under the cholinergic control of the caudoventral pontine tegmentum. In order to test the hypothesis that this area may be a prime mover leading to the simultaneous appearance of these two phasic events as a whole, we investigated, in the present study, the effects of pharmacological stimulation (with carbachol) and inhibition (with atropine) of the caudoventral pontine tegmentum on the production and the characteristics of eye saccades and ponto-geniculo-occipital waves. Cats' eye movements were recorded using the technique of the scleral search coil in a magnetic field, together with sleep-waking parameters. We found that: (i) unilateral microinjections of carbachol (0.4 microg) induced, during waking, a majority of long bursts of ponto-geniculo-occipital waves (i.e. bursts containing at least five waves) which had intra-burst intervals similar to natural ones (48-259 ms) and decreased the frequency of isolated ponto-geniculo-occipital waves; (ii) unilateral microinjections of atropine (2.4 microg) strongly decreased, during paradoxical sleep, the frequency (number/min) of eye saccades in bursts directed contralaterally to the side of the injection (by 48-54%) and reduced the velocity of these saccades to that of isolated eye saccades. Atropine also significantly reduced the frequency (by 60%) of all types of bursts of ponto-geniculo-occipital waves, with a maximal effect (80% reduction) on long bursts of ponto-geniculo-occipital waves, while it increased the frequency of isolated ponto-geniculo-occipital waves. However, atropine did not change the value of intra-burst intervals. These findings support the hypothesis that eye saccades in bursts and associated ponto-geniculo-occipital waves are generated as a whole by a common structure and that this structure is at least partly defined by the caudoventral pontine tegmentum.

Waking selective neurons in the posterior hypothalamus and their response to histamine H3-receptor ligands: an electrophysiological study in freely moving cats.

Neurons which discharge selectively during waking (waking selective) have been found in the tuberomamillary nucleus (TM) and adjacent areas of the posterior hypothalamus. Although they share some electrophysiological properties with aminergic neurons, there is no direct evidence that they are histaminergic. We have recorded from posterior hypothalamic neurons during the sleep-wake cycle in freely moving cats, and investigated the effects on waking selective neurons of specific ligands of histaminergic H3-receptors, which autoregulate the activity of histaminergic neurons. Two types of neurons were seen. Waking selective neurons, termed "waking-on (W-on)," were located exclusively within the TM and adjacent areas, and discharged at a low regular rate during waking (1.71-2.97 Hz), decreased firing during light slow wave sleep (SWS), became silent during deep SWS and paradoxical sleep (PS) and resumed their activity on, or a few seconds before, awakening. "Waking-related" neurons, located in an area dorsal to the TM, displayed a similar, although less regular, low rate of firing (1.74-5.41 Hz) and a similar discharge profile during the sleep-wake cycle; however, unlike "W-on" neurons, they did not completely stop firing during deep SWS and PS. Intramuscular (i.m.) injection of ciproxifan (an H3-receptor antagonist, 1mg/kg), significantly increased the discharge rate of W-on neurons and induced c-fos expression in histamine-immunoreactive neurons, whereas i.m. injection of imetit (an H3-receptor agonist, 1mg/kg) or microinjection of alpha-methylhistamine (another H3-receptor agonist, 0.025-0.1 microg/0.2 microl) in the vicinity of these cells significantly decreased their discharge rate. Moreover, the effect of the antagonist was reversed by the agonists and vice versa. In contrast, "waking-related" neurons were unaffected by these H3-receptor ligands. These data provide evidence for the histaminergic nature of "W-on" neurons and their role in cortical desynchronization during waking, and highlight the heterogeneity of posterior hypothalamic neuronal populations, which might serve different functions during the wakefulness.

A critical role of the posterior hypothalamus in the mechanisms of wakefulness determined by microinjection of muscimol in freely moving cats.

In order to determine critical sites within the hypothalamus responsible for the induction and maintenance of wakefulness (W), we performed microinjections of muscimol, a potent gamma-aminobutyric acid (GABA) agonist, in various lateral hypothalamic regions of freely moving cats. We found that bilateral injections of a small amount of muscimol (0.1-1.0 micrograms/0.5 microliters) in the preoptic and anterior hypothalamus and rostral mesencephalic tegmentum resulted in increased vigilance and insomnia. In contrast, microinjections of muscimol in the middle and anterior parts of the posterior hypothalamus induced long-lasting behavioral and electroencephalographic signs of sleep with short latency. The hypersomnia was characterized by a significant increase in both light and deep slow wave sleep (SWS), and a nearly complete suppression of paradoxical sleep (PS). Animals with muscimol microinjections in the ventrolateral part of the posterior hypothalamus, however, exhibited increased SWS followed by a significant increase in PS. When injected into the posterior hypothalamus of insomniac cats pretreated with p-chlorophenylalanine (PCPA), muscimol induced not only SWS but also PS with short latency. The present data thus support the hypotheses that the posterior hypothalamus plays a critical role in the mechanisms of W and that sleep might result from functional blockade of the hypothalamic waking center.

Involvement of histaminergic neurons in arousal mechanisms demonstrated with H3-receptor ligands in the cat.

The effects of histamine H3-receptor ligands on sleep-waking parameters were studied in freely moving cats. Oral administration of (R)alpha-methylhistamine (alpha MHA), a H3-agonist, caused a significant increase in deep slow wave sleep while that of thioperamide, a H3-antagonist, enhanced wakefulness in a marked and dose-dependent manner. The arousal effects of thioperamide were prevented by pretreatment with alpha MHA or mepyramine, a H1-receptor antagonist. The findings support the hypothesis that the histaminergic neurons are critically involved in arousal mechanisms and suggest that H3-receptors play an active part in these mechanisms by regulating histamine transmission.

The caudo ventral pontine tegmentum is involved in the generation of high velocity eye saccades in bursts during paradoxical sleep in the cat.

Cat eye movements were recorded in the head restrained condition, with the technique of the scleral search coil in a magnetic field, and the maximum velocity/amplitude relationships were analyzed for saccades in the following conditions, (1) during waking (W); (2) during paradoxical sleep (PS); and (3) during W following carbachol microinjections in the medioventral part of the caudal pontine tegmentum. These findings indicate that (1) the neurophysiological mechanisms underlying carbachol induced events are similar to those acting during PS and that the caudal pontine tegmentum might be the generator of high velocity eye saccades in bursts accompanied by ponto geniculo occipital waves (PGOw) during PS, and (2) caudal pontine tegmentum neurons show 'state-dependent' responsiveness to cholinergic inputs, suggesting that a change in the synaptic inputs and/or the membrane properties of these neurons during PS may be responsible for the induction of saccadic eye movements in bursts and associated PGOw.

Carbachol microinjections in the mediodorsal pontine tegmentum are unable to induce paradoxical sleep after caudal pontine and prebulbar transections in the cat.

In 7 cats, total transections of the brainstem at the caudal pontine or the prebulbar level led to preparations which presented neither behavioral nor electrophysiological signs of paradoxical sleep (PS) throughout their survival periods (17-30 days). Carbachol microinjections in the mediodorsal pontine tegmentum (MDPT), which induced PS in the intact cat, were no longer able to induce it in the transected animals. Rapid eye movement (REM) and pontogeniculo-occipital (PGO)-like bursts were evoked by carbachol microinjections in the pontine magnocellular tegmental field (FTM) of cats transected at the prebulbar level, as in the intact cat. Only REM bursts were obtained by the same injections in caudal pontine transected cats. It is concluded that (1) the pons is insufficient to generate PS; (2) complex reciprocal interactions with the medulla are necessary for the generation of this state of sleep; and (3) the production of long REM and PGO bursts is controlled by the caudal pontine tegmentum.

Effect of decerebration on blood pressure during paradoxical sleep in cats.

We investigated the effects of decerebration on long-term variations in arterial blood pressure during paradoxical sleep (PS) in cats. In normal cats, the blood pressure decreased during the transition from slow wave sleep to PS and maintained its lower level throughout PS for several days after surgery. After this early postoperative stage, however, the arterial hypotension was replaced by tonic and phasic rises in blood pressure during PS. Such long-term changes in blood pressure were completely abolished when the brain stem was transected at the ponto-mesencephalic junction, and the cats consistently exhibited a sustained fall in blood pressure throughout the survival periods of 1 month or more.

Long-term variations of arterial blood pressure during sleep in freely moving cats.

Using a new telemetric system for arterial blood pressure recordings, we have investigated long-term postoperative changes in blood pressure during sleep in freely moving cats. Particular attention was paid to the transitional periods at the beginning and end of paradoxical sleep (PS), as well as to the relationship between the blood pressure and ponto-geniculo-occipital (PGO) waves. In the initial postoperative stage lasting 2 to 5 days, the blood pressure decreased during the transition from slow wave sleep (SWS) to PS and maintained its lower level until the end of PS. In contrast, in the later chronic stage, the blood pressure increased tonically during the transition from SWS to PS and maintained its higher level throughout PS on which several phasic rises in blood pressure were superimposed. A significant increase in arterial pressure during the transitional period began shortly after the first appearance of PGO waves. On the other hand, significant phasic rises in arterial pressure during PS shortly preceded the onset of PGO wave bursts.

Mapping of cholinoceptive brainstem structures responsible for the generation of paradoxical sleep in the cat.

In order to determine the cholinoceptive brainstem structures critical for PS generation, we investigated the effect on PS induction of the injection of a small dose and volume (0.4 microgram/0.2 microliter) of the cholinergic agonist carbachol in the following caudal brainstem structures: 1) the caudal mesencephalic reticular formation, especially the nucleus pedunculopontinus pars compacta or X area; 2) the mediodorsal pontine tegmentum, in particular the nuclei locus coeruleus (LC), locus coeruleus alpha (LC alpha), peri-locus coeruleus alpha (peri-LC alpha) and laterodorsalis tegmenti (Ldt); 3) the pontine; and 4) bulbar gigantocellular (FTG) and magnocellular tegmental fields (FTM). We found that the only brainstem area from which a high amount of PS was induced by carbachol applications with short latencies, less than 5 minutes, is the mediodorsal pontine tegumentum, namely the LC alpha and peri-LC alpha, where ChAT-and TH- immunoreactive neurons are intermingled. Injections in an area immediately ventral to the peri-LC alpha induced physiological states resembling PS but lacking certain electrophysiological (PS-like) and behavioral components of PS (dissociated states I and II). The weak PS induction following carbachol administration in the anteromedial part of the FTG was due to the spread of the drug toward the efficient site since the latencies to PS onset were in the range of 20 to 60 minutes. No effects on PS generation were obtained after carbachol microinjections in the LC and the laterocaudal part of the FTG, while carbachol injections in the X area or in the bulbar FTG or FTM resulted in the increase of waking and the decrease of PS. In addition to these effects on PS induction, we also found that carbachol induced: 1) stereotyped PGO-like bursts when injected in the ventral part of the FTG and the rostral part of the FTM, 2) postural atonia with very short latencies, less than two minutes, when injected in the LC alpha and peri-LC alpha; and 3) hippocampal theta waves of 3-5 Hz persisting during light slow wave sleep (S1) when injected in and around the LC alpha and peri-LC alpha and in some points of the mediocaudal part of the FTG. These results support the hypothesis that PS is generated by highly localized neuronal populations and suggest that the mediodorsal pontine tegmentum (namely the nuclei LC alpha and peri-LC alpha) may represent a cholinoceptive PS generator.

Power spectral analysis of blood pressure fluctuations during sleep in normal and decerebrate cats.

Arterial blood pressure fluctuations during sleep were investigated with power analysis technique in both normal and decerebrate cats. In the initial postoperative stage lasting about 3 to 4 days, intact cats displayed, during paradoxical sleep, phasic increases in arterial blood pressure which were superimposed on a tonic hypotension. In the later chronic stage, however, the animals showed the phasic hypertension being superimposed on the background of a tonic hypertension. Regardless of these stages, the blood pressure during paradoxical sleep exhibited a 1/f-like spectrum, expressed by the power spectral density which is inversely proportional to the Fourier frequency f. On the other hand, a power spectral profile of the blood pressure during slow wave sleep presented a white noise-like pattern within the same frequency range of 0.1-0.01 Hz. After brainstem transections at the pontomesencephalic border, the cats exhibited consistently a sustained fall in blood pressure during paradoxical sleep and the power spectral density of the blood pressure displayed a white noise-like pattern throughout the survival periods of one month or more. These observations indicate that the blood pressure fluctuations in the 1/f spectrum during paradoxical sleep originate in rostral brain structures.

Single neuron activity related to natural vestibular stimulation in the cat's visual cortex.

This study examines the possibility of a vestibular input to the visual cortex using chronically implanted cats subjected to horizontal sinusoidal rotation in the dark. In areas 17 and 18 the activity of respectively 14% and 11% of units was modified by vestibular stimulation. Both non-specific and specific influences were observed. Specific influences (42% in area 17 and 33% in area 18) were similar to the types of responses recorded in the vestibular nuclei, and were encountered more frequently within the cortex subserving the peripheral visual field. Our results could provide a neurophysiological basis for some psychophysiological observations concerning visuo-vestibular interactions.

Retinotopic organization of extra-retinal saccade-related input to the visual cortex in the cat.

Single unit activity of 842 cells has been recorded in cat visual cortex and analyzed with respect to vestibular induced, and spontaneous saccadic eye movements performed in the dark. This study has been done in awake, chronically implanted cats, subsequently placed in "acute" conditions to achieve the precise retinotopic mapping of the cortical areas previously investigated. In areas 17 and 18, respectively, 27% and 24% of the cells tested were influenced by horizontal saccadic eye movements in the dark (E.M. cells). In the Clare-Bishop area, the proportion of E.M. cells was 12%, while only 2% of such cells were found in areas 19 and 21. The distribution of E.M. cells in areas 17 and 18 with respect to retinotopy showed that E.M. cells were more numerous in the cortical zones devoted to the representation of the area centralis (38% in area 17, 27% in area 18) than in the zones subserving the periphery of the visual field (17% and 12%, respectively). Two of the characteristics of E.M. cell activations appear dependent on the retinotopic organization. First, larger number of E.M. cells presenting an asymmetry in their responses to horizontal saccadic eye movements in opposite directions (directional E.M. cells) were encountered in the cortical representation of the peripheral visual field. 53% of E.M. cells recorded in area 17 and 71% in area 18 were directional in the cortex corresponding to the peripheral visual field. This percentage was of 23% and 25% respectively in the cortex devoted to area centralis. Second, E.M. cells were found to have a latency from the onset of the saccade systematically larger than 100 ms (i.e., they discharged at, or after the end of the eye movement) if they were located in the cortical representation of the area centralis, while E.M. cells related to the peripheral visual field displayed a wider range of latencies (0-240 ms). Results obtained in Clare Bishop area, although limited to the representation of the peripheral visual field, were quantitatively and qualitatively similar to those observed in the homologous retinotopic zones of areas 17 and 18. It is concluded that an extra-retinal input related to oculomotor activity is sent to the cat visual cortex and is organized, at least in areas 17 and 18, with respect to the retinotopic representation of the visual field. These data support the hypothesis of a functional duality between central and peripheral vision and are discussed in the context of visual-oculomotor integration.

Evidence for the presence of PS-OFF neurons in the ventromedial medulla oblongata of freely moving cats.

Recordings were made from 24 "PS-OFF" neurons, characterized by a slow rhythmic discharge rate during waking the slow wave sleep and a marked decrease in the firing rate during paradoxical sleep, in the ventromedial medulla oblongata of freely moving cats. These neurons were located in either the nuclei raphe magnus and pallidus or the neighboring reticular formation where serotonin-containing neurons are found in the cat. Two types of medullary PS-OFF neurons are described, and the descending projection and slow conduction velocity of some of these neurons are demonstrated.

[Specific neurons for wakefulness in the posterior hypothalamus in the cat]. / Neurones spécifiques de l'éveil dans l'hypothalamus postérieur du chat.

Using a single unit recording technique in freely moving Cats, we have demonstrated the presence of two groups of neurons in the ventrolateral part of the caudal hypothalamus. One is characterized by a tonic discharge during waking and paradoxical sleep, the other is highly selective to the waking state. This group of neurons showed a slow tonic and regular discharge during wakefulness, a significant decrease in firing rate during stage I slow-wave sleep and a complete cessation of firing during stage II slow-wave sleep and subsequent paradoxical sleep.

Eye saccade dynamics during paradoxical sleep in the cat.

Cat eye movements were recorded during wakefulness and paradoxical sleep with the technique of the scleral search coil in a magnetic field. During waking, eye movements consisted of a succession of saccades and fixation phases. During paradoxical sleep, the pattern of eye movements displayed drifts of variable velocity and direction and short fixation phases, upon which saccades superimposed. These saccades displayed a repetitive, stereotyped, asymmetrical pattern. The maximum velocity/amplitude relationships, i.e. the main sequences, were determined for spontaneous and visually induced saccades of waking and for the following types of saccades during paradoxical sleep: (i) isolated saccades accompanied by ponto-geniculo-occipital (PGO) waves, (ii) isolated saccades accompanied by eye movement potentials (EMP), and (iii) saccades in bursts accompanied by PGO waves. The slope of the main sequence relationship of any type of paradoxical sleep saccade (from 21.7 degrees/s/degree for isolated saccades to 35.6 degrees/s/degree for saccades in bursts) was higher than that of any type of waking saccade (11.2 degrees/s/degree for spontaneous saccades to 14.7 degrees/s/degree for visually elicited ones). Furthermore, during paradoxical sleep, saccades in bursts were faster than isolated ones. This demonstrates that different neurophysiological mechanisms subserve the generation of waking saccades, paradoxical sleep isolated saccades and paradoxical sleep saccades in bursts, or that the oculomotor system is in a different state of excitation during these different sets of saccades. These findings throw new light on the functioning of the oculomotor system during paradoxical sleep and are discussed in terms of the functional significance of paradoxical sleep saccades and PGO waves.

Effects of amphetamine and modafinil on the sleep/wake cycle during experimental hypersomnia induced by sleep deprivation in the cat.

Modafinil is a newly discovered waking substance now being used in the treatment of hypersomnia and narcolepsy. We have shown previously in the cat that, unlike amphetamine, modafinil induces long-lasting wakefulness (W) without behavioral excitation and subsequent sleep rebound, and that its waking effect does not depend on endogenous catecholamines. To further characterize the awakening properties of modafinil and current psychostimulants in experimental models of hypersomnia, we examined the effect of oral administration of placebo, modafinil (5 mg kg-1) or amphetamine (1 mg kg-1) on the sleep/wake cycle and power spectral density (PSD) in cats after an 18-h water-tank sleep deprivation period. We found that the placebo had no effect on the dynamics of sleep recovery, while both modafinil and amphetamine induced suppression of cortical slow activity and a waking state lasting 6-8 h. After the amphetamine-induced waking period, both deep slow wave sleep (SWS2) and paradoxical sleep (PS) occurred in greater amounts than after placebo and the PSD during SWS was also increased. Thus, the cumulative time spent in W during a 48-h period was similar to that with placebo, indicating enhanced sleep rebound. In contrast, after the modafinil-induced W, the occurrence and evolution of SWS2 or PS, as well as the PSD during SWS, were similar to those seen with placebo during the same period, so that the total time spent in W in a 48-h period remained significantly higher than the control level, indicating no additional sleep rebound. These results indicate that modafinil is effective against somnolence and hypersomnia and does not produce a subsequent increase in sleep and suggest that the pharmacological profile of modafinil is different from that of amphetamine.

Neurochemical and behavioral effects of ciproxifan, a potent histamine H3-receptor antagonist.

Ciproxifan, i.e., cyclopropyl-(4-(3-1H-imidazol-4-yl)propyloxy) phenyl) ketone, belongs to a novel chemical series of histamine H3-receptor antagonists. In vitro, it behaved as a competitive antagonist at the H3 autoreceptor controlling [3H]histamine release from synaptosomes and displayed similar Ki values (0.5-1.9 nM) at the H3 receptor controlling the electrically-induced contraction of guinea pig ileum or at the brain H3 receptor labeled with [125I]iodoproxyfan. Ciproxifan displayed at least 3-orders of magnitude lower potency at various aminergic receptors studied in functional or binding tests. In vivo, measurement of drug plasma levels, using a novel radioreceptor assay in mice receiving ciproxifan p.o. or i.v., led to an oral bioavailability ratio of 62%. Oral administration of ciproxifan to mice enhanced by approximately 100% histamine turnover rate and steady state level of tele-methylhistamine with an ED50 of 0.14 mg/kg. Ciproxifan reversed the H3-receptor agonist induced enhancement of water consumption in rats with and ID50 of 0.09 +/- 0.04 mg/kg, i.p. In cats, ciproxifan (0.15-2 mg/kg, p.o.) induced marked signs of neocortical electroencephalogram activation manifested by enhanced fast-rhythms density and an almost total waking state. In rats, ciproxifan enhanced attention as evaluated in the five-choice task performed using a short stimulus duration. Ciproxifan appears to be an orally bioavailable, extremely potent and selective H3-receptor antagonist whose vigilance- and attention-promoting effects are promising for therapeutic applications in aging disorders.