Paradoxical REM sleep promoting and permitting neuronal networks

Since its electrophysiological identification in the 1950's, the state of REMS or PS has been shown through multiple lines of evidence to be generated by neurons in the oral pontine tegmentum. The perpetration of this paradoxical state that combines cortical activation with the most profound behavioral sleep occurs through interplay between PS-promoting (On) and PS-permitting (Off) cell groups in the pons. Cholinergic cells in the LDTg and PPTg promote PS by initiating processes of both forebrain activation and peripheral muscle atonia. Bearing alpha1-adrenergic receptors, cholinergic cells, which likely project to the forebrain, are excited by NA and active during both W and PS (W/PS-On), when they promote cortical activation. Bearing alpha2-adrenergic receptors, other cholinergic cells, which likely project to the brainstem, are inhibited by NA and thus active selectively during PS (PS-On), when they promote muscle atonia. Noradrenergic, together with serotonergic, neurons, as PS-Off neurons, thus permit PS in part by lifting their inhibition upon the cholinergic PS-On cells. The noradrenergic/serotonergic neurons are inhibited in turn by local GABAergic PS-promoting neurons that may be excited by ACh. Other similarly modulated GABAergic neurons located through the brainstem reticular formation become active to participate in the inhibition of reticulo-spinal and raphe-spinal neurons as well as in the direct inhibition of motor neurons. In contrast, a select group of GABAergic neurons located in the oral pontine reticular formation and possibly inhibited by ACh turn off during PS. These GABAergic PS-permitting neurons release from inhibition the neighboring large glutamatergic neurons of the oral pontine reticular formation, which are likely concomitantly excited by ACh. In tandem with the cholinergic neurons, these glutamatergic reticular neurons propagate the paradoxical forebrain activation and peripheral inactivation that characterize PS.     

Pontogeniculooccipital waves: spontaneous visual system activity during rapid eye movement sleep

1. Pontogeniculooccipital (PGO) waves are recorded during rapid eye movement (REM) sleep from the pontine reticular formation, lateral geniculate bodies, and occipital cortex of many species. 2. PGO waves are associated with increased visual system excitability but arise spontaneously and not via stimulation of the primary visual afferents. Both auditory and somatosensory stimuli influence PGO wave activity. 3. Studies using a variety of techniques suggest that the pontine brain stem is the site of PGO wave generation. Immediately prior to the appearance of PGO waves, neurons located in the region of the brachium conjunctivum exhibit bursts of increased firing, while neurons in the dorsal raphe nuclei show a cessation of firing. 4. The administration of pharmacological agents antagonizing noradrenergic or serotonergic neurotransmission increases the occurrence of PGO waves independent of REM sleep. Cholinomimetic administration increases the occurrence of both PGO waves and other components of REM sleep. 5. Regarding function, the PGO wave-generating network has been postulated to inform the visual system about eye movements, to promote brain development, and to facilitate the response to novel environmental stimuli.     

Cholinergic microstimulation of the peribrachial nucleus in the cat. II. Delayed and prolonged increases in REM sleep.

The hypothesis that REM sleep is cholinergically mediated is supported by the identification of a cholinoceptive trigger zone in the FTG. Since this trigger zone is devoid of cholinergic neurons, the aim of the present study was to test the hypothesis that a cholinergic drive for REM sleep may come from the cholinergic cells of the PBL region. Chronically implanted freely moving cats with electrodes for sleep and PGO wave recordings were used. Guide tubes were implanted for carbachol microinjections (4 micrograms/250 nl) in the PBL and FTG. All microinjections were delivered in close vicinity of ChAT+ cholinergic cells in the PBL region. Results showed that a single unilateral carbachol microinjection into the PBL induced sustained (24 hr) state-independent ipsilateral PGO wave activity. This PGO wave activity was followed by a prolonged enhancement of REM sleep lasting for more than six days. We also observed that REM enhancement was followed by a delayed but marked enhancement of S sleep episodes with PGO waves (SP), which are normally brief transitions from S to REM sleep. Our findings strongly support the hypothesis that cholinergic drive for REM sleep comes from the lateral pontine tegmentum and we suggest that the PBL region plays a major role in both PGO wave generation and long-term regulation of REM sleep induction.     

An HRP study in the cat of brainstem projections to the spinal cord, with particular reference to sacral afferents

Cells of origin of the spinal projections from the brainstem of the cat have been studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP into various levels of the spinal cord, many labeled cells were found in several structures in the brainstem. The labeled cells occurred in the raphe nuclei, reticular formation, vestibular complex, and nuclei of the dorsolateral pontine tegmentum. In the dorsolateral pontine tegmentum, many labeled cells were found in the nuclei of locus coeruleus, subcoeruleus and K?lliker-Fuse. In the coeruleus and subcoeruleus, the greatest number of labeled cells were found, when HRP was injected into the sacral cord. No difference emerged, however, in the number of labeled cells appearing in the K?lliker-Fuse nucleus after injection of the enzyme into different levels of the spinal cord. It appears that neurons in the lateral vestibular nucleus which project to different levels of the spinal cord are located in different parts of this nucleus.     

A mathematical model for the mechanism of rapid eye movements induced by an anticholinesterase in the decerebrate cat.

The oculomotor pattern which appears in intact preparations during desynchronized sleep is characterized by the irregular occurrence of isolated ocular movements and bursts of rapid eye movements (REM). This complex oculomotor pattern results from the activity of two premotor structures which influence the extraocular motoneurons during this phase of sleep: one is located in the pontine reticular formation, the other in the vestibular nuclei. In the decerebrate preparation the intravenous injection of an anticholinesterase leads to the appearance of a typical pattern of oculomotor activity, which differs from that occurring during physiological sleep in so far as it consists quite exclusively of bursts of REM which appear at very regular intervals. Lesion experiments as well as unit recordings have shown that these bursts of REM depend in particular upon rhythmic discharges of the vestibular nuclear neurons. The underlying anatomical structures responsible for these bursts of REM are therefore the vestibular nuclei, the oculomotor nuclei and the oculo-orbital system. This mechanism is under the influence of cholinergic reticular neurons which generate the oculomotor rhythm. We have postulated the existence of a self-excitatory cholinergic system, located in the pontine reticular formation, whose steady discharge impinges upon an oscillatory neuronal system located in the dorso-lateral pontine tegmentum, which transforms the tonic input into a sinusoidal final output. We have assumed also that the periodic increases in the discharge frequency of this oscillatory system trigger a fast phase generator acting on the different components of the REM system, and that the behavior of each component follows a first-order differential equation. The state of excitation of the components of the system is defined as proportional to frequency of nerve impulses. Assuming ipsilateral and crossed connections, a pattern of oculomotor activity is obtained that simulates the experimental oculomotor output fairly well. The repetition of the eye jerks is described by a Fourier series. The model proposed in this paper may be taken as a first approach in describing the generation mechanism of REM, and as a theoretical guide to new experimental researches and the development of other more realistic models.     

Cholinergic microstimulation of the peribrachial nucleus in the cat. I. Immediate and prolonged increases in ponto-geniculo-occipital waves.

The cholinergic agonist carbachol was injected into the pontine Pb area where PGO bursting cells have been recorded. When microinjections were localized to the ventrolateral aspect of the caudal Pb nucleus near aggregates of ChAT immunolabeled cholinergic neurons, carbachol produced an immediate onset of state-independent PGO waves in the ipsilateral LGB. These state-independent PGO waves persisted for 3-4 days. After the first 24 hrs PGO wave activity increasingly became associated with REM sleep and with REM transitional SP sleep as both of these PGO-related states increased in amount to 3-4 times baseline levels. The increase in amount of PGO-related states peaked on days 2-4 following one carbachol injection and persisted for 10-12 days. These results suggest a two stage process: stage one, PGO enhancement, is the direct consequence of the membrane activation of cholinoceptive PGO burst neurons by carbachol; stage two, REM enhancement, is the consequence of metabolic activation of endogenous cholinergic neurons. This experimental preparation is a useful model for the study of the electrophysiology and functional significance of PGO wave and REM sleep generation.     

Tonic inhibition of dorsal pontine neurons during the postural atonia produced by an anticholinesterase in the decerebrate cat.

1. Experiments performed in precollicular decerebrate cats indicate that neurons located in the caudal part of the locus coeruleus and locus subcoeruleus as well as in the surrounding reticular formation were greatly depressed during the cataplectic episodes induced by i.v. injection of 0.1 mg/kg of eserine sulphate. 2. These units actually showed a slow regular firing rate when the rigidity was present. Moreover their firing rate greatly decreased during the episodes of postural atonia produced by the anticholinesterase. In some instances a complete abolition of firing occurred during these episodes. The depression of unit discharge anticipated the onset of postural atonia and lasted throughout the episodes. 3. Some of the neurons described above responded with steady changes in their discharge rate to natural stimulation of macular labyrinthine receptors during postural rigidity. However, the response of these neurons to lateral tilts was suppressed during the episodes of postural atonia induced by the anticholinesterase, This and other arguments suggested that these units were tonically inhibited during the induced cataplectic episodes. 4. The time course of the rate deceleration shown by these neurons during transition from postural rigidity to muscular atonia represents a mirror image of the rate acceleration which affects most of the pontine reticular neurons located in the gigantocellular tegmental field (FTG) during the induced cataplectic episodes. These reciprocal rate relations suggest that a functional interaction exists between the two cell groups. In particular it is postulated that the pontine FTG neurons are self-excitatory and excitatory to the locus coeruleus neurons, while the last neurons may be self-inhibitory and inhibitory to FTG neurons. These findings can be related to previous observations showing that neurons located in the region of locus coeruleus undergo a rate deceleration during desynchronized sleep which mimics the time course of firing to the pontine reticular neurons. 5. In conclusion it appears that the decerebrate rigidity is present in so far as the cholinergic reticular neurons, which trigger the bulbospinal inhibitory system, are tonically inhibited by neurons located in the monoaminergic structures of the dorsolateral pontine tegmentum. On the other hand the suppression of the decerebrate rigidity ,which occurs during the cholinergically induced cataplectic episodes results from activation of the cholinergic reticular neurons, which escape tonic inhibition from monoaminergic structures.     

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.     

Pontine reticular origin of cholinergic excitatory afferents to the locus coeruleus controlling the gain of vestibulospinal and cervicospinal reflexes in decerebrate cats

1. Previous experiments had shown that the medullary inhibitory reticulospinal (mRS) neurons act 180 degrees out-of-phase with respect to the excitatory vestibulospinal (VS) neurons during the vestibular and the neck reflexes involving the limb extensor motoneurons. This finding suggested that the higher the firing rate of the medullary inhibitory RS neurons in the animal at rest, the greater the disinhibition which affects the limb extensor motoneurons during side-down roll tilt of the animal or side-up neck rotation, thus leading to an increased gain of response of limb extensors to sinusoidal stimulation of labyrinth and neck receptors. The gain of these postural reflexes would then represent a sensitive test to evaluate the background discharge of the inhibitory reticulospinal system of the medulla. 2. The discharge of the inhibitory mRS neurons is under the tonic excitatory control of cholinergic pontine reticular formation (pRF) neurons which are also self-excitatory, while these cholinergic pontine neurons are in turn inhibited by the norepinephrine (NE)-containing locus coeruleus (LC) neurons, which are also self-inhibitory due to mechanisms of recurrent and/or lateral inhibition. The present experiments were performed to find out whether cholinergic and cholinoceptive pontine reticular neurons, which are under the inhibitory control of the LC neurons, also send axons to the LC on which they may exert an excitatory influence. This excitatory effect would then counteract the self-inhibitory influence mediated by the NE, which acts on the alpha 2-adrenoceptors distributed on the somatodendritic membrane of the LC neurons. 3. In precollicular decerebrate cats, local injection into the dorsal aspect of the pontine tegmentum of 0.25 microliter of a solution of the muscarinic blocker atropine sulphate at the concentration of 6 micrograms/microliter of sterile saline did neither modify the postural activity in the ipsilateral limbs nor the response gain of the ipsilateral forelimb extensor triceps brachii to sinusoidal stimulation of labyrinth receptors (roll tilt of the animal at 0.15 Hz, +/- 10 degrees). These negative results were attributed to the fact that in these preparations the activity of the cholinergic and cholinoceptive pRF neurons and the related inhibitory mRS neurons is very low, due to the tonic discharge of the NE-containing LC neurons, which exert a prominent inhibitory influence on the underlying reticular structures.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inhibition of vestibulospinal reflexes following cholinergic activation of the dorsal pontine reticular formation

1. The multiunit EMG activity of the forelimb extensor muscle triceps brachii was recorded in precollicular decerebrate cats, either at rest or during roll tilt of the animal at 0.15Hz, +/- 10 degrees leading to sinusoidal stimulation of labyrinth receptors. Both the spontaneous EMG activity as well as the labyrinthine-induced EMG responses were tested before and after pontine microinjection of a cholinergic agonist. 2. Local injection of the cholinergic agonist carbachol into the dorsal aspect of the pontine tegmentum (usually 0.25 microliter, 0.01-0.2 microgram/microliter) produced a state of postural atonia, and abolished both the spontaneous EMG activity as well as the EMG responses of the triceps brachii to sinusoidal stimulation of labyrinth receptors. This suppression was generally ipsilateral to the side of the injection and persisted throughout the episode of postural atonia, but sometimes it involved also the contralateral limbs. In these instances it could be accompanied by a spontaneous nystagmus, interspersed at regular intervals with bursts of rapid eye movements. 3. Similar effects were also obtained following injection of carbachol in the gigantocellular tegmental field (FTG) (0.25 microliter, 0.5-1.0 microgram/microliter). However, this structure was not critically responsible for the phenomena reported above, which persisted unaltered after kainic acid lesion of the FTG performed ipsilaterally to the side of the pontine injection. 4. Local infusion of the muscarinic blocker atropine sulphate reversed the effects of carbachol injection into the dorsal aspect of the pontine tegmentum, thus indicating that muscarinic receptors were involved. 5. It is postulated that the postural atonia as well as the tonic depression of vestibulospinal reflexes, which occur in the decerebrate cat after local injection of a cholinergic agonist depends, at least in part, on the activation of cholinoceptive neurons located in dorsal pontine reticular structures. These may in turn excite medullary reticulospinal neurons, which are finally responsible for the inhibition of extensor motoneurons.     

Nuclear origins of brainstem reticulocortical systems in the rat

Stereotaxic injections of 5% Fast Blue or 1% horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) were made into various cytoarchitectonic or functional regions of the cerebral cortex of anesthetized adult albino or hooded rats. Sections through the brainstems of these animals were then scrutinized for the presence of retrogradely labeled neurons. The data generated by this study indicate that at least 33 distinct nuclei or subnuclei within the brainstem reticular formation of the rat project directly to the cerebral cortex. More than half of these ascending reticulocortical systems are probably aminergic. The strongest reticulocortical projections emanate from presumed aminergic reticular-cell groups located at isthmic levels: specifically, the rostral serotonin-containing cell groups, as well as the noradrenergic locus coeruleus. However, relatively strong direct reticulocortical projections also originate from lower medullary cell groups which are probably catecholaminergic. Moderately strong reticulocortical projections emanate from cholinergic cell groups located at isthmic levels (the pars compacta of the pedunculopontine nucleus and the X area of Sakai). The most surprising finding in this study was that the classic isodendritic, nonaminergic central core of the brainstem gives rise to direct reticulocortical projections. The ventromedial areas of the medullary brainstem reticular formation give rise to the strongest nonaminergic ascending reticular projections, but all levels of the classic isodendritic reticular core give rise to direct reticulocortical projections. As a whole, cortically projecting reticular neurons are mostly small (10-25 microns in greatest diameter) or medium sized (26-35 microns in greatest diameter) neurons. Previous studies have shown that many of the cortically projecting reticular nuclei also project to the spinal cord, and within these nuclei, reticulocortical neurons often strongly resemble their reticulospinal counterparts with respect to details of neuronal morphology. This in turn suggests that some reticulocortical neurons may also project to spinal levels.     

A novel role for calcium/calmodulin kinase II within the brainstem pedunculopontine tegmentum for the regulation of wakefulness and rapid eye movement sleep

Considerable evidence suggests that the brainstem pedunculopontine tegmentum (PPT) neurons are critically involved in the regulation of rapid eye movement (REM) sleep and wakefulness (W); however, the molecular mechanisms operating within the PPT to regulate these two behavioral states remain relatively unknown. Here we demonstrate that the levels of calcium/calmodulin kinase II (CaMKII) and phosphorylated CaMKII expression in the PPT decreased and increased with 'low W with high REM sleep' and 'high W/low REM sleep' periods, respectively. These state-specific expression changes were not observed in the cortex, or in the immediately adjacent medial pontine reticular formation. Next, we demonstrate that CaMKII activity in the PPT is negatively and positively correlated with the 'low W with high REM sleep' and 'high W/low REM sleep' periods, respectively. These differences in correlations were not seen in the medial pontine reticular formation CaMKII activity. Finally, we demonstrate that with increased PPT CaMKII activity observed during high W/low REM sleep, there were marked shifts in the expression of genes that are involved in components of various signal transduction pathways. Collectively, these results for the first time suggest that the increased CaMKII activity within PPT neurons is associated with increased W at the expense of REM sleep, and this process is accomplished through the activation of a specific gene expression profile.     

Tonic facilitatory influences of dorsal pontine reticular structures on the response gain of limb extensors to sinusoidal labyrinth and neck stimulations

Experiments were performed to find out whether changes in resting discharge of the inhibitory reticulospinal (RS) neurons of the medulla, produced either by selective destruction or by cholinergic activation of a pontine tegmental reticular system, may modify the response gain of limb extensor muscles to given parameters of roll tilt of the animal or neck rotation. In precollicular decerebrate cats, an electrolytic lesion of the dorsal aspect of the pontine tegmentum, which slightly increased the tonic contraction of limb extensors, greatly decreased the amplitude of the multiunit EMG response of forelimb extensor muscles, i.e. of the medial head of the triceps brachii, to roll tilt of the animal and neck rotation (at 0.15 Hz, +/- 10 degrees), leading to selective stimulation of labyrinth or neck receptors. Correspondingly, the response gain of the forelimb extensors to labyrinth and neck stimulation decreased, but no change in the phase angle of the responses was observed. These findings did not depend on the increased postural activity, since they were still observed in the absence of any change in spontaneous EMG activity of the triceps brachii following the lesion. The changes in posture as well as in response gain of the forelimb extensors to labyrinth and neck stimulation produced by the pontine lesion appeared suddenly, and persisted for several hours throughout the survival period. Moreover, these changes involved mainly, but not exclusively, the limbs ipsilateral to the side of the lesion. Histological controls indicated that the structure responsible for the postural and reflex changes described above corresponded to the dorsal aspect of the pontine tegmentum located immediately ventral to the locus coeruleus (LC); this area corresponded to the peri-LC region as well as the surrounding pontine reticular formation (RF), including the dorsal aspect of the central tegmental field. This region closely corresponds to the area from which a tegmentoreticular tract, ending on the medullary inhibitory area, originates. It was previously shown that unilateral or bilateral lesion of the LC, which decreased the extensor tonus in the ipsilateral limbs, greatly enhanced the response gain of the triceps brachii to sinusoidal stimulation of labyrinth and neck receptors. These findings were attributed to suppression of an inhibitory influence that the LC exerts on the dorsal pontine reticular structures described above.(ABSTRACT TRUNCATED AT 400 WORDS)     

Paradoxical (REM) sleep genesis: the switch from an aminergic-cholinergic to a GABAergic-glutamatergic hypothesis.

In the middle of the last century, Michel Jouvet discovered paradoxical sleep (PS), a sleep phase paradoxically characterized by cortical activation and rapid eye movements and a muscle atonia. Soon after, he showed that it was still present in "pontine cats" in which all structures rostral to the brainstem have been removed. Later on, it was demonstrated that the pontine peri-locus coeruleus alpha (peri-LCalpha in cats, corresponding to the sublaterodorsal nucleus, SLD, in rats) is responsible for PS onset. It was then proposed that the onset and maintenance of PS is due to a reciprocal inhibitory interaction between neurons presumably cholinergic specifically active during PS localized in this region and monoaminergic neurons. In the last decade, we have tested this hypothesis with our model of head-restrained rats and functional neuroanatomical studies. Our results confirmed that the SLD in rats contains the neurons responsible for the onset and maintenance of PS. They further indicate that (1) these neurons are non-cholinergic possibly glutamatergic neurons, (2) they directly project to the glycinergic premotoneurons localized in the medullary ventral gigantocellular reticular nucleus (GiV), (3) the main neurotransmitter responsible for their inhibition during waking (W) and slow wave sleep (SWS) is GABA rather than monoamines, (4) they are constantly and tonically excited by glutamate and (5) the GABAergic neurons responsible for their tonic inhibition during W and SWS are localized in the deep mesencephalic reticular nucleus (DPMe). We also showed that the tonic inhibition of locus coeruleus (LC) noradrenergic and dorsal raphe (DRN) serotonergic neurons during sleep is due to a tonic GABAergic inhibition by neurons localized in the dorsal paragigantocellular reticular nucleus (DPGi) and the ventrolateral periaqueductal gray (vlPAG). We propose that these GABAergic neurons also inhibit the GABAergic neurons of the DPMe at the onset and during PS and are therefore responsible for the onset and maintenance of PS.     

与咬肌运动神经元直接联系的运动前神经元在脑干的分布

目的为了定位向咬肌运动神经元投射的最后一级运动前神经元在脑干内的分布。方法注射麦芽凝集素结合的辣根过氧化物酶(WGA-HRP)至咬肌神经逆行跨突触追踪,然后通过免疫组织化学方法显示了该类神经元。结果这类神经元分布在双侧三叉上核(Vsup)、三叉神经感觉主核背侧部(Vpdm)、小细胞网状结构(PCR)和三叉神经脊束核吻侧亚核背侧部(Vodm),以及对侧三叉神经运动核(Vmo)。数量上,Vsup,特别是注射侧Vsup中,标记的神经元数量最多;其他核团内,双侧标记的神经元的数量无明显差别。结论一侧咬肌运动神经元直接接受脑干双侧多个区域调控。     

Selective discharge of pontine neurons during the postural atonia produced by an anticholinesterase in the decerebrate cat.

I. Episodes of postural atonia associated with bursts of REM similar to those which occur spontaneously either in the intact preparation during desynchronized sleep, or in the chronic decorticate or decerebrate preparations, can be elicited in acute decerebrate cats following intravenous injection of small doses of an anticholinesterase. The present experiments were performed in precollicular decerebrate animals in order to identify the pontine neurons which show increases in their firing rate related in time with the appearance of the cataplectic episodes. In particular long-term recordings of single units were obtained before, during and after the episodes of postural atonia produced by i.v. injection of 0.03-0.1 mg/kg of eserine sulphate. Spontaneous discharge rates were used to measure the selectivity of each individual unit, i.e., the tendency of the unit to discharge more during the cataplectic episode than during the postural rigidity. The physiological data obtained from neurons histologically localized in different nuclear groups were then averaged. 2. Neurons localized in the pontine reticular formation as well as in the region of the locus coeruleus and the raphe system showed low rates of discharge when rigidity was present. The same units, however, showed a remarkable increase in firing rate which preceded by several tenths of seconds the onset of postural atonia and lasted throughout the cataplectic episodes. 3. The neurons of the pontine reticular formation had a selectivity which was higher than that of the neurons located in the locus coeruleus-raphe system; moreover the cells of the gigantocellular tegmental field (FTG) had the highest selectivity of all pontine reticular structures studied. 4. The relation of the discharge rate curves to the occurrence of the cataplectic episodes suggests that these neurons constitute output elements of a generator system for postural atonia. It is postulated that these pontine reticular neurons are directly involved in the activation of the bulbospinal inhibitory system, which is finally responsible for the abolition of the decerebrate rigidity. 5. During cataplectic episodes these pontine neurons showed some clustered discharges which appeared in association with bursts of eye movements. In most instances, however, there was no constant relationship of the unit activity to individual eye movements. Moreover large phasic increases in firing rate appeared also during the intervals between successive bursts of REM. 6. The striking increase in firing rate of the FTG neurons observed during the cataplectic episodes cannot be attributed to an increased excitatory input to these neurons. In fact excitatory influences following intense somatic stimulation are unlikely to occur during the cataplectic episodes; moreover the response of these neurons to intense somatosensory stimulations did not reach rates comparable with those occurring spontaneously during the induced cataplectic episodes...     

Paradoxical (REM) sleep genesis: The switch from an aminergic–cholinergic to a GABAergic–glutamatergic hypothesis

In the middle of the last century, Michel Jouvet discovered paradoxical sleep (PS), a sleep phase paradoxically characterized by cortical activation and rapid eye movements and a muscle atonia. Soon after, he showed that it was still present in “pontine cats” in which all structures rostral to the brainstem have been removed. Later on, it was demonstrated that the pontine peri-locus coeruleus α (peri-LCα in cats, corresponding to the sublaterodorsal nucleus, SLD, in rats) is responsible for PS onset. It was then proposed that the onset and maintenance of PS is due to a reciprocal inhibitory interaction between neurons presumably cholinergic specifically active during PS localized in this region and monoaminergic neurons. In the last decade, we have tested this hypothesis with our model of head-restrained rats and functional neuroanatomical studies. Our results confirmed that the SLD in rats contains the neurons responsible for the onset and maintenance of PS. They further indicate that (1) these neurons are non-cholinergic possibly glutamatergic neurons, (2) they directly project to the glycinergic premotoneurons localized in the medullary ventral gigantocellular reticular nucleus (GiV), (3) the main neurotransmitter responsible for their inhibition during waking (W) and slow wave sleep (SWS) is GABA rather than monoamines, (4) they are constantly and tonically excited by glutamate and (5) the GABAergic neurons responsible for their tonic inhibition during W and SWS are localized in the deep mesencephalic reticular nucleus (DPMe). We also showed that the tonic inhibition of locus coeruleus (LC) noradrenergic and dorsal raphe (DRN) serotonergic neurons during sleep is due to a tonic GABAergic inhibition by neurons localized in the dorsal paragigantocellular reticular nucleus (DPGi) and the ventrolateral periaqueductal gray (vlPAG). We propose that these GABAergic neurons also inhibit the GABAergic neurons of the DPMe at the onset and during PS and are therefore responsible for the onset and maintenance of PS.     

Neuronal activities of the visual field of the cerebral cortex modulated by reserpine-induced PGO waves

The modulatory influence of reserpine-induced PGO wave upon the spontaneous activity of visual cortical neurons was examined in acutely prepared cats. Unitary discharge of cortical neurons was recorded extracellularly with glass micropipettes. Of twenty three neurons three showed a vigorous discharge synchronously with a certain phase of PGO wave. One neuron was strongly suppressed by the occurrence of PGO wave. Three neurons showed an increase and one neuron showed a decrease, respectively, in discharge in a loose correlation with PGO wave. This study has demonstrated the presence of a unique group of neurons which show a burst discharge or a complete silence in a precisely phase-lock manner when reserpine-induced PGO wave occurred.     

Nitric oxide in B6 mouse and nitric oxide-sensitive soluble guanylate cyclase in cat modulate acetylcholine release in pontine reticular formation.

ACh regulates arousal, and the present study was designed to provide insight into the neurochemical mechanisms modulating ACh release in the pontine reticular formation. Nitric oxide (NO)-releasing beads microinjected into the pontine reticular formation of C57BL/6J (B6) mice significantly (P < 0.0001) increased ACh release. Microdialysis delivery of the NO donor N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino)-ethanamine (NOC-12) to the mouse pontine reticular formation also caused a concentration-dependent increase in ACh release (P < 0.001). These are the first neurochemical data showing that ACh release in the pontine reticular formation of the B6 mouse is modulated by NO. The signal transduction cascade through which NO modulates ACh release in the pontine reticular formation has not previously been characterized. Therefore, an additional series of studies quantified the effects of a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), on ACh release in the cat medial pontine reticular formation. During naturally occurring states of sleep and wakefulness, but not anesthesia, ODQ caused a significant (P < 0.001) decrease in ACh release. These results show for the first time that NO modulates ACh in the medial pontine reticular formation of the cat via an NO-sensitive sGC signal transduction cascade. Isoflurane and halothane anesthesia have been shown to decrease ACh release in the medial pontine reticular formation. The finding that ODQ did not alter ACh release during isoflurane or halothane anesthesia demonstrates that these anesthetics disrupt the NO-sensitive sGC-cGMP pathway. Considered together, results from the mouse and cat indicate that NO modulates ACh release in arousal-promoting regions of the pontine reticular formation via an NO-sensitive sGC-cGMP pathway.     

Brainstem neurons responsible for postural, masseter or pharyngeal muscle atonia during paradoxical sleep in freely-moving cats

In this mini review, we summarize our findings regarding the brainstem neurons responsible for the postural, masseter, or pharyngeal muscle atonia observed during paradoxical sleep (PS) in freely moving cats. Both the pons and medulla contain neurons showing tonic activation selective to PS and atonia, referred to as PS/atonia-on-neurons. The PS/atonia-on neurons, characterized by their most slow conducting property and located in the peri-locus coeruleus alpha (peri-LCa) and adjacent LCa of the mediodorsal pontine tegmentum, play a critical executive role in the somatic and orofacial muscle atonia observed during PS. Slow conducting medullary PS/atonia-on neurons located in the nuclei reticularis magnocellularis (Mc) and parvocellularis (Pc) may play a critical executive role in the generation of, respectively, antigravity or orofacial muscle atonia during PS. In addition, either tonic or phasic cessation of activity of medullary serotonergic neurons may play an important role in the atonia of genioglossus muscles during PS via a mechanism of disfacilitation.