Identification of genes that restrict astrocyte differentiation of midgestational neural precursor cells.

During development of the mammalian CNS, neurons and glial cells (astrocytes and oligodendrocytes) are generated from common neural precursor cells (NPCs). However, neurogenesis precedes gliogenesis, which normally commences at later stages of fetal telencephalic development. Astrocyte differentiation of mouse NPCs at embryonic day (E) 14.5 (relatively late gestation) is induced by activation of the transcription factor signal transducer and activator of transcription (STAT) 3, whereas at E11.5 (mid-gestation) NPCs do not differentiate into astrocytes even when stimulated by STAT3-activating cytokines such as leukemia inhibitory factor (LIF). This can be explained in part by the fact that astrocyte-specific gene promoters are highly methylated in NPCs at E11.5, but other mechanisms are also likely to play a role. We therefore sought to identify genes involved in the inhibition of astrocyte differentiation of NPCs at midgestation. We first examined gene expression profiles in E11.5 and E14.5 NPCs, using Affymetrix GeneChip analysis, applying the Percellome method to normalize gene expression level. We then conducted in situ hybridization analysis for selected genes found to be highly expressed in NPCs at midgestation. Among these genes, we found that N-myc and high mobility group AT-hook 2 (Hmga2) were highly expressed in the E11.5 but not the E14.5 ventricular zone of mouse brain, where NPCs reside. Transduction of N-myc and Hmga2 by retroviruses into E14.5 NPCs, which normally differentiate into astrocytes in response to LIF, resulted in suppression of astrocyte differentiation. However, sustained expression of N-myc and Hmga2 in E11.5 NPCs failed to maintain the hypermethylated status of an astrocyte-specific gene promoter. Taken together, our data suggest that astrocyte differentiation of NPCs is regulated not only by DNA methylation but also by genes whose expression is controlled spatio-temporally during brain development.

Medullary reticulospinal tract mediating a generalized motor inhibition in cats: III. Functional organization of spinal interneurons in the lower lumbar segments.

The previous report of intracellular recording of hindlimb motoneurons in decerebrate cats [ 511] has suggested that the following mechanisms are involved in a generalized motor inhibition induced by stimulating the medullary reticular formation. First, the motor inhibition, which was prominent in the late latency (30-80 ms), can be ascribed to the inhibitory effects in parallel to motoneurons and to interneuronal transmission in reflex pathways. Second, both a group of interneurons receiving inhibition from flexor reflex afferents and a group of Ib interneurons mediate the late inhibitory effects upon the motoneurons. To substantiate the above mechanisms of motor inhibition we examined the medullary stimulus effects upon intracellular (n=55) and extracellular (n=136) activity of spinal interneurons recorded from the lower lumbar segments (L6-L7). Single pulses or stimulus trains (1-3) pulses, with a duration of 0.2 ms and intensity of 20-50 microA) applied to the medullary nucleus reticularis gigantocellularis evoked a mixture of excitatory and inhibitory effects with early (<20 ms) and late (>30 ms) latencies. The medullary stimulation excited 55 interneurons (28.8%) with a late latency. Thirty-nine of the cells, which included 10 Ib interneurons, were inhibited by volleys in flexor reflex afferents (FRAs). These cells were mainly located in lamina VII of Rexed. On the other hand, the late inhibitory effects were observed in 67 interneurons (35.1%), which included cells mediating reciprocal Ia inhibition, non-reciprocal group I (Ib) inhibition, recurrent inhibition and flexion reflexes. Intracellular recording revealed that the late inhibitory effects were due to inhibitory postsynaptic potentials with a peak latency of about 50 ms and a duration of 50-60 ms. The inhibitory effects were attenuated by volleys in FRAs. Neither excitatory nor inhibitory effects with a late latency were observed in 69 (36.1%) cells which were located in the intermediate region and dorsal horn. These results suggest the presence of a functional organization of the spinal cord with respect to the production of the generalized motor inhibition. Lamina VII interneurons that receive inhibition from volleys in FRAs possibly mediate the postsynaptic inhibition from the medullary reticular formation in parallel to motoneurons and to interneurons in reflex pathways.

Changes in the excitability of hindlimb motoneurons during muscular atonia induced by stimulating the pedunculopontine tegmental nucleus in cats.

We have previously reported that electrical stimulation delivered to the ventral part of the pedunculopontine tegmental nucleus (PPN) produced postural atonia in acutely decerebrated cats [Neuroscience 119 (2003) 293]. The present study was designed to elucidate synaptic mechanisms acting on motoneurons during postural atonia induced by PPN stimulation. Intracellular recording was performed from 72 hindlimb motoneurons innervating extensor and flexor muscles, and the changes in excitability of the motoneurons following the PPN stimulation were examined. Repetitive electrical stimulation (20-50 microA, 50 Hz, 5-10 s) of the PPN hyperpolarized the membrane potentials of both the extensor and flexor motoneurons by 2.0-12 mV (6.0 +/- 2.3 mV, n = 72). The membrane hyperpolarization persisted for 10-20 s even after termination of the stimulation. During the PPN stimulation, the membrane hyperpolarization was associated with decreases in the firing capability (n = 28) and input resistance (28.5 +/- 6.7%, n = 14) of the motoneurons. Moreover the amplitude of Ia excitatory postsynaptic potentials was also reduced (44.1 +/- 13.4%, n = 14). After the PPN stimulation, these parameters immediately returned despite that the membrane hyperpolarization persisted. Iontophoretic injections of chloride ions into the motoneurons reversed the polarity of the membrane hyperpolarization during the PPN stimulation. The polarity of the outlasting hyperpolarization however was not reversed. These findings suggest that a postsynaptic inhibitory mechanism, which was mediated by chloride ions, was acting on hindlimb motoneurons during PPN-induced postural atonia. However the outlasting motoneuron hyperpolarization was not due to the postsynaptic inhibition but it could be due to a decrease in the activity of descending excitatory systems. The functional role of the PPN in the regulation of postural muscle tone is discussed with respect to the control of behavioral states of animals.

Medullary reticulospinal tract mediating the generalized motor inhibition in cats: parallel inhibitory mechanisms acting on motoneurons and on interneuronal transmission in reflex pathways.

The present study was designed to elucidate the spinal interneuronal mechanisms of motor inhibition evoked by stimulating the medullary reticular formation. Two questions were addressed. First, whether there is a parallel motor inhibition to motoneurons and to interneurons in reflex pathways. Second, whether the inhibition is mediated by interneurons interposed in known reflex pathways. We recorded the intracellular activity of hindlimb motoneurons in decerebrate cats and examined the effects of medullary stimulation on these neurons and on interneuronal transmission in reflex pathways to them. Stimuli (three pulses at 10-60microA and 1-10ms intervals) delivered to the nucleus reticularis gigantocellularis evoked inhibitory postsynaptic potentials in alpha-motoneurons (n=147) and gamma-motoneurons (n=5) with both early and late latencies. The early inhibitory postsynaptic potentials were observed in 66.4% of the motoneurons and had a latency of 4.0-5.5ms with a segmental delay of more than 1.4ms. The late inhibitory postsynaptic potentials were observed in 98.0% of the motoneurons and had a latency of 30-35ms, with a peak latency of 50-60ms. Both types of inhibitory postsynaptic potentials were evoked through fibers descending in the ventrolateral quadrant. The inhibitory postsynaptic potentials were not influenced by recurrent inhibitory pathways, but both types were greatly attenuated by volleys in flexor reflex afferents. Conditioning medullary stimulation, which was subthreshold to evoke inhibitory postsynaptic potentials in the motoneurons, neither evoked primary afferent depolarization of dorsal roots nor reduced the input resistance of the motoneurons. However, the conditioning stimulation often facilitated non-reciprocal group I inhibitory pathways (Ib inhibitory pathways) to the motoneurons in early (<20ms) and late (30-80ms) periods. In contrast, it attenuated test postsynaptic potentials evoked through reciprocal Ia inhibitory pathways, and excitatory and inhibitory pathways from flexor reflex afferent and recurrent inhibitory pathways. The inhibitory effects were observed in both early and late periods. The present results provide new information about a parallel inhibitory process from the medullary reticular formation that produces a generalized motor inhibition by acting on alpha- and gamma-motoneurons, and on interneurons in reflex pathways. Interneurons receiving inhibition from flexor reflex afferents and a group of Ib interneurons may mediate the inhibitory effects upon motoneurons.

Inactivation of the pons blocks medullary-induced muscle tone suppression in the decerebrate cat.

The pontomedullary region is responsible for the reduction of muscle activity in rapid-eye-movement sleep and contributes to the control of muscle tone in waking. This study sought to clarify the nature of the interaction between the pontine and medullary reticular formation in mediating muscle tone suppression. The degree of medullary-induced neck muscle tone suppression in the decerebrate cat was assessed before and after microinjection of lidocaine into the pontine reticular formation. Medullary stimulation-induced suppression of neck muscle tone was blocked after pontine lidocaine microinjection. The maximum blockade was observed at 16.6 minutes on average after the injection, and recovery occurred within 45 minutes. We conclude that descending mechanisms from the medulla are not sufficient for the triggering of muscle tone suppression. A two-way interaction between the medulla and pons is hypothesized to play a crucial role in the control of muscle tone.

Tonic and phasic inhibition indices are constant among nights: new indices for evaluating the degree of the two types of motor inhibition during REM sleep.

BACKGROUND: Tonic inhibition index (TII) and phasic inhibition index (PII) were proposed as indices for evaluating the degree of two types of motor inhibition activity during rapid eye movement (REM) sleep. METHODS: In the present study, therefore, six healthy men underwent two consecutive all-night polysomnography, and reproducibility of TII and PII was evaluated. RESULTS: TII was 0.85+/-0.07 (mean+/-SD) on the first night and 0.88+/-0.08 on the second; and PII was 3.4+/-2.1 on the first night and 4.9+/-1.8 on the second. Neither TII nor PII was significantly different between the two nights. CONCLUSION: One night sleep study is considered sufficient for using TII and PII as a tool for evaluating motor inhibition activity during REM sleep in adults.

Phasic muscle activity during REM sleep in infancy-normal maturation and contrastive abnormality in SIDS/ALTE and West syndrome.

The generation of phasic muscle activity during REM sleep is regulated by the brainstem. We proposed two sleep indices for phasic muscle activity during REM sleep, and examine their usefulness in assessing normal brainstem maturation and functional brainstem impairment during infancy. One - the dissociation index (DI) - seems to reflect maturation of the tonic inhibitory system functioning during REM sleep, and the other - % body movements in REMs bursts (%BMs-R) - to reflect that of the phasic one. In normal infants, DI showed a gradual, linear and significant increase with age, whereas %BMs-R showed a gradual and significant decrease with age. In infants with sudden infant death syndrome (SIDS) and one who had experienced apparent life-threatening events (ALTE), the DI values were lower than those in controls, although %BMs-R values were identical in the controls. In contrast, DI was variable in infants with West syndrome (WS), while %BMs-R exceeded normal values. The tonic inhibitory system seemed to be specifically involved in SIDS and ALTE, but the phasic inhibitory one in WS. Anatomical differences between these inhibitory systems are also discussed.

Phasic loss of intercostal muscle activity occurring with rapid eye movements during REM sleep.

We tried to estimate the phasic motor inhibition occurring with rapid eye movements (REMs) during REM sleep in children by means of polysomnography. Phasic inhibition of intercostal muscle activity with REMs has been proved by averaging the integrated surface electromyograms in three children. The average latency from the onset of REMs to this inhibition was 38.0 ms, their average duration being 237.0 ms. We discussed the possibility that the REM-related phasic inhibition obtained here was involved in the brainstem-spinal cord inhibitory system functioning during REM sleep.

Pontine microinjection of carbachol and critical zone for inducing postural atonia in reflexively standing decerebrate cats.

Pontine carbachol injection sites critically related to the induction of postural atonia were explored in reflexively standing acute decerebrate cats. Carbachol (4.0 micrograms/0.25 microliter) and atropine (2.0 micrograms/0.25 microliter) were focally injected into the pontomedullary reticular formation, and their effects on hindlimb extensor muscle tone were studied. The effective carbachol injection sites were concentrated in the region between P 1.5 and P 3.5, H -3.0 and H -5.0, and LR 1.2 and LR 2.5 (Horsley-Clarke coordinates). The effective sites corresponded to the dorsomedial part of both the nucleus reticularis pontis oralis (NRPo) and the rostral portion of the nucleus reticularis pontis caudalis (NRPc). The mean latency to the beginning of carbachol-induced postural atonia was about 90 s (92 +/- 28 s; n = 24).

A quantitative assessment of the maturation of phasic motor inhibition during REM sleep.

During rapid eye movement (REM) sleep, phasic and further motor inhibition occurs during clusters of REMs besides tonic motor inhibition. We describe the age-related quantitative change of the activity of this REM-related phasic motor inhibition. For this purpose, we introduced the phasic inhibition index (PII). PII is the rate of simultaneous occurrence of bursts of horizontal REMs and phasic mentalis muscle activity during REM sleep. We examined these phasic REM sleep parameters in 87 healthy children from premature babies to preadolescents. The incidence of bursts of REMs showed no age-related change, while that of the phasic mentalis muscle activity increased with age. The simple ratio between the incidence of bursts of REMs and that of phasic mentalis muscle activity showed no significant age-related change, whereas PII decreased rapidly during infancy and reached low constant values thereafter. We concluded that this age-related PII decline reflected the maturation of REM-related phasic motor inhibition. This is the first quantitative description on the development of human motor inhibition. Taken with the neuronal basis underlying REM-related phasic motor inhibition, we hypothesize that a PII value is within the normal low range as far as both the rostral pontine tegmentum and the brainstem inhibitory pathways are functionally intact.

Phasic motor activity reduction occurring with horizontal rapid eye movements during REM sleep is disturbed in infantile spasms.

Single polysomnography was performed before treatment in 17 patients with infantile spasms (IS) (13 with a cryptogenic type and 4 with a symptomatic one). Their sleep components during rapid eye movement (REM) sleep were compared with those in 22 age-matched controls. The tonic muscle atonia during REM sleep was observed in all IS patients as in controls. The amount of REM sleep in IS patients was significantly lower, while the incidences of gross movements, phasic chin muscle activity, and bursts of horizontal rapid eye movements were identical with those in controls. The phasic inhibition index (PII), i.e., the rate of simultaneous occurrence of phasic chin muscle activity and bursts of horizontal rapid eye movements, was significantly higher in IS than in controls. The PII value was the only parameter that reflected our patients' prognosis among the obtained REM sleep parameters. We presume that the elevated PII in IS reflects the weakness of the phasic motor activity reduction occurring with horizontal rapid eye movements, and attribute this disturbance to a functional instability of the rostral pontine tegmentum. We propose that PII is a useful parameter for assessing the prognosis of IS. Considering the neural basis for elevated PII in IS, this index is expected to provide a clue for explaining the pathophysiology of IS.

Rapid eye movement sleep in breath holders.

One-night polysomnography was performed on seven subjects suffering from breath-holding spells, including one whose death was suggested to be a consequence of a breath-holding spell. The fatal case showed no rapid eye movements (REMs) during REM sleep, although he exhibited REMs during wakefulness. The average numbers of both REMs and bursts of REMs in REM sleep in the other six breath holders were significantly lower than those in age-matched controls. The breath holders showed no airway obstruction, desaturation, or sleep fragmentation. Since the rapid ocular activity in REM sleep is generated in the brain stem, we hypothesized that a functional brainstem disturbance is involved in the occurrence of breath-holding spells.

REM sleep atonia: responsible brain regions, quantification, and clinical implication.

Muscle tone is profoundly suppressed during rapid-eye-movement sleep. Two indices that quantify this muscle activity suppression were introduced: the tonic inhibition index (TII) and the phasic inhibition index (PII). TII expresses the shortening of phasic chin muscle activity, and PII indicates the degrees of suppression of the occurrence of phasic chin muscle activity in the period of the burst of rapid eye movements. TII increased significantly with age, while PII decreased significantly. TII was found to reach the adult level at 12.3 years of age, while PII decreased to the adult value at 0.4 years. According to this difference in age between their maturation, the human nervous systems involved in muscle activity suppression are hypothesized to comprise at least two independent systems. TII and PII are also hypothesized to be affected by the activity of the brainstem inhibitory centers, which might be implicated in the suppression of muscle activity during wakefulness as well.

Polysomnographical assessment of the pathophysiology of West syndrome.

In this brief review, the sleep studies on patients with West syndrome (WS) were summarized. In addition to the previously reported common finding for sleep in WS--reduction of the amount of rapid-eye-movement (REM) sleep--weakness of phasic suppression of chin muscle activity in WS patients has recently been found. The degree of this weakness is quantified by the phasic inhibition index (PII), which has been found to reflect a patient's prognosis as to convulsions. PII is proposed to be a useful parameter for assessing the prognosis of WS. Since the pontine tegmentum is involved in the production of the REM-related phasic loss of muscle activity in REM sleep, WS patients are hypothesized to have a functional instability of the pontine tegmentum. After adrenocorticotropin (ACTH) treatment, PII decreased significantly in all WS patients examined. Taken together with the effects of corticosteroids on PII, and the incidence of phasic chin muscle activity in patients with congenital adrenal hyperplasia and nephrotic syndrome, ACTH is hypothesized to suppress the spasms in WS patients not only through corticosteroids, but also through a direct action on the pontine tegmentum. Since PII has been reported to be elevated in patients with an autistic tendency, the appearance of an autistic tendency is also hypothesized to be involved in the functional disturbance of the pontine tegmentum.

Polygraphic features of a victim of sudden infant death syndrome and of infants with apparent life-threatening event.

We analyzed a polygram of a victim of sudden infant death syndrome (SIDS) which had been taken five weeks prior to his death. The findings are discussed in association with the serial polygraphic observations of four infants who had suffered from apparent life-threatening event (ALTE), and twenty neurologically normal infants. Frequencies of respiratory pauses were high in SIDS, and average durations of respiratory pauses showed higher values in ALTE than in the controls. Normal paradoxical motions between chest and abdominal wall during active sleep period (AS) were completely abolished in the records of SIDS and of one ALTE. Normal developmental decreases of localized movements (LMs) on mental muscle with age were insufficient in ALTE. The numbers of twitch movements (TMs) were low in SIDS and in two of ALTE, while those of gross movements in the subjects were identical with those in the controls. Dissociation indexes (ratio of the number of TMs against the sum of the numbers of TMs and LMs) were low in SIDS and in two of ALTE. These findings seemed to be the physiological reflection of the impairment of arousal responsiveness and of the developmental disturbance of the brainstem in SIDS and ALTE. Polygraphic evaluations on the respiratory pattern during AS and the dissociation state of TMs from LMs may be helpful in the early detection of SIDS and/or ALTE in asymptomatic infants.

Brainstem control of phasic muscle activity during REM sleep: a review and hypothesis.

For the generation of phasic muscle activity during rapid eye movement (REM) sleep, strong motor excitation to overcome both tonic and phasic inhibition is needed at the motoneuron level. Descending pathways originating in the rostral pons (cholinoceptive (nucleus reticularis pontis oralis-->nucleus reticularis gigantocellularis, peri-locus coeruleus pars alpha-->nucleus reticularis magnocellularis) and cholinergic (pedunculopontine tegmental nucleus-->nucleus reticularis paramedianus) pathways) are involved in motor inhibition during REM sleep. Since the origins of excitatory drives related to phasic muscle activity during REM sleep are also in the brainstem, the occurrence of phasic muscle activity can be said to be determined by brainstem activity. We review the basic and clinical studies on phasic muscle activity during REM sleep and propose the possibility that it can be a beneficial parameter for assessing brainstem activity, especially in relation to its maturation during early stage of life.

Disturbance of phasic chin muscle activity during rapid-eye-movement sleep.

In patients with Rett syndrome (RS), a peculiar type of disturbance in phasic chin muscle activity during rapid-eye-movement sleep (REMS) (e.g. an elevation of phasic inhibition index (PII) without an affection of tonic inhibition index (TII)) has been reported. The similar disturbance in REMS was reported not only in child patients with infantile spasms, severe myoclonic epilepsy in infancy (SMEI), severe nocturnal enuresis, and autism but also in adult patients with Parkinson's disease (PD). Except for SMEI and PD, patients with the other four clinical entities including RS could express autistic tendency. Since the responsible lesion for the occurrence of an elevation of PII with a normal TII value is likely to be in the pontine tegmentum, this subcortical structure is hypothesized to be involved in the appearance of autistic tendency.

A case of Dandy-Walker malformation: consideration on the teratogenic period and sleep structures.

An 11-month-old girl suffering from Dandy-Walker malformation (DWM) associated with tetralogy of Fallot (TOF) is presented. There has been no report describing a case of DWM associated with TOF. Our case may raise a new discussion on the teratogenic period of these anomalies. A polysomnogram was obtained, and basic sleep components, such as the proportion of each sleep stage and the numbers of body movements and rapid eye movements, showed no significant differences from those in the controls, despite hydrocephalus, pachygyria of the cerebral cortex and a large low density area in the posterior fossa.

A case of chronic epileptic encephalopathy of neonatal onset. A probable concern of human cytomegalovirus.

A 10-year-old male patient, who had suffered from intractable convulsions from the neonatal period, is presented. Serial brain images suggested slow, gradual destruction of neural elements. Human cytomegalovirus (HCMV) DNA was detected in his cerebrospinal fluid (CSF) by means of the polymerase chain reaction. Intrathecal interferon had a favorable effect on his seizures. We assume a close relationship between HCMV and some chronic types of epileptic encephalitis/encephalopathy.