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Hiroshi Onimaru

Publications and source records attributed to Hiroshi Onimaru.

18 recordsLinked to original sources
PubMed2006

Novel axonal projection from the caudal end of the ventrolateral medulla to the intermediolateral cell column.

We used an optical imaging technique to investigate whether axons of neurons in the caudal end of the ventrolateral medulla (CeVLM), as well as axons of neurons in the rostral ventrolateral medulla (RVLM), project to neurons in the intermediolateral cell column (IML) of the spinal cord. Brain stem-spinal cord preparations from neonatal normotensive Wistar-Kyoto and spontaneously hypertensive rats were stained with a voltage-sensitive dye, and responses to electrical stimulation of the IML at the Th2 level were detected as changes in fluorescence intensity with an optical imaging apparatus (MiCAM-01). The results were as follows: 1) depolarizing responses to IML stimulation during low-Ca high-Mg superfusion were detected on the ventral surface of the medulla at the level of the CeVLM, as well as at the level of the RVLM, 2) depolarizing responses were also detected on cross sections at the level of the CeVLM, and they had a latency of 24.0 +/- 5.5 (SD) ms, 3) antidromic action potentials in response to IML stimulation were demonstrated in the CeVLM neurons where optical images were detected, and 4) glutamate application to the CeVLM increased the frequency of excitatory postsynaptic potentials (EPSPs) and induced depolarization of the IML neurons. The optical imaging findings suggested a novel axonal and functional projection from neurons in the CeVLM to the IML. The increase in EPSPs of the IML neurons in response to glutamate application suggests that the CeVLM participates in the regulation of sympathetic nerve activity and blood pressure and may correspond to the caudal pressor area.

Action Potentials↗
PubMed2006

Respiration-related rhythmic activity in the rostral medulla of newborn rats.

There are at least two respiration-related rhythm generators in the medulla: the pre-Bötzinger complex, which produces inspiratory (Insp) neuron bursts, and the parafacial respiratory group (pFRG), which produces predominantly preinspiratory (Pre-I) neuron bursts. The pFRG Pre-I neuron activity has not been correlated with motor neuron activity in slice or block preparations of rostral medulla. In this study, we attempted to detect pFRG Pre-I activity as motor output in the rostral medulla. We recorded respiratory activity of the facial nerve in the brain stem-spinal cord preparation of 0- to 2-day-old rats. Facial nerve activity consisted of preinspiratory, Insp, and postinspiratory activity. Pre- and postinspiratory activity corresponded well with membrane potential trajectories of Pre-I neurons in the rostral ventrolateral medulla. In response to perfusion of 1 microM DAMGO (a mu-opiate agonist), fourth cervical ventral root (C4) Insp activity was depressed and facial nerve activity continued to synchronize with Pre-I neuron bursts. After transverse sectioning between the levels of the pre-Bötzinger complex and the pFRG, C4 Insp activity recovered within 15 min, but facial nerve activity was inhibited. When DAMGO was applied, C4 Insp activity was inhibited, and rhythmic facial nerve activity recovered. Subsequent elevation of K+ concentration reinduced C4 activity, but facial nerve activity was inhibited. Whole cell recordings in the rostral block revealed the presence of putative Pre-I neurons, the activity of which was synchronized with facial nerve activity. These results show that the rostral medulla, not including the pre-Bötzinger complex, produces Pre-I-like rhythmic activity that can be monitored as facial nerve motor output in newborn rat in vitro preparations.

Action Potentials↗
PubMed2006

Mechanisms of CO2/H+ chemoreception by respiratory rhythm generator neurons in the medulla from newborn rats in vitro.

We investigated mechanisms of CO(2)/H(+) chemoreception in the respiratory centre of the medulla by measuring membrane potentials of pre-inspiratory neurons, which are putative respiratory rhythm generators, in the brainstem-spinal cord preparation of the neonatal rat. Neuronal response was tested by changing superfusate CO(2) concentration from 2% to 8% at constant HCO(3)(-) concentration (26 mm) or by changing pH from 7.8 to 7.2 by reducing HCO(3)(-) concentration at constant CO(2) (5%). Both respiratory and metabolic acidosis lead to depolarization of neurons with increased excitatory synaptic input and increased burst rate. Respiratory acidosis potentiated the amplitude of the neuronal drive potential. In the presence of tetrodotoxin (TTX), membrane depolarization persisted during respiratory and metabolic acidosis. However, the depolarization was smaller than that before application of TTX, which suggests that some neurons are intrinsically, and others synaptically, chemosensitive to CO(2)/H(+). Application of Ba(2+) blocked membrane depolarization by respiratory acidosis, whereas significant depolarization in response to metabolic acidosis still remained after application of Cd(2+) and Ba(2+). We concluded that the intrinsic responses to CO(2)/H(+)changes were mediated by potassium channels during respiratory acidosis, and that some other mechanisms operate during metabolic acidosis. In low-Ca(2+), high-Mg(2+) solution, an increased CO(2) concentration induced a membrane depolarization with a simultaneous increase of the burst rate. Pre-inspiratory neurons could adapt their baseline membrane potential to external CO(2)/H(+) changes by integration of these mechanisms to modulate their burst rates. Thus, pre-inspiratory neurons might play an important role in modulation of respiratory rhythm by central chemoreception in the brainstem-spinal cord preparation.

Acidosis↗
PubMed2005

Electrophysiological properties of rostral ventrolateral medulla neurons in angiotensin II 1a receptor knockout mice.

We compared the electrophysiological properties of neurons in the rostral ventrolateral medulla of neonatal angiotensin II type 1a receptor knockout mice and wild-type mice with responses to angiotensin II, its type-1 receptor blocker candesartan, and its type-2 receptor blocker PD123319. Using the whole-cell patch-clamp technique, we examined the characteristics of rostral ventrolateral medulla neurons in brain stem-spinal cord preparations in which the sympathetic neuronal network is preserved. Baseline membrane potential and firing rate were almost similar between angiotensin II type 1a receptor knockout mice and wild-type mice. Superfusion with angiotensin II depolarized rostral ventrolateral medulla bulbospinal neurons in wild-type mice, whereas it hyperpolarized those in angiotensin II type 1a receptor knockout mice. Because pretreatment with candesartan significantly prevented the angiotensin II-induced depolarization in wild-type mice, the angiotensin II type 1 receptor is crucial for this depolarization. Superfusion with PD123319 depolarized rostral ventrolateral medulla bulbospinal neurons in angiotensin II type 1a receptor knockout mice. PD123319 prevented the angiotensin II-induced hyperpolarization in angiotensin II type 1a receptor knockout mice, and, rather, it induced depolarization. These results suggest that the angiotensin II type 2 receptor in rostral ventrolateral medulla plays an antagonistic role against the angiotensin II type 1a receptor in controlling the neuronal activity of rostral ventrolateral medulla.

Angiotensin II↗
PubMed2005

Optical imaging of respiratory neuron activity from the dorsal view of the lower brainstem.

1. We visualized respiratory-related neuron network activity in the dorsal part of the pons and medulla of an in vitro preparation from newborn rats by optical recordings using a voltage-sensitive dye. We measured optical signals from several seconds before to several seconds after the inspiratory phase using the inspiratory motor nerve discharge as the trigger signal and we averaged the optical signals of 20-50 respiratory cycles to obtain an optical image correlating specifically to inspiratory activity. 2. Four areas that were excited or inhibited corresponding to the respiratory cycles were detected. (i) The most rostral activity was in the rostral and lateral parts of the pons, with activity mainly in the inspiratory phase, corresponding to the pontine-respiratory group. (ii) In the midpontine level, inspiratory activity followed by long-lasting hyperpolarization appeared in the midlateral parts. This part was presumed to reflect activity in the locus coeruleus. The hyperpolarization became almost negligible after treatment with the alpha-adrenergic antagonist, phentolamine. (iii) In the dorsal medulla, the predominantly inspiratory activity was detected at the rostral level of the area postrema. This part was considered to reflect activity mainly of the hypoglossal nucleus. (iv) At a similar level, we also detected weak and disperse inspiratory activity extending more laterally and caudally than that of the hypoglossal nucleus activity. This might reflect activity of the dorsal respiratory group. 3. In conclusion, the present optical recording study revealed that the dorsal part of the lower brainstem in the in vitro preparation is noticeably active as well as the ventral part shown in the previous study. This method is very useful for analysis of pharmacological properties, as well as the spatio-temporal pattern of respiratory-related network activity in the brainstem.

Animals↗
PubMed2005

Cannabinoid suppressed bicuculline-induced convulsion without respiratory depression in the brainstem-spinal cord preparation from newborn rats.

Previous studies have suggested that cannabinoid compounds are anticonvulsants and that these compounds depress respiratory activity. However, the anticonvulsant potential of cannabinoids and their depressive effect on respiration have not been evaluated simultaneously. In the present study, we used a brainstem-spinal cord preparation model to investigate changes in inspiratory activity and the anticonvulsant effects of a cannabinoid receptor agonist, WIN 55, 212-2, in bicuculline-induced convulsion. Application of 10 microM WIN 55, 212-2 caused no change in inspiratory activity (6.9+/- 0.89 bursts/min vs. 8.0+/- 1.3 bursts/min, not significant) and decreased bicuculline-induced seizure-like nerve activity (number of seizure-like activities in 10 min, 11+/- 7.4 bursts vs. 1.5+/- 1.6 bursts, P< 0.01; average duration of seizure-like activity, 8.9+/- 4.0 sec vs. 4.7+/- 2.1 sec, P> 0.01). Our results suggest that administration of an appropriate dose of cannabinoid receptor agonist WIN 55,212-2 has an anticonvulsant effect but does not cause respiratory depression.

Animals↗
PubMed2004

Facilitation of respiratory rhythm by a mu-opioid agonist in newborn rat pons-medulla-spinal cord preparations.

We investigated the effect of a mu-opioid agonist, DAGO, on the respiratory frequency of pons-medulla-spinal cord preparations from newborn rats. Bath application of a low concentration of DAGO (0.2 microM) facilitated respiratory rhythm in pons-medulla-spinal cord preparations, whereas it induced respiratory depression in medulla-spinal cord preparations (without pons). At a higher concentration (1.0 microM), at which the inspiratory burst generation in the medulla was strongly depressed, the respiratory rhythm in half of the pons-medulla-spinal cord preparations increased and then decreased, thus showing a biphasic response. In the other half of these preparations, only the facilitatory effect was observed. The burst rate of pre-inspiratory neurons in the rostral ventrolateral medulla was also facilitated by DAGO application. Such facilitation of the respiratory rhythm is probably due to disinhibition of a pontine inhibitory system. Our findings also suggest the existence of a pontine excitatory system, which is depressed by the pontine inhibitory system under control conditions.

Action Potentials↗
PubMed2004

In vitro visualization of respiratory neuron activity in the newborn mouse ventral medulla.

To clarify the neuronal organization of the respiratory center of the mouse, we analyzed the spatio-temporal pattern of respiratory neuron activity in the ventral medulla of a newborn mouse preparation, using optical recordings. We also demonstrated optical images of the respiratory activity of two different lines of knock-out mice (Tlx3-/-, Pbx3-/-) that exhibit respiratory failure leading to neonatal death from dysfunction of central respiratory neuron activity. In the wild type mice, the respiratory neuron activity in the para-facial region of the rostral medulla appeared prior to inspiratory activity in the more caudal ventrolateral medulla. This rostral to caudal activity pattern was basically preserved in Tlx3-/- mice though the activity was more dispersed and weaker than in the wild type mice. Such an activity pattern was not clearly detected in Pbx3-/- mouse preparations. The difference in the spatio-temporal pattern between Tlx3-/- and Pbx3-/- suggests different levels of functional disorder of the respiratory center.

Animals↗
PubMed2004

Malfunction of respiratory-related neuronal activity in Na+, K+-ATPase alpha2 subunit-deficient mice is attributable to abnormal Cl- homeostasis in brainstem neurons.

Na+, K+-ATPase 2 subunit gene (Atp1a2) knock-out homozygous mice (Atp1a2-/-) died immediately after birth resulting from lack of breathing. The respiratory-related neuron activity in Atp1a2-/- was investigated using a brainstem-spinal cord en bloc preparation. The respiratory motoneuron activity recorded from the fourth cervical ventral root (C4) was defective in Atp1a2-/- fetuses of embryonic day 18.5. The C4 response to electrical stimulation of the ventrolateral medulla (VLM) recovered more slowly in Atp1a2-/- than in wild type during superfusion with Krebs' solution, consistent with the high extracellular GABA in brain of Atp1a2-/-. Lack of inhibitory neural activities in VLM of Atp1a2-/- was observed by optical recordings. High intracellular Cl- concentrations in neurons of the VLM of Atp1a2-/- were detected in gramicidin-perforated patch-clamp recordings. The alpha2 subunit and a neuron-specific K-Cl cotransporter KCC2 were coimmunoprecipitated in a purified synaptic membrane fraction of wild-type fetuses. Based on these results, we propose a model for functional coupling between the Na+, K+-ATPase alpha2 subunit and KCC2, which excludes Cl- from the cytosol in respiratory center neurons.

Amino Acid Sequence↗
PubMed2004

Tlx3 and Tlx1 are post-mitotic selector genes determining glutamatergic over GABAergic cell fates.

Glutamatergic and GABAergic neurons mediate much of the excitatory and inhibitory neurotransmission, respectively, in the vertebrate nervous system. The process by which developing neurons select between these two cell fates is poorly understood. Here we show that the homeobox genes Tlx3 and Tlx1 determine excitatory over inhibitory cell fates in the mouse dorsal spinal cord. First, we found that Tlx3 was required for specification of, and expressed in, glutamatergic neurons. Both generic and region-specific glutamatergic markers, including VGLUT2 and the AMPA receptor Gria2, were absent in Tlx mutant dorsal horn. Second, spinal GABAergic markers were derepressed in Tlx mutants, including Pax2 that is necessary for GABAergic differentiation, Gad1/2 and Viaat that regulate GABA synthesis and transport, and the kainate receptors Grik2/3. Third, ectopic expression of Tlx3 was sufficient to suppress GABAergic differentiation and induce formation of glutamatergic neurons. Finally, excess GABA-mediated inhibition caused dysfunction of central respiratory circuits in Tlx3 mutant mice.

Amino Acid Transport Systems↗
PubMed2004

Pbx3 deficiency results in central hypoventilation.

Pbx proteins comprise a family of TALE (three amino acid loop extension) class homeodomain transcription factors that are implicated in developmental gene expression through their abilities to form hetero-oligomeric DNA-binding complexes and function as transcriptional regulators in numerous cell types. We demonstrate here that one member of this family, Pbx3, is expressed at high levels predominantly in the developing central nervous system, including a region of the medulla oblongata that is implicated in the control of respiration. Pbx3-deficient mice develop to term but die within a few hours of birth from central respiratory failure due to abnormal activity of inspiratory neurons in the medulla. This partially phenocopies the defect in mice deficient for Rnx, a metaHox homeodomain transcription factor, that we demonstrate here is capable of forming a DNA-binding complex with Pbx3. Rnx expression is unperturbed in Pbx3-deficient mice, but its ability to enhance transcription in vitro as a complex with TALE proteins is compromised in the absence of Pbx3. Thus, Pbx3 is essential for respiration and, like its DNA-binding partner Rnx, is critical for proper development of medullary respiratory control mechanisms. Pbx3-deficient mice provide a model for congenital central hypoventilation syndrome and suggest that Pbx3 mutations may promote the pathogenesis of this disorder.

Animals↗
PubMed2003

Contribution of Ca2+-dependent conductances to membrane potential fluctuations of medullary respiratory neurons of newborn rats in vitro.

Ca2+-dependent conductances were studied in respiratory interneurons in the brainstem-spinal cord preparation of newborn rats. omega-Conotoxin-GVIA attenuated evoked postsynaptic potentials, spontaneous or evoked inspiratory spinal nerve activity and blocked spike afterhyperpolarization. Furthermore, omega-conotoxin-GVIA augmented rhythmic drive potentials of pre-inspiratory and inspiratory neurons and increased respiratory-related spike frequency of pre-inspiratory cells with no effect on inspiratory hyperpolarization. In contrast, omega-agatoxin-IVA depressed drive potentials of pre-inspiratory and inspiratory neurons and attenuated inspiratory hyperpolarization and spike frequency of pre-inspiratory cells. It did not affect spike shape and exerted only minor, non-significant, attenuating effects on spontaneous or evoked nerve bursts or evoked postsynaptic potentials. Nifedipine diminished drive potentials and spike frequency of pre-inspiratory neurons and shortened drive potentials in some cells. omega-Conotoxin-MVIIC attenuated drive potentials and intraburst firing rate of pre-inspiratory neurons and decreased substantially respiratory frequency. Respiratory rhythm disappeared following combined application of omega-conotoxin-GVIA, omega-conotoxin-MVIIC, omega-agatoxin-IVA and nifedipine. Apamin potentiated drive potentials and abolished spike afterhyperpolarization, whereas charybdotoxin and tetraethylammonium prolonged spike duration without effect on shape of drive potentials. The results show that specific sets of voltage-activated L-, N- and P/Q-type Ca2+ channels determine the activity of particular subclasses of neonatal respiratory neurons, whereas SK- and BK-type K+ channels attenuate drive potentials and shorten spikes, respectively, independent of cell type. We hypothesize that modulation of spontaneous activity of pre-inspiratory neurons via N-, L- and P/Q-type Ca2+ channels is important for respiratory rhythm or pattern generation.

Animals↗
PubMed2003

A novel functional neuron group for respiratory rhythm generation in the ventral medulla.

We visualized respiratory neuron activity covering the entire ventral medulla using optical recordings in a newborn rat brainstem-spinal cord preparation stained with voltage-sensitive dye. We measured optical signals from several seconds before to several seconds after the inspiratory phase using the inspiratory motor nerve discharge as the trigger signal; we averaged the optical signals of 50-150 respiratory cycles to obtain an optical image correlating particularly to inspiratory activity. The optical images we obtained from the ventral approach indicated that neuron activity first appeared during the respiratory cycle in the limited region of the rostral ventrolateral medulla (RVLM), preceding the onset of inspiratory activity by approximately 500 msec. During the inspiratory phase, plateau activity appeared in the more caudal ventrolateral medulla at the level of the most rostral roots of the XIIth nerve. Comparison with electrophysiological recordings from respiratory neurons in the RVLM suggested that the optical signals preceding the inspiratory burst reflect preinspiratory neuron activity in this area. This RVLM area was determined to be ventrolateral to the facial nucleus and close to the ventral surface. We referred to this functional neuron group as the para-facial respiratory group (pFRG). Partial, bilateral electrical lesioning of the pFRG significantly reduced the respiratory frequency, together with changes in the spatiotemporal pattern of respiratory neuron activity. Our findings suggest that the pFRG comprises a neuronal population that is involved in the primary respiratory rhythm generation in the rostrocaudally extending respiratory neuron network of the medulla.

Animals↗
PubMed2002

Opioid-resistant respiratory pathway from the preinspiratory neurones to abdominal muscles: in vivo and in vitro study in the newborn rat.

We report that after spontaneous breathing movements are stopped by administration of opioids (opioid-induced apnoea) in neonatal rats, abdominal muscles continue to contract at a rate similar to that observed during periods of ventilation. Correspondingly, in vitro bath application of a mu opioid receptor agonist suppresses the activity of the fourth cervical root (C4) supplying the diaphragm, but not the rhythmic activity of the first lumbar root (L1) innervating the abdominal muscles. This indicates the existence of opioid-resistant rhythmogenic neurones and a neuronal pathway transmitting their activity to the abdominal motoneurones. We have investigated this pathway by using a brainstem-spinal cord preparation of the neonatal rat. We identified bulbospinal neurones with a firing pattern identical to that of the L1 root. These neurones were located caudal to the obex in the vicinity of the nucleus retroambiguus. Resting potentials ranged from -49 to -40 mV (mean +/- S.D. -44.0 +/- 4.3 mV). The mean input resistance was 315.5 +/- 54.8 MOmega. The mean antidromic latency from the L1 level was 42.8 +/- 4.4 ms. Axons crossed the midline at the level of the cell body. The activity pattern of the bulbospinal neurones and the L1 root consisted of two bursts per respiratory cycle with a silent period during inspiration. This pattern is characteristic of preinspiratory neurones. We found that 11 % of the preinspiratory neurones projected to the area where the bulbospinal neurones were located. These preinspiratory neurones were found in the rostral ventrolateral medulla close (200-350 microm) to the ventral surface at the level of the rostral half of the nucleus retrofacialis. Our data suggest the operation of a disynaptic pathway from the preinspiratory neurones to the L1 motoneurones in the in vitro preparation. We propose that the same pathway is responsible for rhythmic activation of the abdominal muscles during opioid-induced apnoea in the newborn rat.

Abdominal Muscles↗
PubMed2002

Development of the rat respiratory neuron network during the late fetal period.

We studied developmental changes in respiratory-like C4 activity and respiratory-related neurons in the ventrolateral medulla (VLM) of brainstem-spinal cord preparations from rat fetuses after embryonic day 16 (E16). In addition to respiratory nerve activity, non-respiratory activity was recorded from the C4 ventral root of preparations before E19. The burst duration of respiratory nerve discharge increased markedly at E19/20. Subtypes of neurons similar to newborn respiratory neurons were found in preparations with prolonged burst duration (more than 400 ms) after E20. These subtypes were not evident in preparations with short burst duration (less than 300 ms) before E19. About 60% of the inspiratory neurons in E17-19 preparations produced voltage-dependent burst activity, which was preserved in low Ca(2+)/high Mg(2+) synaptic blockade solution. In about 11% of the inspiratory neurons of E18-19 preparations, activation of one neuron induced activation of the inspiratory neuron network and generation of a full C4 inspiratory burst. The present findings suggest that respiratory neuron networks mature functionally to the level of the neonatal respiratory neuron networks during gestation period E19/20. Potentiation of synaptic interaction between respiratory neurons, causing developmental changes in the burst pattern, might be involved in the maturation process during late fetal stages.

Animals↗
PubMed2002

Rostral ventrolateral medulla neurons of neonatal Wistar-Kyoto and spontaneously hypertensive rats.

We compared the electrophysiological properties of neurons in the rostral ventrolateral medulla (RVLM) of neonatal Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), and responses to angiotensin II and its type 1 receptor antagonist candesartan. Using the whole-cell patch-clamp technique, we examined the characteristics of RVLM neurons in brainstem-spinal cord preparations with a preserved sympathetic neuronal network. The baseline membrane potential of irregularly firing neurons was less negative (-50.1+/-0.6 versus -52.0+/-0.6 mV) and the firing rate was faster (3.0+/-0.2 versus 2.0+/-0.2 Hz) in SHR (n=56) than in WKY (n=38). Superfusion with angiotensin II (6 micromol/L) significantly depolarized the RVLM bulbospinal neurons in SHR (5.4+/-1.1 mV, n=15) but not in WKY. In contrast, candesartan (0.12 micromol/L) induced a significant membrane hyperpolarization (-3.7+/-0.4 mV; n=14) and a decrease in the firing rate in RVLM bulbospinal neurons of SHR but not of WKY. These results suggest that endogenously generated angiotensin II binds to type 1 receptors on RVLM bulbospinal neurons, thus tonically contributing to a higher membrane potential and a faster firing rate in SHR. The electrophysiological properties of RVLM neurons and their responses to angiotensin II and candesartan differ between neonatal WKY and SHR. These differences in RVLM neurons suggest a mechanism that possibly leads to elevation in blood pressure.

Action Potentials↗