Biomedical subjects

H Onimaru

Publications and source records attributed to H Onimaru.

34 records · Page 2Linked to original sources

PubMed1993

Possible mutual excitatory couplings between inspiratory neurons in caudal ventrolateral medulla of brainstem-spinal cord preparation isolated from newborn rat.

In in vitro brainstem-spinal cord preparations, projection of inspiratory neurons in the caudal ventrolateral medulla (CVL) was examined electrophysiologically, and connectivity between bilateral inspiratory neurons in the CVL was analyzed by pulse-cross correlation (PCC) analysis. CVL inspiratory neurons were found to project to the contralateral CVL and/or mainly ipsilateral spinal cord. PCC analysis revealed significant peaks with different latency on both sides of time zero in 3 of 8 pairs. Results were consistent with mono- or oligo-synaptic excitatory connections between bilateral inspiratory neurons in the CVL.

Acetylcholine↗

PubMed1993

Correlation analysis of respiratory neuron activity in ventrolateral medulla of brainstem-spinal cord preparation isolated from newborn rat.

Cross-correlation analysis was used to study functional connections between one inspiratory (I) neuron and another, and between one pre-inspiratory (Pre-I) neuron and another, in 54 brainstem-spinal cord preparations isolated from newborn rats. Pre-I neurons usually fired in the pre- and post-inspiratory phases. Neurons were recorded extracellularly with pairs of microelectrodes placed on the same or opposite sides of the brainstem. Fourteen pairs of Pre-I neurons recorded bilaterally in the rostral ventrolateral medulla (RVL), 14 pairs of ipsilateral Pre-I neurons in the RVL, 14 pairs of bilateral I neurons in the RVL and 12 pairs of ipsilateral I neurons in the ventrolateral medulla were studied. Cross-correlation histograms (CCHs) were computed. Significantly high peak bin counts were detected in 24 of 54 pairs. Peaks on one side of the origin of the CCHs were observed for one pair of ipsilateral Pre-I neurons, four pairs of bilateral I neurons and five pairs of ipsilateral I neurons. These findings suggest mono- or oligo-synaptic excitatory connections between paired neurons or shared inputs. Only one trough suggesting an oligo-synaptic inhibitory connection was evident in a CCH obtained from the pair of bilateral I neurons. This CCH revealed the peak and the trough on opposite sides of the origin, which was consistent with reciprocal excitatory and inhibitory connections between recorded neurons. Peaks on both sides of the origin were observed for three pairs of bilateral I neurons. From auto-correlation analysis and the latencies of these peaks, two of the three CCHs were consistent with reciprocal excitatory connections between recorded neurons, whereas the other CCH suggests shared inputs. Peaks at the origin were observed for two pairs of ipsilateral Pre-I neurons, four pairs of bilateral I neurons and five pairs of ipsilateral I neurons. These results suggest shared inputs. For Pre-I neurons recorded in opposite sides, no significant bin counts were detected. Peaks on one side were detected for three pairs. Present results suggest short-term synchronisation of I neurons, and of Pre-I neurons via excitatory coupling, and the likelihood of comparatively strong interaction between I neurons, which may be important in maintaining the I burst.

Animals↗

PubMed1993

Effects of NMDA on respiratory neurons in newborn rat medulla in vitro.

In 30 brain stem-spinal cord preparations isolated from newborn rats, we examined effects of 10 microM N-methyl-D-aspartate (NMDA) on 21 pre-inspiratory (Pre-I) and 26 inspiratory (I) neurons during perfusion in a synaptic blockade (low Ca2+, high Mg2+) bath, referred to here as low Ca. Application of NMDA to 9 Pre-I neurons that burst rhythmically by NMDA. Application of NMDA had no effect on 20 I neurons out of 26 tested. NMDA made one I neuron that was otherwise silent burst rhythmically in low Ca. The results suggest that, in this preparation, activation of NMDA receptors could contribute to induction or facilitation of burst activity by respiratory neurons, especially Pre-I neurons.

Animals↗

PubMed1992

Effect of substance P on respiratory rhythm and pre-inspiratory neurons in the ventrolateral structure of rostral medulla oblongata: an in vitro study.

The pre-inspiratory (Pre-I) neurons which fire in the pre- and usually also during the post-inspiratory phase are located in the ventrolateral structures of the rostral medulla. They are suggested as primary rhythm generating neurons for respiration. These have been studied in isolated brainstem-spinal cord preparations from newborn 0-5-day-old rats. We have found that application of substance P (SP) enhanced the respiratory rhythm as measured by C4 ventral root and pre-I neuronal activities. Furthermore, the effect of SP was dependent on basal respiratory rate. An increase of the Pre-I and C4 burst rate by SP was clearer when the basal respiratory rhythm was somewhat lower. Moreover, long lasting depression of respiratory rate after the application of the alpha 2-agonist clonidine was reversed by SP. On the other hand, an inhibitory effect appeared in preparations with a higher basal respiratory rate, while the Pre-I burst rate tended to increase during SP perfusion. During chemical synaptic transmission blockade by perfusion with low Ca2+, high Mg2+ solution, a pre-I burst retained or completely blocked was found to be enhanced or reactivated by SP perfusion. The results suggest a direct postsynaptic action of SP, which could strongly stimulate burst generating properties of Pre-I neurons.

Animals↗

PubMed1992

Whole cell recordings from respiratory neurons in the medulla of brainstem-spinal cord preparations isolated from newborn rats.

In brainstem-spinal cord preparations isolated from newborn rats, a whole cell recording technique was applied to record membrane potentials of inspiratory (Insp) and pre-inspiratory (Pre-I) neurons in the ventrolateral medulla. Labelling of these respiratory neurons with Lucifer Yellow allowed analysis of their locations and morphology. Intracellular membrane potentials from 25 Insp neurons were recorded. Average resting membrane potential was -49 mV (n = 25) and input resistance was 306 M omega. Insp neurons were classified into three types from the patterns of synaptic potentials. Type I neurons (n = 11) had a high probability of excitatory postsynaptic potentials (EPSPs) in the pre- and post-inspiratory phases. Type II neurons (n = 7) showed abrupt transition to the burst phase from the resting potential level without increased EPSPs in the preinspiratory phase. Type III neurons (n = 7) were hyperpolarized by inhibitory postsynaptic potentials (IPSPs) in the pre- and post-inspiratory phases. These Insp neurons, located in the ventrolateral medulla 80-490 microns from the ventral surface, were 10-30 microns in diameter, and had various soma shapes (pyramidal, spherical or fusiform). Intracellular membrane potentials from 24 Pre-I neurons were recorded. The average resting membrane potential was -45 mV (n = 24), and the input resistance was 320 M omega. Typical Pre-I neurons showed fairly great depolarization accompanied by action potentials during their burst phase and repolarization during the inspiratory phase. Most Pre-I neurons appeared to have a high level of synaptic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Excitation of inspiratory neurons by preinspiratory neurons in rat medulla in vitro.

In brain stem-spinal cord preparations isolated from newborn rats, we examined synaptic connections to inspiratory neurons from preinspiratory (Pre-I) neurons, by spike-triggered averaging. Potentials were simultaneously recorded intracellularly from inspiratory neurons, and extracellularly from Pre-I neurons in the ipsilateral ventrolateral medulla. The Pre-I neuron pulses were used to trigger computer averaging of potential changes. A total of 16 pairs were analyzed, and EPSP-like depolarizing potentials locked to the triggering Pre-I spikes were obtained from three pairs. Latency from the Pre-I spikes was 3.4-4.5 ms, and the amplitude was 0.07-0.4 mV. These connections were concluded to be monosynaptic, because the antidromic latency was 3.6 +/- 1.5 ms. The present results suggest the presence of excitatory synaptic connections from Pre-I neurons to inspiratory neurons in the ventrolateral medulla. These excitatory synaptic connections are probably important in the initiation of inspiratory burst activity.

Animals↗

PubMed1990

Inhibitory synaptic inputs to the respiratory rhythm generator in the medulla isolated from newborn rats.

Involvement of chloride-dependent, gamma-aminobutyric acid-(GABA-) like synaptic inhibition in the generation of respiratory rhythm was studied in brainstem-spinal cord preparations isolated from newborn rats. Primary respiratory rhythm is presumably generated within the rostral ventrolateral medulla, the site of Pre-I neurones, the firing of which precedes inspiration. Therefore, we examined the responses of Pre-I and inspiratory neurones to GABA antagonists (picrotoxin and bicuculline), a glycine antagonist (strychnine) and reduced chloride concentration in the perfusate. These antagonists (2-20 microM) and reduction of chloride concentration reversibly blocked the transient inhibition of Pre-I activity that occurred during the inspiratory phase. The rhythmic Pre-I and inspiratory neurone activity remained. Changes in the firing properties of Pre-I and inspiratory neurones in 10 microM bicuculline, 10 microM picrotoxin, 5 microM strychnine or reduction of chloride concentration to 40% of normal were analysed statistically. Burst rate of Pre-I neurones tended to increase during these treatments. Delay time from initiation of Pre-I firing to the peak of C4 motorneurone inspiratory activity tended to decrease except during reduced chloride concentration. Changes in mean intraburst firing frequency of Pre-I neurones were not consistent; increase (32%), no change (38%) or decrease (30%). Burst duration of inspiratory neurones decreased. Intraburst firing frequency of inspiratory neurones tended to increase except in 5 microM strychnine. GABA (0.1 mM) or glycine (0.2 mM) reduced the intraburst firing frequency and burst rate of Pre-I neurones, but did not affect the intraburst firing frequency of inspiratory neurones. The burst duration of inspiratory neurones increased during GABA and glycine treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Respiration-related neurons in the ventral medulla of newborn rats in vitro.

In brainstem-spinal cord preparations isolated from newborn rats, we examined functions of the ventral medulla in respiratory rhythm generation, and located respiratory neurons in that region. Removal of the dorsal half of the medulla caused only modest reduction of the rate of inspiratory bursts from the cervical (C4 or C5) ventral root and moderate changes in the burst pattern. We describe here two types of respiratory neurons; Pre-I neurons that are presumably crucial in primary rhythm generation, and inspiratory (I) neurons that we presume to be important in inspiratory pattern generation. Pre-I neurons were located close to phenylethanolamine N-methyltransferase (PNMT)-immunoreactive (IR) neurons that are common in the reticular formation of the rostral ventrolateral medulla (RVL). Distributions of I neurons and Pre-I neurons overlapped in the RVL, and I neurons were also near the nucleus ambiguus in the more caudal part of the ventrolateral medulla. The results indicate that the ventral medulla is essential to inspiratory pattern generation as well as rhythm generation. It is suggested that the RVL is an important site in rhythm generation. The region of inspiratory pattern generation may extend more caudally in the ventral medulla.

Action Potentials↗

PubMed1989

Firing properties of respiratory rhythm generating neurons in the absence of synaptic transmission in rat medulla in vitro.

It has previously been demonstrated that Pre-I neurons, localized in the rostral ventrolateral medulla, are important in the generation of the primary respiratory rhythm in brainstem-spinal cord preparations from newborn rats. To investigate whether or not Pre-I neurons have endogenous pacemaker properties, we examined Pre-I neuron activity before and after chemical synaptic transmission was blocked by incubation in a low Ca2+ (0.2 mM), high Mg2+ (5 mM) solution (referred to here as low Ca). After incubation for about 30 min in low Ca, 28 (52%, type-1) out of 54 neurons tested in 27 preparations retained apparent rhythmic (phasic) activity after complete disappearance of C4 inspiratory activity. Sixteen neurons (30%, type-2) fired tonically and 10 (18%, type-3) were silent. We examined the effects of synaptic blockade on 14 inspiratory neurons in the RVL. The firing of all 14 neurons in 9 preparations disappeared concomitantly with the disappearance of C4 activity in low Ca. When the pH of the low Ca solution was lowered with a decrease in NaHCO3 concentration from 7.4 to 7.1, the firing rate of the Pre-I neurons (type-1) increased from 12 to 18/min. In conclusion, the generator of respiratory rhythm in the newborn rat is probably a neuronal network with chemical synapses that functions mainly through the endogenous Pre-I pacemaker cells. Intrinsic chemoreception in the rhythm generator is probably important in frequency control of respiratory rhythm.

Action Potentials↗

PubMed1988

Primary respiratory rhythm generator in the medulla of brainstem-spinal cord preparation from newborn rat.

It has been previously demonstrated that rhythmically firing neurons (Pre-I neurons) preceding cervical root (C4 or C5) inspiratory activity, localized in the rostral ventrolateral medulla (RVL), are important in the generation of the basic respiratory rhythm in brainstem-spinal cord preparations from newborn rats. We examined the effects of single and continuous electrical stimulation applied to the RVL on Pre-I and C4 activities in these preparations. We verified that the phase of respiratory rhythm was reset when Pre-I firing was induced in both right and left RVL by single shock stimulation, whether C4 activity appeared or not. Lower frequency and intensity of continuous pulse train stimulation in the RVL enhanced Pre-I activity, and hence C4 activity, whereas higher frequency and intensity inhibited both. The results suggest that synchronous burst activity between the right and left Pre-I neurons must be above a certain level (in its intraburst firing rate) to trigger C4 inspiratory activity and, therefore, that cooperation among Pre-I neurons is important for induction of rhythmic inspiratory drive. After bilateral lesions of the caudal ventrolateral medulla, Pre-I neurons retained their rhythmic activity, while C4 activity disappeared. Present results further confirmed our hypothesis that Pre-I neurons are the primary generator of respiratory rhythm. We propose a hypothetical model of the generation of rhythmic respiratory activity.

Animals↗

PubMed1988

Thermode for deep focal cooling.

A cooling thermode is described that can be used to reversibly lesion deep structures with minimal penetration damage. Construction, associated equipment, and use of this thermode are simpler and less expensive, and it can be made smaller in size, than previously described thermodes. The user has a choice of a simple, inexpensive control arrangement that is somewhat more complicated to use, or a more expensive control system that is simpler to use. The diameter of this thermode can be at least as small as 0.3 mm, which is smaller than any previously described thermode. The cooling agent, Co2, is used in such small quantities that toxicity is no problem.

Animals↗

PubMed1987

Localization of respiratory rhythm-generating neurons in the medulla of brainstem-spinal cord preparations from newborn rats.

We describe the location of Pre-I neurons, which are important to respiratory rhythm generation, in the rostral medulla of brainstem-spinal cord preparations isolated from newborn rats. This neuronal group was delimited in the reticular formation slightly medial to the caudal area of the facial nucleus and near the ventral surface. The effects of electrical stimulation and lesions in that region were also examined with respect to respiratory rhythm generation. Single shock stimulation induced Pre-I neuron firing and reset the phase of the respiratory rhythm. Electrolytic lesions in the Pre-I neuron region reduced the respiratory rate.

Animals↗

PubMed1987

Cross-correlation between vagal afferent impulses from pulmonary mechanoreceptors and high-frequency inflation (HFI) and deflation (HFD) in rabbits.

The effects of high-frequency airway inflation (HFI) and high-frequency airway deflation (HFD) generated by a triangular pressure pulse generator on pulmonary mechanoreceptors were examined. The cross-correlograms between vagal afferent impulses from the slowly adapting (SAR) and the rapidly adapting receptors (RAR) and the HFI or the HFD pulses were analysed. HFI stimulated SAR and RAR and HFD stimulated RAR, but inhibited SAR. The time lag of the mode in the correlogram between SAR and HFI was shorter than that of the mode in the correlogram between RAR and HFI. The span of the mode and the trough of SAR was shorter than the span of the mode of RAR. This may indicate that the time to peak of the generator potential of RAR is longer than that of SAR.

Adaptation, Physiological↗

PubMed1987

Respiratory rhythm generator neurons in medulla of brainstem-spinal cord preparation from newborn rat.

Rhythmic neuronal activity preceding C4 inspiratory activity (Pre-I neuron activity) was recorded in rostral ventrolateral (near ventral surface) medulla of brainstem-spinal cord preparation isolated from newborn rat. Vagal stimulation inhibited C4 activity but not Pre-I neuron activity. Rhythmic Pre-I neuron-like activity was still recorded in the block of rostral medulla after transection. Results suggest that Pre-I neurons generate the basic respiratory rhythm and trigger inspiratory activity.

Animals↗

PubMed1985

The effects of high-frequency inflation and high-frequency deflation on respiration in rabbits.

High-frequency inflating and deflating triangular pulses of pressure were applied to air in the trachea of urethane-chloralose-anesthetized rabbits. Expiratory time was increased by high-frequency inflation (HFI) and decreased by high-frequency deflation (HFD). Both had little effect on inspiratory time or tidal phrenic nerve activity. HFD provoked more tonic type phrenic activity, with discharges being evident during the expiratory phase. It was demonstrated that HFI, which probably stimulates pulmonary stretch receptors, inhibits the initiation of inspiration and HFD, which probably stimulates irritant receptors, facilitates inspiration.

Animals↗

PubMed1984

Effects of histamine inhalation and airway vibration on phrenic nerve activity in rabbits.

Experiments were performed on 8 rabbits under urethane-chloralose anesthesia. Histamine aerosol (5%) administered into the trachea by a cannula produced tonic activity of the phrenic nerve, with discharges also being evident during the expiratory phase. Airway vibration (100 Hz) inhibited this tonic activity and caused silence during the expiratory phase.

Adaptation, Physiological↗