Biomedical subjects

J L Feldman

Publications and source records attributed to J L Feldman.

At least 73 records · Page 4Linked to original sources

PubMed1991

Skeletal muscle satellite cell diversity: satellite cells form fibers of different types in cell culture.

Following skeletal muscle injury, new fibers form from resident satellite cells which reestablish the fiber composition of the original muscle. We have used a cell culture system to analyze satellite cells isolated from adult chicken and quail pectoralis major (PM; a fast muscle) and anterior latissimus dorsi (ALD; a slow muscle) to determine if satellite cells isolated from fast or slow muscles produce one or several types of fibers when they form new fibers in vitro in the absence of innervation or a specific extracellular milieu. The types of fibers formed in satellite cell cultures were determined using immunoblotting and immunocytochemistry with monoclonal antibodies specific for avian fast and slow myosin heavy chain (MHC) isoforms. We found that satellite cells were of different types and that fast and slow muscles differed in the percentage of each type they contained. Primary satellite cells isolated from the PM formed only fast fibers, while up to 25% of those isolated from ALD formed fibers that were both fast and slow (fast/slow fibers), the remainder being fast only. Fast/slow fibers formed from chicken satellite cells expressed slow MHC1, while slow MHC2 predominated in fast/slow fibers formed from quail satellite cells. Prolonged primary culture did not alter the relative proportions of fast to fast/slow fibers in high density cultures of either chicken or quail satellite cells. No change in commitment was observed in fibers formed from chicken satellite cell progeny repeatedly subcultured at high density, while fibers formed from subcultured quail satellite cell progeny demonstrated increasing commitment to fast/slow fiber type formation. Quail satellite cells cloned from high density cultures formed colonies that demonstrated a similar change in commitment from fast to fast/slow, as did serially subcloned individual satellite cell progeny, indicating that the observed change from fast to fast/slow differentiation resulted from intrinsic changes within a satellite cell. Thus satellite cells freshly isolated from adult chicken and quail are committed to form fibers of at least two types, satellite cells of these two types are found in different proportions in fast and slow muscles, and repeated cell proliferation of quail satellite cell progeny may alter satellite cell progeny to increasingly form fibers of a single type.

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PubMed1991

Decussation of bulbospinal respiratory axons at the level of the phrenic nuclei in adult rats: a possible substrate for the crossed phrenic phenomenon.

The axonal trajectories of inspiratory bulbospinal neurons were examined after deposition of the anterograde neuronal tracer phaseolus vulgaris leucoagglutinin (PHA-L) into the rostral ventral respiratory group in rats. At the level of the phrenic nucleus, PHA-L-labeled bulbospinal axons crossed the midline of the spinal cord in both the anterior gray and the anterior white commissure. These spinally decussating neurons provide a possible anatomical substrate for the respiratory reflex known as the crossed phrenic phenomenon.

Animals↗

PubMed1991

Respiratory pattern generation in mammals: in vitro en bloc analyses.

The development of in vitro en bloc preparations of mammalian neuraxis that retain functional circuits for respiratory pattern generation has led to novel observations that have expanded our understanding of this important motor/homeostatic system. This experimental approach is a powerful and unique way to study complex integrative neural function concurrently at cellular, synaptic, and network levels.

Animals↗

PubMed1991

Role of excitatory amino acids in the generation and transmission of respiratory drive in neonatal rat.

1. The involvement of excitatory amino acids in the generation and transmission of rhythmic respiratory drive was studied in an in vitro neonatal rat brain stem-spinal cord preparation. The subclasses of excitatory amino acid receptors studied included: (i) N-methyl-D-aspartate (NMDA) receptors, (ii) (R, S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) and kainate (non-NMDA) receptors and (iii) 2-amino-4-phosphonobutyric acid (AP-4)-sensitive receptors. Respiratory motoneurone population discharge was recorded from glossopharyngeal (IX), vagus (X), and hypoglossal (XII) cranial nerves, as well as cervical (C1-C5) and thoracic (T2-T5) spinal ventral roots. This activity is generated in the motoneurone pools that transmit respiratory drive to upper airway, accessory, diaphragm and intercostal muscles. Perturbations of motor nerve discharge were analysed after excitatory amino acid receptor antagonists or agonists were added to bathing solutions surrounding either the spinal cord or brain stem. The excitatory amino acid receptor antagonists included: (i) NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imin-H-maleate (MK-801) and (ii) non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The agonists included: (i) NMDA, (ii) non-NMDA receptor agonists AMPA and kainic acid. The effects of perturbations of AP-4-sensitive receptors with AP-4, and of inhibiting excitatory amino acid uptake with dihydrokainic acid (DHK) were also studied. 2. Block of non-NMDA receptors in the medulla by CNQX resulted in an antagonist concentration-dependent decrease in the respiratory motoneuronal burst frequency. Non-NMDA receptor activation with kainic acid or AMPA caused a concentration-dependent increase in burst frequency, with competitive interactions with CNQX. 3. Inhibition of excitatory amino acid uptake in the medulla with DHK resulted in a reversible, dose-dependent increase in respiratory frequency. A similar increase in respiratory frequency was induced by DHK when medullary NMDA receptors were blocked with MK-801, confirming that endogenously released excitatory amino acids act at non-NMDA receptors to modulate rhythm. 4. Non-NMDA receptor block reduced and ultimately abolished the amplitude of integrated cranial and spinal respiratory motoneuronal discharge when added to the solution bathing the medulla and spinal cord, respectively. 5. NMDA receptor block in the medulla with MK-801 did not perturb the spontaneous respiratory burst frequency, although bath application of NMDA produced a dose-dependent increase in frequency, with non-competitive interactions with MK-801. MK-801 also did not perturb the amplitude of cranial or bulbospinal premotoneurone discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗

PubMed1990

Ventral respiratory group projections to phrenic motoneurons: electron microscopic evidence for monosynaptic connections.

The hypothesis that excitatory drive is transmitted monosynaptically from bulbospinal medullary respiratory neurons to spinal respiratory motoneurons was tested by an ultrastructural analysis of the phrenic motoneuronal pool in the rat. Combined anterograde labeling of the principal inspiratory bulbospinal neuron population (ventral respiratory group) and retrograde labeling of the phrenic motoneuron pool demonstrated the presence of labeled synaptic profiles, indicating that at least some bulbospinal inspiratory neurons make monosynaptic contacts with phrenic motoneurons. The synaptic boutons of ventral respiratory group neurons that were labeled in the phrenic nucleus had asymmetrical membrane densities at sites of synaptic contact with labeled phrenic somal or dendritic profiles, supporting the notion that this bulbospinal pathway has excitatory contacts with phrenic motoneurons. The morphological types of labeled boutons included three of the eight previously identified bouton types in the phrenic nucleus (Goshgarian and Rafols: Journal of Neurocytology 13:85-109, 1984), including the "S"-terminal, the "NFs"-terminal, and the "F"-terminal. There was no conclusive evidence of labeled double synapses, indicating that this type of synaptic contact is not common in the intact bulbospinal pathway.

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PubMed1990

Brainstem connections of the rostral ventral respiratory group of the rat.

The pontomedullary connections of the rostral division of the ventral respiratory group (rVRG), the largest medullary population of inspiratory bulbospinal and propriobulbar neurons, were identified in the rat by retrograde and anterograde tracing techniques. These experiments revealed that: (i) the Kölliker-Fuse nucleus, portions of the medial and lateral parabrachial nuclei, and all levels of the ipsilateral and contralateral VRG complex have dense reciprocal connections with the rVRG; (ii) the lateral paragigantocellular nucleus has reciprocal but less dense connections with rVRG; (iii) portions of the nucleus of the solitary tract have prominent projections to, but weaker inputs from rVRG; (iv) the raphe, magnocellular tegmental field and spinal trigeminal nuclei have minor projections to rVRG and receive only sparse inputs from rVRG, and; (v) the retrotrapezoid nucleus, pontine lateral tegmental field and area postrema each have only efferent projections to rVRG. These findings are consistent with previous studies of pontomedullary connections of rVRG in the cat, and further document the extensive reciprocal connections between principal respiratory groups. These connections are likely to be important for generation of the respiratory pattern, for the coordination of effector responses of the cranial and spinal respiratory motor neurons to afferent stimuli, and coordination of the central respiratory and cardiovascular control systems.

Animals↗

PubMed1990

Subnuclear organization of the lateral tegmental field of the rat. I: Nucleus ambiguus and ventral respiratory group.

Three classes of neurons within the lateral tegmental field of the rat medulla having different target projections were identified by retrograde labelling with three different fluorescent tracers. Labelled bulbospinal premotor and propriobulbar interneurons of the ventral respiratory group and vagal motoneurons of nucleus ambiguus formed partially intermingled longitudinal columns encompassed within a common region of the lateral tegmental field. Labelled neurons of each class were organized in a nonuniform distribution within these columns forming subdivisions distinguished by neuron morphology, orientation, and target projection. The three major rostrocaudal divisions of the ventral respiratory group (VRG) previously identified in the cat and rabbit were identified here in the rat, suggesting a common pattern of VRG organization among these species.

Action Potentials↗

PubMed1990

Subnuclear organization of the lateral tegmental field of the rat. II: Catecholamine neurons and ventral respiratory group.

Bulbospinal and propriobulbar respiratory neurons of the ventral respiratory group and catecholamine neurons of the A1 and C1 cell groups were simultaneously labelled in the rat medulla by a combination of retrograde tracing and immunohistochemical identification. The ventral respiratory group and catecholamine cell groups form adjacent, parallel cell columns in the lateral tegmental field of the ventrolateral medulla. The ventral respiratory group is located immediately dorsal to the A1 and C1 groups, although some A1 neurons are intermingled with neurons of the rostral ventral respiratory group, and some C1 neurons are intermingled with those of the Bötzinger complex. The proximate populations of respiratory, catecholamine, and (presumptive) cardiovascular neurons identified in this study provide further support to the hypothesis that this region of the lateral tegmental field of the ventrolateral medulla is a site of cardiorespiratory coordination.

Animals↗

PubMed1990

Respiratory activity in retrotrapezoid nucleus in cat.

An anatomic projection from the retrotrapezoid nucleus to the ventral respiratory group in cat was previously reported by our laboratory (J. C. Smith, D. E. Morrison, H. H. Ellenberger, M. R. Otto, and J. L. Feldman. J. Comp. Neurol. 281: 69-96, 1989). We now report on the properties of neurons in the retrotrapezoid nucleus, investigated with extracellular recording techniques in 10 chloralose-urethane anesthetized, paralyzed, mechanically ventilated cats. A ventral exposure of the medulla facilitated recording from neurons in the retrotrapezoid nucleus, located ventral to the facial nucleus near the medullary surface. Respiratory-modulated, as well as irregularly discharging, spontaneous unit activity was recorded within the retrotrapezoid nucleus. Twelve respiratory-modulated units in the retrotrapezoid nucleus exhibited inspiratory (8 units), expiratory (3 units), or multimodal (1 unit) discharge patterns. Chemical activation of an inspiratory unit in the retrotrapezoid nucleus by pressure ejection of DL-homocysteic acid (less than 0.5 nl of 10 mM solution) demonstrated that the respiratory-modulated activity originated from the cell soma and not fibers of passage coursing through the retrotrapezoid nucleus region. Electrical microstimulation (20-40 microA, approximately 70-microseconds duration, biphasic pulse) within the ipsilateral ventral respiratory group elicited antidromic activation of 7 units in the retrotrapezoid nucleus, three of which were not spontaneously active. Electrical stimulation (5-80 microA, 70-microseconds pulse width, 100 Hz, 400- to 500-ms trains) at sites within retrotrapezoid nucleus affected the respiratory motor output when delivered during late expiration, eliciting premature onset of inspiration. These results suggest that retrotrapezoid nucleus projections to the ventral respiratory group (and dorsal respiratory group) may influence respiratory timing and pattern, perhaps by conveying signals originating in the rostral ventrolateral medulla that result from ventral surface perturbations.

Animals↗

PubMed1990

Neurogenesis of respiratory rhythm and pattern: emerging concepts.

We present three hypotheses related to the nervous system control of breathing in mammals: 1) that neural mechanisms controlling breathing change with state and that the relationship between mechanisms in different states can be described in terms of either modulation or a basic transformation of properties, or both; 2) that the mechanisms generating respiratory rhythm and pattern are separate; and 3) that conditional pacemaker cell activity is the basis for respiratory rhythm in highly reduced states.

Animals↗

PubMed1990

Excitatory amino acid-mediated transmission of inspiratory drive to phrenic motoneurons.

1. The role of excitatory amino acids (EAAs) in the bulbospinal transmission of inspiratory drive was studied by intracellular and single-electrode voltage-clamp recordings from phrenic motoneurons in the in vitro neonatal rat brain stem spinal cord. 2. In all brain stem-spinal cord preparations there were spontaneously generated rhythmic membrane depolarizations and associated spiking of phrenic motoneurons during the inspiratory phase of the respiratory cycle. The envelope of the motoneuron drive potential had a rapid onset to peak (50 ms) followed by a plateau/declining phase that lasted 400-700 ms. The peak potential was approximately 10-20 mV above base-line potential. The drive current under voltage clamp had a similar shape and duration to the drive potential with a peak current greater than 1.5 nA. 3. The involvement of EAAs in the bulbospinal transmission of inspiratory drive was demonstrated by checking the effects of various EAA receptor antagonists on the phrenic motoneuron inspiratory drive. When kynurenic acid (KYN), an antagonist acting on all three subtypes of EAA receptors, was applied to the solution bathing the spinal cord, the motoneuron action potentials were abolished, and the amplitude of inspiratory drive potential was significantly reduced. To further classify the role of the different EAA receptor subtypes in the synaptic transmission of inspiratory drive, the effects on the drive potential of either 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a specific non-N-methyl-D-aspartic acid (non-NMDA) receptor antagonist, or DL-2-amino-5-phosphonovaleric acid (AP5), DL-2-amino-7-phosphonoheptanoic acid (AP7), and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imin emaleate (MK-801), NMDA receptor antagonists, were investigated. Bath or local application of CNQX induced a dose-dependent decrease of the inspiratory drive potential without changing intrinsic motoneuron membrane properties. On the other hand, application of AP7 or MK 801 had a small effect on the inspiratory drive potential or the inspiratory drive current when the motoneuron membrane potential was clamped near end-expiratory potentials (-60 to -75 mV). 4. To establish the presence of EAA receptors on the phrenic motoneuronal membrane and to provide information on the available receptor subtypes for action of the endogenously released transmitter, we tested the effects of agonists for the major EAA receptor subtypes after blocking synaptic transmission (produced by axonal action potentials) by bath application of tetrodotoxin (TTX).(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗

PubMed1990

Neural mechanisms generating respiratory pattern in mammalian brain stem-spinal cord in vitro. I. Spatiotemporal patterns of motor and medullary neuron activity.

1. An analysis of the spatial and temporal patterns of activity of neurons of the respiratory motor-pattern generation system in an in vitro neonatal rat brain stem-spinal cord preparation is presented. Impulse discharge patterns of spinal and cranial moto-neurons as well as respiratory neurons in the medulla were analyzed. Patterns of motoneuronal discharge were characterized at the population level from recordings of motor-nerve discharge and at the single-cell level from intracellular recordings. These patterns were compared to patterns generated in the neonatal rat and adult mammal in vivo to establish the correspondence between in vitro and in vivo states. 2. The in vitro system generated a complex spatiotemporal pattern of spinal and cranial motoneuron activity during inspiratory (I) and expiratory (E) phases of the respiratory cycle. The respiratory cycle consisted of three distinct phases of neuronal activity (I, early E, and late E phase) similar to the temporal organization of the cycle in the intact mammal. The spike discharge pattern of motoneurons during the I phase consisted of a rapidly peaking-slowly decrementing discharge envelope with a high degree of synchronization on a time scale of 25-50 ms (approximately 20-40 Hz). A similar pattern was generated in the neonate in vivo under conditions comparable with the in vitro state (i.e., nervous system isolated from mechanosensory afferent inputs). However, the I-phase-motoneuron discharge pattern and cycle-phase durations differed from those characteristic of the intact neonatal or adult systems in vivo. This difference could be accounted for primarily by removal of vagal mechanosensory afferent inputs. 3. The synaptic drive potentials of spinal motoneurons during the I phase in vitro consisted of a rapidly peaking-slowly decrementing potential envelope similar in shape to the spike-frequency histogram of single motoneurons and the envelope of the motoneuron-population discharge. The drive potentials had prominent high-frequency amplitude fluctuations superimposed on the slower drive-potential envelope that were temporally correlated with the generation of motoneuron action potentials. The dominant frequency components of these fast-membrane-potential oscillations (20-35 Hz) were similar to the frequency components of the amplitude fluctuations in the motoneuron-population discharge. One class of medullary neurons with I-phase discharge also exhibited a rapidly peaking-slowly decrementing pattern of impulse discharge and synaptic drive potential with similar high-frequency components.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Are there serotonergic projections from raphe and retrotrapezoid nuclei to the ventral respiratory group in the rat?

The relationship of serotonergic neurons in raphe and ventrolateral medullary regions to neurons projecting to the rostral ventral respiratory group in the rat were investigated using combined immunohistochemical and retrograde labeling techniques. Serotonergic and non-serotonergic neurons retrogradely labeled with rhodamine beads were found intermingled in the larger population of serotonin-immunoreactive neurons in raphe pallidus, obscurus and magnus. In addition, a cell group analogous to the retrotrapezoid nucleus in the cat was identified in the rat ventrolateral medulla. Retrotrapezoid neurons, which exhibited exclusively ipsilateral projections to the ventral respiratory group, were located lateral to clusters of serotonergic cells near the ventral surface, but were not serotonin immunoreactive.

Animals↗

PubMed1989

Brainstem projections to the major respiratory neuron populations in the medulla of the cat.

Efferent and afferent connections of the dorsal and ventral respiratory groups in the medulla of the cat were mapped by axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase. Injections of wheat germ agglutinin-horseradish peroxidase into the dorsal respiratory group and the three principal subdivisions of the ventral respiratory group (caudal, rostral, and Bötzinger Complex) revealed extensive interconnections between these regions and with a limited number of other brainstem neuron populations. Major neuron populations with efferent projections to the regions of the dorsal and ventral respiratory groups include the parabrachial nuclear complex (medial parabrachial, lateral parabrachial, and Kölliker-Fuse nuclei), subregions of the lateral paragigantocellular reticular nucleus, subregions of the lateral and magnocellular tegmental fields, inferior central and postpyramidal nuclei of the raphe, and sensory trigeminal nuclei. A previously unidentified neuron population with extensive efferent projections to the dorsal and ventral respiratory groups was found near the ventral surface of the rostral medulla; we refer to this group as the retrotrapezoid nucleus. The results suggest that the dorsal and ventral respiratory groups form an extensively interconnected neuronal system receiving convergent inputs from the same brainstem nuclear groups, consistent with the hypothesis that the dorsal and ventral groups are primarily sites for integration of sensory and premotor respiratory drive inputs. Neuron populations in the rostral ventrolateral medulla with projections to both the dorsal and ventral respiratory groups, particularly the retrotrapezoid nucleus and neighboring subregions of the lateral paragigantocellular reticular nucleus, are candidate sites for participation in respiratory rhythmogenesis or other critical functions of the brainstem respiratory control system such as intracranial chemoreception.

Action Potentials↗

PubMed1989

Monoaminergic and GABAergic terminations in phrenic nucleus of rat identified by immunohistochemical labeling.

The termination patterns of axons in the phrenic nucleus immunoreactive to synthetic enzymes for catecholamines and for serotonin and GABA were studied in rats. Spinal cord tissue in which phrenic motoneurons were retrogradely labeled with horseradish peroxidase was incubated with antisera against dopamine beta-hydroxylase, phenylethanolamine-N-methyltransferase, 5-hydroxytryptamine, and GABA to identify presumptive terminations of monoaminergic and GABAergic neurons onto identified phrenic motoneurons. In the C3 to C5 spinal cord, 5-hydroxytryptamine-, dopamine beta-hydroxylase- and GABA-like positive terminals with varicosities formed a dense network, with presumptive synaptic contacts on dendrites and somas of phrenic motoneurons. A similar pattern of terminations was also observed in adjacent (non-respiratory muscle) motoneuron pools. There were fewer phenylethanolamine-N-methyltransferase-positive terminal arborizations in the cervical spinal cord compared to thoracic spinal cord; phenylethanolamine-N-methyltransferase terminals were not seen in the vicinity of phrenic motoneurons. These results suggest that phrenic motoneuronal activity is influenced by multiple supraspinal inputs utilizing different neurotransmitters. These transmitters also mediate inputs to other (nearby) spinal motoneurons and thus are not unique for signal transmission to phrenic motoneurons.

Animals↗

PubMed1989

Cellular mechanisms underlying modulation of breathing pattern in mammals.

Understanding the generation and modulation of respiratory pattern requires knowledge of the cellular and network properties of the central nervous system controller. Although considerable efforts have focused on network properties, recent efforts in several laboratories have emphasized the importance of cellular mechanisms. Using a novel experimental in vitro system, we have been able to investigate several classes of cellular mechanisms difficult or impossible to study in vivo or in tissue slices. The conclusions and hypotheses that we have made include the following: 1. Respiratory rhythm and spatiotemporal patterns of (pre)motoneuronal activity are separately generated. 2. Cl- -dependent inhibition is critical in burst pattern formation. 3. Cl- -dependent and at least one type of K+-dependent (GABAB) inhibition is not necessary for rhythm generation. 4. Inhibitory neurotransmitters, including those acting through second messenger systems, can modulate respiratory rhythm and pattern. 5. Pacemakers underlie rhythm generation. 6. Excitatory inspiratory drive to respiratory motoneurons is mediated by an excitatory amino acid, which acts on both post- and presynaptic receptors. The effort to verify these conclusions and test these hypotheses should greatly enhance our understanding of the nervous control of respiration.

Animals↗

PubMed1989

Involvement of excitatory amino acids in neurotransmission of inspiratory drive to spinal respiratory motoneurons.

The role of excitatory amino acids in the transmission of bulbospinal respiratory drive to spinal motoneurons was investigated in the in vitro and in vivo spinal cord of the rat. In vitro studies were performed with a preparation of neonatal rat brain stem and spinal cord that spontaneously generates rhythmic respiratory drive to spinal respiratory motoneurons. This in vitro system allowed examination of the effects of pharmacological agents on spinal motoneuron activity, without perturbing the activity of bulbospinal neurons transmitting the respiratory drive. The amplitude of spontaneous motor discharge in spinal ventral roots containing phrenic and intercostal motor axons was reduced in a dose-dependent manner by antagonists to excitatory amino acids acting at NMDA receptors [D,L-2-amino-5-phosphonovaleric acid (D,L-AP5)] and non-NMDA receptors [kynurenic acid, gamma-D-glutamylglycine, gamma-D-glutamyltaurine, and L- and D,L-2-amino-4-phosphonobutyric acid (L-AP4,D,L-AP4)]. The order of potency of the antagonists for complete block of the motor output was L-AP4 greater than D,L-AP4 greater than kynurenic acid greater than gamma-D-glutamylglycine greater than D,L-AP5 greater than or equal to gamma-D-glutamyltaurine. Amino acid uptake inhibitors augmented the spontaneous motoneuron activity, further confirming the involvement of endogenous excitatory amino acids in transmission of respiratory drive. The results obtained in vitro with AP4, kynurenic acid, and amino acid uptake inhibitors were confirmed in vivo by bathing segments of the rat spinal cord in situ with solutions containing antagonists and uptake inhibitors. The present results suggest that an important component of the neurotransmission of bulbospinal respiratory drive involves endogenous excitatory amino acids acting at AP4-sensitive sites and other non-NMDA (quisqualate/kainate) receptors. The bulbospinal-spinal respiratory motoneuron synapse may provide a convenient model synapse in the spinal cord for detailed analysis of mechanisms underlying excitatory amino acid-mediated synaptic transmission of motor drive.

Amino Acids↗

PubMed1988

Intracellular recording from phrenic motoneurons receiving respiratory drive in vitro.

Stable, long-term (2-4 h) intracellular recordings were obtained from phrenic motoneurons receiving respiratory drive in an in vitro neonatal rat brainstem-spinal cord preparation. Several passive and active phrenic motoneuron properties in vitro, including resting membrane potential, inspiratory drive potentials, and threshold depolarization levels, are similar to those in the adult mammal in vivo. Manipulations of the extracellular fluid environment by the addition or washout of chemicals affecting motoneuronal activity and spinal synaptic transmission of respiratory drive did not affect the quality of the intracellular recordings. These results establish the feasibility of long-term intracellular recording from the in vitro brainstem-spinal cord preparation for studies of cellular and synaptic mechanisms underlying control of respiratory movements.

Action Potentials↗