Biomedical subjects

J Lipski

Publications and source records attributed to J Lipski.

At least 55 records · Page 3Linked to original sources

PubMed1992

Synaptic inputs to medullary respiratory neurons from superior laryngeal afferents in the cat.

Synaptic inputs from afferents in the superior laryngeal nerve (SLN) to medullary respiratory neurons (n = 154) in the dorsal respiratory group (DRG), ventral respiratory group (VRG) and the region of the Bötzinger complex (BOT) were studied in anesthetized cats. Single pulse stimulation of the SLN-evoked monosynaptic EPSPs in most inspiratory bulbospinal (I-BS) neurons in the DRG, and disynaptic or oligosynaptic chloride-dependent IPSPs in other I-BS neurons in the DRG and VRG. Stimulation of laryngeal afferents also inhibited oligosynaptically expiratory bulbospinal neurons in the VRG, and all types of respiratory neurons recorded in the BOT region. Oligosynaptic potentials (usually EPSPs) were recorded in inspiratory and expiratory laryngeal motoneurons. These results provide evidence of a processing of SLN-evoked synaptic responses by all tested groups of medullary respiratory neurons. The pathways mediating these synaptic responses are discussed.

Afferent Pathways↗

PubMed1992

Substance P immunoreactive boutons form synapses with feline sympathetic preganglionic neurons.

In this study, the relationship between substance P-immunoreactive boutons and antidromically activated sympathetic preganglionic neurons was examined by light and electron microscopy. Sympathetic preganglionic neurons in the T2-T4 spinal segments of the cat were identified by intracellular recording and antidromic activation from the corresponding white ramus. Neurons were filled with lucifer yellow and then stained to reveal, simultaneously, substance P and lucifer yellow immunoreactivity. All of the neurons examined with the light microscope (n = 13) received appositions from substance P-immunoreactive boutons. Appositions were found on all parts of the neuron, including the somata, dendrites, and axon initial segment. In most cases (11/13) few close appositions were seen; however, two neurons received large numbers of appositions from substance P-immunoreactive boutons. On one neuron, 16 substance P-immunoreactive varicosities that were identified as being closely apposed at the light microscope level were serially sectioned and examined with the electron microscope. Of these 16 varicosities, eight either directly contacted the neuron or formed morphologically identifiable synapses. The remaining eight varicosities were separated from the neuron by thin glial processes. Two other sympathetic preganglionic neurons that were examined ultrastructurally also received substance P-immunoreactive synapses and close contacts. These findings suggest that substance P-containing nerve fibres could affect all sympathetic preganglionic neurons but are likely to be important in regulating the activity of only a small proportion of these neurons.

Animals↗

PubMed1992

The role of inhibitory amino acids in control of respiratory motor output in an arterially perfused rat.

The respiratory effects of drugs affecting GABAergic and glycinergic transmission were examined in order to assess the role of synaptic inhibition in breathing rhythmogenesis. Experiments were performed in the arterially perfused in situ brainstem-spinal cord preparation from adult rats (Hayashi et al., 1991, J. Neurosci. Meth. 36:63-70). Administration to the perfusate of agonists of GABAA, GABAB, and glycine receptors reduced both the frequency and amplitude of the activity recorded from the phrenic and hypoglossal nerves. Similar effects were observed following the infusion of aminooxyacetic acid (a blocker of GABA-transaminase). Picrotoxin (0.1-2 microM), bicuculline (0.05-0.2 microM), strychnine (0.1-1 microM) and phaclofen (0.1-0.2 mM) usually increased the frequency and amplitude of inspiratory bursts. Perfusion with low Cl- (8 mM) solution elicited tonic discharge followed by reversible arrest of the respiratory activity. It is concluded that synaptic inhibition is involved in the respiratory rhythm generation process in the mature mammalian brain. As data from the literature indicate that interference with central inhibitory processes does not largely affect the rhythm generation process in newborn rats, a possibility is discussed that the brainstem respiratory generator undergoes a developmental change from a 'pacemaker' driven circuit at the neonatal stage to a network requiring post-synaptic inhibition in the mature brain.

Amino Acids↗

PubMed1992

Morphology and electrophysiology of superior laryngeal nerve afferents and postsynaptic neurons in the medulla oblongata of the cat.

Intra-axonal recordings were made from 24 afferent fibres of the superior laryngeal nerve in and around the nucleus tractus solitarius, in 26 pentobarbitone-anaesthetized cats. Conduction velocity ranged from 15 to 38 m/s. Four afferents were injected with horseradish peroxidase. They showed dense terminal arborization in the region of the ventral and ventrolateral subnuclei of the nucleus tractus solitarius, both rostral and caudal to the obex. Six other intra-axonal recordings were thought to originate from axons of neurons postsynaptic to superior laryngeal afferents; one of these was injected with horseradish peroxidase and showed a similar arborization pattern to that of the afferent axons. In the same region, intracellular recordings were made from 124 neurons which responded to superior laryngeal nerve stimulation with excitatory postsynaptic potentials (mean latency 2.7 +/- 1.0 ms). Ninety-nine of these neurons were thought to receive a monosynaptic input. The stimulation threshold evoking these responses was similar to that which inhibited phrenic nerve discharge. Eleven of the monosynaptically excited neurons were injected with horseradish peroxidase. They had fusiform or stellate somata and simple dendritic trees, radiating mainly in the transverse plane. In one experiment, in which both a superior laryngeal nerve afferent fibre and a neuron were labelled, afferent terminal varicosities were found in close apposition with the postsynaptic membrane of the injected neuron. Four of 14 (29%) tested neurons could be antidromically activated from the C3 spinal segment. The stimulus thresholds and onset latencies of the responses of superior laryngeal nerve afferents and medullary neurons to stimulation of the superior laryngeal nerve are consistent with their involvement in the reflex inhibition of respiratory neurons evoked by superior laryngeal nerve stimulation.

Afferent Pathways↗

PubMed1991

Efferent projections of pulmonary rapidly adapting receptor relay neurons in the cat.

Axonal projections of second order neurons activated by vagal afferent fibers originating from pulmonary rapidly adapting receptors (RARs) were studied electrophysiologically in Nembutal-anesthetized, paralyzed and artificially ventilated cats. Extracellular recordings from these neurons (referred to as 'RAR-cells') were made in the commissural subnucleus (COM) of the nucleus of the solitary tract (NTS). They were identified by a combination of stimuli including stimulation of the vagus nerve(s), hyperinflation and deflation of the lungs, and a brief period of ammonia vapor inhalation. A total of 80 RAR-cells were tested for axonal projections to a respiration-related area in the brain-stem, either the dorsolateral rostral pons or the dorsal respiratory group (DRG) or the ventral respiratory group (VRG) or the Bötzinger complex (BOT) and/or the spinal cord. Twenty-two of the 47 (47%) RAR-cells tested for ipsilateral pontine projection could be antidromically activated, and in 8 cases evidence for axonal arborization was obtained. Only 1 of the 11 RAR-cells tested for DRG projection, and 1 of the 10 RAR-cells tested for VRG projection, were antidromically activated. No RAR-cells were activated from the BOT (n = 8) or from the C3-C4 segments of the spinal cord (n = 11). Bilateral lesions of the COM abolished the reflex responses induced by ammonia inhalation or hyperinflation of the lungs, but not the Hering-Breuer reflex. These results indicate that a pathway from the COM to the rostral pons forms part of the reflex arc originating from RARs.

Animals↗

PubMed1991

Prolonged augmentation of respiratory discharge in hypoglossal motoneurons following superior laryngeal nerve stimulation.

Experiments were conducted to investigate long-lasting effects of brief superior laryngeal nerve (SLN) stimulation on respiratory discharge in the hypoglossal nerve. In paralyzed, decerebrate and artificially ventilated cats, SLN stimulation (Hz, 3-5, s, 3-5 times threshold for inhibition of phrenic nerve discharge) immediately increase hypoglossal activity. Following stimulation, the amplitude of respiratory activity in the hypoglossal nerve was augmented (478 +/- 205%), and slowly decayed to prestimulus levels with a time constant of 106 +/- 16 s. In contrast, phrenic nerve activity was completely inhibited during the SLN stimulation and for several seconds thereafter. After activity resumed, phrenic burst frequency remained depressed (33 +/- 6%). Stimulation of the carotid sinus nerve elicited similar effects on hypoglossal nerve activity. Intracellular recordings from hypoglossal motoneurons indicated that SLN stimulation increased central respiratory drive potentials (CRDPs) following a stimulus train, but had inconsistent effects on resting membrane potential. Intracellular depolarizing current pulses (5-15 nA; 2 s) had no prolonged effects on membrane potential or CRDPs. The possible role of serotonin in prolonged augmentation of hypoglossal activity following SLN stimulation was investigated. Intracellular injection of horseradish peroxidase (HRP) into hypoglossal motoneurons and immunohistochemistry for serotonin revealed some close appositions between serotonin immunoreactive boutons and HRP-labeled neurons, but such appositions were sparse. Pretreatment with methysergide had little effect on prolonged augmentation of hypoglossal discharge following SLN stimulation. These results indicate that: (1) SLN stimulation causes prolonged augmentation of hypoglossal activity probably via increased synaptic inputs to hypoglossal motoneurons; and (2) serotonin is not necessary in the underlying mechanism.

Animals↗

PubMed1991

Dual fluorescence combined with a two-color immunoperoxidase technique: a new way of visualizing diverse neuronal elements.

A method is described that allows an estimation of the neurotransmitter-related immunoreactivity, morphology and relationship to other immunoreactive elements, of single functionally identified neurons in the central nervous system. First, neurons are identified electrophysiologically using intracellular recording and labelled by iontophoresis of lucifer yellow (LY). After fixation and sectioning of the brain tissue, the location of the labelled neuron is determined by fluorescence microscopy. Sections are then processed using an indirect immunofluorescence procedure in order to determine the antigen content of the labelled neurons. Antisera to LY and an avidin-biotin immunoperoxidase technique is then used to localize LY in a permanent form, while the other previously localized antigen is permanently visualised by using the fluorescent-labelled second antibody as a bridge antibody in a peroxidase anti-peroxidase technique. The method is illustrated by an examination of neurons in the medulla oblongata of the rat, that have been stained intracellularly with LY, their content of tyrosine hydroxylase assessed, and their relationship to other tyrosine hydroxylase immunoreactive neurons determined.

Animals↗

PubMed1991

Intracellular recording from respiratory neurones in the perfused 'in situ' rat brain.

The study describes an arterially perfused in situ rat brain preparation, which uses an 'open circuit' flow of blood substitute with or without an oxygen carrier (2% perfluorotributylamine). The respiratory motor output was recorded from the phrenic and hypoglossal nerves, and could be maintained for up to 11 h from the start of perfusion (temperature of perfusate: 27-30 degrees C). The preparation allowed stable intracellular recordings from respiratory neurons in the brain stem and cervical spinal cord, and should be suitable for other studies which cannot be performed in standard whole animal models. The advantages of this approach compared with other in vitro or perfused in situ preparations are discussed.

Animals↗

PubMed1991

Identification of neurons receiving input from pulmonary rapidly adapting receptors in the cat.

1. Extracellular and intracellular recordings were made in the caudal subdivisions of the nucleus tractus solitarii (NTS) to locate and characterize neurons excited by afferents from pulmonary rapidly adapting receptors (RARs) in Nembutal-anaesthetized cats. 2. Neurons identified as second-order cells activated by RARs (RAR-cells) were activated by electrical stimulation of myelinated afferents in the cervical portion of the vagus nerve(s) and by at least two of the following 'physiological' stimuli: (a) collapse of the lungs to atmospheric pressure; (b) hyperinflation of the lungs by either increasing tidal volume or maintained lung inflations; and (c) brief inhalation of ammonia vapour. 3. Of the ninety-nine RAR-cells identified and studied extracellularly, eighty-four were localized within the commissural nucleus of the NTS. Seventy-four cells responded monosynaptically to electrical stimulation of both ipsi- and contralateral vagal stimulation. The remaining ten RAR-cells located in the commissural nucleus and the fifteen located in the caudal portion of the medial subnucleus of the NTS rostral to the obex, responded to the ipsilateral vagus only. 4. Under control ventilatory conditions (bilateral pneumothorax, positive end-expiratory pressure of approx. 2 cmH2O), forty-eight of the ninety-nine RAR-cells showed spontaneous ventilator-related activity, occurring primarily during ventilator-induced deflations (thirty of forty-eight). 'Reversal' of this ventilator-related modulation, from firing predominantly during lung deflations to lung inflations, and vice versa, could be induced in eleven of the RAR-cells by changing the lung volume or by the inhalation of ammonia vapour. 5. Modulation of firing in synchrony with the central respiratory rhythm was observed in the activity of fourteen of the ninety-nine RAR-cells. 6. Intracellular recordings were made from twenty-two NTS neurons caudal to the obex that received monosynaptic excitatory postsynaptic potentials (EPSPs) from both ipsi- and contralateral vagus nerves. Two were positively identified as RAR-cells. 7. It is concluded that the commissural nucleus of the NTS is the major location of RAR-cells, and that the response characteristics of these neurons largely, but not entirely, correspond to the known properties of RARs.

Afferent Pathways↗

PubMed1990

An intracellular study of respiratory neurons in the rostral ventrolateral medulla of the rat and their relationship to catecholamine-containing neurons.

Intracellular recording and labelling with Lucifer yellow of respiratory neurons in the rostral ventrolateral medulla were carried out in urethane-anaesthetised rats. A combined immunofluorescence and immunoperoxidase technique enabled an assessment of the tyrosine hydroxylase immunoreactivity, as well as an examination of the morphology of inspiratory and expiratory neurons in this part of the medulla oblongata. The results demonstrate: a) that respiratory neurons in the rostral ventrolateral medulla of the rat are intermingled with catecholamine-containing neurons of the C1 cell group, but are not themselves catecholamine-containing; b) that many non-spinally projecting respiratory neurons have axonal arborisations within the ventrolateral medulla in the same region as the C1 cell group, other respiratory neurons, and neurons reported to have a cardiovascular function; and c) that the dendrites of respiratory neurons in this region radiate throughout the ventrolateral medulla and frequently approach the ventral surface.

Animals↗

PubMed1990

Respiratory interneurons in the C5 segment of the spinal cord of the cat.

Extracellular recordings were made in the C5 segment of the spinal cord of anaesthetised cats from 129 units which showed respiratory phased discharge. The majority of recordings (88%) were thought to arise from the somata of respiratory spinal interneurons. Inspiratory units and expiratory units comprised 42% and 52% of all recorded units. A small number of postinspiratory units were also found (n = 5). Most units did not respond to electrical stimulation of the ipsilateral superior laryngeal (SLN) and phrenic nerves (PN), but a few expiratory (n = 2) and postinspiratory units (n = 1) were excited by SLN stimulation, while 6 inspiratory units had their discharge suppressed by the same stimulus. PN stimulation evoked a long latency (2-7 ms) burst of firing in 2 inspiratory and 1 expiratory interneurons. It is concluded that these respiratory interneurons may provide a segmental input to phrenic motoneurons, in addition to synaptic drives mediated by bulbospinal pathways.

Animals↗

PubMed1990

GABA-immunoreactive boutons make synapses with inspiratory neurons of the dorsal respiratory group.

Intracellular labelling with horseradish peroxidase (HRP) combined with gamma-aminobutyric (GABA) immunocytochemistry was used to assess the GABAergic input to inspiratory bulbospinal neurons of the dorsal respiratory group in the cat. The relationship between GABA-immunoreactive (GABA-IR) boutons and intracellularly labelled neurons was examined at the light microscopic and ultrastructural levels. At the light microscopic level, GABA-IR boutons were frequently found in close apposition to dendrites and cell bodies of labelled neurons. The presence of synapses was confirmed with electron microscopy. In addition, synaptic specializations were observed between immunoreactive boutons and unlabelled terminals which in turn formed synaptic contacts with HRP-labelled dendrites, a finding consistent with presynaptic inhibition. These results demonstrate a direct GABAergic input to a functionally defined population of medullary respiratory neurons, and suggest involvement of this neurotransmitter in the control of these neurons.

Animals↗

PubMed1990

Serotonin immunoreactive boutons form close appositions with respiratory neurons of the dorsal respiratory group in the cat.

The aim of this study was to examine the location of serotonin immunoreactive boutons on both the soma and dendrites of neurons in the dorsal respiratory group by using a combination of intracellular recording and labelling and immunohistochemistry. Inspiratory neurons in the ventrolateral nucleus of the solitary tract (vl-NTS) were intracellularly labelled with horseradish peroxidase (HRP) in anaesthetised adult cats. The morphology of 23 neurons, all antidromically activated from the contralateral C3 spinal segment, was examined. Six neurons displayed pronounced dendritic arborizations outside the vl-NTS, with prominent dorsal and/or medial projections. The dendrites of the remaining neurons were almost entirely confined to the vl-NTS. Intramedullary axon collaterals were detected in four of nineteen examined axons. Serotoninergic fibres were immunohistochemically demonstrated in the NTS, and the apposition of immunoreactive boutons to the HRP-filled neurons examined at the light microscopic level. Boutons were identified in close apposition with the somata, proximal and distal dendrites of these neurons. However, the density of contacts was found to be substantially less than in a previous study of phrenic motoneurons (Lipski et al: Soc. Neurosci. Abst. 14:379, '88; Pilowsky et al: J. Neurosci. in press, '90). The relative paucity of contacts of serotonin immunoreactive boutons with premotor inspiratory neurons of the dorsal respiratory group indicates that the serotoninergic system affects respiratory pathways mainly at the level of respiratory motoneurons or at brainstem sites outside the vl-NTS.

Action Potentials↗

PubMed1990

Extensive monosynaptic inhibition of ventral respiratory group neurons by augmenting neurons in the Bötzinger complex in the cat.

Axonal projections and synaptic connectivity of expiratory Bötzinger neurons with an augmenting firing pattern (Bot-Aug neurons) to neurons in the ipsilateral ventral respiratory group (VRG) were studied in anaesthetized cats. Antidromic mapping revealed extensive axonal arborizations of Bot-Aug neurons (24 of 45) to the rostral or caudal VRG, with some having arbors in both regions. Of 234 pairs of neurons studied with intracellular recording and spike-triggered averaging, monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked in 49/221 VRG neurons by 38/98 Bot-Aug neurons. The highest incidence of monosynaptic inhibition was found in inspiratory bulbospinal neurons (10 of 23 tested). Evidence was also found for monosynaptic inhibition, by a separate group of Bot-Aug neurons, of expiratory bulbospinal neurons (12/58), while excitatory postsynaptic potentials (EPSPs) were identified in another two of these neurons. In addition, monosynaptic IPSPs were recorded from 13 of 53 identified laryngeal motoneurons, and from 14 of 100 respiratory propriobulbar neurons. Presumptive disynaptic IPSPs were recorded from 11 of the 221 VRG neurons. We conclude that Bot-Aug neurons exert widespread inhibition on all major neuron categories in the ipsilateral VRG, and should be regarded as an important element in shaping the spatiotemporal output pattern of both respiratory motoneurons and premotor neurons.

Animals↗

PubMed1990

Serotonin immunoreactive boutons make synapses with feline phrenic motoneurons.

In anesthetized cats, phrenic motoneurons were intracellularly labeled with HRP. Immunohistochemistry was used to localize serotonin-like immunoreactivity that was present in numerous boutons and nerve fibers within the ventral horn of the C5 spinal segment. Immunoreactive boutons were frequently found in apposition to phrenic motoneurons, but these close contacts were more common on the dendrites than the cell body. At the electron microscope level, serotonin-immunoreactive boutons were found to make synapses with well-defined postsynaptic densities on proximal and distal dendrites of phrenic motoneurons. These results suggest that serotonin-containing neurons may directly affect the excitability of phrenic motoneurons, mainly through an input onto their extensive dendritic trees.

Animals↗

PubMed1989

Synaptic inhibition of phrenic motoneurones evoked by stimulation of the superior laryngeal nerve.

Synaptic responses evoked in phrenic motoneurones (PMNs) by stimulation of the superior laryngeal nerve (SLN) were analysed in anaesthetised cats. Stimulation of the SLN was followed by inhibition of ipsilateral phrenic nerve discharge with the latency of 9.5 +/- 2.3 ms (mean +/- S.D.) and hyperpolarizations of ipsilateral PMN membrane potentials (latency, 8.4 +/- 2.1 ms) which were observed after stimuli applied both during inspiration and expiration. During the injection of Cl ions, the hyperpolarizations were either reversed or flattened in all 28 tested PMNs, thus indicating a direct inhibition. The possibility that the inhibitory postsynaptic potentials are produced by segmental respiratory interneurones is discussed.

Action Potentials↗

PubMed1988

Limitations of the technique of pressure microinjection of excitatory amino acids for evoking responses from localized regions of the CNS.

The aim of this study, performed on anaesthetized cats and rabbits, was to test the assumption that pressure microinjections of excitatory amino acids cause long-lasting excitation of neurones located close to the injection site. Unitary action potentials or antidromic field potentials were recorded from respiratory or 'reticular' neurones in the medulla oblongata and from phrenic motoneurones at different distances from the injection site. Injection of 10-150 nl (5-150 nmol) of L-glutamate or DL-homocysteic acid into these areas resulted in complex and widespread neuronal events. Generally, more distant neurones (500-1300 microns) were excited for variable periods of time (3-15 min), while neurones in the vicinity of the injection site (0-500 microns) showed, after a brief period of excitation time, a long-lasting (up to 30 min) decrease in excitability or silencing of discharge, probably due to a depolarizing block and disturbances in the ionic composition of the extracellular space. These findings show that interpretation of physiological responses following such injections should not be based on an assumption of local neuronal excitation. Some recommendations regarding the use of this technique are made.

Action Potentials↗

PubMed1988

Distribution of recurrent inhibition within a motor nucleus. I. Contribution from slow and fast motor units to the excitation of Renshaw cells.

The relation between the size of a monosynaptic reflex (MSR) to triceps surae and the resulting Renshaw cell discharge was used to evaluate the contribution from slow and fast motor units to the excitation of Renshaw cells. It is, however, difficult to interpret these results in terms of excitation contributed by slow and fast motor units because of the following reasons. First, the size of the MSR recorded in ventral roots is not linearly related to the number of recruited motor units, since larger motor axons contribute more to the size of the MSR than smaller ones. Second, the number of spikes evoked in a Renshaw cell burst is not linearly related to the excitatory input because Renshaw cell discharge saturates in the case of large responses. The contribution of small, early-recruited motoneurones to Renshaw cell excitation is consequently overestimated. Procedures were introduced to deal with these problems. It is concluded that the last-recruited motor units (probably 'fast twitch, fast fatiguing') on average contribute four times as much excitation to Renshaw cells as the first recruited ('slow twitch') motor units.

Animals↗