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Biomedical subjects

J Lipski

Publications and source records attributed to J Lipski.

At least 73 records · Page 4Linked to original sources
PubMed1987

Morphological properties of respiratory intercostal motoneurons in cats as revealed by intracellular injection of horseradish peroxidase.

This study was undertaken to describe details of the location and cellular morphology of functionally identified (inspiratory or expiratory) external and internal intercostal motoneurons on the basis of intracellular injection of horseradish peroxidase (HRP). Sixty HRP-labeled motoneurons were examined; 44 in transverse, 16 in sagittal sections. In the upper thoracic segments (T3-T4), there was only a small overlap in the location of inspiratory external and internal intercostal motoneurons; the inspiratory external motoneurons were generally found more ventromedially within the ventral horn than either inspiratory or expiratory internal intercostal motoneurons. No major morphological differences were observed between the types of motoneurons studied. The number of primary dendrites ranged from 6 to 10. The dendrites projected mainly along the medial or the lateral border of the ventral horn, and rostrocaudally up to 1,760 micron from the cell body. The paths taken by dendrites to fill the territory occupied by the dendritic trees appeared to depend upon location of the cell body. Few dendrites penetrated the white matter. Axon diameters varied from 1.1 to 6.7 micron (mean 3.6 +/- 1.3 micron, n = 55). Collateral branches were identified in 78% of axons. The number of branches arising from a given axon varied from 1 to 4. It is concluded that the respiratory intercostal motoneurons form a morphologically homogeneous population, in spite of their functional differences.

Animals↗
PubMed1987

Respiratory rhythmicity in a split medulla preparation of the cat.

Splitting the medulla in the cat resulted in the disappearance of inspiratory activity in the phrenic but not in the recurrent laryngeal nerves with minor changes in respiratory cycle duration. In one animal a complete desynchronization of respiratory rhythms was observed in the opposite recurrent laryngeal nerves. We conclude that each half of the cat's brain stem has its own respiratory phase-switching mechanism. Commissural connections are involved in the bilateral synchronization of activity and the mutual excitatory interactions between medullary respiratory neurons.

Action Potentials↗
PubMed1987

Monosynaptic excitation of thoracic motoneurones by inspiratory neurones of the nucleus tractus solitarius in the cat.

1. The connection between inspiratory neurones in the ventrolateral nucleus tractus solitarius (n.t.s.) and intercostal motoneurones was examined. 2. Descending axonal projections to contralateral T3-T5 spinal segments were found for 110 of 142 (77%) ventrolateral n.t.s. neurones examined. 3. Antidromic mapping was used to locate the axons of thirty-nine ventrolateral n.t.s. neurones in T4, and evidence for axon collaterals was found for thirty-two of forty-seven (68%) neurones examined. Axon collaterals were found in both T3 and T4 for four of nine neurones examined and in T3, T4 and T5 for two of three neurones examined. 4. Cross-correlation histograms were calculated for sixty-five ventrolateral n.t.s. neurones with the contralateral intercostal nerves. Peaks in the cross-correlograms were assessed for significance by calculating k, the ratio of the peak bin count to the mean bin count. Significant peaks (k ratios 1.07-1.24, mean 1.15) were found for twenty-eight (39%) cross-correlograms. Twelve of thirty-three (36%) were for the whole external intercostal nerve, ten of twenty-seven (37%) were for the whole internal intercostal nerve and six of eleven (54%) were for external intercostal nerve filaments. 5. Six of the cross-correlogram peaks were less than or equal to 1.2 ms in width at a level half-way between the peak and the mean bin count. The rest ranged from 2.0 to 4.6 ms (mean 3.0 ms). 6. Intracellular recordings from either internal or external intercostal motoneurones were made and averages of the intracellular potentials were computed using ventrolateral n.t.s. neurone spikes as triggers. 7. Thirty-two spike-triggered averages were computed for pairings between nineteen ventrolateral n.t.s. neurones and thirty-two intercostal motoneurones (twenty-five internal, seven external). Fast-rising, short-lasting depolarizations indicative of a monosynaptic e.p.s.p. were found for five ventrolateral n.t.s. neurones. 8. The characteristics of the cross-correlogram peaks were considered with respect to the e.p.s.p. shapes and it was concluded that the intercostal motoneurones receive a significant monosynaptic excitation from ventrolateral n.t.s. neurones.

Action Potentials↗
PubMed1987

Inputs to intercostal motoneurons from ventrolateral medullary respiratory neurons in the cat.

The investigation examined the synaptic input from medullary respiratory neurons in the nucleus retroambigualis (NRA) to external (EIM) and internal (IIM) intercostal motoneurons. Antidromic mapping revealed that 112/117 (96%) tested NRA units had axons descending into thoracic spinal cord with extensive arborizations at many thoracic segments, mainly contralaterally. The conduction velocities ranged from 10 to 105 m X s-1. The descending projections did not appear to be somatotopically arranged. Cross-correlation of the spike trains of NRA inspiratory units with the discharge of external intercostal nerves (performed usually with 4 contralateral nerves) showed significant narrow peaks only in 5 out of 40 averages. Of the 25 trigger units tested for the thoracic projection in this series of experiments, 24 were antidromically activated. Intracellular recordings were made from 52 IIMs [mean membrane potential 65.3 mV, central respiratory drive potentials (CRDPs) greater than 1 mV present in 23/52] and 53 EIM (mean membrane potential 54.3 mV, CRDPs in 31/53). During the depolarizing phase of the CRDPs, synaptic noise with frequent and apparently unitary EPSPs with amplitudes in excess of 1 mV was observed. Spike-triggered averages of synaptic noise were computed for 153 pairings between 137 NRA neurons and 105 contralateral intercostal motoneurons. Only four PSPs were revealed: two monosynaptic EPSPs between expiratory NRA units and IIMs and two probably disynaptic EPSPs between inspiratory NRA units and EIMs. When advancing the microelectrode down to the motoneuron pools, frequent recordings were made from interneurons with spontaneous respiratory discharge (inspiratory or expiratory) located dorsal and medial to the motor nuclei. The interneurons could be excited following stimulation of segmental afferents. It is concluded that monosynaptic connections between respiratory NRA neurons and intercostal motoneurons are rare (connectivity no more than approximately 4%). Segmental interneurons, interposed between the majority of descending respiratory axons and intercostal motoneurons, are likely to produce large unitary EPSPs and, thus, short-term synchronization in the discharge of intercostal motoneurons as observed by others.

Animals↗
PubMed1986

Decreased excitability of respiratory motoneurons during hypercapnia in the acute spinal cat.

This study was undertaken to examine the effects of hypercapnia on the excitability of respiratory motoneurons. The action of CO2 on phrenic (inspiratory) and internal intercostal (expiratory) motoneurons was compared with that exerted on non-respiratory motoneurons of the musculocutaneous nerve. The experiments were performed on spinalized (C1 segment), partially deafferented cats that were exposed to different CO2/O2 mixtures (end-tidal CO2 3 +/- 0.3, 6 +/- 0.5 and 9 +/- 0.5%). Changes in neuronal excitability were assessed by: measuring the amplitudes of antidromic field potentials recorded from a population of motoneurons; analysis of the amplitude and latency of the orthodromic response recorded from a given nerve and evoked by microstimulation within the corresponding motor nucleus; monitoring the membrane potentials during intracellular recordings from phrenic motoneurons; and recording ongoing activity of the phrenic and internal intercostal nerves. Hypercapnia (end-tidal CO2 6 +/- 0.5 or 9 +/- 0.5%) decreased the excitability of phrenic and musculocutaneous motoneurons, the effect being larger at the higher CO2 level. Internal intercostal motoneurons were generally more resistant to the effects of CO2. A depression of their excitability was observed only at end-tidal CO2 9 +/- 0.5%. The decreased excitability of phrenic motoneurons was associated with membrane hyperpolarization. It is concluded that the depressant action of CO2 is present in both respiratory and non-respiratory spinal motoneurons. The action of hypercapnia on respiratory motoneurons may oppose the excitatory effects exerted through specific chemoreflexes.

Animals↗
PubMed1986

An electrophysiological investigation of propriospinal inspiratory neurons in the upper cervical cord of the cat.

This study was performed in order to describe the location, axonal projection and possible synaptic action of the inspiratory neurons recently described in the upper cervical cord. In 26 cats anaesthetized with Nembutal, extracellular recordings were made from 224 cervical inspiratory units which were found near the lateral border of lamina VII and formed a column extending from the caudal end of the nucleus retroambigualis at the C1 segment to the rostral half of the C3 segment. Most of the units (approximately 85%) could be excited antidromically from the thoracic cord. Antidromic mapping showed collateral branches to the C5 segment in the vicinity of the phrenic nucleus, occasionally crossing the midline. No synaptic connections with phrenic motoneurones could be revealed either by cross-correlation of the activity of the cervical units with the discharge of C5 phrenic root, or by spike-triggered averaging (STA) of the post-synaptic noise recorded intracellularly from phrenic motoneurons. Extensive branching was found in the examined T3-T5 segments with arborizations near the ipsilateral intercostal motor nuclei and often extending across the midline. Cross-correlation experiments did not show clear monosynaptic connections to the inspiratory intercostal motoneurons. Intracellular recording from intercostal motoneurons and STA resulted in a few (2 out of 37) small, probably disynaptic, e.p.s.p.s. It is concluded that the upper cervical neurons are involved in the control of phrenic and intercostal motoneurons, probably through a disynaptic pathway involving segmental interneurons.

Animals↗
PubMed1986

Short latency inputs to phrenic motoneurones from the sensorimotor cortex in the cat.

Short latency responses were recorded from C5 phrenic roots and intracellularly from phrenic motoneurones following stimulation of the pericruciate cortex or medullary pyramids in cats anaesthetized with Nembutal or chloralose-urethane. Focal stimulation of the cortical surface (single pulses, 0.5-2 ms, 0.3-8 mA) during inspiration evoked EPSPs (latency 4.7 +/- 1.7 ms, rise time 1.9 +/- 1.1 ms, amplitude 0.22 to 3.94 mV) in 42% of motoneurones studied (n = 107). The EPSPs were absent, or on average 60% smaller, following stimulation during expiration. In all but two motoneurones, during both inspiration and expiration, hyperpolarizing potentials were observed either following the initial depolarization or alone. They could be reversed by hyperpolarizing current or chloride injection. Stimulation of the pyramidal tract at mid medullary level (1 to 3 pulses, 0.2 ms) evoked short latency excitation in phrenic motoneurones only with currents of more than 200 microA. Smaller stimuli applied to the medial reticular formation above the pyramidal tract evoked excitation (onset latency 1.5-3.2 ms) in which the earliest part was probably monosynaptic. These results show that the corticospinal responses in phrenic motoneurones are both excitatory and inhibitory. They are not transmitted through the pyramidal tract and are at least disynaptic. Excitation evoked from the medullary pyramidal tract can be explained by current spread beyond the pyramidal tract fibres.

Animals↗
PubMed1986

Stabilization of intracellular recordings in the cat spinal cord using high-frequency ventilation.

Stabilization of intracellular recordings by a substantial reduction of respiratory motion may be accomplished by the use of high-frequency ventilation (600-800 breaths/min). The technique is a simple one and enables maintenance of relatively constant blood gas tensions. Although the improved stability was demonstrated in experiments performed on alpha motoneurones in the thoracic spinal cord, it is anticipated that a reduced respiratory movement should benefit recordings in other spinal and supraspinal sites.

Animals↗
PubMed1985

Recurrent inhibition of cat phrenic motoneurons.

These experiments were performed to re-examine the presence of a recurrent inhibitory pathway to phrenic motoneurons in cats. Following intracellular staining of 49 phrenic motoneurons with horseradish peroxidase, initial axon collaterals were demonstrated in six axons (12%). Intracellular recording and averaging of the synaptic responses evoked by stimulation of the phrenic roots with an intensity subthreshold for axons of the examined motoneurons revealed (in spinalized cats with dorsal roots cut) inhibitory postsynaptic potentials (i.p.s.p.s) in 11/28 (40%) motoneurons (amplitude, 115 +/- 69 (SD) microV; latency, 3.0 +/- 0.6 msec; duration from 12 to 25 msec). In the vicinity of the phrenic nucleus, Renshaw-like units were extracellularly recorded, which fired high-frequency bursts of action potentials following the stimulation of the phrenic roots (burst duration, 8 to 21 msec). Antidromic activation of the C5 phrenic root reduced the firing probability of fibers in the C6 root. The duration of the reduced firing probability corresponded to the duration of both the i.p.s.p.s and the Renshaw units' firing period. It is concluded that Renshaw inhibition is present in phrenic motoneurons. The inhibitory effects of this recurrent pathway may be greater than judged from the small amplitude of the i.p.s.p.s recorded in individual motoneurons, particularly when the whole phrenic pool is activated and when motoneurons are near threshold. It is suggested that one of the functions of the pathway is to control phrenic motoneurons supplying the dorsal part of the diaphragm through the C6 root when the more ventral part of the diaphragm is strongly activated.

Animals↗
PubMed1984

Is there electrical coupling between phrenic motoneurons in cats?

The possibility of electrical coupling between phrenic motoneurons was studied in anesthetized cats. In animals with C4-C7 dorsal roots cut (spinal cord intact), no sign of short-latency increase in the firing probability was observed in one phrenic rootlet following stimulation of the other phrenic rootlet. Intracellular recording from 21 phrenic motoneurons, in cats spinalized at the C1 segment, revealed no graded, short-latency antidromic depolarizations, even when the collision technique was used. Conditioning depolarizations of the impaled motoneurons never resulted in an increase of cell firing following test antidromic activation of adjacent motoneurons. It is concluded that the short-term discharge synchronization, observed within the phrenic nucleus by other authors, must be due to the action of chemical synapses.

Animals↗
PubMed1984

Effects of carotid chemoreceptor excitation on medullary expiratory neurons in cats.

A previous report (Lipski et al., 1977, J. Physiol. (London) 269, 797-810) demonstrated an inhibition of the medullary dorsal inspiratory neurons when a phasic chemoreceptor stimulus was applied during expiration. The present study tested the response of expiratory neurons which might mediate this inhibition. Recordings were made in cats anaesthetized with chloralose-urethane from the C5 phrenic rootlet and mainly from the rostral (Bötzinger) and caudal (nucleus retroambigualis, NRA) groups of medullary expiratory neurons. Carotid chemoreceptors were excited by close arterial injections of CO2-equilibrated saline. The stimuli were applied automatically with a preset delay within the respiratory cycle. The stimuli applied in inspiration excited both the phrenic activity and ventral inspiratory neurons within less than 0.5 sec. The stimuli applied in expiration excited 17 out of 25 NRA units, none of which projected to the contralateral dorsal (NTS) respiratory group. Four out of 9 units within be responsible for the expiratory inhibition of NTS inspiratory cells produced by chemoreceptor stimulation, while the caudal expiratory neurons are involved in the mediation of the chemoreceptor-induced effects upon the spinal neurons.

Animals↗
PubMed1984

Two-processor system, based on the ZX-Spectrum microcomputer and the CAMAC modular system, for the analysis of physiological data.

The cost-efficient computer system composed of easy accessible elements was designed and set up for the purpose of both ON-line and OFF-line analysis of data obtained in physiological experiments. The system was supplied with the standard software, including special cross-assembler for CAMAC. The features of the system were verified during the experiments on respiratory neurons. It facilitates the analysis of experimental results.

Animals↗
PubMed1983

Two descending medullary inspiratory pathways to phrenic motoneurones.

Synaptic connections of the medullary inspiratory neurones of the nucleus tractus solitarius (NTS) and nucleus retroambigualis (NRA) with phrenic motoneurones were studied using spike triggered averaging of the synaptic noise of phrenic motoneurones. More than 60% of NTS inspiratory neurones made monosynaptic connections with phrenic motoneurones, while similar connections between NRA and phrenic motoneurones could be shown in less than 7% of studied neuronal pairs. Relations between cross-correlations and observed synaptic connectivity of the phrenic motoneurones are also discussed.

Animals↗
PubMed1983

Synaptic action of R beta neurons on phrenic motoneurons studied with spike-triggered averaging.

The functional role of dorsal medullary inspiratory neurons with excitatory input from lung stretch receptors (R beta neurons) is a matter of controversy. The present study, performed on chloralose-anesthetized and paralyzed cats, ventilated mainly with a phrenic-controlled servorespirator, deals with the spinal projection of these neurons, a property which suggests their involvement in the efferent part of the medullary respiratory complex. Out of 37 inspiratory neurons which could be excited antidromically following microstimulation within the contralateral C6 phrenic nucleus (latency 2.0 ms +/- 0.4, S.D.), 17 were classified by the 'no-inflation' test as R beta. Intracellular recording of synaptic potentials from phrenic motoneurons using the 'spike-triggered averaging' technique were made. In 10 phrenic motoneurons, the averaging revealed individual EPSPs (peak amplitude 150 +/- 110 microV, rise time 0.5 +/- 0.2 ms) time-locked to action potentials of 5 out of 7 R beta neurons tested. Cross-correlation of the R beta neurons firing with the activity of C5 and C6 phrenic rootlets indicated a divergence of excitatory action within the phrenic nucleus. For comparison, in 3 phrenic motoneurons individual EPSPs were recorded when the activity of 3 R alpha cells was used to trigger the averaging. It is concluded that at least some R beta neurons, similarly to R alpha neurons, project to the contralateral phrenic nucleus and can make monosynaptic excitatory connections with phrenic motoneurons. The finding that individual EPSPs were similar when averaging was triggered by the activity of either R beta or R alpha neurons provides new evidence for our earlier hypothesis that bulbospinal inspiratory neurons of the solitary tract nucleus may be subdivided into two categories only on a quantitative basis.

Animals↗
PubMed1983

Origin of the expiratory inhibition of nucleus tractus solitarius inspiratory neurones.

Respiratory neurones from retrofacial (NRF) and Bötzinger nuclei (BOT) were tested electrophysiologically for projection to the contralateral inspiratory region of the nucleus of the tractus solitarius (NTS). Antidromic activation was demonstrated for 30 expiratory neurons (out of a mixed population of 61). There was evidence of extensive branching within NTS for these axons. Histological localization of projecting BOT neurones was confined to the medial border of the NRF. NTS inspiratory neurones were impaled in the vicinity of BOT axonal arborizations, and averages of post-synaptic noise were made, using the simultaneously recorded BOT spike trains to trigger the averager. Unitary IPSPs were found in 5 out of 9 pairs so analyzed. The waveforms of these IPSPs were similar to previously recorded monosynaptic IPSPs. 25 expiratory neurones, recorded from the caudal part of nucleus retroambigualis (NRA), were tested for projection to NTS; no projections could be demonstrated. 8 NTS inspiratory neurones were tested, using spike-triggered averaging of post-synaptic noise, for functional connections from caudal NRA expiratory neurones; no PSPs were seen. It is concluded that the expiratory inhibition of NTS inspiratory neurones is due, in part at least, to inputs from BOT expiratory neurones. Caudal NRA expiratory neurones do not appear to contribute to this inhibition.

Animals↗
PubMed1981

Common interneurones in reflex pathways from group 1a and 1b afferents of ankle extensors in the cat.

1. Input from group I afferents of ankle and toe extensors, other muscles, skin nerves and descending tracts to interneurones of Rexed's laminae V-VI in the cat spinal cord was analysed using intracellular recording from these interneurones. Adequate stimuli (muscle stretches) were used to activate selectively group Ia muscle spindle afferents of triceps surae and plantaris while other fibre systems were excited electrically. 2. Ia and Ib afferents of ankle and toe extensors were found to co-excite, co-inhibit or exert opposite synaptic actions in 41, 33, and 50% of the analysed interneurones, respectively. Taking into account both excitatory and inhibitory input from these two groups of afferents, 64% of the interneurones appeared to be used in common in reflex pathways from muscle spindles and tendon organs of ankle and toe extensors. 3. Selective input from Ib afferents of triceps surae and plantaris (excitation and/or inhibition) was found in 36% of the interneurones; there was evidence for a similarly selective input from Ia afferents. 4. A great majority (over 90%) of the interneurones excited by group I afferents were also inhibited by group I afferents, from either the same or other muscles. 5. Both monosynaptic and disynaptic e.p.s.p.s from Ia and/or Ib afferents from other muscles and from fibres in the ipsilateral funiculi were found in a great proportion of the same interneurones, together with disynaptic e.p.s.p.s from low threshold cutaneous afferents. 6. Intracellular staining with horseradish peroxidase revealed four different patterns of axonal projections of the analysed interneurones: (i) projections to motor nuclei and the intermediate region, (ii and III) projections only to the intermediate region, locally or combined with projections to different rostro-caudal levels, and (iv) projections to the opposite side of the spinal cord. 7. A large proportion of interneurones projecting to motor nuclei displayed input from both Ia and Ib afferents although such an input was a feature of interneurones with other projections as well. No systematic differences in the input from group I afferents were found for interneurones with different axonal projections. In contrast disynaptic e.p.s.p.s of cutaneous origin and monosynaptic e.p.s.p.s upon stimulation of ipsilateral spinal tracts appeared predominantly in interneurones projecting to motor nuclei.

Afferent Pathways↗