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V P Lebedev

Publications and source records attributed to V P Lebedev.

At least 55 records · Page 3Linked to original sources
PubMed1984

[Neuronal organization of the sympathetic system-activating structures of the ventro-lateral surface of the medulla oblongata].

In anesthetized cats, activating effects of the bulbar ventro-lateral surface (BVLS) upon the spinal sympathetic neurons were shown to be transmitted via output sympathoactivating neurons (OSN) with descending axons. Antidromic discharge of these neurons elicited by stimulation of the spinal dorso-lateral funiculus were found in the intermediate zone of the BVLS at the depth of about 400-2000 mu. Stimuli applied to different regions of the BVLS activate at least two groups of surface fibers (conducting velocities 6.7-8.0 and 2-3.2 m/sec) which in their turn activate OSN with a delay of about 20 msec. The mechanism of the delay formation seems to be concentrated in the intermediate zone and formed, probably, by a chain of interneurons. A possible scheme of neuronal organization of the sympathoactivating BVLS structure is discussed.

Animals↗
PubMed1984

[Role of sympatho-activating structures of the ventrolateral surface of the medulla oblongata in vasomotor regulation].

In anesthetized cats, the cold block or coagulation of intermediate zones of the bulbar ventro-lateral surface (BVLS) resulted in profound decrease of the blood pressure (BP) level. The descending tonic activation of spinal vasomotor mechanism in formed by spontaneous discharges of antidromically identified output sympatho-activating neurons with mean firing rate about 14.4/sec. After coagulation of the intermediate zone, pressure reflexes of the BP and late somato-sympathetic response in white rami disappear whereas the spino--bulbo--spinal somato--somatic reflex remains unchanged. The reflex discharges of single sympatho--activating neurons were within the time limits of the late somato--sympathetic response and followed by the silent period. The preferable inhibition of the long-latency white rami discharges elicited by BVLS stimulation arise 200-250 msec after R-wave of the ECG. The inhibition of long-latency discharges was observed during the increase of the BP level induced with vasoconstrictor drugs. The intermediate zone structures of BVLS seem to play the key role in supporting of the BP level and organization of pressure reflexes. These structures are suggested to be the actual elements of the bulbar vasomotor center.

Animals↗
PubMed1983

[Nonuniformity of the descending pathways activating the sympathetic preganglionic neurons of the superior thoracic segment of the spinal cord].

In anesthetized, immobilized and artificially ventilated cats, excitatory influences from the ventrolateral part of medulla are mediated to sympathetic preganglionic neurons of T2 segment via two types of descending pathways with conduction velocity 12.3 +/- 3.2 m/sec and about 6 m/sec. The descending excitatory influences on sympathetic neurons of T4 and more caudal segments are mediated via pathways of the latter type only. According to characteristics of the white rami responses elicited by stimulation of different points of the bulbar ventrolateral surface, both types of descending fibers are the axons of neurons located in caudal part of zone M and in zone S. Moreover, the T2 sympathetic neurons are activated by descending pathways with conduction velocity about 5.7 +/- 0.6 m/sec originating in dorsocaudal part of the medulla. The high speed descending pathways to T2 were shown to take part in transmission of pupillo-dilatory impulses. On the basis of comparison of the white rami responses elicited by stimulation of different points of the bulbar ventrolateral surface with different impulse intensity, the neuronal organization of sympathoexcitatory structures of this region of medulla is suggested.

Animals↗
PubMed1982

[Responses in the white rami communicantes of different segments of the spinal cord to stimulation of the ventral surface of the medulla oblongata].

In anesthetized curarized cats, the responses in T3-4, T10-11 and L2-3 white rami (WR) to stimulation of different zones of the bulbar ventral surface (BVS) were maximal when the region about 4 mm laterally from midline was stimulated. Threshold surface stimulation of all these zones elicited only the long-latency responses in WR. The short-latency responses appeared in WR when supramaximal stimuli were applied to the region up to 6 mm rostrally from the hypoglossal nerve root level (zone S and caudal part of zone M). Descending influences from BVS were conducted by fibers of the spinal dorsolateral funiculus with conduction velocity about 5.6 +/- 0.6 m/sec. These pathways differed from previously studied sympathoexcitatory pathways originating from sympathoexcitatory neurons in caudal medulla. A possible neuronal organization of sympathoexcitatory structures of BVS is suggested.

Animals↗
PubMed1982

[Late somatosympathetic reflex responses in the thoracic and lumbar white rami communicantes].

In anesthetized and immobilized cats with intact nervous system, late somato-sympathetic reflexes (LB) in T3 and L2-3 white rami elicited by stimulation of ipsi- and contralateral thoracic and lumbar segmental nerves included at least two typical waves: LR-I, LR-II, LR-I was only elicited by stimulation of corresponding and neighbouring segmental ipsilateral nerves and had equal latency at the thoracic and lumbar levels. The appearance of LR-II in thoracic and lumbar white rami did not depend on the level of spinal entrance of the stimulated afferent nerves. The LR-II latency increased in white rami originated in more caudal segments. The data obtained suggest LR-I to be the spinal reflex, and LR-II--the suprasegmental one.

Animals↗
PubMed1980

Do sympathetic preganglionic neurones have a recurrent inhibitory mechanism?

In anaesthetized and immobilized cats 32.5% of the intermediolateral sympathetic preganglionic neurones (B2-SPN) in T3, T8-9 and L2 spinal segments can be re-excited antidromically by repeated stimuli only at very long interstimulus intervals (16 ms and more) considerably exceeding the refractoriness of the somata and axons of these neurones. This was observed in the absence of any association with subnormality or other peculiarities B2-SPN axons. In this group of B2-SPNs with prolonged time interval between repeated antidromic discharges, orthodromic spikes effectively inhibited the generation of antidromic ones for a period which was substantially longer than the possible collision time. The preceding antidromic activation of a fraction of the B2-SPN segmental pool partly inhibited the orthodromic reactions of the others in this segmented elicited by stimulation of segmental afferent fibres or spinal descending pathways. These data definitely indicate that some of the B2-SPN group have a recurrent inhibitory mechanism.

Adrenergic Fibers↗
PubMed1980

[Level at which baroreflex sympatho-inhibitory effects are achieved].

The interaction between the descending sympathoexcitatory "vasomotor" and the inhibitory baroreceptor systems was studied in cats. The spontaneous activity and reflex discharges of the identified bulbar sympathoexcitatory neurons were unaffected during the stimulation of baronlferents and the elevation of the arterial blood pressure. It was found that baroreceptor impulses inhibit the spinal interneuron system which take part in transmission of descending sympathoexcitatory influences.

Animals↗
PubMed1980

[Specialization of the descending sympatho-activating pathways of the dorsolateral funiculus of the spinal cord].

In anesthetized curarized cats the degree of specialization of the descending sympathoexcitatory axons which activate sympathetic preganglionic (vasomotor) B2--neurons of the lateral horn, was studied. These sympathoexcitatory fibers with conduction velocity of 4.0--8.9 m/sec activate especially onlg the sympathetic B2--units of the spinal cord. Other neurons (phrenic and intercostal mofoneurons and sacral parasympathetic preganglionic neurons) are activated by different groups of descending fibers with conduction velocity greater than that of descending sympathoexcitatory fibers.

Animals↗
PubMed1978

[Discharges in the white rami communicantes evoked by stimulation of various sections of the hypothalamus].

Electrical responses in L2--L3 white rami on stimulation of anterior and posterior hypothalamus were studied in anesthetized and immobilized cats. The stimulation evoked a complex response consisting of waves I, II, and III with mean latency 19.7 +/- 4.5 msec, 34.0 +/- 5.9 msec, 61.8 +/- 8.7 msec, and 20.5 +/- 6.8 msec, 30.;7 +/- msec, 66.0 +/- 14.9 msec for anterior and posterior hypothalamus respectively. In experiments with simultaneous recording of arterial pressure and hypothalamo-sympathetic discharges, after 10-sec period of tetanic (100/sec) stimulation of the hypothalamus, the early I and early II components were facilitated, while the late component of the hypothalamo-sympathetic discharge was depressed. The duration of this inhibition corresponded to the period of pressure reaction and, therefore, is of baroreceptor origin. Possible mechanisms of hypothalamic regulation of the activity of sympathetic preganglionic neurons are discussed.

Animals↗
PubMed1978

[Identification and study of sympathoactivating neurons of the medulla oblongata].

The neurons with descending axons which activate the lateral horn sympathetic preganglionic (vasomotor) neurons were searched in the lower brain stem of the cat. Localization of these sympathoactivatory neurons in the limit zone of medulla was outlined by means of scanning stimulation. The identification of single bulbar sympathoactivatory neurons was based on the recording of their antidromic discharges elicited by stimulation of descending sympathoactivatory pathways with conduction velocity about 4--8.9 m/s in the dorsolateral funiculi of the cervical spinal cord. The neurons studied have a very low frequency spontaneous discharges (0.1--1.0 imp/s) unrelated with cardiac and respiratory cycles. The alterations of spontaneous discharge frequency were in strict correlation with pressor phases of Maer waves and pressor reflex reactions. The inhibitory effects of the baroreceptor nerve stimulation on spontaneous and elicited discharges of these neurons were never seen. A possible role of the sympathoactivatory neurons identified as an output elements of the bulbar "vasomotor" centre is discussed.

Animals↗