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Biomedical subjects

O G Baklavadzhian

Publications and source records attributed to O G Baklavadzhian.

At least 19 recordsLinked to original sources
PubMed2000

[A comparative analysis of the descending projections of areas 5 and 7 of the parietal cortex to the cat brain stem].

Relative quantity of descending fibres of parietal fields 5 and 7 of cat brain stem was studied. Maximal projections of these field were determined, maximal projections of fields 5 and 7 to red nucleus reticular nucleus of midbrain and nucleus proprius of pons were shown. Topographic and quantitative overlapping of projections of fields 5 and 7 in red nucleus and reticular nucleus of midbrain was noted. Field 5 is maximally presented in ventral nucleus while field 7 has maximal number of projections in lateral nucleus. Projection of fields 5 an 7 to superior colliculus of tectum of the midbrain was determined that was significant although less pronounced than in the above mentioned nuclei. The number of fibres projecting onto the superior colliculus of tectum of the midbrain (its caudal part) from field 7 exceeds that from field 5. There are less fibres in inferior colliculus of tectum of the midbrain than in superior colliculus. The number of fibres projecting from field 5 is greater than those from field 7 in inferior colliculus. In caudal reticular nucleus of pons the presence of fields 5 and 7 was not significant. Comparison of the authors' data with that available in literature allows to suggest the possible inhibitory, i.e. modulating influence of parietal cortex on nuclei of the pons.

Animals↗
PubMed2000

[The role of the thalamic ventrolateral nucleus in the cortical effect on the activity of vestibular neurons].

Electrocoagulation of lateral vestibular nucleus (NVL) reduces inhibitory effect of the motor and somatosensory areas and enhances the inhibitory effect of limbic, vestibular, and orbital cortical areas. Facilitating effect was enhanced by electrostimulation of the motor area and reduced by the stimulation of other cortical areas. Following the coagulation of the NVL, the ascending afferent flow to the cortex seems to be reduced. This results in diminishing of the cortical neurones tone and readjusts the descending influences upon the NVL neurones activity.

Animals↗
PubMed1999

[Effect of mediodorsal thalamic nucleus on the respiratory neurons from medulla oblongata and the rat respiration during hypoxia].

In the normal as well as in the oxygen deficiency conditions the research has been conducted to study the influence of associative mediodorsal (MD) nucleus of thalamus on impulsive activity of respiratory neurons of medulla oblongata of respiration. In conditions of normal atmospheric pressure, before the uplift of the animals, the electrical stimulation of MD of nucleus of thalamus has had mainly inhibiting influence. In the initial phase, on 4-5 thousand meter altitude, activation of frequent discharge of neurons occurred, the respiration has become frequent as well. In this situation the inhibiting influence of stimulation of MD nucleus of thalamus was more accentuated than in conditions of normoxia. In the second phase, 7.5-8 thousand meters, the opposite occurred, i.e. reduction of respiratory center activity of medulla oblongata and thalamus. In this difficult conditions of hypoxia, a reduction of impulsive activity of neurons has been observed; the respiration was becoming slower and surface. Meanwhile, the inhibiting influence of thalamus was not significant.

Altitude↗
PubMed1999

[The role of various parts of the amygdaloid complex in the regulation of activity of respiratory neurons].

In microelectrophysiological investigations influences of different nuclear regions of the amygdaloid complex on the spike activity of the functionally identified single respiratory neurons of the medulla oblongata were studied in anesthetized cats. It was established a qualitative different character of the changes of unit activity of the medullary respiratory neurons in case of stimulation of phylogenetically old corticomedial or new basolateral nuclear groups of the amygdala. It was shown higher reactivity of the investigated neurons to stimulation of the corticomedial nuclei than basolateral. The influences of the corticomedial nuclear groups on the bulbar inspiratory and expiratory neurons were facilitatory as well as inhibitory with prevailing excitatory effects. It was found that influences of the phylogenetically new neoamygdaloid structures of basolateral region on spike activity of the bulbar respiratory neurons differ accordingly to their topographical differentiation. Mechanisms of amygdaloid control of activity of the medullary respiratory neurons are discussed.

Amygdala↗
PubMed1998

[Involvement of amygdala central nucleus in the regulation of cardiovascular functions].

Effects of high frequency stimulation of the amygdala central nucleus involved a selective decrease in the activity: an increase in the activity of the inferior cardiac nerve and a simultaneous decrease in the activity of the vertebral nerve, as well as an obvious BP increase. Bilateral electrolytic lesions of the same amygdala structure accompanied with an overload of the higher nervous activity induced no hypertensions. The role of the amygdala central nucleus in control of cardiovascular functions is discussed.

Amygdala↗
PubMed1998

[Neuron mechanisms of the regulation of bulbar vagosolitary activity by structures of basolateral amygdala nuclei in cats].

Neuronal reactivity to single stimuli applied to both the peripheral nerves and the cortex, was the same in the cat solitary tract nucleus. The 1-20 Hz stimulation frequency rendered the reactivity either tonic in character or with reduced firing rate. A high degree of convergence (80.2%) on baso-lateral nuclei neurons was established, as well as a significant cortico-fugal effect (71%) on the viscero-sensory units of these nuclei. Single shocks and tetanic stimulation of the baso-lateral amygdala evoked mostly phasic responses of the primary as well as secondary vagal neurons. Feed-back mechanisms of the amygdaloid control of the bulbar viscero-sensory units are discussed.

Amygdala↗
PubMed1997

[The influence of the limbic cortex and hypothalamus on the impulse activity of the bulbar respiratory neurons and on respiration under hypoxia].

The response of bulbar respiratory neurons and the total inspiration to stimulation of the limbic cortex and hypothalamus was not identical as a result of different sensitivity of the studied structures. The hypothalamus exerts mainly facilitating influence both in norm and at the maximal altitude (7500-8000 m). The limbic cortex exerts mainly inhibitory influence. At the maximal altitude no typical reactions of the respiratory neurons and the total respiration were observed in response to stimulation.

Acute Disease↗
PubMed1996

[Correlation of changes in the electrical activity and indices of tissue respiration of brain structures in rabbits exposed systematically to vibration].

The electrical activity and tissue respiration of the cortex and subcortex (posterior hypothalamic nucleus, Deiters' vestibular nucleus) have been studied in the rabbits during 3-month exposure to vibration (60H2, for 3h daily). On days 15-30 of exposure to vibration the electrocorticogram demonstrated the prevalence of alfa-waves whereas in the subcortex the teta-waves were dominated. On long-term vibration exposure (2-3 months), the synchronized slow waves were recorded on the EEG. Comparison of a changed electrical activity of the various structures of the brain with the level of oxidizing metabolism enabled us to reveal their definite interrelationship. In the early stage of vibration exposure there has been observed an increased absorption of oxygen by the brain structures and the elevated activity of succinate dehydrogenase. The prolonged vibration resulted in a decreased level of tissue respiration and activity of respiratory enzyme. Under vibration exposure there has been revealed a statistically significant direct relationship between the content of absorbed oxygen, activity of succinate dehydrogenase and the shifts in the electrical activity of cerebral structures.

Animals↗
PubMed1995

[The effect of stimulation of the orbitofrontal cortex on the activity of the bulbar respiratory neurons and on respiration in normal rats and in hypoxia].

Stimulation of the orbito-frontal cortex inhibited activity of bulbar expiratory, inspiratory and reticular (non-respiratory) neurons. The first phase of hypoxia generated facilitatory influence of cerebral activating structures, whereas the second phase led to a contrary effect (depression). Subcortical activating structures, however, retained some of their facilitatory influence thus maintaining the oxygen homeostasis of the organism.

Action Potentials↗
PubMed1995

[Cortical mechanisms of regulation of neuron activity of Deiters vestibular nucleus during vibration].

The peculiarities of the effect of vestibular, somatosensory, motor and limbic areas of brain cortex on the activity of neurons of lateral vestibular nucleus (LVN) are studied in the nembutal and chloralose anesthetized rabbits by the extracellular lead method before and after vibration exposure. It is found that the responses of neurons of Deiters's nucleus at all frequency ranges to stimulation of different areas of the cortex were predominantly of inhibitory type, being more pronounced during stimulation of the vestibular and motor areas. The facilitating corticofugal effect was noted in 20-30 % of cells and more pronounced influence was during stimulation of somatosensory and limbic areas of the cortex. During vibration there was a multidirectional effect of cortical areas on the neuronal activity of LVN. The vibration stimulus decreases an inhibitory effect and increases stimulating influence of vestibular cortex on the activity of Deiters's nucleus. The noted effect was more pronounced in neurons with low frequency of initial activity. On stimulation of other areas of the cortex an increase of inhibitory and suppression of facilitating descending effects were noted. The greatest amount of inhibited neurons was recorded during stimulation of motor cortex. The peculiarities and functional significance of the observed effects are discussed.

Animals↗
PubMed1994

[The role of the paraventricular hypothalamic nuclei in the development of chronic neurogenic hypertension and the formation of a self-stimulation reaction].

Effects of bilateral electric lesion of the hypothalamic paraventricular nuclei on cardiovascular components of the defense response and on the self-stimulation operant behaviour, were studied in rats. Overloading of the highest nervous activity induced no hypertension in these animals, though the self-stimulation frequency increased.

Animals↗
PubMed1994

[The characteristics of the neuronal organization of the sympathetic-activating and sympathetic-inhibiting mechanisms of the visceral area of the limbic cortex].

Effects of high frequency stimulation of dorsal and ventral regions of anterior area 25 of the limbic cortex on the tonic electrical activity of two postganglionic sympathetic nerves of stellate ganglion-inferior cardiac and vertebral nerves and arterial blood pressure were studied in anesthetized cats. It was revealed three types of medullary influences: generalized activation of both sympathetic nerves and pressor responses mainly in case of stimulation of ventral structures, generalized inhibition of electrical activity of both sympathetic nerves and depressor responses in case of stimulation of dorsal region of area 25 and selective modulation of activity, namely increase in activity of inferior cardiac nerve and simultaneous decrease of activity of vertebral nerve. According to data of our previous comparative studies of sympathetic responses of inferior and vertebral postganglionic nerves to stimulation of anterior and posterior hypothalamus as a working hypothesis it is supposed that the dorsal region of area 25 of limbic cortex is the analogy of trophotropic system of anterior hypothalamus, the ventral region--of ergotrophic system of posterior hypothalamus.

Animals↗
PubMed1992

[The reactions of the viscerosensory neurons of the nucleus solitarius to stimulation of the posterior and anterior hypothalamus].

The "vagal" neurons of the solitary tract nucleus responded to stimulation of anterior and posterior hypothalamus in 78.7 and 27.6 per cent, resp., the responses being mainly of the activation type. The descending effect from the hypothalamus involved primary as well as secondary "vagal" neurons. The responses were of mono-, oligo- and polysynaptic nature.

Action Potentials↗
PubMed1991

[The role of specific and nonspecific afferent systems in the mechanism of the changes in cortical evoked responses during vibration].

The correlation in activity of specific and unspecific afferent systems was measured in mechanisms changing electrical activity of the cortex during vibration. The character of postvibration shifts of vestibulo-, reticulo-cortical EPs was studied by means of isolated and combined exclusion of specific (vestibular) and unspecific afferent systems of the brain. The vestibular afferents seem to play a significant role in the mechanisms of postvibration shifts of vestibulo-cortical EPs. Impulses originating from the unspecific afferent systems, as well as proprioceptive, somatic and visceral afferents play similar role for the reticulo-cortical system.

Afferent Pathways↗
PubMed1991

[The reaction of the respiratory neurons of the medulla oblongata to stimulation of the amygdaloid complex nuclei in hypoxia].

Under atmospheric pressure, stimulation of amygdala induced an activating effect on the medullary respiratory and reticular neurons. At the initial stage of hypoxia (altitude 4000-5000 metres), against the background of hypoxic activation of the firing rate, facilitating influence of tetanic stimulation of the amygdala was lesser even though prevailing over its inhibiting action. At the maximal altitude (7500-8000 m), against the background of hypoxic suppression of unit activity, the stimulation of amygdala exerted mainly an activating effect. The response was particularly obvious in the neurons with low spontaneous activity.

Amygdala↗
PubMed1991

[The physiological mechanisms of the neurohumoral regulation of vascular tonus].

Neuronal organisation of hypothalamo-bulbar mechanisms of regulation of vascular tonus was studied in anesthetised and immobilised cats. The descending influence of posterior, tuberal and anterior structures of the hypothalamus on the activity of antidromically identified sympatho-activating reticulospinal neurons of the ventrolateral region of medulla oblongata is realised by mono-, oligo- and polysynaptic mechanisms. Chronic neurogenic hypertension was induced in rats by overloading the higher nervous activity. Arterial hypertension did not develop in chemically desympathized cats. Central and peripheral neurohumoral mechanisms of vascular tonus regulation are discussed.

Action Potentials↗