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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 77 (1997), S. 359-365 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. Networks constructed of biologically realistic model neurons (neuroids) were used to study how in a neural assembly using pulse (interval)-coded information slow rhythmical oscillations with possible mode transitions might occur and how the efferent commands might be structured and their phase-shifts created. The simulations show that slow oscillations (in the hertz range) can be derived from reverberatory spiking in relatively short closed loops (fewer than ten neuroids) with the inputs protected against disturbing afferent signals and the outputs coupled by convergence on a common neuroid. Slow oscillations can be modified by a tonic activity entering the network; this activity changes the transmission time in the coupled loops involved. The structuring of the regulatory commands (in the millisecond range) was achieved by simulation of sequential activity propagation in a non-ring neuronal assembly supervised by a tonic activity in a set of inputs. The tonic activity acted as an instructive signal influencing the pattern of the functional connectivity in such a way that a particular efferent command was generated by the instructed network.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Epileptogenic cortical focus ; Catecholamines ; Voltammetry ; Penicillin ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Differential pulse voltammetry with carbonfibre microelectrodes was used in chloralhydrate-anaesthetized rats to test the influence of the penicillin-G-Na (PNC)-induced (topical application, approximately 2000 IU) epileptic activity on the catecholamine content (catechol-oxidative current, CA.OC) in the parietal cortex. In the experimental group (n = 4) after PNC a nonlinear CA.OC lowering was observed; this decrease during the first 10 min was faster than in the control group (n = 4). Significantly different values were observed from the 4th min after application. The best fit for this experimental curve gave the logarithmic function (f(t) = a + b.ln(t), a =105.8, b= -10.6) with regression coefficient r = 0.98. From the 12th min after PNC application until the end of the experiments (54th min) CA.OC values ranged from 78% to 84% of the control group.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-9007
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Activity of reticulospinal neurons evoked by stimulation of the ventral, ventrolateral, dorsolateral, and dorsal funiculi of the spinal cord was recorded extracellularly in cats anesthetized with chloralose. Responses of 57 reticulospinal neurons, of which 22 projected into the ventral funiculus, 20 into the ventrolateral, and 15 into the dorsolateral, were studied. The functional properties (conduction velocity and refractory period) and the location of the neurons of the above-mentioned groups in the medulla did not differ appreciably. The most effective synaptic activation of all neurons was observed during stimulation of the dorsal and dorsolateral funiculi. Responses to stimulation of the dorsal funiculus had the lowest threshold. These responses arose in reticulospinal neurons of the ventral and ventrolateral funiculi after the shortest latent period. The effectiveness of synaptic influences from the dorsal and dorsolateral funiculi was identical in the group of neurons of the dorsolateral funiculus. Correlation between activity evoked by stimulation of the dorsal funiculus in reticulospinal neurons and peripheral nerves indicated that the responses appeared in these cells to stimulation of muscular (groups I and II) and cutaneous (group II) afferent fibers. The results indicate that impulses from low-threshold muscular and cutaneous afferents, which effectively activate reticulospinal neurons, are transmitted along ascending pathways of the dorsal funiculi.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-9007
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Synaptic processes in reticulospinal neurons of the pons and medulla during the startle reaction evoked by somatic stimulation were investigated in cats anesthetized with chloralose. The main type of response of reticulospinalneurons was found to be PSPs involving intrareticular (proprioreticular) pathways of varied complexity: oligosynaptic (including supposedly monosynaptic) and polysynaptic. Comparison of EPSP characteristics with parameters of spino-bulbospinal (SBS) discharges recorded simultaneously in the intercostal nerves showed that polysynaptic EPSPs evoked through corresponding proprioreticular pathways were most effective in creating a descending SBS volley. About half the reticulospinal neurons of the pons and medulla were involved at any one time in the synaptic relay process during the startle reflex. The conduction velocity in axons of these neurons varied from 30 to 98 m/sec (means 64.5 Mp 16.5 m/sec). Some distinguishing features of the functional organization of the reticular "center" for the startle reaction are discussed.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-9007
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Early (spinal) and late (spino-bulbo-spinal) responses of interneurons in segments T9–10 to stimulation of the splanchnic and intercostal nerves and the dorso-lateral and ventral funiculi of the spinal cord (at the C3 level) were investigated in experiments on cats anesthetized with chloralose. The experiments showed that interneurons activated by spinal and spino-bulbo-spinal mechanisms differ in their distribution in the dorso-ventral plane of the spinal cord. Cells of layers I–V were excited by spinal pathways only, but those of layers VII and VIII by both spinal and spino-bulbo-spinal or only by the latter. Spino-bulbo-spinal effects were evoked in interneurons by both somatic and visceral afferent waves. A conditioning spino-bulbo-spinal wave evoked deep and prolonged inhibition of late activity induced by somatic or visceral afferent impulses. Early (spinal) activity was inhibited only partially under these circumstances. This inhibition was shown to take place with the participation of supraspinal structures. The possible types of spinal and supraspinal mechanisms of inhibition of early and late activity in spinal neurons are discussed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-9007
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Experiments on cats anesthetized with chloralose showed that repetitive stimulation of the locus coeruleus is accompanied by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons. The effect appeared 600 msec after the beginning of stimulation and reached its maximum after 1500–2000 msec. Repetitive stimulation of the locus coeruleus did not change the membrane potential and did not affect EPSPs or IPSPs evoked by stimulation of low-threshold muscle afferents; EPSPs due to activation of high-threshold cutaneous and muscle afferents likewise remained unchanged. Repetitive stimulation of more central regions of the brain stem was accompanied not only by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons, but also by a decrease in amplitude of EPSPs arising in response to stimulation of these same afferents in flexor motoneurons. These effects were not connected with activation of monoaminergic structures, for unlike effects arising during stimulation of the locus coeruleus, they were also found in previously reserpinized animals.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-9007
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Participation of the reticular formation and descending reticulospinal system in the motor control functions of the spinal cord is examined. The data indicate that the reticular formation may participate in the regulation of specific motor actions. This is shown by the results of experiments to analyze the properties of membranes of reticulospinal neurons and the principles of organization of cortico-reticular monosynaptic relays, and to the investigation of characteristics of responses of "ensembles" of reticular neurons in cats, and also by data obtained in a study of correlation of unit activity in the reticular formation with movements elaborated in rats. The functional role of differential characteristics of the reticular formation is discussed and prospects for future research into reticular membranous, neurochemical, and neuronal mechanisms as a step toward the understanding of reticular control of motor functions are described.
    Type of Medium: Electronic Resource
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