[Effect of diadynamic currents on the respiratory center and respiratory muscles after lung and chest surgery].
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Electrical activity of the phrenic, external and internal intercostal nerves was studied in anesthetized cats during electrical stimulation of the inspiratory "points" of the reticular gigantocellular nucleus (medial zone of the respiratory center). Structural characteristics of reflex responses of phrenic and intercostal nerves to stimulation of various respiratory and nonrespiratory bulbar sites as well as their respiratory modulation, were analyzed. The organisation of probably neurophysiological mechanism of phrenic and intercostal responses to stimulation of the medial nucleus of the respiratory center, is discussed.
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Reticular neurons of the respiratory center are divided into three groups. One group is located in the medial zone of the center and receives afferent spike activity from structures of the respiratory apparatus and chemoreceptors. Another is located in the inspiratory and expiratory areas of the respiratory center, and takes part in integrating signals and activating the effector mechanisms of the center. The third group is found in both zones of the center and organizes its effector activity. Electrical stimulation of medulla oblongata nuclei could transform reticular neurons of the lateral zone of the center into respiratory neurons. Evidence for this was obtained in the form of short-latency and long-latency evoked potentials in reticular neurons.
During infancy respiratory patterns change with maturation. However, there is no documentation of the development of the neurons thought to be related to respiratory control. Relevant neurons in the medulla oblongata were examined using Golgi impregnation methods. Dendritic spines increased prenatally and decreased postnatally in the medullary respiratory centers (i.e., dorsal vagal nucleus, nucleus tractus solitarii and reticular formation). The prenatal neuronal maturation is earlier in the reticular formation than the vagal nucleus. These changes in neuronal dendrites may be related to the development of central respiratory control and the occurrence of primary apnea in prematurity and sleep apnea in sudden infant death syndrome.
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The authors consider the respiratory centre to be the regulator of the respiratory system and to consist of 3 main functional blocks: chemoregulator, respiratory rhythm autogenerator and mechanoregulator, functions of which are provided by the neurons of medulla oblongata. The main aim of chemoregulator block is to maintain the level of ventilation volume speed, which is necessary to compensate the difference between the signals of setting and the firing from the chemoreceptors. The main aim of mechanoregulator block is to provide the functioning of the regulation loop of the respiratory muscles comparing the signals which come from the respiratory autogenerator, and the firing of the mechanoreceptors. The generator unit of the respiratory centre is a set of rhythm-forming associations, the system of 4 neurons (early and late inspiratory and expiratory) are typical among them. The neurons are connected by recurrent inhibitory bonds: the neuron of each rhythm-forming group, successively becoming excited, inhibits the two preceding neurons in the cycle; for all this the neuron of the successive group is released from inhibition and in such a way the rhythmogenesis occurs. The respiratory centre forms a common unit for chemo- and mechanoreceptor loops, through which the circuits of feedback for both loops are connected, providing the regulation of breathing.
The asymmetrical reactions of respiratory neurons of the right and left halves of the respiratory center and varied changes in bioelectrical activity of external intercostal muscles on both sides of the chest were discovered in experiments on anesthetized cats in response to successive electrical stimulation of the symmetrical cortical areas of the right and left cerebral hemispheres before and after callosotomy. It was demonstrated that callosotomy increased on both sides of the respiratory center the quantity of neurons responsive to ipsilateral cortical stimulation and determined the character of the asymmetrical reactions of right and left respiratory neurons and intercostal muscles. On the basis of the data obtained it is concluded that the corpus callosum contributes to the functional integration of both halves of the respiratory center.
Impulse activity of respiratory neurones and respiration during electric stimulation of the inspiratory and expiratory sites of the respiratory center was studied in cats anesthetized with nembutal. The study was made with an object of imposing a new rhythm on these sites and of recovering respiratory function. It has been established that stimulation of the inspiratory and expiratory sites of the giganto-cellular nucleus and of some structures of the solitary tract nucleus enables one to impose the new rhythm on the respiratory neurones of the ventral and respiratory nuclei and on respiration as well as to renew the respiration arrested.
The reactions of 181 respiratory neurons of solitary and ambiguous nuclei were studied on 64 cats in the course of stimulation of inspiratory and expiratory zones of gigantocellular nuclei. A study was also made of the reactions of 224 reticular and 9 respiratory neurons of these zones during stimulation of solitary and ambiguous nuclei. Various reactions were recorded in response to the stimulation. Therefore the nuclei of the respiratory center possess various information. In the course of stimulation of the gigantocellular nucleus there predominated an increase in the neuronal electrical activity. On the contrary, inhibition of respiratory and reticular neurons of the gigantocellular nucleus was predominant in the course of stimulation of solitary and ambiguus nuclei. It is suggested that the interactions described underlie the formation of circular rhythms of respiratory center stimulation.
The responses of breathing and of respiratory neurons to microinjections of penicillin into the respiratory center area were studied in anesthetized and spontaneously breathing rats. The injections caused different alterations of the respiration, of the activity of respiratory neurons and their spatial distribution, and initiated respiratory moments of apneustic and gasping types. the hyperactivation of the respiratory center neurons by penicillin seems to cause a reversible development of pathological types of respiration.
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