Synaptic responses of medulla oblongata neurons to stimulation of the spinal stepping atria in the cat

Synaptic responses of medulla oblongata (bulbar) neurons to microstimulation of stepping points in the spinal dorsolateral funiculi were recorded in decrebrate cats. Upon stimulation of the stepping point both in the ipsi- and contralateral funiculi, 40% of the neurons generated synaptic responses; the remaining cells responded to stimulation of only one stepping point. A part of the bulbar neurons responds to stimulation of stepping points both at the C₂ and Th₁₂ level. The latent periods of the synaptic responses of the bulbar neurons to stimulation of the stepping point at the C₂ level were in the 2–10 msec range. The data obtained indicate that bulbar neurons, along with propriospinal neurons, can participate in evoking locomotion upon stimulating the stepping point.Institute of Information Transmission Problems, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 328–333, May–June, 1991.     

Effects of stimulus parameters on cardiovascular responses to medullary stimulation in the cat

The results of this study indicated that when stimulus intensity, pulse frequency and train duration were varied the basic topography of the cardiovascular responses to medullary stimulation did not change, but was merely increased or diminished in magnitude. Pressor responses were usually obtained in conscious cats, and also narcosis produced reversal effect on rare occasions. It is suggested that the reversal in cardiovascular responses is probably locus specific, and the medullary loci yielding reversal effect are more limited than those eliciting consequently pressor responses.     

A mapping study of cardiorespiratory responses to chemical stimulation of the midline medulla oblongata in ventilated and freely breathing rats

The aim of this study was to examine the cardiorespiratory effects of chemically stimulating neurons in the midline medulla oblongata (MM) of artificially ventilated and freely breathing anesthetized rats. Earlier studies reported that stimulation of the MM elicits increases or decreases in mean arterial pressure (MAP) and phrenic nerve activity, depending on the mode and site of stimulation, anesthetic, and species. In the first series of experiments, rats were anesthetized with urethane, artificially ventilated, paralyzed, and bilaterally vagotomized. The rostrocaudal extent of the MM was mapped by microinjections of DL-homocysteic acid or L-glutamate (both 100 mM, 100 nl), and, in line with previous studies, most injections produced only small responses in MAP, heart rate, and splanchnic sympathetic nerve activity. Increases in respiratory parameters were evoked in caudal regions. However, activation of a discrete region of the MM at the level of the caudal pole of the facial nucleus (CP7) consistently caused a dramatic reduction in phrenic nerve amplitude and/or frequency and, in six rats, produced a prolonged apnea. The second series of experiments was carried out on freely breathing pentobarbitone sodium-anesthetized rats, with a diaphragmatic electromyogram used to monitor respiratory activity. Respiratory activity could again be abolished at CP7 after microinjections of glutamate (100 mM, 50 nl); however, these responses were accompanied by large decreases in MAP and moderate reductions in heart rate. This depression of respiratory activity may be due to activation of propriobulbar inhibitory neurons that project to known respiratory centers in the brain stem.     

Response of respiratory neurons of the medulla oblongata to the septum stimulation in hypoxia

In the oxygen deficiency conditions, we studied influence of irritation of ventral (BNST), lateral (LSN) and medial (MSN) nuclei of the septum on the impulse activity of the bulbar respiratory neurons and on respiration. Phases of hypoxia were the model of experiment. In conditions of normal atmospheric pressure, the electrical stimulation of BNST, LSN and MSN nuclei of the septum exerted inhibiting as well as activating influence with the inhibiting influence prevailing. In difficult conditions of hypoxia (7.5-8 thousand meters) on the reduction of the impulse activity of neurons, stimulation of septum nucleuses induced uncharacteristic reactions of those neurons.     

大鼠延髓腹面降压区微量注射L—精氨酸对心血管活动的影响

目的：观察NO前体L－精氨酸（L－Arg)微量注入大鼠延髓腹面降压区（VSMd）对心血管活动的影响及其和L－谷氨酸（L－Glu)降压作用的关系。方法：采用延髓腹外侧部微量注射法,以整体灌流肾为模型观察与NO有关的药物对心血管活动的影响。结果：①VSMd内微量注入L－Arg,动脉血压（AP）呈剂量依赖性升高,肾灌流压（PPK）与AP同步上升,与注入生理盐水对照,差异均具有显著意义,但L－Arg对心率无显著影响;②预先在VSMd内注入甲基蓝可取消L－Arg的升压、升PPK作用;③VSMd内注入L－Glu,AP下降。如预先注入L－Arg后5min再注入L－Glu,L-Glu的降压效应被衰减,其衰减程度依赖于L－Arg剂量。结论：VSMd的L－Arg-NO通路参与延髓心血管中枢对AP的调控,其机制之一可能是通过cGMP抑制VSMd内的谷氨酸能神经突触。     

Serotonin-mediated cardiovascular responses to electrical stimulation of the raphe nuclei in the rat.

The dorsal and median raphe nuclei in rats were electrically stimulated and blood pressure and heart rate were recorded. Stimulation of each raphe nucleus caused an increase in blood pressure without affecting heart rate. The size of the increase in blood pressure depended upon the stimulus-intensity.Significant increases were already obtained with 5 sec. trains of 0.3 msec., 200 μA stimuli given at a frequency of 50 Hz. The increases in blood pressure could be obtained with electrodes within the raphe nuclei.Pretreating rats with para-chlorophenylalanine (pCPA, 100 mg/kg.day for 3 days) significantly diminished the increases in blood pressure obtained during electrical stimulation of the median raphe nucleus. However, similar pretreatment did not affect blood pressure rises induced by dorsal raphe stimulation.These data are discussed in relation to the role of central serotoninergic mechanisms in cardiovascular control.     

大鼠延髓尾端加压区微量注射L—精氨酸对血压、心率和肾灌流压的影响

目的：研究NO前体L-Arg微量注入大鼠延髓尾端加压区（CPA）对心血管活动的影响。并探讨其可能的机制。方法：采用延髓腹外侧部微量满面主射法,以整体灌流肾为模型观察与NO代谢有关的试剂对心血管活动的影响。结果：（1）CPA内微量注入L-Arg(60-100nmodl)。动脉血压与心率呈剂量依赖性下降,肾灌流压下降,与生理盐水对照,差异有显著意义;（2）预先在CPA内注入鸟苷酸环化酶抑制剂甲基蓝可取消L-Arg的降压降肾灌流压作用;（3）CPA内注入lu,AP上升,如预先注入L-Arg后5min再注入L-Glu,L-Glu的升压效应被衰减,期衰减程度与L-Arg是剂量依赖性关系。结论：CPA内的L-Arg-NO通路参与延髓心血管中枢对AP的调控,其机制之一可能是通过cGMP抑制CPA内谷氨酸能神经突触。     

The capacitive function of the spleen during electrical stimulation of the structures of the ventral section of the medulla oblongata

In acute experiments on cats under perfusion with constant blood expenditure of hemodynamically isolated spleen the authors studied the reactions of its vessels in the electrical stimulation of ventral brainstem. It was shown that the stimulation of the rostral zone of these structures increased vein outflow from the spleen. It was shown the deterioration of the parametres which characterize a capacitance function of the spleen by stimulation of a causal depressor zone of the brainstem by means of the current of threshold size and its increase by irritation of the brain structures with a 2 threshold current size. There have been made a supposition has been made about the participation of the pointed structures of the brain in the regulation of a vasomotion tonus of the spleen vessels.     

Substance P in the ventrolateral medulla oblongata regulates ventilatory responses.

Local injection of substance P (SP) into the ventral portion of the nucleus gigantocellularis, nucleus reticularis lateralis, and nucleus retrofacialis of the ventrolateral medulla oblongata (VLM) or direct application on the ventral surface of the medulla oblongata caused marked stimulation of tidal volume (VT) and/or minute ventilation (VE). The ventilatory response to hypoxia was significantly blunted after SP in the VLM but not in the dorsal medulla oblongata (DM) (nucleus tractus solitarius). The SP antagonist [D-Pro2,D-Trp7,9]SP almost completely inhibited this response when applied locally to a wide area of the superficial layer of the VLM but not of the DM. Unilateral or bilateral application of 0.3-1.5 nmol of the SP antagonist in the VLM (corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment) markedly attenuated the response to a 5% CO2 inhalation. The inhibition of the CO2 response was seen after [D-Pro2,D-Trp7,9]SP in the rostral areas of the medulla oblongata corresponding to the corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment of the cervical cord. Electric somatosensory-induced ventilatory stimulation could be depressed by approximately 70% by [D-Pro2,D-Trp7,9]SP locally applied on the surface of the VLM. We conclude that SP is involved in the hypoxic, hypercapnic, and somatosensory ventilatory responses in the rat. However, these respiratory reflexes are mediated via different neuronal pools in the medulla oblongata, mainly the VLM.