Identification of medullary loci critical for neurogenesis of gasping

We hypothesized that a discrete medullary locus, critical for gasping neurogenesis, could be identified. In decerebrate, cerebellectomized, vagotomized, paralyzed, and ventilated cats, activities of phrenic, hypoglossal, and recurrent laryngeal nerves were monitored. Gasping was induced by freezing the brain stem, via a fork thermode, at the pontomedullary junction. By reversible cooling of the medulla, chemical lesions with kainic acid, and radio-frequency lesions, a critical area for gasping neurogenesis was localized bilaterally 2-3 mm rostral to obex, 2.0-2.5 mm lateral to midline, and 3-4 mm ventral to medullary surface. Electrical stimulation in this area elicited premature gasps, whereas unilateral lesions or lidocaine injections eliminated gasping activities in all nerves. These procedures did not cause similar changes during eupnea. In apneusis, however, lidocaine injections markedly altered the pattern or caused apnea. We conclude that discharge of neurons in a discrete portion of the lateral tegmental field of medulla is required for gasping neurogenesis. Our results are consistent with these neurons comprising the central pattern generator for gasping.     

Independent brain stem sites for ventilatory neurogenesis

The purpose was to determine if independent ventilatory rhythms could be generated in each half of completely separated brain stems. In decerebrate, cerebellectomized, vagotomized, paralyzed, and ventilated cats, activities of phrenic, recurrent laryngeal (RLN), and/or hypoglossal nerves were monitored. Midsaggital brain stem divisions were performed by sections and lesions. Eupnea continued following divisions of mesencephalon and pons. Hypoglossal and phrenic activities were eliminated after sections approximating the obex. In most preparations, RLNs discharged with independent rhythms after completion of midsagittal brain stem section and a C1 transection. Independent rhythms were also obtained from each half of medulla following transections at the pontomedullary junction and at C1, and midsagittal medullary divisions. In other animals with transections between pons and medulla and at C1, synchronized RLN and hypoglossal activities persisted after sagittal medullary divisions, 2.0 mm lateral to midline contralaterally. Data demonstrate that there is more than one potential brain stem site for ventilatory neurogenesis. It is hypothesized that there are many such sites, possibly having pacemaker cells, in pons and medulla.     

Inspiratory neuron activity in the ventrolateral medulla of the dog

The purpose of this study was to describe the distribution and activity pattern of respiratory neurons located in the ventrolateral medulla (VLM) of the dog. Spike activity of 129 respiratory neurons was recorded in 23 ketamine-anesthetized spontaneously breathing dogs. Pontamine blue dye was used to mark the location of each neuron. Most VLM neurons displaying respiratory related spike patterns were located in a column related closely to ambigual and retroambigual nuclei. Both inspiratory and expiratory neurons were present with inspiratory units being grouped more rostrally. The predominant inspiratory neuron firing pattern was "late" inspiratory, although eight "early" types were located. All expiratory firing patterns were the late expiratory variety. Each neuron burst pattern was characterized by determining burst duration (BD), spikes per burst (S/B), peak frequency (PF), time to peak frequency (TPF), rate of rise to peak frequency (PF/TPF), and mean frequency. CO2-induced minute ventilation increases were associated with decreases in BD and TPF and increases in PF, S/B, and PF/TPF. In 11 experiments the relative influences of vagotomy and tracheal occlusion on late inspiratory units were compared. Tracheal occlusion increased late inspiratory BD and S/B but did not alter PF/TPF. Vagotomy increased BD and S/B beyond those obtained by tracheal occlusion and, in some neurons, decreased the PF/TPF. We conclude that the location of respiratory units in the VLM of the dog is similar to that in other species, the discharge pattern of VLM respiratory units is similar to those in cat VLM, and vagotomy and tracheal occlusion affect discharge patterns differently.     

Respiratory bursts at the midline of the rostral medulla of the lamprey

The contribution of a rostral crossed pathway to the coordination of fictive breathing was tested in isolated brains of adult lampreys, Ichthyomyzon unicuspis. Periodic bursts of small spikes were recorded at the midline at the rostral level of the V motor nuclei. These occurred prior to bursts by respiratory motoneurons in the IX-X cranial nerve roots. The bursts at the midline could be generated in the rostral half of the medulla, since they continued after isolation of the isthmic-trigeminal region by transections. Stimulation at the rostral midline excited respiratory motoneurons monosynaptically and could entrain or reset the respiratory rhythm. Sections of the midline sparing the rostral site still permitted bilateral synchronization of respiratory bursts. Alternatively, sections of the rostral midline still allowed coordination of respiratory bursts through crossed caudal pathways, although abnormal timing patterns were observed. It is concluded that the motor pattern for respiration is partly generated and coordinated in the rostral half of the medulla of the lamprey and is transmitted to respiratory motoneurons through descending pathways.     

大鼠心率变异性频谱中高频成分的中枢机理分析

本文探讨心率变异性（ＨＲＶ）频谱中高频成分的中枢机理。对正常ＳＤ大量给予不同频率的人工通气并电刺激延髓疑核,观察ＨＲＶ频谱的改变,记录与呼吸节律同步的延髓头端腹外侧区（ｒＶＬＭ）及其周围区神经元细胞外单位放电,对ＨＲＶ和放电变异性进行相干函数分析。结果显示：（１）ＨＲＶ的高频成分的中心频率随着人工通气频率的增加而增加,呈高度线性相关,（ｒ＝０．８３,Ｐ〈０．０００１）;（２）对ｒＶＬＭ及其周围区与     

刺激家兔腹部迷走神经外周端降压效应中枢机制的研究

应用电解损毁和脑室内注射药物的方法研究了刺激家兔腹部迷走神经外周端所致降压效应的中枢机制。结果表明:1.电刺激延脑闩部尾侧1.5—2mm、中线旁开0.25mm、深1—2mm 处主要引起降压反应。2.电解损毁该部位可以使刺激腹部迷走神经外周端所引起的降压效应显著减弱(n=20,P<0.001),但对刺激减压神经所致降压反应无影响。3.在延脑闩部水平电解损毁减压神经纤维在孤束核的主要投射区可以使刺激减压神经所致降压反应显著减弱,而对刺激腹部迷走神经外周端所致降压反应无影响。4.第四脑室注射5,6-双羟色胺的动物较之注射人工脑脊液的动物颈、胸髓5-羟色胺含量明显降低、动物动脉压增高、心率明显增快、刺激减压神经所致降压反应未见减弱,而刺激腹部迷走神经外周端所致降压反应却明显减小。因此,我们认为家兔腹部迷走神经外周端所致降压效应依赖于延脑闩下部的中缝隐核及连合核等结构,而与减压神经的投射部位无关。延脑中缝核至脊髓的下行性5-HT能神经纤维抑制脊髓交感节前神经元的活动,是这个降压效应的中枢机制之一。     

Respiration and airway reflexes after transversal brain stem lesions in cats

The effect of brain stem transection at different levels of the pons Varolii and the medulla oblongata on respiration and on cough and the aspiration and expiration reflex elicited by mechanical stimulation of the relevant parts of the respiratory tract was studied in experiments on 13 anaesthetized, unparalyzed cats. The results of 142 respiratory reflex elicitation tests showed that: 1. Compared with the control state, transection of the upper and middle part of the pons Varolii and transection at the level of the pontomedullary junction reduced the respiration rate (p less than 0.001), increased the duration of inspiration and expiration (p less than 0.001, transection 10 mm rostrally to the obex) and gave rise to apneustic breathing (8 mm), or to tonic, respiration-modulated activity of the phrenic nerve and diaphragm (6 mm). 2. Successive transection of the pons and the pontomedullary junction region led chiefly to a drop in maximum expiratory pleural pressure values (p less than 0.01-0.001) during cough and the expiration reflex and to a drop in maximum inspiratory pleural pressure values during the aspiration reflex (p less than 0.02-0.001). 3. Transection of the upper part of the medulla oblongata always led to permanent arrest of rhythmic respiration, during which cough and the expiration reflex could not be elicited while the aspiration reflex persisted (though in a weakened form). This state was followed by gasping, during which only a highly elicitable aspiration reflex persisted. 4. It can be assumed from the above findings that the central mechanisms responsible for the development of powerful expiratory efforts in cough and the expiration reflex could be localized in the pons Varolii, while those integrating the aspiration reflex are probably localized mainly in the medulla oblongata.     

阻断猫基底动脉引起的延髓缺血和呼吸血压效应的研究

目的 :通过结扎基底动脉主干不同节段观察脑干缺血范围和神经元形态学变化以及呼吸活动和动脉血压的变化 ,为进一步探讨脑干缺血影响呼吸和循环等功能活动的机制和防治措施提供依据。方法 :以猫为实验对象 ,结扎基底动脉主干不同节段 ,分析脑干缺血区血管密度和神经元形态学变化 ,以膈肌肌电和股动脉血压为指标 ,观察呼吸活动和血压的变化。结果 :结扎基底动脉可引起延髓血管密度减小 ,引起延髓缺血。结扎基底动脉不同节段引起的缺血范围有明显重叠 ,缺血区主要位于闩平面吻端的延髓。缺血区神经元胞体肿胀 ,尼氏染色着色变浅 ,尼氏体减少。动物的吸气时程 (TI)和呼气时程 (TE)缩短 ,呼吸频率 (RF)增快 ,平均动脉血压 (MBP)下降 ,均P <0 .0 5,呼吸幅度 (A)无明显变化。结论 :基底动脉不同节段对延髓的血液供应有明显重叠 ,延髓缺血可引起呼吸和血压改变 ,延髓缺血性神经元损伤是引起呼吸、血压改变的结构基础     

Projection of ventrolateral medullary (A1) catecholamine neurons toward nucleus tractus solitarii

Summary The distribution and interconnections of brainstem catecholamine cell groups thought to be important in cardiovascular control were studied using histochemical and ultrastructural techniques in the rabbit. Lesions and microinjections of horseradish peroxidase (HRP) were made in the nucleus tractus solitarii in the dorsomedial medulla, and in the ventrolateral medulla. After lesions of the dorsomedial medulla the fluorescence intensity of the Al-group of catecholamine neurons was increased, and swollen axons could be seen coursing from the ventrolateral medulla toward the lesions on the same side, but not the opposite side. Most of these axons ran in a band about 2 mm in width, centered at the level of the obex. Electron microscopically, specific cells, identified as A1-catecholamine neurons, showed evidence of chromatolysis after the dorsomedial lesions. Following injection of HRP into the nucleus tractus solitarii, A1-catecholamine cells in the ventrolateral medulla on the same side contained the reaction product. Lesions of the ventrolateral medulla did not produce evidence of a reciprocal projection of A2-catecholamine neurons toward the ventrolateral medulla.Thus axons of the A1-group of catecholamine neurons in the ventrolateral medulla project toward the ipsilateral nucleus tractus solitarii in a relatively compact band at the level of the obex. On the other hand, the A2-group of catecholamine neurons in the dorsomedial medulla does not appear to send projections toward the A1-group.These studies were supported by grants from the National Heart Foundation of Australia and The Life Insurance Medical Research Fund of Australia and New Zealand, and Merck Sharp and Dohme (Australia) Pty Limited     

Activity of bulbar respiratory neurones during cough and other respiratory tract reflexes in cats

Changes evoked by mechanical stimulation of the relevant parts of the respiratory tract in the activity of inspiratory and expiratory neurones in the ventral respiratory group of the medulla oblongata, and in pleural pressure and the diaphragmatic electromyogram, were determined during cough, sneeze and the aspiration and expiration reflexes in 17 anaesthetized (but not paralysed) cats. The results of 72 tests of elicitation of the given reflexes showed that: Compared with the control inspiration, both the mean and the maximum discharge frequency of spontaneously active inspiratory neurones rose during the inspiratory phase of cough, sneeze and the aspiration reflex. Regular recruitment of new inspiratory units was also observed in the inspiratory phase of cough and the aspiration reflex. Compared with the control expiration, both the mean and the maximum discharge frequency of spontaneously active expiratory neurones rose during the cough, sneeze and expiration reflex effort. Recruitment of latent expiratory neurones was always observed in the expulsive phase of the given respiratory processes. The recruitment of latent expiratory neurones was accompanied by reciprocal inhibition of the activity of inspiratory units and recruitment of latent inspiratory neurones by inhibition of the activity of expiratory units and recruitment of latent inspiratory neurones by inhibition of the activity of expiratory units. Regular recruitment of the same expiratory neurones in all expulsive respiratory processes, together with the similar incidence of inspiratory neurones in the inspiratory phase of sneeze and the aspiration reflex, indicates that they are "nonspecific" in character.     

Raphe modulation of the pre-Bötzinger complex respiratory bursts in in vitro medullary half-slice preparations of neonatal mice

Spontaneous respiratory bursts which begin in the pre-Bötzinger complex were recorded from the hypoglossal (XIIth) nerve rootlets of in vitro slices prepared from newborn mice. First, we examined the respiratory bursts before and after a midline or para-midline transection which spared the caudal raphe nuclei: the raphe obscurus and raphe pallidus. After a midline transection, the respiratory bursts in both half-slices were desynchronized and had slightly decreased amplitudes and frequencies. After a para-midline transection, the bursts continued with similar frequencies in the half slice containing the raphe obscurus and raphe pallidus. Second, to analyze the effects of modulation by the raphe obscurus and raphe pallidus, a dorsal or ventral midline lesion was used to damage either the raphe obscurus or raphe pallidus. After a dorsal lesion, the synchronized respiratory bursts persisted with slightly decreased frequencies. In contrast, after a ventral lesion, the bursts were almost completely abolished, but recovered significantly after the addition of 5-HT. The present results demonstrated that the pre-Bötzinger complex on each side of the medulla can independently generate rhythmic respiratory activity. It is suggested that the 5-HT released from the ventral part of the raphe nuclei (predominantly the raphe pallidus) plays a critical role in sustaining rhythmic respiratory bursts.     

缓冲神经在刺激兔下丘脑诱发室性期前收缩中的作用

1.静脉注射氰化钾(0.3mg/kg)可引起血压升高和室性心律失常,并能使刺激下丘脑诱发的室性期前收缩增多。去除双侧窦神经后,上述现象消失。2.刺激降压神经时,刺激下丘脑诱发的室性期前收缩显著减少。3.切断双侧缓冲神经后短时内,刺激下丘脑诱发的室性期前收缩极度增多,并且不易被躯体传入冲动所抑制。二小时后,这种室性期前收缩减少,且可为刺激腓深神经所抑制。4.电刺激延髓中线区不仅可以降低血压,而且能减弱刺激下丘脑诱发的升压反应、抑制刺激下丘脑诱发的室性期前收缩。损毁该区后,刺激腓深神经不再能抑制刺激下丘脑诱发的室性期前收缩。5.上述结果表明:化学感受性反射能易化刺激下丘脑诱发的室性期前收缩,而压力感受性反射可以抑制这种室性期前收缩,但躯体传入冲动对这种心律失常的抑制作用并不依赖于缓冲神经的存在,而有赖于延髓中线核群的完整性。     

Cough and laryngeal muscle discharges in brainstem lesioned anaesthetized cats

Experiments were carried out to determine whether there are separate drives from the selected neuronal networks of the brainstem affecting the discharge patterns of laryngeal and respiratory pump muscles during cough. Twenty-four non-decerebrate spontaneously breathing cats anesthetized with sodium pentobarbitone were used. Microinjections of kainic acid into the lateral tegmental field of the medulla, medullary midline or pontine respiratory group eliminated the cough evoked by mechanical stimulation of the tracheobronchial and laryngopharyngeal mucosa. These stimuli, in most cases, provoked irregular bursts of discharges in the posterior cricoarytenoid and thyroarytenoid laryngeal muscles (or they had no effect on them). No pattern of laryngeal muscle activities following lesions resembled the laryngeal cough response. Lesions of the target regions did not result in any apparent changes in the eupnoeic pattern of laryngeal activity. Neurons of the medullary lateral tegmental field, raphe nuclei and the pontine respiratory group seem to be indispensable for the configuration of the central cough motor pattern. However, these neurons do not appear to be essential for the discharge patterns of laryngeal motoneurons during eupnoea. The residual laryngeal "cough" responses are probably mediated by an additional motor drive.     

Glutamate receptors in RVLM modulate sympathetic baroreflex in conscious rabbits

In this study, we examined the effect of excitatory amino acid (EAA) receptor blockade in the rostral ventrolateral medulla (RVLM) on the renal sympathetic baroreflex in conscious rabbits. Rabbits were implanted with guide cannulas for bilateral microinjections into the RVLM (+2 to +3 mm from the obex, n = 8) or into the intermediate ventrolateral medulla (IVLM; 0 to +1 mm from the obex, n = 5) and with an electrode for measuring renal sympathetic nerve activity (RSNA). After 7 days of recovery, microinjection of the EAA receptor antagonist kynurenate (10 nmol) into the RVLM did not affect resting RSNA or arterial pressure. Kynurenate decreased the gain of the RSNA baroreflex by 53% but did not change the reflex range. By contrast, injection of kynurenate into the IVLM increased resting arterial pressure and RSNA by 27 mmHg and 88%, respectively, but did not alter the RSNA baroreflex gain or range. Pentobarbital sodium anesthesia attenuated the gain and range of the RSNA baroreflex by 78 and 40%, respectively. Under these conditions, microinjection of kynurenate into the RVLM did not cause any further change in the gain of this reflex. These results suggest that endogenous EAA neurotransmitters in the RVLM are important in modulating the sympathetic baroreflex in conscious rabbits. Anesthesia can mask the functional significance of EAAs in the RVLM in modulating the baroreflexes, which may explain why previous studies in anesthetized animals found no effect of blocking EAA receptors in the RVLM on sympathetic baroreflexes.     

家兔延髓腹侧区在吗啡抑制呼吸机制中的作用

实验在36只麻醉、制动和人工通气的家兔上进行。探讨了延髓腹侧区在吗啡引起呼吸抑制机制中的作用。结果观察到:将浸透吗啡药液的滤纸片敷贴于延髓腹侧面的S区,可以引起膈神经放电抑制;将纳洛酮置于同一区域可翻转吗啡的效应;谷氨酸钠用于S区可引起膈神经放电加强;脑桥臂旁内侧核(NPBM)微量注射吗啡引起的膈神经放电抑制效应可被钠洛酮用于S区所预防;电刺激NPBM 主要引起延髓腹侧区单位放电的抑制反应,在这些出现抑制反应的单位中,大部分对微电泳给予吗啡也表现为放电的抑制。上述结果表明,家兔延髓腹侧区存在能激活膈神经放电的神经元;将吗啡微量注射于 NPBM,可通过激活延髓腹侧区的阿片受体使该区域某些神经元抑制,进而引起膈神经放电的抑制。     

非NMDA受体参与双相呼气和吸气神经元电活动的调节

在新生大鼠延髓脑片上同步记录舌下神经根和双相呼气神经元／吸气神经元单位的放电活动,并在灌流的改良Kredbs液中先后加以非NMDA受体的激动剂KA和拮抗剂DNQX,观察对神经元单位放电的影响,以进一步探讨非NMDA受体在对双相呼气神经元之间交互兴奋和吸气神经元兴奋性突触输入中的作用,结果表明,使用非NMDA受体激动剂KA以后,双相呼气神经元的放电频率和蜂频率都明显增大,吸气神经元中期放电的频率和非NMDA受体激动剂KA以后,双相呼气神经元的放电频率和峰频率都明显增大,吸气神经元中期放电的频率和峰频率也显著增大,而早期和晚期放电的频率无明显改变,用相应拮抗剂以后,上述效应明显被抑制,结果提示,非NMDA受体参与了双相呼气神经元之间的交互兴奋作用,并且也介导了吸气神经元的兴奋性突触输入／     

Retrofacial lesions: effects on CO2-sensitive phrenic and sympathetic nerve activity.

We made unilateral chemical (10- or 50-nl microinjections; 4.7 mM kainic acid) or electrolytic (5-15 mA; 15 s) lesions in a region of the rostral ventrolateral medulla (VLM) caudal to the retrotrapezoid nucleus in 10 decerebrate, paralyzed, vagotomized, and servo-ventilated cats. The lesions were 3.0-4.2 mm lateral to the midline, within 2 mm caudal to the facial nucleus, and within 2.5 mm of the VLM surface. Four control injections (mock cerebrospinal fluid and fluorescent beads alone) produced small and inconsistent effects over 3-5 h. The predominant effect of the lesions was a significant decrease in baseline integrated phrenic nerve amplitude (PNA) (apnea in 2 cases), total respiratory cycle duration, and the response to increased CO2 (slope < 15% of control in 3 cases). The respiratory-related peak amplitude of the integrated sympathetic signal, blood pressure, and the sympathetic nerve activity response to CO2 were also decreased after the majority of lesions. Not all lesions produced all effects, and some lesions resulted in increased PNA and respiratory cycle duration. The lesioned region appears functionally to represent a caudal extension of the retrotrapezoid nucleus containing neurons necessary for normal baseline PNA and CO2 sensitivity. In addition, it contains neurons involved in the determination of resting respiratory frequency and normal sympathetic activity and blood pressure. The pattern of mixed responses among animals suggests that a heterogeneity of function is present within a relatively small VLM region.     

Identification of a subsurface area in the ventral medulla sensitive to local changes in PCO2.

The exact location of the central respiratory chemoreceptors sensitive to changes in PCO2 has not yet been determined. To avoid the confounding effects of the cerebral circulation, we used the in vitro brain stem-spinal cord of neonatal rats (1-5 days old) to identify areas within 500 microns of the ventral surface of the medulla where changes in PCO2 evoked a sudden increase in the rate of respiratory neural activity. The preparation was superfused with mock cerebrospinal fluid (CSF) while maintained at constant temperature (26 +/- 1 degrees C) and pH (7.34). Respiratory frequency increased linearly with decreases in superfusate pH (r2 = 0.92, P less than 0.001), indicating that the respiratory circuitry for the detection of CO2 and stimulation of breathing was intact in this preparation. The search for central chemoreceptors was performed with a specially designed micropipette that allowed microejection of 2-10 nl of mock CSF equilibrated with different CO2-O2 gas mixtures. The pipette was advanced in 50- to 100-microns steps by use of a microdrive to a maximum depth of 500 microns from the surface of the ventral medulla. Depending on the location of the micropipette, ejection of CO2-acidified mock CSF at depths of 100-350 microns below the ventral surface of the medulla stimulated neural respiratory output. Using this response as an indication of the location of central respiratory chemoreceptors, we found that chemoreceptive elements were located in a column in the ventromedial medulla extending from the hypoglossal rootlets caudally to an area 0.75 mm caudal to VI nerve in the rostral medulla.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory pattern generation in adult lampreys (Lampetra fluviatilis): interneurons and burst resetting

The central pattern generator for the respiratory rhythm in adult lampreys was studied in isolated brain preparations. At least three different types of respiratory units were found in intra- and extracellular recordings near the trigeminal nucleus (Fig. 1), including: units that start firing before the motorneurons, recorded from the ventral surface (Figs. 2 and 3), follower cells near rostral nucleus V (Fig. 4), units bursting after the motorneurons, found in the sulcus limitans (Figs. 5 and 6). Transections of the medulla indicated that the rostral half of nucleus V could be removed without reducing the respiratory frequency (Fig. 8). The earliest respiratory events that could be recorded from the ependymal surface or the cranial nerves were observed near nuclei IX-VII-caudal V during quiet breathing. There was a rostrocaudal delay in the onset of bursts of more caudal motorneurons (Figs. 9, 10, and 12). The rostrocaudal delay became reversed, such that bursts started earlier in n.X than n.IX, during episodes of intense breathing that were accompanied by prolonged discharges in the medial reticular formation (Fig. 11). Stimulation of the medulla surface, near the base of nerve V, could trigger bursts prematurely and reset the timing of the respiratory rhythm, yielding a discontinuous phase response curve (Fig. 14). In sum, 6 types of respiratory interneurons can presently be distinguished (Fig. 15). The sulcus limitans near nucleus V is a candidate location for components of the pattern generator.