正常猫膈神经单纤维电活动特征

在麻醉猫和麻痹的切断迷走神经的清醒猫,观察了膈神经单纤维电活动特征。1.电活动类型:按膈神经单纤维放电与其总干放电的相位关系分为三种类型。(1)完全同步型,即单纤维放电与总干放电同时开始并同时停止,占76.9％。(2)部分同步型占15.4％,其中早期同步,即单纤维放电与总干放电同时开始,但提前终止,占1.9％,中期同步,即单纤维放电较总干放电开始晚,又提前终止,占5.8％,晚期同步,即单纤维放电较总干放电开始晚,但两者同时终止,占7.7％。(8)非同步型,即吸气相和呼气相都有放电,但呼气相时冲动频率较低,占7.7％。前两型为单纯的吸气性放电,共占92.3％。2.单纤维放电平均参数值:麻醉猫每次吸气发放11个冲动,其频率为21次/秒,清醒猫每次吸气发放18个冲动,其频率为34次/秒。结果表明:猫膈神经单纤维放电类型和文献上报导的直接记录膈神经运动神经元放电一致,即以单纯的吸气性放电为最多。     

吸入刺激性气体对迷走神经传出纤维单位放电的影响

记录兔迷走神经传出纤维单位放电,并观察SO_2及氨水刺激对它放电的影响。 共记录到68支传出单纤维放电,其形式可大致分为四个类型。 Ⅰ型:有一个快而短促的吸气相放电,在吸入SO_2或氨水时,以及由气管内抽气时,频率增加;向气管内注入空气时,则频率降低。 Ⅱ型:吸气期放电频率高,呼气期频率低。吸入SO_2或氨水后发放冲动增多;但向气管内注入空气或抽出空气对放电活动没有影响。 Ⅲ型:呈现不规则的与吸节律无明显关系的放电活动。这些纤维对上述刺激均不发生反应. Ⅳ型:通常没有自发性发放,只是在给予SO_2或氨水刺激后以及向管内注入空气或抽出空气后,才出现高波幅的呼气相放电。 对照我们过去的实验,ⅠⅡⅣ三类纤维可能是支配呼吸道的迷走传出纤维,给SO_2或氨水吸入刺激放电频率增加,大概是由于刺激了支气管内激惹型感受器,反射性引起支气管收缩。     

延髓腹外侧Btzinger复合体呼吸时相转换效应的研究

实验在４０只氨基甲酸乙酯麻醉的成年家兔上进行，观察电刺激Ｂ¨ｏｔｚｉｎｇｅｒ复合体（Ｂ¨ｏｔＣ）对呼吸节律的影响。结果表明：（１）吸气相早期短串电刺激Ｂ¨ｏｔＣ导致膈神经放电被短暂抑制，被抑制的程度与刺激强度呈正相关。当刺激落位在吸气相中、晚期时，可导致吸气提前终止（“吸气切断”），之后跟随一缩短的呼气相。导致“吸气切断”的阈强度与刺激落位呈负相关。（２）呼气相短串电刺激Ｂ¨ｏｔＣ，可诱导膈神经短暂放电，呼气相晚期诱导出现放电之后往往跟随一正常的吸气放电，结果导致该呼气相缩短。该效应亦具有刺激强度、刺激落位依赖性。结果提示：Ｂ¨ｏｔＣ参与吸气向呼气以及呼气向吸气的时相转换。     

刺激兔皮层感觉运动区和静注士的宁引起的肋间神经放电效应

在30例清醒,肌肉麻痹、切断迷走神经的家兔,观察到刺激对侧皮层感觉运动区时,胁间神经的放电效应包括两种成分。在呼气相电刺激,肋间外神经的第一效应表现为短暂的放电,肋间内神经表现为呼气放电的抑制;在吸气相电刺激,肋间外神经的第一效应表现为吸气放电的抑制,肋间内神经表现为短暂的放电。肋间外神经的第二效应表现为吸气放电的提前出现,吸气时程和呼气时程的缩短;肋间内神经的第二效应表现为吸气时程的缩短和呼气时程的延长,呼气放电的幅度明显增加。上述结果说明,皮层直接控制脊髓的通路既能兴奋也能抑制肋间吸气或呼气运动神经元的活动,且吸气与呼气运动神经元之间表现交互抑制。静注士的宁引起肋间神经梭形放电的发生过程和放电频率,与膈神经上表现相同;但恢复过程不同,膈神经上吸气放电恢复早,肋间神经上呼吸性放电恢复迟。此外,肋间神经的呼吸性放电不具有高频振荡现象。     

延髓腹外侧B(x)tzinger复合体呼吸时相转换效应的研究

实验在40只氨基甲酸乙酯麻醉的成年家兔上进行,观察电刺激Btzinger复合体(Bt.C)对呼吸节律的影响.结果表明: (1)吸气相早期短串电刺激Bt.C导致膈神经放电被短暂抑制,被抑制的程度与刺激强度呈正相关.当刺激落位在吸气相中、晚期时,可导致吸气提前终止("吸气切断"),之后跟随一缩短的呼气相.导致"吸气切断"的阈强度与刺激落位呈负相关.(2)呼气相短串电刺激Bt.C,可诱导膈神经短暂放电,呼气相晚期诱导出现放电之后往往跟随一正常的吸气放电,结果导致该呼气相缩短.该效应亦具有刺激强度、刺激落位依赖性.结果提示: Bt.C参与吸气向呼气以及呼气向吸气的时相转换.     

家兔人工通气和窒息时刺激舌咽神经对膈神经放电和血压的影响

切断大鼠舌咽神经(包括窦神经)可导致通气反应减弱。刺激舌咽神经可引起膈神经放电抑制,呼气相刺激则诱发成束放电。吸气相刺激舌咽神经咽支引起膈神经放电加强,呼气相出现兴奋反应。但是,舌咽神经舌支能否影响呼吸和血压,咽支对血压有无影响尚不清     

刺激兔丘脑不同核团和胼胝体引起的膈神经放电效应

实验在33例清醒、肌肉麻痹和切断双侧迷走神经的家兔上进行,观察了刺激丘脑不同核团(VIL,VL,VPM 和 MI)和胼胝体纤维以激活皮层时膈神经的放电效应。当在吸气相(膈神经放电时)给予上述核团及胼胝体纤维电脉冲刺激,可使膈神经放电短暂抑制,随后的呼气相缩短、吸气相提前出现。如果在呼气相刺激上述核团,也能使该呼气时相缩短,随后的吸气时相提前出现。当在皮层接受 VL 投射的局部区域给予回苏灵后,再刺激 VL,皮层诱发电位增大,除使原先的膈神经放电效应更为明显外,还可在呼气相刺激时引起膈神经即刻的短暂放电。以上实验结果提示,当用回苏灵使皮层活动加强后,刺激丘脑 VL 引起的膈神经放电效应明显增强。损毁红核或切断皮层下行传导束但保留皮层脊髓束后,刺激丘脑引起的膈神经放电效应均不受影响,表明传入冲动激活皮层后引起的膈神经放电效应可能主要经皮层脊髓束下传,而皮层红核脊髓束不起重要作用。     

家兔膈神经呼气相电活动的观察

在52只麻醉兔和4只清醒兔上均观察到,自然呼吸时膈神经于呼气相有紧张性放电。同时引导膈肌肌电表明这种活动与膈肌紧张性的维持有关。这种电活动在切断引导电极外周段的膈神经后仍然存在。通气量不足、动脉血 PCO_2增加或 PO_2减少使其减少或消失;吸入纯氧或过度通气引起相反效应。切断窦神经或延髓腹外侧面化学敏感区局部贴敷浸有普鲁卡因的滤纸片,使膈神经呼气相放电增强;颈动脉窦区注入30—75μg NaCN 或将 pH=6的酸性人工脑脊液滤纸片贴于延髓化学敏感区,使膈神经呼气相放电减弱。本工作提示正常血气浓度及其变化经相同的外周和中枢化学感受机制同时发动两种调节过程:1.通过调节吸气肌位相性活动而调节肺通气量;2.通过调节吸气肌呼气相紧张性活动而调节肺机能余气量。     

呼吸道迷走神经感受器概述

肺以及气道与外界环境之间存在着巨大的界面,因此需要有效的防御反射机制。呼吸道感受器是肺部神经反射的起始点,其重要性不言而喻,采用组织,解剖与电生理学方法,经过一个世纪的研究,我们对于呼吸道感受器的认识,特别对其结构的认识,仍然有限,据电生理实验结果,肺部感受器至少可被分为三大类;慢适应感受器,快适应感受器以及C纤维感受器,按血供来源,后者又可分为气道（体循环）与肺（肺循环）两类,近来发现呼吸道中存在着第四类感受器,它们由迷走神经的Aδ传入纤维传递冲动,其放电活动不同于上述各类,对肺充气反应阈值高,故称之为高阈值Aδ感受器,功能上前两类基本属于机械性感受器,而后两类可归为化学敏感性感受器,另外,用组织学方法,观察到气道内有一些神经内分泌细胞,它们可以散在分布,亦可集聚成小体。这些神经上皮小体受多种神经支配,其结构复杂,形态酪似感受器,虽然我们对其形态了解颇深,但对其放电形式一无所知,本文对以上各类感受器进行了评述与探讨。     

家兔孤束核区微量注射羟基马桑毒素对膈神经放电的影响

实验在44只乌拉坦麻醉、肌肉麻痹、切断双侧颈迷走神经的日本大耳白兔上进行。于一侧孤束核区微量注射不同浓度(0.1μg/μl,1μg/μl,5μg/μl,10μg/μl)的羟基马桑毒素1μl,可以引起膈神经放电活动产生可逆的吸气时程和呼气时程缩短,呼吸频率加快及膈神经放电积分的峰幅度降低。羟基马桑毒素0.1μg/μl组作用最弱,1μl/μl组作用最强。5μg/μl组,10μg/μl组还可使膈神经放电活动在呼气期出现短时的吸气性放电及呼气期间歇性不规则延长等呼吸节律紊乱现象。出现上述现象时血压、心率无明显变化,脑电图也未出现异常改变。结果提示:家兔孤束核区参与呼吸时相的转换,而羟基马桑毒素可能作用于孤束核区的呼吸时相转换机制,促进呼吸时相的转换。     

Effects of ouabain and flecainide on CO(2)-induced slowly adapting pulmonary stretch receptor inhibition in the rabbit

The inhibitory effect of CO2 on slowly adapting pulmonary stretch receptors (SARs) was examined before and after administration of ouabain, a Na+-K+ ATPase inhibitor, and flecainide, a Na+ channel blocker. The experiments were performed in anesthetized, artificially ventilated rabbits after vagus nerve section. CO2 inhalation (maximal tracheal CO2 concentration ranging from 9.2 % to 10.4%) for about 60 sec decreased the receptor activity during both inflation and deflation. The magnitude of decreased SAR activity during deflation was greater than that seen during inflation. Administration of ouabain (25 microg/kg) initially stimulated SAR activities during inflation and deflation, and after 20 min, the SAR response was still kept excitatory in both inflation and deflation phases. Under these conditions, CO2 inhalation inhibited SAR activities during inflation and deflation. Flecainide treatment (3 mg/kg) that abolished veratridine (30 microg/kg)-induced SAR excitation had no significant effect on the inhibitory responses of SAR activity to CO2. These results suggest that the inhibitory effect of CO2 occurs when ouabain results in intracellular Na+ concentration ([Na+]i) increases in the SAR endings, and that CO2-induced SAR inhibition may not be related to the reduction of influx of Na+ through voltage-gated Na+ channels.     

Inhibitory mechanism of slowly adapting pulmonary stretch receptors after release from hyperinflation in anesthetized rabbits

In anesthetized, artificially ventilated rabbits with vagus nerve section, release from 10 consecutive hyperinflations (inflation volume = 3 tidal volume) caused an inhibition of the slowly adapting pulmonary stretch receptor (SAR) activity for 16-22 sec. Intravenous administration of tetraethylammonium (TEA, 10 and 20 mg/kg), a K+ channel blocker, did not significantly alter either basal SAR discharge or tracheal pressure (PT). Although TEA treatment at 10.0 mg/kg had no significant effect on the magnitude and duration of inhibited SAR activity seen after release from hyperinflation, the increasing dose of this K+ channel blocker up to 20 mg/kg inhibited these effects of the receptor activity but this inhibition was small. The Na+ -K+ ATPase inhibitor ouabain (5 and 10 microg/kg) that had no significant effect on SAR activity and P(T) in the control abolished or attenuated the inhibitory action of SARs in a dose-dependent manner. Furthermore, the changes in dynamic lung compliance (Cdyn) and P(T) in response to post-hyperinflation were not significantly influenced by pretreatment with either TEA or ouabain. These results suggest that the inhibitory action of receptors seen during post-hyperinflation corresponded with the induction of slow afterhyperpolarization (sAHP), and that the mechanism of generating the sAHP of SARs is mainly mediated by the activation of Na+ -K+ pump activity.     

Effects of sodium and potassium channel blockers on hyperinflation-induced slowly adapting pulmonary stretch receptor stimulation in the rat

The excitatory responses of slowly adapting pulmonary stretch receptor (SAR) activity to hyperinflation (inflation volume = 3 tidal volumes) for approximately 10 respiratory cycles were examined before and after administration of flecainide, a Na+ channel blocker, and 4-aminoprydine (4-AP), a K+ channel blocker. The experiments were performed in anesthetized, artificially ventilated rats after unilateral vagotomy. During hyperinflation the SARs increased their activity during inflation and decreased their discharge during deflation. The magnitude of increased SAR activity during inflation became more prominent as compared to that of decreased receptor activity during deflation. Flecainide treatment (6 mg/kg) that was sufficient to block veratridine (50 microg/kg)-induced SAR stimulation did not significantly alter the excitatory response of SAR activity to hyperinflation. Subsequent administration of 3 mg/kg flecainide (a total dose, 9 mg/kg) resulted in a greater inhibition of hyperinflation-induced SAR stimulation. Although administration of 4-AP (2 mg/kg) usually stimulated SAR activity, particularly in the deflation phase, in the control ventilation, 4-AP treatment had no significant effect on hyperinflation-induced SAR stimulation. These results suggest that the excitatory effect of hyperinflation on SAR activity may not be involved in the activation of either flecainide-sensitive Na+ channels or 4-AP-sensitive K+ channels.     

The inhibitory effect of ouabain on the response of slowly adapting pulmonary stretch receptors to hyperinflation in the rabbit

The combined effects of ouabain (Na(+)-K(+) ATPase inhibitor) and hyperinflation (inflation volume=three tidal volumes) on slowly adapting pulmonary stretch receptors (SARs) were studied before and after administration of nifedipine (an L-type Ca(2+) channel blocker) and KB-R7943 (a reverse-mode Na(+)-Ca(2+) exchanger blocker) in anesthetized, artificially ventilated rabbits after bilateral vagotomy. Before ouabain administration, hyperinflation stimulated SAR activity. After 20 min of ouabain administration (30 microg/kg) the SARs increased discharge rates in normal inflation. Under these conditions, hyperinflation initially stimulated SAR activity but subsequently inhibited the activity at peak inflation. Additional administration of 60 microg/kg ouabain (total dose=90 microg/kg) caused a further stimulation of SAR activity, but 20 min later both normal inflation and hyperinflation resulted in a greater inhibition of the receptor activity. The hyperinflation-induced SAR inhibition in the presence of ouabain (30 microg/kg) was not significantly altered by administration of either nifedipine (2 and 4 mg/kg) or KB-R7943 (1 and 3 mg/kg). In another series of experiments, we further examined the combined effects of ouabain and hyperinflation in veratridine (a Na(+) channel opener, 40 microg/kg)-treated animals. After recovery from the veratridine effect on SAR activity, which vigorously stimulated the receptor activity, ouabain treatment (30 microg/kg) that silenced the receptor activity at peak inflation greatly inhibited hyperinflation-induced SAR stimulation. These results suggest that hyperinflation-induced SAR inhibition in the presence of ouabain may be related to a Na(+) overload, but not to a Ca(2+) influx via activation of L-type Ca(2+) channels, in the SAR endings.     

Spectrum of myelinated pulmonary afferents

Myelinated pulmonary afferents are classified as rapidly adapting receptors (RARs) or slowly adapting receptors (SARs) by their adaptation rate. Behavior of SARs varies greatly, and therefore the present study tries to further categorize SARs according to their mechanical properties. Single-fiber activity of 104 SARs was examined in anesthetized, open-chest, artificially ventilated rabbits. According to the increase or decrease in activity during removal of positive-end-expiratory pressure (PEEP), SARs were divided into two groups. In one group mean activity increased from 31 +/- 6 to 46 +/- 7 impulses per second (imp/s; n = 11); in another group mean activity decreased from 44 +/- 2 to 25 +/- 1 imp/s (n = 93). The first group of SARs has high adaptation indexes (RAR-like), which increased with inflation pressure (36 +/- 3, 44 +/- 3, and 47 +/- 3% for 10, 15, and 20 cmH(2)O, respectively; P < 0.005). Their peak activity shifted from inflation phase to deflation phase during PEEP removal. The second group of SARs has low-adaptation indexes (typical SARs), which were not affected by inflation pressure (19 +/- 1, 18 +/- 1, and 17 +/- 1% for 10, 15, and 20 cmH(2)O; P = 0. 516). Their peak activity did not shift during PEEP removal. Because there are overlaps in other characteristics, it is proposed that myelinated vagal afferents are viewed as a heterogeneous group; their behaviors are like a spectrum, where typical RARs and SARs represent two extremes of the spectrum. The receptor behavior might be determined by anatomic location and its environment.     

Effects of 20-HETE on Na+ transport and Na+ -K+ -ATPase activity in the thick ascending loop of Henle

Previous studies have indicated that 20-hydroxyeicosatetraenoic acid (20-HETE) inhibits Na+ transport in the medullary thick ascending loop of Henle (mTALH), but the mechanisms involved remain uncertain. The present study compared the effects of 20-HETE with those of ouabain and furosemide on intracellular Na+ concentration ([Na+]i), Na+ -K+ -ATPase activity, and 86Rb+ uptake, an index of Na+ transport, in mTALH isolated from rats. Ouabain (2 mM) increased, whereas furosemide (100 microM) decreased, [Na+]i in the mTALH of rats. Ouabain and furosemide inhibited 86Rb+ uptake by 91 and 30%, respectively. 20-HETE (1 microM) had a similar effect as ouabain and increased [Na+]i from 19 +/- 1 to 30 +/- 1 mM. 20-HETE reduced Na+ -K+ -ATPase activity by 30% and 86Rb+ uptake by 37%, but it had no effect on 86Rb+ uptake or [Na+]i in the mTALH of rats pretreated with ouabain. 20-HETE inhibited 86Rb+ uptake by 12% and increased [Na+]i by 19 mM in mTALH pretreated with furosemide. These findings indicate that 20-HETE secondarily inhibits Na+ transport in the mTALH of the rat, at least, in part by inhibiting the Na+ -K+ -ATPase activity and raising [Na+]i.     

Airway mechanoreceptor deactivation.

Airway sensors play an important role in control of breathing. Recently, it was found that pulmonary slowly adapting stretch receptors (SARs) cease after a brief excitation following sodium pump blockade by ouabain. This deactivation can be explained by overexcitation. If this is true, mechanical stimulation of the SARs should also lead to a deactivation. In this study, we recorded unit activity of the SARs in anesthetized, open-chest, and mechanically ventilated rabbits and examined their responses to lung inflation at different constant pressures. Forty-seven of 137 units had a clear deactivation during the lung inflation. The deactivation threshold varied from unit to unit. For a given unit, the higher the inflation pressure, the sooner the deactivation occurs. For example, the SARs deactivated at 3.0 +/- 0.3 and 4.8 +/- 0.4 s when the lungs were inflated to constant pressures of 30 and 20 cmH(2)O, respectively (n = 25, P < 0.0001). The units usually ceased after a brief intense discharge. In some units, their activity shifted to a lower level, indicating a pacemaker switching. Our results support the notion that SARs deactivate due to overexcitation.     

Control of brain slice respiration by (Na+ + K+)-activated adenosine triphosphate and the effects of enzyme inhibitors.

The involvement of membrane (Na+ + K+)-ATPase (Mg2+-dependent, (Na+ + K+)-activated ATP phosphohydrolase, E.C. 3.6.1.3) in the oxygen consumption of rat brain cortical slices was studied in order to determine whether (Na+ + K+)-ATPase activity in intact cells can be estimated from oxygen consumption. The stimulation of brain slice respiration with K+ required the simultaneous presence of Na+. Ouabain, a specific inhibitor of (Na+ + K+)-ATPase, significantly inhibited the (Na+ + K+)-stimulation of respiration. These observations suggest that the (Na+ + K+)-stimulation of brain slice respiration is related to ADP production as a result of (Na+ + K+)-ATPase activity. However, ouabain also inhibited non-K+ -stimulated respiration. Additionally, ouabain markedly reduced the stimulation of respiration by 2,4-dinitrophenol in a high (Na+ + K+)-medium. Thus, ouabain depresses brain slice respiration by reducing the availability of ADP through (Na+ + K+)-ATPase inhibition and acts additionally by increasing the intracellular Na+ concentration. These studies indicate that the use of ouabain results in an over-estimation of the respiration related to (Na+ + K+)-ATPase activity. This fraction of the respiration can be estimated more precisely from the difference between slice respiration in high Na+ and K+ media and that in choline, K+ media. Studies were performed with two (Na+ + K+)-ATPase inhibitors to determine whether administration of these agents to intact rats would produce changes in brain respiration and (Na+ + K+)-ATPase activity. The intraperitoneal injection of digitoxin in rats caused an inhibition of brain (Na+ + K+)-ATPase and related respiration, but chlorpromazine failed to alter either (Na+ + K+)-ATPase activity or related respiration.     

Cardiac glycosides stimulate phospholipase C activity in rat pinealocytes

Ouabain and related cardiac glycosides stimulate phospholipase C activity 5-fold in rat pinealocytes. The combined treatment of ouabain and norepinephrine, which also stimulates phospholipase C, produces an additive effect. The effects of either ouabain or norepinephrine are blocked by EGTA. However, there are notable differences. The stimulatory effect of ouabain is lost when extracellular Na+ is reduced to 20 mM and is not blocked by prazosin. In contrast, the stimulatory effect of norepinephrine is not blocked when extracellular Na+ is reduced to 20 mM but is blocked by prazosin. Ouabain appears to increase phospholipase C activity through a mechanism involving inhibition of Na+,K+-ATPase, and an accumulation of intracellular Na+ and Ca2+, not involving alpha 1-adrenoceptors. These findings raise the possibility that activation of phospholipase C might be a more general effect of cardiac glycosides.     

Half of the (Na+ + K+)-transporting-ATPase-associated K+-stimulated p-nitrophenyl phosphatase activity of gastric epithelial cells is exposed to the surface exterior.

Ouabain inhibited 86RbCl uptake by 80% in rabbit gastric superficial epithelial cells (SEC), revealing the presence of a functional Na+,K+-ATPase [(Na+ + K+)-transporting ATPase] pump. Intact SEC were used to study the ouabain-sensitive Na+,K+-ATPase and K+-pNPPase (K+-stimulated p-nitrophenyl phosphatase) activities before and after lysis. Intact SEC showed no Na+,K+-ATPase and insignificant Mg2+-ATPase activity. However, appreciable K+-pNPPase activity sensitive to ouabain inhibition was demonstrated by localizing its activity to the cell-surface exterior. The lysed SEC, on the other hand, demonstrated both ouabain-sensitive Na+,K+-ATPase and K+-pNPPase activities. Thus the ATP-hydrolytic site of Na+,K+-ATPase faces exclusively the cytosol, whereas the associated K+-pNPPase is distributed equally across the plasma membrane. The study suggests that the cell-exterior-located K+-pNPPase can be used as a convenient and reliable 'in situ' marker for the functional Na+,K+-ATPase system of various isolated cells under noninvasive conditions.