摘要:

AbstractExperiments were performed on cats to explore the integrated cardiovascular responses whenexcitatory(chemoreceptor) andinhibitory(baroreceptor or cardiac receptor) influences are simultaneously presented to the medullary cardiovascular areas. At a given sinus pressure in the low or medium pressure range, the systemic blood pressure and the vascular resistance were higher when the chemoreceptors were stimulated, while a high, pulsating sinus pressure,i.e.a strong baroreceptor stimulation, could suppress completely even an intense chemoreceptor activation. Thus, the set point and the gain of the baroreflex were increased by a concomitant chemoreceptor activation. These effects are compatible with a simple, mutual ‘summation’ of excitatory and inhibitory influences on a common population of central vasomotor neurons. The reflex vasodilator effects elicitedviavagal cardiac afferents were found to be more effectively suppressed by a concomitant chemoreceptor stimulation than were the baroreceptor effects, provided a primary chemoreceptor response (bradycardia) was at hand, while the heart rate responses were essentially uninfluenced by the prevailing chemoreceptor activity. This chemoreceptor suppression of the reflex vasodilatation from cardiac receptors, which may be of great importance in hypoxic situations,e.g.during a dive, suggests a more complex, neuronal interaction between the two reflex mechanisms in the

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10166.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractGastrin concentrations were measured in the gastric blood of eviscerated cats. Blood flow was recorded concomitantly thus enabling quantitative determination of the gastrin output. Electrical vagal stimulation within the “physiological” frequency range (0.5–3 Hz) did not regularly result in any detectable changes in the peripheral gastrin level but an increase in this level was always observed on stimulation with frequencies above 3 Hz. A constant gastrin release per stimulus was then obtained, as long as the total number of vagal stimuli did not exceed 2000–3000. A larger number of impulses resulted in rapid fatigue of the release mechanism, indicating either a rapid and sustained fatigue of the neural control mechanism or the existence of a rather small pool of gastrin for immediate release—amounting to less than one per cent of the total antral store of immunoreactive gastrin. The rate at which such a releasable pool was refilled would suffice to compensate for the depletion induced by vagal stimuli at physiological frequencies,i.e.<3–4 Hz only. The two vagi innervate separate gastrin pools, which behave independently as far as release and refilling ar

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10167.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe input impedance of twitch muscle fibres of the Atlantic hagfish has been measured with sinusoidal transmembrane currents. The apparent specific membrane resistance and capacitance decreased markedly with frequency, and were relatively independent of fibre diameter. A model of the T‐system based on anatomical observations, was used to predict the input impedance in the normal solution (artificial sea water). The changes in input impedance produced by glycerol treatment, low chloride solution, reduced pH and isotonic solutions with low ionic strength were easily interpreted in terms of the same model. The model predicts severe attenuation of the action potential if conducted electrotonically by the transverse tubules towards the center of the fibr

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10168.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe membrane constants of the slow muscle fibres from the Atlantic hagfish were determined by analyzing the responses to sinusoidal currents at different frequencies. The apparent low frequency membrane resistance was 20–50 kΩcm2and was not significantly altered by replacing external chloride with methyl sulphate. The low frequency capacitance was 2.1–2.4 μF/cm2and decreased to about 1 μF/cm2at 100 Hz. A model of the T‐system consisting of a number unbranched T‐tubules was fitted to the impedance locus. About 15 tubules per sarcomere with a length approximately 8 times the fibre radius gave good fit to the observed impedance locus. The electrical characteristics of the T‐system allow an efficient electrotonic spread of the junction potential through the fibre c

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10169.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractSingle motor units of the cat's lateral rectus muscle were activated with short intracellular current pulses delivered through an intracellular micropipette penetrating a single motoneuron, and the mechanical responses in the muscle were recorded. Lateral rectus unit responses fell within the same range as those obtained earlier with extracellular stimulation of inferior oblique units, confirming that in the latter case single and not multiple motor units had been studied. It was also found that both fast and slow contracting muscle units were connected to fast conducting, large size motoneurons. The organization of motor unit recruitment in eye movements would thus seem different from the recruitment pattern in limb muscles.Intracellular stimulation of abducens nucleus “interneurons” did not initiate contractions at the ipsilateral lateral rectus muscle. These “interneurons”, therefore, did not appear to have excitatory inputs to the abducens motoneurons, but may be involved in relaying information to the other extraocular muscle nuclei or to other brain

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10170.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractImmature rat pineal grafts were transplanted bilaterally to the anterior eye chamber of adult male rats. The transplants matured and became sympathetically innervated from the host iris and synthesized 5‐hydroxytryptamine as revealed by fluorescence histochemistry. Transplants were used to investigate whether the newly formed nerve terminals were functional and thus could induce a rhythm in pineal N‐acetyltransferase (NAT) enzyme activity and hydroxyindole‐O‐methyl transferase (HIOMT) enzyme activity. Thein situpineal glands from the recipient animals exhibited NAT and HIOMT levels and diurnal variations of enzyme activities no different from control rats without transplants. Sympathetically innervated transplants showed lower NAT enzyme activity than thein situpineals but did yield a highly significant increase in darkness NAT activity as compared to light NAT activity (20:1). Sympathetically denervated transplants showed a much smaller rise in darkness NAT enzyme activity as compared to light values (1.8:1) but the rhythm was still statistically significant (p<0.01). Sympathetically innervated transplants had a higher HIOMT activity in darkness than in light (2.7:1). The HIOMT activity of the sympathetically denervated grafts was invariably low. Protein contents of transplants were found to be significantly lower thanin situpineal protein content but failed to show a diurnal va

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10171.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractCerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) were measured in rats under nitrous oxide anaesthesia, using a133Xenon modification of the Kety and Schmidt inert gas technique with sampling of cerebral venous blood from the retroglenoid vein. Extracerebral contamination of the venous blood sampled was studied by comparing the rates at which the activity of133Xenon decreased in blood and tissues. Contamination was avoided by gentle compression of the contralateral retroglenoid vein during sampling. CBF and CMRo2of the rat brain were 80±2 and 7.6 ± 0.2 ml·(100 g)‐1, min‐1, respectively. These values are about 25% lower than those previously obtained for cerebral cortical tissue under similar conditions. Induced hypercapnia (Paco2about 70 mm Hg) or hypocapnia (Paco215–20 mm Hg) gave rise to expected changes in CBF but did not alter CMRo2The CMRo2of the rat brain is at least twice that of the human brain. This species difference, which is similar to that previously reported for the oxygen uptake of cerebral tissuein vitro, probably reflects on inverse relationship between brain weight and neuronal packing

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10172.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe effect of changes in the muscle temperature on their ability to store elastic energy was studied by having 5 trained subjects perform maximal vertical jumps on a force platform, with and without counter movement, at muscle temperatures between about 32°C and 37°C. The results showed that the heights of vertical jumps were considerably reduced at lowered temperature, but thegain in heightafter a counter movement in the form of a jump down from a height of 0.4 m over the force platform, was significantly higher in the cold condition. To test whether this was due to an increased stiffness of the muscles, experiments with imposed sinusoidal length variations at 14 Hz were performed. Δforce ×Δlength‐1(i.e.stiffness) increased with isometric tension independent of muscle temperature. Experiments in which the rate of tension development and relaxation in voluntary maximal isometric contractions were measured at different muscle temperatures showed that maximal isometric tension changed by less than 1 % per degree but the rate of tension development and relaxation by 3–5 % and 5 % per degree, respectively, in the temperature range studied (30° to 40°). These data may be explained by the hypothesis that the series elastic components of the active muscle are located in the cross‐bridges between myosin and actin filaments. The storage of elastic energy would be enhanced if the rate of breaking of these bridges were decreased at lower

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10173.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe activity of phenylethanolamine‐N‐methyl transferase (PNMT) has been measured in the chromaffin tissue of the head kidney and in the sympathetic neurons of the coeliac ganglion/splanchnic nerve in the cod. The content of adrenaline and noradrenaline in these tissues and in other adrenergically innervated tissues and blood plasma was also determined. Adrenaline dominates over noradrenaline in most sympathetically innervated tissues, in the chromaffin tissue and in blood plasma, but not in the muscularis mucosae of the swimbladder. High PNMT activity was found in the chromaffin tissue in the walls of the posterior cardinal veins, and also in sympathetic neurons. It is concluded that the adrenaline found in the sympathetic nerves may originate from intraneuronal adrenaline synthesis, but also from circulating adrenaline which is taken up and sto

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10174.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractIsoprenaline and dopamine increased cyclic AMP (cAMP) content and contracile activity of isolated perfused rat hearts. The changes of cAMP levels depended on the mode of drug administration. Isoprenaline (4 × 10‐10mol) administered to the perfused heart as a relatively concentrated bolus, caused a substantial, rapid and transient increase of cAMP. Isoprenaline (2 × 10‐10mol and 4 × 10‐10mol) and dopamine (10‐7mol) diluted in 40 ml of perfusate which was continuously recirculated through the heart, caused a gradual increase of cAMP content which approached an apparent steady state. cAMP accumulation occurred at isoprenaline concentrations above 10‐9M and at dopamine concentrations above 10‐6M. Both agents also increased cAMP labelling from14C‐adenine in the perfusate, probably indicating increased cAMP synthesis. Isoprenaline at 2 × 10‐8M and 10‐7M increased labellingmorethan content of cAMP. Isoprenaline and dopamine also increased phosphorylaseaactivity. An association between increased cAMP contents and increased contractile activity was revealed by both the time‐response and the dose‐response curves of hearts exposed to isoprenaline and dopamine. Since both agents stimulate adrenergic β‐receptors in cardiac muscle, the results are concordant with the hypothesis that cAMP is involved as a mediator of the inotropic response

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1976.tb10175.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY