摘要:

Intracellular recordings have been made from myotomal motoneurones during “fictive swimming” in the in vitro preparation of the lamprey spinal cord, while monitoring the efferent burst activity in the ventral roots. The pattern of rhythmic activity in the motoneurones is described, as well as how synaptic inputs from the premotoneuronal level exert their control of motoneurone activity. (1) All motoneurones investigated displayed rhythmic, symmetric oscillations of their membrane potential during “fictive swimming”. The period of depolarization occurred in phase with the burst discharge in the ventral root containing the motoneurone axon. (2) About one‐third of the cells fired bursts of action potentials during the depolarized phase, while the remaining motoneurones exhibited subthreshold oscillations. (3) Intracellular injection of chloride ions reversed the sign of the hyperpolarized phase, demonstrating phasic active inhibition of the motoneurones during rhythmicity. (4) The depolarized phase was unaffected after chloride injection, showing that the motoneurones also received phasic active excitation. (5) “Pre‐triggered” averaging of the motoneurone recording (using the ventral root spikes from other motoneurones for triggering), revealed that some degree of synchronous excitation of several motoneurones occurred, suggesting common excitation from the same premotor‐interneurones. It is concluded that the rhythmic oscillations of membrane potential in lamprey myotomal motoneurones during “fictive locomotion” depend on phasic excitation alternating with phasic active inhibition. The premotoneuronal mechanism responsible for this control may consist of reciprocally organized groups of excitatory and inh

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07193.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The effect of venous pressure elevation upon capillary filtration rate in the limb was studied in 6 chronically sympathectomized patients. Five healthy subjects served as controls. Volume changes of the forearm or calf were recorded by a strain‐gauge plethysmograph. Relative blod flow in subcutaneous and muscle tissue during venous stasis was measured by the local133Xe washout technique. In the denervated limbs there was a linear relationship between net capillary filtration rate and venous pressure elevation. In the controls a non‐linear relationship was seen as venous pressure elevation of 40 mmHg only caused an increase in net filtration rate of about 66% of that expected from a linear relationship. In the denervated limbs blood flow in muscle and subcutaneous tissue remained constant during venous pressure elevation of more than 30 mmHg whereas in the non‐denervated limbs blood flow decreased by about 50% in both tissues. The results suggest that a local sympathetic veno‐arteriolar (axon) reflex plays a dominant role for the reduced increase in net capillary filtration rate during large increases in venous pressure. The local axon reflex may therefore act as an edema protecting

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07194.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

An implanted radio‐telemetrical device, which consists of a Geiger‐Müller detector, a high voltage supply and a FM transmitter, incapsulated in araldite® (weight 130 g) was used to measure the body disappearance rate of125I‐iothalamate following a single i. v. bolus in unrestrained and undisturbed rabbits. The disappearance curve is practically monoexponential from 10 to 60 minutes after administration of the indicator and the disappearance rate constant (ke) is closely correlated to the “final slope” of the plasma disappearance curve of125I‐iothalamate (kp) (r=0.99). A linear correlation was also found between keand GFR measured simultaneously by constant infusion clearance technique, using an indicator not detected by the Geiger‐Müller detector (51Cr‐EDTA) (r=0.98), The ratios between the renal clearances of125I‐iothalamate,51Cr‐EDTA and inulin were determined by constant infusion clearance technique in a separate series of experiments since no data were available in the present literature. The results show that GFR can be determined by means of the telemetrical method and in a seriers of experiments in undisturbed rabbits GFR was found to be on average 4.7 ml min‐1, kg‐1(expressed as inulin clearance). Using the same technique in lightly pentobarbital anesthetized rabbits GFR was on a

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07195.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Isolated slowly adapting stretch receptors of the crayfish (Astacus fluviatilis) were exposed to sinusoidal length changes. The mechanical force, the receptor current and the receptor potential were analysed in terms of frequency response (Bode plots) and input/output functions. Within the frequency range investigated (0.3 to 80 Hz) the mechanical force was found to be only slightly dependent on the frequency of the sinusoidal stimuli, the slope of the gain function in the Bode plot being close to zero. Dynamic length‐force curves exhibited a characteristic hysteresis. In potential clamp experiments, the receptor current induced by sinusoidal length changes was dependent on the clamp potential attaining maximal amplitude at a membrane potential of about ‐20 to ‐30 mV for 80 Hz mechanical stimulation. The membrane potential at which the receptor current changed sign (the reversal potential) increased with increasing frequency. In Bode plots of the receptor current the gain was represented by a straight line, having a slope of about 1.2 dB/octave. The phase shift was positive at low frequencies. Bode plots of the receptor potential gain exhibited a characteristic peak in the region of 15 Hz. Below this peak the gain increased with about 1.2 dB/oct, above the peak the gain decreased with about 4.8 dB/oct. There was a small positive phase shift at low frequencies; at high frequencies the phase shift became negative. The impedance of the cell, as calculated from the receptor potentials and the current responses at resting membrane potential, gave Bode plots comparable to a simple resistive‐capacitive filter compatible with the electrical properties of the receptor cell membrane. The cut‐off frequency of this low pass filter decreased with decreasing stretch amplitude. One physiological significance of this finding, is that the performance of the receptor is improved at low levels of stimulation by reducing the bandwidth of t

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07196.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

In previous reports we have suggested that nervous reflexes are involved in the pathophysiology of cholera secretion and that these nervous reflexes involve a cholinergic synapse and a neuron with vasoactive intestinal polypeptide (VIP) as neurotransmitter. These proposals were further analyzed in this study. Tetrodotoxin (TTX) and lidocaine applied on the serosal surface inhibited cholera secretion in segments of rat small intestine. Fluid absorption in control rats was not significantly changed. Hexamethonium given i. v. decreased cholera secretion in the cat. No additional inhibition of cholera secretion was observed after giving TTX close i. a. Furthermore, the intestinal secretion evoked by VIP was not influenced by hexamethonium given i. v. or TTX given close i. a. The present observations support the hypothesis of a role for nervous reflexes in cholera secretion. The results suggest that at least a major part of the proposed nervous reflex(es) in cholera have a cholinergic synapse. Furthermore, the VIP‐ergic neuron is situated “distal” to the cholinergic neuron in the reflex(es) closer to the effector

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07197.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The effect of acute and chronic administration of three different prostaglandin (PG) synthesis inhibitors–aspirin, indomethacin and naproxen–on the basal and CO2‐stimulated cerebral blood flow (CBF) was studied in healthy subjects, using the N2O wash‐in technique for assessment of CBF. The regional O2extraction over the brain, the regional production of free fatty acids (FFA)–including the PG precursor arachidonic acid (AA)–and the regional production of two prostacyclin (PGI2) metabolites, were also measured. The efficacy of cyclo‐oxygenase inhibition by these drugs was monitored through AA‐induced platelet aggregation in blood samples taken before and after drug administration. In the basal state there was no detectable release of AA, other FFA or PGI2metabolites over the brain. Acute administration of aspirin (45 mg/kg) failed to affect CBF, as did chronic administration of this drug (15 mg/kg × 3 daily). Indomethacin (1.5 mg/kg) significantly (p<0.05)reduced CBF after acute administration, but after one week's treatment (0.8 mg/kg × 3 daily) this effect had disappeared. Acute administration of naproxen (4 mg/kg) did not affect O2extraction over the brain, thus indicating that CBF was unchanged. After chronic administration, naproxen (4 mg/kg × 2 daily) also failed to change CBF. During inhalation of CO2, no release of AA, other FFA or PGI2metabolites occurred in untreated subjects. In subjects given indomethacin there was a small but significant release of AA during inhalation of CO2. Both acute and chronic administration of aspirin failed to affect the CO2‐induced elevation of CBF, whereas both forms of indomethacin administration significantly reduced this rise. Chronic administration of naproxen did not affect the CO2‐induced increase in CBF. We conclude that in healthy subjects: 1) local PGI2production does not appear to be involved in the regulation of cerebral blood flow: 2) indomethacin reduces basal and CO2‐stimulated CBF, an effect not shared by the other structurally unrelated cyclo‐oxygenase inhibitors: 3) the mechanism(s) of indomethacin‐induced reduction of CBF does not appear to be related to inhibition of PG‐synthesi

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07198.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The effect of endurance training on skeletal muscle myoglobin concentration in man was investigated. 8 healthy sedentary males (20–31 yrs) trained on cycle ergometers 40 min/day, 4 days a week for 8 weeks. The work consisted of continuous exercise at a work load that during the last 5 weeks corresponded to 75% of the pretraining maximal oxygen uptake (VO2max). The training program resulted in a 7% increase in VO2max (p<0.01). The activities of the mitochondrial enzymes citrate synthase (CS), succinate dehydrogenase (SDH) and cytochrome c oxidase (Cyt‐c‐ox) in the fluadriceps femoris muscle, as indicators of muscle respiratory capacity, increased by 62–82% (p<0.01). The metabolic adaptation of skeletal muscle was further indicated by a 17% increase in the work load corresponding to a blood lactate concentration of 4 mmol/1, as determined by a progressive exercise test (p<0.05). There was, however, no change in the myoglobin concentration of the thigh muscle with training (‐1%, NS). It is suggested that endurance exercise in man at 75% of the maximal oxygen uptake does not severely tax the functions of myoglobin in skelet

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07199.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The relationship between maximum voluntary concentric strength, muscle fibre type distribution and muscle cross‐sectional areas were examined in 23 subjects (7 female and 11 male phys. ed. students as well as 5 male bodybuilders). Maximal knee and elbow extension as well as elbow flexion torque at the angular velocities 30, 90 and 180 degrees per second was measured. Muscle biopsies were taken from vastus lateralis and m. triceps brachii. The muscle cross‐sectional area of the thigh and upper arm was measured with computed tomography scanning. The maximal torque correlated strongly to the muscle cross‐sectional area times an approximative measure on the lever arm (body height). Maximal tension developed per unit of muscle cross‐sectional area did not correlate significantly with per cent type I fibre area and did not differ between the female and male students or bodybuilders. Neither did the relative decrease in torque with increasing contraction velocity show any significant relationship to the per cent type I fibre area. The total number of muscle fibres was estimated by dividing the muscle cross‐sectional area with the mean fibre area of m. triceps brachii. The number of fibres did not seem to differ between

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07200.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The effects of different time patterns in presynaptic spike trains on the transmission of information across an inhibitory synapse is examined in the muscle receptor organs of the crayfish abdomen. With regular input, the system would be strongly affected by phaselocking (Perkel et al. 1964), and it is shown that a similar phenomenon would occur during closedloop inhibitory feedback. The conditions under which different degrees of phaselocking occur is studied in simple models of the system, and the model predictions is compared with experimental observations of pre‐ and postsynaptic spike trains. The results suggest that phaselocking is uncommon during the normal operation of these sense organs, due to the special design of its neuronal elements, which promote irregular time patterns of impulse firing in both receptors and inhibitory neuron

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07201.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

We have followed the time course of the effect of the carbonic anhydrase inhibitor acetazolamide injected i. v. in unanesthetized healthy human beings. The dose administered was 500 mg as a bolus. Cerebral blood flow (CBF) was measured continuously before, during and after the injection, using a pulsed ultrasound doppler system, which measured the instantaneous mean velocity across the lumen of the internal carotid artery, just below its entrance into the skull. Ventilation, heart‐rate, end‐expiratory PCO2‐ arterial PCO2, pH and systemic blood pressure was also measured. We found that acetazolamide caused a rise in CBF which could be detected as early as 2 min after the injection. A maximal average response of 75% increase in CBF was seen after 25 min. The half‐time of the declining phase of the response was 95 min. There were no systematic differences in the CO2reactivities, given as ACBF/ΔPACO2in % of CBF at normocapnia, before and after acetazolamide injection, regardless of the absolute PACO2level. The present dose of the drug caused no change in ventilation, alveolar and arterial PCO2or in arterial blood pH indicating that the carbonic anhydrase was not fully inhibited. Our observations show that acetazolamide nevertheless caused a rapid vasodilation in the brain and over a wide range of PCO2′s. We suggest that this agent has a local vasodilator effect on the cerebral arterioles, unrelated to its specific effects as a carbonic anhydrase

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07202.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY