Tetanic Responses Research Articles

In vivo CO-2 buffer curves of skeletal and cardiac muscle.

In vivo CO-2 buffer curves of skeletal and cardiac muscle.

Pharmacology and fine structure of peripheral muscle innervation in the cockroach Periplaneta americana.

Drugs affecting a cholinergic system (i.e. acetylcholine, nicotine, paraoxon, eserine, atropine, succinylcholine) and drugs having no cholinergic effects (i.e. norepinephrine, harmine, gamma-aminobutyric acid) were perfused into the metathoracic leg of the cockroach Periplaneta americana , and the physiological results were observed. Nicotine produced a reversible tetanic response, and succinylcholine decreased the amplitude of the contraction. All the other drugs had no effect. Electron micrographs of the peripheral neuromuscular system revealed a typical insect junction: no junctional folds, synaptic vesicles, and a synaptic cleft of 200 Å. The sarcoplasmic reticulum of the cockroach muscle is extensive and consists of a series of tubules and cisternae often seen as a three-dimensional collar around the myofibrils. Sarcolemmal invaginations formed dyads with the sarcoplasmic reticulum supposedly providing the pathway for rapid transmission of excitation to the interior of the muscle fibre. The morphological evidence indicates that the junction is chemically mediated, but the physiological data demonstrate that the mediator is not acetylcholine.

EFFECT OF SODIUM TOLBUTAMIDE ON PREGNANT ALBINO RATS AND THEIR YOUNG.

The sodium salt of tolbutamide, in dosages ranging from 12.5 mg./kg. to 125 mg./kg. body weight, was administered to pregnant albino rats to determine its effect upon litter size, individual fetal weight, normal development of the young, and the fetal skeleton. As the dosage level increased, a statistically significant decrease in fetal weight was observed. Tolbutamide administration had no detrimental effect upon the total number of implantations; however, a large number of resorptions occurred at the 125 mg./kg. level resulting in a decreased litter number. The number of rats having litters with fetuses weighing less than three grams increased as the dosage increased from 12.5 mg./kg. to 100 mg./kg. levels. No adverse effect on the maternal animal was noted except at the 100 mg./kg. and 125 mg./kg. levels. At these levels all animals experienced a localized tetanic response which varied in duration according to the level of injection. The number of sternebrae, metacarpals, and metatarsals, as well as long bones, indicated that the number and size of bones varied inversely with increased dosage levels. Normal skeletal development occurred despite dosages up to and including the 37.5 mg./kg. level. Abnormalities were observed from the 50 mg./kg. to the 125 mg./kg. level of administration.

Summation and tetanus in postmortem human heart muscle

Induced isometric contractions were recorded from trabeculae carneae from the left ventricles of human hearts obtained at autopsy. Increasing the frequency of stimulation from a driving rate of 1/sec. up to 10/sec. resulted in complete tetanic contractions in the majority of experiments. The tetanic response was usually coupled with summation. The occurrence or nonoccurrence of tetanus was correlated with the contraction time-refractory period ratios. Submitted on December 16, 1958

The role of acetylcholine in the development of tetanic single response and afterpotentials in the nerve trunk of cold-blooded animals

Experiments were performed on the nerve trunks of frogs in which the production of acetylcholine was disturbed by removal of the pancreas. This brought about an increase of the negative afterpotential and prologation of tetanized single response on the 4th to 10th day following the operation. The compensatory administration of acetylcholine removed these changes in the majority of cases. Preliminary administration of eserine to normal frogs resulted in decrease of the negative afterpotential. With administration of eserine the conditions for appearance of the tetanized single response deteriorated. Evidently, acetylcholine promotes the decrease of the duration of residual processes of excitation in the nerve tissue.

Coxo-Subalar Muscle in the Mesothorax of Diptera

TWO types of muscle are recognized in the mesothorax of Diptera: first, the large specialized dorsal longitudinal and dorsoventral indirect-flight muscles; secondly, the less specialized muscles that operate the legs and the pleural or so-called direct-wing, or direct-flight, muscles1–4. The indirect-flight muscles are described as of a fibrous or fibrillar nature, give a twitch response to stimuli and develop the extremely rapid thoracic vibrations that produce the main flight movements of the wings in Diptera (and Hymenoptera). The second group of less specialized muscles are described as of a tubular nature and give a tetanic response to stimuli; those connected with the wing base are presumed to set the wings and so be responsible for variations in the actual mode of flying.

THE EFFECT OF PHYSOSTIGMINE ON THE RESPONSES OF EARTHWORM BODY WALL PREPARATIONS TO SUCCESSIVE STIMULI

1. The longitudinal muscles of the body wall of the earthworm (Lumbricus terrestris) show augmented responses when stimulated by successive single shocks at low frequencies. The facilitating condition lasts not more than 0.5 second after the response to a single shock.2. A frequency of 14 per second results in a complete summation of the contractions or a condition of tetanus.3. The magnitude of a summated response elicited by a series of shocks is proportional to the duration of the burst of shocks and to the frequency of the shocks within the burst.4. The tetanic responses to repeated bursts of stimuli show an increasing augmentation of the initial contractions. The production of this "staircase" effect is affected by the frequency of the shocks, the duration of the bursts, and the length of the interval between bursts.5. After a brief tetanus the facilitating condition persists for nearly 30 seconds.6. The application of physostigmine increases the augmentation of responses and tends to produce a condition of tonus.7. Physostigmine delays the decay of the facilitating property so that augmented responses are produced with intervals as long as 3 minutes between bursts of stimuli, suggesting the rôle of acetylcholine in the production of the augmented responses.

The relation between the durations of the isometric twitch and of the after-action of tetanus

In skeletal muscle with its circulation intact (1) increase within physiological limits of the initial passive tension of the muscle not only ( increases the active tension developed by the muscle in tetanic contraction, but ( also increases the duration, of the tetanic plateau after cessation of the exciting stimuli. For convenience, this after-continuance of the tension was termed the “ after-action.” As Gad and Heymans (2, see their fig. 17a) many years ago suggested—not knowing of the increased duration of the twitch with increasing tension—that the duration of a single response was nearly the same as that of the after-action, the question of the relation between these two phases of muscular activity at once presents itself. As the method of recording previously employed (1) was not of sufficient delicacy to admit of accurate comparison between these relatively brief intervals, the more precise optical device recently described (3) has been utilised for the present investigation. Since the electrical responses have been in all cases recorded simultaneously with the mechanical, the duration of the twitch has been taken as the interval between the beginning of the electrical change and the “ angle ” at the end of the twitch plateau (see IV)—two points which can be measured significantly to 0.001 sec. In the previous communication referred to above (1), the after-action was measured from the cessation of the stimuli to half-relaxation. Much more accurate than this, however, for the first point is the beginning of the last electrical change of the tetanus; and since, as will be shown presently, there is at the end of the tetanic response of a fresh preparation an “ angle ” (fig. 1, Plate 32) comparable to that of the twitch, the interval between these two 'points—the beginning of the last electrical response and the plateau “ angle —has been termed the after-action. The intact gastrocnemius muscles of decerebrate frogs (R. freshly caught) prepared in the usual way (3, 4) were used throughout. Special precautions were taken to ensure normal circulation in the recording muscle and adequate respiration of the preparation.

Societies and Academies

Societies and Academies