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B T Stokes

Publications and source records attributed to B T Stokes.

82 records · Page 5Linked to original sources
PubMed1982

Development of contractile properties in avian embryonic skeletal muscle.

The development of the twitch and tetanic responses of the embryonic chick posterior latissimus dorsi muscle has been studied during the last week in ovo. Normalized twitch and tetanic forces increased 3- and 12-fold, respectively, during this period. The changes in the kinetics of the twitch and tetanic responses differed during this developmental period. The time to peak twitch force progressively decreased. The decrease in time to half-peak tetanic force and the increase in the time differential of force production of the tetanic response did not continue after day 18. A prolonged tonic contractile component was described for both the twitch and tetanic responses, particularly in muscles from the younger embryos (days 14-18). A large decrease in the time to one-half relaxation of the twitch response also takes place during the final week in ovo. This detailed description of the development of the contractile properties provides a model system of fast-twitch muscle development in which neurogenic and myogenic components of muscular differentiation can be studied from several approaches.

Animals↗
PubMed1982

Isometric contractile properties and velocity of shortening during avian myogenesis.

Isometric twitch and tetanic contractile properties and velocity of unloaded shortening (V0) of whole avian posterior latissimus dorsi muscle (PLD) were examined between embryonic day 15 and the first 2 wk after hatching. The time to peak twitch force, time to half-relaxation of the twitch response, and time to half-peak tetanic force all change significantly during the final week in ovo but do not change during the first 2 wk ex ovo. Comparisons with previously published reports by others indicate that the twitch half-relaxation time at hatching is approximately the same as that of the adult PLD. The velocity of unloaded shortening increases 2.3-fold during the period studied. It has previously been shown by other that the velocity of shortening is well correlated with a muscle's myosin ATPase activity. Therefore, the observed changes in V0 suggest that the myosin ATPase activity of the avian PLD increases between embryonic day 15 and the first 2 wk posthatching, and this change could account, at least in part, for some of the changes in the isometric properties that were measured.

Adenosine Triphosphatases↗
PubMed1982

O2 tension in the spinal cord of the avian embryo.

A small recessed-tip O2 microelectrode was used to construct frequency distributions of PO2 in the chicken embryonic spinal cord during the last week of development (15-20 days). PO2 was remarkably low and stable at a given spinal locus. Electrode movement led to little change in the absolute level of tissue PO2 for a given day in the development. Spontaneous fluctuations occurred, predominantly in the motor columns, whose frequencies were dependent on the stage of incubation. PO2 decreased progressively; the most significant decline occurred between 16 and 17 days in ovo [19.2 +/- 1.7 (SD) to 11.5 +/- 2.7 Torr, respectively]. This decline in tissue PO2 at 16 days precedes dramatic alterations in spinal cord electrical activity and the resulting embryonic behavior.

Animals↗
PubMed1981

Oxygen fields in specific spinal loci of the canine spinal cord.

Oxygen tension (PO2) measurements were made in the dog spinal cord with a small recessed-tip oxygen microelectrode. The use of vibration and specific marking techniques has allowed the elimination of tissue compression artifacts and the mapping of regional PO2 in the thoracic spinal cord. A symmetrical distribution of PO2 values can be shown for the lateral white funiculi; the gray matter and dorsal columns have multimodal distributions. Statistical evaluation showed all these areas to have different PO2 profiles; PO2 values (mmHg) were 61.2 +/- 12.4 for the lateral white funiculi, 55.3 +/- 19.0 for the dorsal columns, and 30.0 +/- 13.6 in spinal gray. The relatively normal distribution patterns of these oxygen tensions indicate that traditional statistical methods may be used to compare and evaluate oxygen diffusion fields in the adult spinal cord.

Animals↗
PubMed1980

Acute modification of embryonic spinal cord activity induced by hypoxia.

The effects of acute environmental hypoxia on spinal cord polyneuronal activity throughout the later stages (14, 16 or 19 days) of chick incubation were studied. Bioelectrical activity was recorded in ovo from lumbosacral regions of the spinal cord, and frequency histograms were computed from multiunit (burst) activity during a 5-min control, an altered environment (10% O2) period, and a recovery period following hypoxic episodes. An hypoxic environment inhibited burst activity at 14 and 19 but not at 16 days. An age-dependent ability to recover from an acute hypoxic depression of neural activity was apparent, but multiple episodes of hypoxia depressed burst frequency to the same level independent of age. Hypoxia may inhibit the functional expression of specific neuron pools. The different responses to and recovery from hypoxia observed in this embryonic series may be dependent on the relative development of different components of the neuroaxis in the chick. Metabolic processes with age-related capabilities may also influence the different responses which were observed.

Animals↗
PubMed1978

A neurophysiological analysis of the effects of hypercapnia on the embryonic spinal cord.

Progressive hypercapnia in the normal chick embryo late in incubation (14-19 days) is temporally associated with a gradual decline in motor activity and the corresponding frequency of polyneuronal (burst) activity in the spinal cord. We have studied the possible correlation between the increasing hypercapnia and the declining frequency of burst activity seen during these later stages of incubation by systematic manipulation of CO2 levels. Burst frequency was seen to decrease as a result of a 5-min exposure to different carbon dioxide environments at all ages studied. The magnitude of this inhibition and the ability to recover from consecutive bouts of hypercapnia (pulses) is pulse and age dependent. These short-term (less than 5.0 min) changes differ qualitatively from the long-term (greater than 2.5 h) effects of subsequent hypercapnic episodes. This evidence suggests a role for metabolic factors in the normal developmental changes in motility and electrophysiological activity in the chicken embryo spinal cord.

Age Factors↗
PubMedDate not supplied

MR imaging of acute spinal cord trauma.

The thoracic spinal cords of five mongrel dogs were imaged with a 1.5 T MR scanner before and after trauma induced by a well-established method of spinal cord impaction that produces central cord hemorrhagic necrosis. The anesthetized dogs were studied acutely with a 5-in. circular surface coil, 12-cm field of view, sagittal and axial partial-saturation (TR = 600, TE = 25 msec) and spin-echo (TR = 2000, TE = 25-100 msec) techniques. One normal dog was used as a control. The cords were surgically removed and histologically examined. Direct correlation of the pathologic findings and imaging data showed that at the level of trauma there was obliteration of epidural fat and CSF spaces secondary to central cord hemorrhage and edema. The traumatized cords expanded to fill the bony canal, and there was loss of visualization of the internal anatomy of the cord (gray- and white-matter structures). We conclude that MR can accurately identify cord hemorrhage and edema within a few hours of spinal trauma.

Animals↗