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B T Stokes

Publications and source records attributed to B T Stokes.

At least 73 records · Page 4Linked to original sources
PubMed1991

Three-dimensional computer-assisted analysis of graded contusion lesions in the spinal cord of the rat.

Histological analysis of spinal cord injury in experimental animals has focused primarily on the microanatomy of damaged tissue. The current study presents an analysis of the three-dimensional structure of lesion sites in the spinal cord of rats contused with an injury device which produces consistent lesions. Three levels of injury were produced by systematically varying the cord displacement and the duration of the displacement during impact. The resulting groups of subjects exhibited mild, moderate, and severe neurological deficits. Comparisons of equivalent mild impacts made at thoracic versus lumbar spinal cord levels were also made. The results indicate that the overall shape of the lesions is generally biconical, with extensions in the base of the dorsal funiculus, irrespective of the degree of damage or the spinal level of the injury. Lower displacement injuries yielded shorter lesions rostrocaudally with less spread into the white matter. Similar impacts in the lumbar versus thoracic spinal cord produced shorter, more truncated lesion sites at lumbar levels with less involvement of the white matter than in the thoracic lesions. Three-dimensional analyses can can provide additional information about the lesion beyond that available from conventional histopathological measures. Such information could be useful in assessing the results of posttraumatic manipulations which are directed at reducing tissue damage or tissue replacement via transplantation.

Animals↗
PubMed1991

The effects of elevation and depletion of intracellular free calcium on progesterone and prostaglandin production by the primate corpus luteum.

The role of the phosphatidylinositol second messenger system in luteal regulation has not been extensively studied, particularly in the primate. The objectives of this study were (1) to further characterize the response of the primate CL to the calcium ionophore A23187, in terms of intracellular free calcium concentrations ([Ca2+]i) and progesterone (P) production; and (2) to assess the effects of depleting, as well as elevating, available calcium on luteal P and prostaglandin (PG) production. The response to A23187, in terms of [Ca2+]i, was measured by fura-2 fluorescence microscopy of single small and large luteal cells. A23187 significantly increased [Ca2+]i in both cell types (p less than 0.01). P production (basal and hCG-stimulated) by dispersed primate luteal cells incubated for various times (1-8 h) with and without A23187 was measured. Treatment with A23187 rapidly (within 1-2 h) attenuated (p less than 0.05) the time-dependent increase in basal and hCG-stimulated P production. Luteal P and PG production following treatment with the calcium ionophore, ionomycin, alone or in combination with additional CaCl2, was also monitored. Treatment with ionomycin (p less than 0.01) and CaCl2 (p less than 0.01) inhibited luteal P production. In contrast, treatment with ionomycin stimulated (p less than 0.01) luteal PG production. To determine the effects of Ca2+ depletion on luteal function, P and PG production by cells incubated for 2 and 8 h in the absence and presence of the Ca(2+)-chelator EGTA was measured. Luteal production of both P and PG was inhibited by 8-h treatment with EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Spinal cord repair: is tissue oxygenation an important variable?

We have demonstrated the reliability and feasibility of making PtO2 recordings from graft and host tissue in the injured spinal cord. The data suggest that the oxygen microenvironment of developing graft and host spinal tissue is clearly different from that found in normal spinal tissue or in transplants that have not survived or integrated well. These same constraints seem to apply to cavitation in developing grafts and poorly developed graft/host interfaces. The similarity between these findings and those from previous studies in other fetal vertebrates suggests that oxygen tensions in the spinal cord probably reflect the developmental status of the regenerating tissue. Our future studies will seek to define the relationship between anatomical development of transplant tissue and these functional (PtO2, microvascular development and tissue metabolism) indicators of graft development. These investigations should also provide a background for those later studies which seek to establish the mechanisms by which these relationships come about i.e. oxygen consumption of host/transplant tissue, blood flow to transplants, studies of glycolytic metabolism (2-DG autoradiography), etc. In this way, we can begin to understand the role of tissue metabolism in graft-mediated repair.

Animals↗
PubMed1989

Energy depletion-repletion and calcium transients in single cardiomyocytes.

Rapid fluctuations of intracellular free calcium in single adult rat heart myocytes were monitored by time-resolved fura-2 fluorescence microscopy. Under controlled aerobic conditions (35 degrees C, pH 7.3), electrical stimulation at 0.5 Hz produced a concave negative staircase of calcium transients. When the myocytes were challenged with 3 mM amobarbital (Amytal) and 2 microM carbonyl cyanide m-chlorophenylhydrazone (CCCP) to deplete ATP, the cells became unresponsive to electrical stimulation within 1 min but responded to 10 mM caffeine with a large increase in free calcium. After the development of rigor contracture, the cellular response to caffeine was blunted. Free calcium increased at a variable rate in individual cells, reaching values of 300-1,000 nM after 15 min. When the inhibitors were removed, calcium declined toward control values, and spontaneous contractile activity and calcium transients were invariably observed. During subsequent electrical stimulation, there was a decrease in the half-widths of the calcium transients and an attenuation of the negative staircase. Parallel experiments with cells in suspension indicated that Amytal and CCCP caused ATP to fall from 27.6 +/- 1.6 to 0.7 +/- 0.2 nmol/mg protein, and the percent rod-shaped cells to fall from 70 to 0% in 5 min. Removal of the inhibitors after 15 min caused a rebound in ATP to 5.3 +/- 1.5 nmol/mg within 2 min and 6.6 +/- 1.3 nmol/mg after 10 min.

Adenosine Triphosphate↗
PubMed1989

Hyperthyroid adult rat cardiomyocytes. II. Single cell electrophysiology and free calcium transients.

The effects of hyperthyroidism on electrophysiological properties and intracellular free calcium transients in single adult rat cardiomyocytes were studied using conventional microelectrodes and time-resolved single cell fura-2 fluorescence microscopy. Under control conditions, resting membrane potentials and triggered action potentials were not different in euthyroid and hyperthyroid myocytes. Calcium transients produced by electrical stimulation, however, were markedly abbreviated in hyperthyroid myocytes. During a train of stimuli, the duration of the calcium transients at half peak amplitude (half time) was 124 +/- 14 ms at the fifth beat in hyperthyroid cells vs. 287 +/- 35 ms in euthyroid cells. Isoproterenol (1 microM) prolonged time to 50% repolarization (APD50) of the action potentials and increased the peak calcium transients in both euthyroid and hyperthyroid myocytes. It also shortened the half time of the calcium transients in euthyroid myocytes but had little effect on the half time in hyperthyroid cells. These data are consistent with the electrophysiology and mechanical performance in intact euthyroid and hyperthyroid cardiac tissues, and the intrinsic changes in hyperthyroid tissues can therefore be illustrated in single ventricular myocytes. Furthermore, the results suggest that alterations in intracellular calcium handling by sarcoplasmic reticulum may account for contractile changes of the heart induced by hyperthyroidism.

Action Potentials↗
PubMed1988

Effects of immobilization on the isometric contractile properties of embryonic avian skeletal muscle.

Chicken embryos were chronically immobilized by applying a neuromuscular blocking agent, curare, to the chorioallantoic membrane from day 8 through day 16 of incubation to study the effects of a deficit in motor activity on the development of contractile properties of skeletal muscle. Compared with control embryos, spontaneous embryonic motor activity was depressed by 60 to 90% in the curare-treated animals during the treatment period. Growth of the posterior latissimus dorsi muscle, a fast-twitch muscle in the adult, was greatly affected by immobilization. The average blotted mass of the muscles from curare-treated 18- to 19-day embryos was approximately 20% of that from control embryos. The isometric contractile properties of posterior latissimus dorsi muscles isolated from control and curare-treated embryos were compared at 18 to 19 days of incubation. The times to peak tension and to one-half relaxation of the twitch and tetanic responses were significantly greater for the muscles from the immobilized embryos. The peak twitch and tetanic tensions, normalized for muscle cross-sectional area, were significantly less than control values for the muscles from curare-treated embryos. The maximal rate of tetanic tension production was, however, unaffected by immobilization. The results of this study demonstrate that the development of isometric contractile properties of embryonic skeletal muscle is significantly altered by an experimentally induced reduction of spontaneous motor activity. A disruption in the functional development of the sarcoplasmic reticulum following a similar decrease in motor activity, as reported by others, is discussed as a potential mechanism for the altered contractile properties of muscles from the curare-treated embryos.

Animals↗
PubMed1988

Myocyte deenergization and intracellular free calcium dynamics.

Intracellular free calcium in adult rat heart ventricular myocytes was monitored by single cell fura-2 fluorescence microscopy. The average resting free calcium in rod-shaped quiescent cells was 125 nM (range 70-200 nM). When cells were deenergized with an inhibitor (amytal) and an uncoupler (carbonyl-cyanide m-chlorophenylhydrazone) of oxidative phosphorylation, there was a small but significant increase (125-380 nM) in intracellular free calcium during the transition to a highly contracted (square) rigor form. After the onset of contracture, which occurred 5-15 min after addition of the above compounds, the increase in free calcium was slow for the first 20 min, reaching a value of only 750 nM. Thereafter, the rate of increase accelerated and 50 min after contracture, free calcium was approximately 3 microM. The increase in free calcium was absolutely dependent on extracellular calcium but was not inhibited by high concentrations of verapamil (2-7 microM), suggesting influx via the Na+-Ca2+ exchange transporter as the cause of calcium increase. However, in calcium repletion protocols the rate of increase in sodium-loaded myocytes was greatly accelerated if cells were not depleted of ATP, confirming suggestions that ATP loss partially inhibits Na+-Ca2+ exchange.

Adenosine Triphosphate↗
PubMed1987

Quantitation of intracellular free calcium in single adult cardiomyocytes by fura-2 fluorescence microscopy: calibration of fura-2 ratios.

Isolated rat myocytes incubated with the acetoxy methyl ester of fura 2 contained partially hydrolyzed esters, necessitating in vivo calibration of the signals obtained by fluorescence microscopy for calculation of pCa. Ionophores did not produce reliable R'max and R'min values in respiring myocytes, and elevated free calcium caused individual cells to hypercontract and burst. These difficulties were overcome by superfusion with a glucose-free buffer containing an inhibitor and an uncoupler of oxidative phosphorylation. R'max and R'min values obtained by ionophore treatment of deenergized myocytes were normalized to an in vitro calibration curve. Resting pCa derived from the individual curves averaged 6.9 for calcium-tolerant rod-shaped myocytes.

Adenosine Triphosphate↗
PubMed1987

Spinal cord extracellular microenvironment. Can the changes resulting from trauma be graded?

It is now clear that alternatives are available to the standard method of producing spinal injury with the Allen drop technique. We have shown that small groups of animals with predictably consistent mechanical injury descriptors can now be produced for studies of this type. These groups can easily be selected to have minimal or maximal injury results, depending upon this series of mechanical descriptors. In addition, important physiological variables seem to show acute recovery patterns consistent with recovery of function in chronic animals. Since marginal injuries are likely to be more responsive to pharmacological or surgical intervention, a sensible approach would be to design studies in which animals are close to, but not at, some degree of injury from which they will spontaneously recover. Shifts of the acute physiological, chronic behavioral, or histopathological recovery curves would then indicate the potential therapeutic index of different interventions. Only in this way can significant advances be made in the selection of protocols for human trials.

Animals↗
PubMed1987

Functional analysis of an electromechanical spinal cord injury device.

Feedback control in our injury device allowed the impactor to be sensitive to the biomechanical characteristics of the spinal cord and produce mechanically predictable injuries. We tested the hypotheses that (i) extracellular calcium [( Ca2+]e) in the rat spinal cord recovers with a time course dependent on the magnitude of injury intensity, (ii) [Ca2+]e is initially depressed at the injury epicenter to the same degree independent of injury severity, and (iii) acute (less than 3.0 h) recovery of [Ca2+]e to normal values occurs in that group of animals that shows only transient neurologic deficits in the postinjury period. Three levels of injury (light, intermediate, and heavy) were produced by controlling spinal displacement during the injury process. After injury, [Ca2+]e at the injury site decreased to values less than 0.1 mM and then recovered during the next 3 h. Incomplete recoveries occurred in the intermediate- and heavy-injury groups (0.72 +/- 0.01 and 0.58 +/- 0.01 mM, respectively). [Ca2+]e activity in the lightly injured group recovered to normal values by 3 h. Specific injury protocols therefore resulted in reproducible responses in the cellular microenvironment. Behavioral recovery could be predicted from mechanical impact parameters. Animals in the light-injury group had transient neurologic deficits in some behavioral tests (open-field walking) with no alteration in others (inclined-plane analysis). Neurologic tests that required coordination between fore and hind limbs (grid walking) did not reveal significant deficiencies until 14 days postinjury. Those animals in the intermediate and heavy groups showed initial and continuing neurological effects in all behavioral measures. It is therefore probable that acute mechanical descriptors and hypocalcia transients are predictive of the ongoing and subsequent pathology of spinal cord injury.

Animals↗
PubMed1984

Improvement in injury induced hypocalcia by high-dose naloxone intervention.

Naloxone hydrochloride was used to re-establish normal calcium activities in the extracellular space of the injured spinal cord. The micromolar levels of calcium which occur immediately after injury were improved above control values by 1 h 30 min post-injury; normal activities occurred at 2 h 45 min. Such a restitution of ionic levels after injury may contribute to the beneficial effects of naloxone in traumatic injury.

Animals↗
PubMed1983

Four neural circuit models and their role in the organization of voluntary movement.

Four neural circuit models and their role in the organization of voluntary movement are presented here. These circuits collectively control a ballistic type biped voluntary movement. The structure of each circuit, and its function is discussed. Three of the circuits are central and contribute to the construction of two classes of inputs, analogous to the alpha signals and gamma signals in biological systems. The fourth circuit plays a role in stabilization of the movement, and in compensation for the receptors. Digital computer simulations are undertaken to demonstrate the construction of all the intermediate signals and the response of a two link biped to these efferent signals.

Animals↗
PubMed1983

Extracellular calcium activity in the injured spinal cord.

The extracellular concentration of calcium ion was measured in canine spinal cord subsequent to spinal injury. In the control animal, we found that calcium activities changed little independent of electrode placement in the spinal cord, were stable during the 3 h necessary to make injury measurements, and were comparable to other estimates of calcium in the interstitial space. After injury, calcium activities decreased to micromolar levels that were incompatible with neural function. An incomplete recovery of extracellular calcium occurred during the next 3 h to about one-third (0.44 +/- 0.01 mM) of the normal value (1.1 +/- 0.08 mM). Such a pattern of changes in extracellular calcium was specific for the injury site itself and did not occur at nearby anatomic loci. These results are interpreted as having both short- and long-term effects on neuronal function and subsequent reorganization of spinal pathways.

Animals↗