Search PubMed⌕ Search

Biomedical subjects

H J Bryant

Publications and source records attributed to H J Bryant.

31 records · Page 2Linked to original sources
PubMed1985

A quantitative [14C]-2-deoxy-D-glucose study of brain stem nuclei during horizontal nystagmus induced by lesioning the lateral crista ampullaris of the rat.

A study of the brainstem of the rat during horizontal nystagmus using the quantitative 2-deoxy-D-glucose technique reflected changes in the functional activity of cell groups based on their glucose utilization rates. Horizontal nystagmus was induced by unilateral crista ampullectomy of the horizontal canal. Comparisons of glucose utilization rates were made between experimental and control groups as well as from side to side within each group. There was a decrease of the ipsilateral medial and superior vestibular nuclei with a concomitant increase in the contralateral medial vestibular nucleus when compared to control. The medial rectus motor division of the ipsilateral oculomotor nucleus showed an increase whereas the ipsilateral abducens and the ipsilateral nucleus prepositus hypoglossi exhibited a decline in their utilization rates. The extra ocular motor nuclei responsible for the excitatory fast phase of nystagmus utilizes more substrate than those involved in the slow phase. An increase was also measured in the ipsilateral lobule of the cerebellar nodulus. The lateral reticular nucleus showed a bilateral decrease in its glucose utilization rate when compared to control.

Abducens Nerve↗
PubMed1985

In vivo membrane potentials of smooth muscle cells in the caudal artery of the rat.

Membrane potentials measured in vivo may differ significantly from those measured in vitro in part due to humoral factors, innervation, and wall tension. These studies were initiated to determine whether it is feasible to record membrane potentials from vascular smooth muscle cells in vivo in the caudal artery of the pentobarbital-anesthetized male Wistar rat. Membrane potentials were measured using glass microelectrodes and correlated with systolic, diastolic, and mean blood pressures. For systolic blood pressures between 100 and 140 mmHg the average resting membrane potential was -38.4 +/- 0.48 mV. There was good correlation of systolic, diastolic, and mean blood pressures with membrane potential between 100 and 140 mmHg (r = 0.89, 0.75, and 0.89, respectively). Below 80 mmHg the arterial muscle cells became more depolarized than would be expected if the membrane potential were determined solely by transmural pressure. The depolarized membrane potential at low arterial pressures may be due to enhanced neural input. Spontaneous electrical activity was observed in some of the in vivo cells. When action potentials were present, they were generated at rates between 1-2/s and 6-7/min. These studies indicate that it is feasible to measure membrane potentials from arterial smooth muscle cells in vivo in the caudal artery of the rat.

Action Potentials↗
PubMed1985

Vascular smooth muscle membrane potentials in rats with one-kidney, one clip and reduced renal mass-saline hypertension: the influence of a humoral sodium pump inhibitor.

Ninety to 120 min after removal of the caudal arteries, vascular smooth muscle cells from one-kidney, one clip (1-K, 1C) hypertensive animals were depolarized relative to those in appropriate control animals but cells from reduced renal mass-saline (RRM-S) hypertensive animals were not. However, supernatants of boiled plasma from both of the hypertensive models depolarized vascular smooth muscle cells in arteries taken from normotensive animals. These studies suggest that an agent in the plasma of these animals depolarizes vascular smooth muscle cells. This could help to explain the vasoconstriction in these hypertensive animals.

Animals↗
PubMed1984

Computer processing of phrenic neurograms.

Manual processing of large numbers of electrophysiological waveforms is a tedious process prone to subjective errors in judgment. To eliminate these problems, we developed computer algorithms and techniques to analyze cat phrenic neurograms produced in response to step changes in end-tidal PCO2. The computer analyzed the neurogram in terms of a model waveform, which consisted of 1) base-line activity made up primarily of noise, 2) an initial sharp increase from base line, 3) a slower ramplike increase in activity, 4) a peak value, and 5) a rapid decrease in activity back to base line. Parameters describing these model elements as well as inspiratory and expiratory times were calculated by the computer. Computer-produced parameters were compared with manually calculated parameters from chart recordings for over 200 individual neurograms. Repeated manual processing of the neurogram had a variability of +/- 10% in the parameter estimates. The computer-produced parameters fell within this range more than 89% of the time. Although the techniques described are directed specifically toward phrenic neurogram analysis, the methods are general enough to be useful in computer processing of other types of physiological waveforms.

Animals↗
PubMed1983

An analysis of respiratory drive components during flow-resistive respiratory loading.

Inspiratory flow-resistive loading normally causes an additional respiratory drive that limits the resistance-induced decrease in minute ventilation (load compensation). Occlusion pressures (P100) were measured during CO2 rebreathing with and without added inspiratory loads in normal persons and persons with obstructive sleep apnea (OSA). At each point obtained during loaded breathing, the additional drive due to resistive loading was determined by subtracting CO2-dependent drive (estimated from the nonloaded run) from total drive. In normal subjects, the additional drive correlated with each of four different estimates of load magnitude. In OSA subjects, there was no significant increase in drive due to loading and ventilation decreased markedly during loading. The relationships among ventilation rate, load, and drive, with and without load compensation, were analyzed using a 4-quadrant feedback control diagram. The diagram enables the prediction of ventilation rate for any end-tidal CO2 in the loaded and nonloaded cases, and the flow decrement that will occur as a result of added inspiratory resistance.

Airway Resistance↗
PubMed1983

The development and evaluation of a low-cost microdensitometer for use with the 2-deoxy-D-glucose method of functional brain mapping.

The conversion of a standard laboratory compound microscope into a microdensitometer for use in the 2-deoxy-D-glucose autoradiographic method of functional mapping in the brain is described. A solid-state detector was attached to the camera port of a Zeiss Universal Microscope and minor modifications to the microscope optics were made to produce a microdensitometer with a field of view 0.15 mm in diameter. Details are presented showing the modifications to the microscope which do not permanently destroy its functional ability to perform as a viewing microscope. A simple electronic circuit is presented to digitally display the output of the photo detector. Calibration of the instrument in terms of optical density or 2-deoxy-D-glucose activity is also described. The primary design goal was the construction of a simple, reliable, inexpensive microdensitometer that could be assembled by laboratory personnel. This densitometer should allow laboratories on modest budgets to have access to quantitative methods for the study of brain functional activity at a cost considerably less than the price of a commercial microdensitometer.

Animals↗
PubMed1979

Action potentials in single axons: effects of hyperbaric air and hydrostatic pressure.

Resting potential and action potential parameters of crayfish (Procambarus acutus) single axon were examined under hyperbaric air and hydrostatic pressure to 8.6 atmospheres absolute to determine if evidence for the basis of neurological dysfunctions that may occur in diving in this pressure range is detectable at the membrane level. Hyperbaric air increased the maximum rates of depolarization and repolarization of the action potential by (2.2 +/- 0.2) and (2.1 +/- 0.2)%/atm, respectively. Hydrostatic pressure had an opposite effect, decreasing the maximum rates of depolarization and repolarization by (0.57 +/- 0.13) and (0.9 +/- 0.3)%/atm, respectively. Action potential duration was decreased (0.91 +/- 0.19)%/atm by hyperbaric air. Action potential amplitude, resting potential, and threshold were unchanged by increasing pressure. Increasing the nitrogen tension alone produced results consistent with hyperbaric air compression. Thus, increased hydrostatic and nitrogen pressures oppositely affect the rates of polarization of the action potential in a reversible manner at pressures in the range encountered by human divers.

Action Potentials↗
PubMed1979

Modification of synaptic facilitation and bursting patterns in Aplysia californica by hyperbaric air.

We have studied the effects of air pressure to 10 atmospheres absolute on several electrophysiological characteristics of identified neurons in Aplysia californica. These pressures did not affect the resting potential, rates of polarization, amplitude, or duration of action potentials in cell R2. Repetitive stimulation of the right pleurovisceral connective nerve produced a frequency-dependent train of unitary excitatory postsynaptic potentials (PSPs) in cell R15 which showed marked facilitation near the end of the train. The amount of facilitation of the last four PSPs increased significantly (approximately 20%) at 9 ATA air pressure. The amplitude of the first PSP was not altered by pressure. Changes in extracellular [Ca2+] or oxygen tension did not influence these pressure effects. Increases in air pressure also reduced the number of action potentials per burst, burst duration, and interburst interval of cell R15 but left the overall firing frequency unchanged. These results indicate that fundamental neurophysiological processes can be altered by increased gas tensions similar to those confronting animals experiencing narcotic symptoms at less than 300 ft of seawater.

Action Potentials↗
PubMed1978

Interpretation of light scattering associated with prolonged neural activity and temperature changes.

Changes in light scattering from lobster giant axon which accompany the action potential were observed during periods of prolonged stimulation and as a function of temperature. At an initial temperature of 10 degrees C most (more than 90%) axons produced positive light scattering signals which increased in amplitude when the temperature was lowered. At 2 and 5 degrees C approximately half of the axons produced positive scattering signals. The remaining half produced negative scattering signals which became positive when the temperature was raised to 10 degrees C. The amplitude of the negative signals followed sigmoid transition to positive values as a function of time. The time and temperature dependence of the signal are interpreted in terms of differential changes between the indices of refraction of the membrane matrix and the open or closed early activation channel.

Action Potentials↗
PubMed1977

Light scattering and excitation in lobster giant axon. Effects of ion substitution.

Changes in the light scattering signal from single giant axons of lobster were observed during the propagation of the action potential in order to correlate membrane excitability with possible structural changes reflected in the optical properties of the axolemma. Substitution of guanidine and aminoguanidine for sodium resulted in a decreased action potential amplitude to 69 and 50% of control values, respectively. The amplitude of the light signal was, however, not significantly changed by these substitutions and is, therefore, reported to be independent of the transmembrane potential and current. The venom of the scorpion Leiurus quinquestriatus caused a marked prolongation of the action potential and the light scattering signal without significantly altering their amplitudes. A two-state model of the early (sodium) activation channel is suggested, in which the light scattering signal is correlated with a possible difference in the scattering efficiency between the states of the channel.

Action Potentials↗
PubMed1975

Excitability modulation by taurine: action on axon membrane permeabilities.

Taurine, a ubiquitous sulfonic amino acid, has been described as a regulator of membrane activity in both normal and pathologic states of nerve and muscle. The common feature of its effects on brain activity and its interaction with muscle, can be summarized in terms of a stabilizing function on excitable membranes. In this paper, we report data on the ionic mechanisms by which taurine modulates membrane behavior of the lobster giant axon. Our data show that taurine increases membrane permeabilities to potassium and chloride but not to sodium. This increase is transient, showing membrane desensitization during taurine application. A reversal potential for the taurine response was observed at about -85 mV, causing the membrane potential to stabilize near the resting level. In addition, taurine causes a reduction of the action potential duration, resulting primarily from an acceleration of the depolarization phase. These ionic actions of taurine may explain its overall inhibitory effects in the central nervous system and in the retina and may account for its antiarrhythmic properties.

Action Potentials↗
PubMedDate not supplied

A control system for high-frequency jet ventilation.

The design of a system for high-frequency jet ventilation is described. Jets of 10-40 psig humidified air were introduced into the trachea through an 8-gauge needle inserted through the cricothyroid membrane. Gas flow to the needle was interrupted by a solenoid valve operated by a controller circuit. The controller allowed the independent setting of duty cycle (ratio of inspiratory time to total cycle time) from 10-50% and respiratory frequency from 10-350/min. When the electrical control signal was set equal to the desired duty cycle, the actual mechanical duty cycle erred from the desired value by as much as 109%. These errors were caused by unequal time delays for solenoid opening and closing. Tests of a commercially available jet-ventilator also demonstrated frequency-dependent errors caused by unequal time delays and changes in wave shape. The controller described here compensates for differences in opening and closing delays and delivers volumes within 3.4% of those calculated from continuous flows.

Animals↗