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Biomedical subjects

D W Arnett

Publications and source records attributed to D W Arnett.

12 recordsLinked to original sources
PubMed1983

Prolonged electromechanical coupling time intervals in skeletal muscle of pigs susceptible to malignant hyperthermia.

Electromechanical properties of skeletal muscle were compared between malignant hyperthermia (MH)-susceptible and control pigs. These muscle properties were studied both in vivo and in vitro. The in vivo time interval from nerve stimulation to onset of mechanical tension was longer in muscle of pigs susceptible to MH. Kinetics of formation of the in vivo compound muscle action potential did not differ between pig groups, whereas the time from peak of the muscle action potential to tension onset was longer for MH muscle. In vitro the time from direct stimulation to tension onset was also longer for MH muscle. These results suggest that the mechanism causing longer electromechanical time intervals in MH skeletal muscle is distal to the myoneural junction. Data comparing contraction kinetics between muscle from MH and control pigs indicates that the mechanism contributing to the longer time interval involves the transfer of signal from the transverse tubule to the sarcoplasmic reticulum in the pigs studied.

Animals↗
PubMed1981

Spatio-temporal cross-correlation analysis of catfish retinal neurons.

1. The receptive field properties of visual neurons in the retina of the catfish are studied by a white noise spatio-temporal stimulus. The spatial and temporal inputs of the stimulus are independent and lead to complete linear characterizations and local nonlinear characterizations of the neural response. 2. Horizontal cells, bipolar cells, and sustained or Type N amacrine cells all yield spatially coherent linear correlations. The horizontal cells have the shortest latency by these methods and exhibit a late depolarizing component that is wider in spatial extent than the initial hyperpolarizing component. Depolarizing Type N neurons have center-hyperpolarizing local nonlinearity. 3. Transient or Type C amacrine cells do not correlate well with the intensity of the stimulus, even though the Fast variety responds vigorously to the stimulus. 4. Ganglion cells are classified into Excitatory, Inhibitory and biphasic classes based upon their linear correlations. Some ganglions exhibit responses dependent upon the orientation of stimulus. Although linear correlation of the Excitatory class is similar to that of the depolarizing Type N cell, the locally nonlinear character of these cell types is distinct. The receptive field of the inhibitory ganglion cells has strong locally excitatory nonlinearity.

Animals↗
PubMed1980

Economic value and course of infection after treatment of cattle having a low level of nematode parasitism.

To determine whether it is economically advantageous to treat calves having inapparent parasitism, we conducted experiments from 1971 to 1976, involving more than 1,800 calves from 30 pens or lots, using formulations of thiabendazole, levamisole, and crufomate (ruelene). Differential egg counts, cultured larvae, and cultured parasitic stages were used to estimate the kind and degree of nematode parasitism. Differentiation of infective larvae consistently established Cooperia as the predominating (%) genus in all fecal samplings. Bunostomum, when initially present, decreased or disappeared, whereas Trichostrongylus increased; other genera fluctuated less consistently. These qualitative generic fluctuations were not primarily the result of treatment, but more likely were seasonal variation. Judged by average daily gain (ADG), anthelmintic treatment was statistically advantageous at one or more points during the observation periods in 10 of 13 treated groups. In seven treated groups, the observation periods were concluded with statistical advantage in ADG, whereas in three groups, compensatory gain by corresponding controls had neutralized earlier advantages. The comparative influence of the various anthelmintics was not consistent from year to year. When total cost/kilogram gain was calculated from feed efficiency measuremnts and other costs, economic treatment advantage was evident in seven of 11 tests (7 of 10 treatment groups) from 1973 through 1976. This financial advantage, due primarily to feed efficiency and noted after 28 to 51 days, justified anthelmintic treatment. This advantage was not likely lost by the animals in subsequent periods (to 218 days) on pasture or in lots, since ADG indicated the treated calves performed either as well as, or better than, the nontreated controls. Considering all aspects of the study, the results indicate calves coming into Kansas from southern states and weighing 184 to 267 kg may possess a level of subclinical (symptomless) nematode parasitism that when treated will result in a response justifying expense for using anthelmintics.

Animals↗
PubMed1978

Statistical dependence between neighboring retinal ganglion cells in goldfish.

Simultaneous recordings were made of the spontaneous discharge of neighboring retinal ganglion cells in goldfish. Crosscorrelation analysis indicates two types of correlation. Neighboring units with like receptive field organization tend to discharge together while units having complementary receptive field organization tend not to discharge together.

Action Potentials↗
PubMed1975

Correlation analysis of units recorded in the cat dorsal lateral geniculate nucleus.

Spike activity was simultaneously recorded from pairs of units consisting of both optic tract fibers and relay cells in the cat dLGN. The unit pairs were classified with regard to the types of receptive fields involved, the relative location of receptive fields, and their occular drive. Statistical dependencies between the discharge patterns of the simultaneously observed units were assessed by computing their auto- and crosscorrelogram during a period of maintained discharge. Two distinctly different types of statistical dependence were observed. Unit pairs having like and overlapping receptive field centers exhibited statistical dependencies manifested in their crosscorrelograms by a peak near the origin. Conversely, unit pairs having opposite and overlapping receptive field centers were characterized by a prominent valley in their crosscorrelograms near the origin. These statistical dependencies are inferred to represent functional interaction most probably occurring in the retina and characterized by a common element exerting an influence on both units.

Action Potentials↗
PubMed1972

Spectral and polarization sensitivity of the dipteran visual system.

Spectral and polarization sensitivity measurements were made at several levels (retina, first and third optic ganglion, cervical connective, behavior) of the dipteran visual nervous system. At all levels, it was possible to reveal contributions from the retinular cell subsystem cells 1 to 6 or the retinular cell subsystem cells 7 and 8 or both. Only retinular cells 1 to 6 were directly studied, and all possessed the same spectral sensitivity characterized by two approximately equal sensitivity peaks at 350 and 480 nm. All units of both the sustaining and on-off variety in the first optic ganglion exhibited the same spectral sensitivity as that of retinular cells 1 to 6. It was possible to demonstrate for motion detection and optomotor responses two different spectral sensitivities depending upon the spatial wavelength of the stimulus. For long spatial wavelengths, the spectral sensitivity agreed with retinular cells 1 to 6; however, the spectral sensitivity at short spatial wavelengths was characterized by a single peak at 465 nm reflecting contributions from the (7, 8) subsystem. Although the two subsystems exhibited different spectral sensitivities, the difference was small and no indication of color discrimination mechanisms was observed. Although all retinular cells 1 to 6 exhibited a preferred polarization plane, sustaining and on-off units did not. Likewise, motion detection and optomotor responses were insensitive to the polarization plane for long spatial wavelength stimuli; however, sensitivity to select polarization planes was observed for short spatial wavelengths.

Animals↗
PubMed1971

Receptive field organization of units in the first optic ganglion of diptera.

Centripetal spike potentials were recorded from two classes of units (transient and sustained) in the intermediate chiasma of flies. On-off units were characterized by a transient discharge after the onset and cessation of a light spot presented within its elliptical receptive field. Receptive fields of sustaining units were composed of three roughly circular regions arranged adjacently along a line; stimulation of the center region elicited a sustainied discharge, whereas stimulation of either adjacent region elicited an off discharge. Adjacent regions antagonized the central region, for stimulation of either inhibited the discharge resulting from stimulation of the central region.

Animals↗