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Biomedical subjects

J F Baker

Publications and source records attributed to J F Baker.

87 records · Page 5Linked to original sources
PubMed1986

Production characters of first generation cows of a five-breed diallel: reproduction of mature cows and preweaning performance of calves by two third-breed sires.

The fourth through sixth parity of 5- to 10-yr-old cows were used to evaluate trade-offs involved with sires of large mature size vs medium mature size in a terminal sire crossbreeding program and to characterize five breeds and their crosses for their potential as dam lines. Charolais and Red Poll bulls, representing large (L) and medium (M) mature size, respectively, were mated to cows representing Angus (An), Brahman (Br), Hereford (He), Holstein (Ho) and Jersey (Je) and their crosses (reciprocals pooled). Cows were randomly assigned for mating to either an L or M bull for each breeding. Size of calf sire did not influence (P greater than .10) the subsequent calving interval of cows. Calving intervals for the straightbred (SB) dairy breeds (Ho and Je) were longer than for SB An and He, but the difference did not exist among the respective crossbred (CB) cows. As a group, Br crosses had shorter intervals than the other CB groups. Crossbred cows exhibited intervals that were 16 d shorter (P less than .05) than SB. Calves sired by L bulls were larger (P less than .01) and faster gaining (P less than .01) for all measures of size and growth studied, but exhibited lower (P less than .01) survival rates to weaning than M-sired calves. Calves of CB dams were 1.5 kg heavier (P less than .01) at birth than calves of SB dams and slightly greater (nonsignificant) hip and shoulder measurements were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Direction-specific adaptation in area MT of the owl monkey.

Single neurons were recorded in owl monkey middle temporal visual cortex (MT). Directional neurons showed direction-selective adaptation to pattern motion: responses to motion in the preferred direction were reduced by adaptation to motion in the preferred direction and enhanced by adaptation in the opposite direction. Non-directional neurons did not show significant adaptation.

Adaptation, Physiological↗
PubMed1985

Production characters of first-generation cows of a five-breed diallel: reproduction of young cows and preweaning performance of inter se calves.

Data from cows of a five-breed diallel involving Angus, Brahman, Hereford, Holstein and Jersey were analyzed. Females were used in inter se matings to produce three second-generation parturitions per cow. Crossbred (CB) cows were 43 d younger (P less than .05), 14 kg heavier (P less than .05) and 2 cm taller (P less than .05) at first calving than straightbred (SB) cows; however, no differences were detected (P greater than .10) between the two groups for pelvic measurements. Although large differences among breed types existed for gestation length, crossbreds generally did not differ from straightbreds for this character. Crossbred cows exhibited a 7.5 d shorter (P less than .05) interval from parturition to first service, but did not exhibit a shorter interval from parturition to conception (P greater than .10). The dairy breeds (Holstein and Jersey) and their crosses exhibited similar postpartum and calving intervals as Angus, while Brahman and their crosses had longer intervals. Crossbred calves were 1.3 kg heavier (P less than .01) and had greater (P less than .01) shoulder and hip dimensions at birth than SB calves, but no difference in the amount of calving difficulty was detected (P greater than .10) between the two groups. Higher (P less than .01) rates of survival to 24 h (3.7%) and to weaning (8.7%) were observed for CB calves compared with SB calves. Heterotic effects for weaning weight (15.2 kg), weaning height (2 cm) and preweaning average daily gain (68 g) were large and illustrate the importance of individual and maternal heterosis for these characters. These results suggest that substantial amounts of heterosis may be retained for survival and weaning characters of calves in early generations of inter se mating of CB.

Analysis of Variance↗
PubMed1982

The disposition of quinfamide in the rat.

The disposition of quinfamide 1-(dichloroacetyl)-6-(2-furoyloxy)-1, 2, 3, 4-tetrahydroquinoline, an enteric anti-amoebic agent, was studied in the rat. A peak blood level equivalent to 2.3 micrograms/ml of quinfamide was observed at 7 hr following a 20 mg/kg oral dose. Urinary recovery of radioactivity was much higher (84%) following intravenous than oral (48%) administration. Drug levels, in all of the tissues examined. were low. The major pathways of quinfamide metabolism in the rat involve hydrolysis of one or both ester groups, acetylation of the de-acylated product to 1-acetyl-1, 2, 3, 4-tetrahydro-6-quinolinol, oxidation of this to the 1-glycolyl metabolite, and aromatization to 6-hydroxyquinoline.

Animals↗
PubMed1981

Visual response properties of neurons in four extrastriate visual areas of the owl monkey (Aotus trivirgatus): a quantitative comparison of medial, dorsomedial, dorsolateral, and middle temporal areas.

1. The response properties of 354 single neurons in the medial (M), dorsomedial (DM), dorsolateral (DL), and middle temporal (MT) visual areas were studied quantitatively with bar, spot, and random-dot stimuli in chronically implanted owl monkeys with fixed gaze. 2. A directionality index was computed to compare the responses to stimuli in the optimal direction with the responses to the opposing direction of movement. The greater the difference between opposing directions, the higher the index. MT cells had much higher direction indices to moving bars than cells in DL, DM, and M. 3. A tuning index was computed for each cell to compare the responses to bars moving in the optimal direction, or flashed in the optimal orientation, with the responses in other directions or orientations within +/- 90 degrees. Cells in all four areas were more sharply tuned to the orientation of stationary flashed bars than to moving bars, although a few cells (9/92( were unresponsive in the absence of movement. DM cells tended to be more sharply tuned to moving bars than cells in the other areas. 4. Directionality in DM, DL, and MT was relatively unaffected by the use of single-spot stimuli instead of bars; tuning in all four areas was broader to spots than bars. 5. Moving arrays of randomly spaced spots were more strongly excitatory than bar stimuli for many neurons in MT (16/31 cells). These random-dot stimuli were also effective in M, but evoked no response or weak responses from most cells in DM and DL. 6. The best velocities of movement were usually in the range of 10-100 degrees/s, although a few cells (22/227), primarily in MT (14/69 cells), preferred higher velocities. 7. Receptive fields of neurons in all four areas were much larger than striate receptive fields. Eccentricity was positively correlated with receptive-field size (r = 0.62), but was not correlated with directionality index, tuning index, or best velocity. 8. The results support the hypothesis that there are specializations of function among the cortical visual areas.

Animals↗
PubMed1980

Disposition of trilostane in the rat and monkey.

The metabolism of trilostane, a novel inhibitor of adrenal steroidogenesis, was studied in the rat and monkey. In the rat, a peak blood level, equivalent to 2 microgram/ml of trilostane, was observed following a 25 mg/kg oral dose; excretion was mainly via the feces. In the monkey, the peak plasma level, equivalent to 15 microgram/ml, was observed 2 hr after a 20 mg/kg oral dose; elimination of radioactivity was predominantly in the urine. The five major metabolites of trilostane in monkey urine have been isolated and partially characterized. The primary metabolic pathways involved hydroxylation and glucuronide formation.

Androstanols↗
PubMed1978

Radioimmunoassay for danazol in human and monkey plasma.

A sensitive method is described for the radioimmunoassay of danazol in monkey and human plasma. Antiserum was developed in rabbits, and a second antibody was used to separate bound from free danazol. The radioimmunoassay was specific for danazol, and the limit of detection ranged from 1.4 to 2.8 ng/ml. Exogeneous danazol could be quantitated accurately in both monkey and human plasma. The radioimmunoassay results agreed with values obtained by inverse isotope dilution after intravenous administration of 14C-danazol to monkeys. The assay was used successfully to measure danazol in plasma from human volunteers receiving 200 mg of danazol.

Animals↗
PubMed1978

Absorption and disposition of N-(1, 1-dimethylethyl)-N'-[2-(4-pyridinyl)-4-pyrimidinyl]urea in rats and dogs.

N-(1, 1-Dimethylethyl)-N'-[2-(4-pyridinyl)-4-pyrimidinyl]urea, Win 40, 882, was eliminated from the blood stream of dogs by two apparent first-order processes with alpha- and beta-phase half-lives of 0.2 hr and 1.4 hr, respectively. Radioactivity of the administered dose was excreted by rats in the feces and via the kidneys; about 40-45% of the dose was recovered in the feces, with the remainder in the urine, over a six day period. One of the terminal methyl groups of the tert-butyl moiety of Win 40,882 is sequentially oxidized by the rat to the alcohol, aldehyde and carboxylic acid. In addition, some of the aldehyde was further metabolized to generate two different monohydroxylated aldehydic metabolites; these hydroxyaldehydes accounted for less than 10% of the dose administered. An unusual metabolic pattern was noted in the excretion of Win 40,882. Over 30% of the urinary metabolites contained the carboxaldehyde function; only8% of the urinary radioactivity was represented by the further oxidation of the aldehyde group to generate the carboxylic acid.

Absorption↗
PubMedDate not supplied

Dynamics of adaptive change in human vestibulo-ocular reflex direction.

Adaptive modification of vestibuloocular reflex (VOR) direction was characterized in humans by recording vertical and horizontal VOR eye movements during horizontal rotations in darkness at frequencies of 0.05 to 1 Hz before and after exposure to a VOR direction adaptation procedure. This procedure paired yaw horizontal vestibular rotation at 0.25 Hz with synchronous pitch vertical optokinetic motion. Saccades were removed from eye position records and VOR gain and phase were recorded. With an onset time constant of 36 min, the VOR measured during horizontal rotation in complete darkness acquired a vertical component in phase with the optokinetic stimulus presented during adaptation. The amplitude of this newly acquired vertical VOR component was maximal during rotation at the frequency of adaptation; at other frequencies, the amplitude was lower, but still significant. Unlike VOR direction adaptation in cats, the phase of the adaptive VOR component in humans did not show significant leads or lags at test frequencies below or above the adaptation frequency. These data suggest that, like the cat, the human VOR can be directionally adapted, and the pathways involving the adaptive component of the VOR are frequency specific.

Adaptation, Physiological↗
PubMedDate not supplied

Metabolism of amrinone in animals.

The biotransformation of 14C-amrinone was studied in rats, dogs, and monkeys by automated gradient high-performance liquid chromatography. The major pathways of metabolism elucidated are: A) glucuronidation at the primary amino nitrogen atom and/or the enolized oxygen atom of the pyridone ring; B) addition of glutathione at the pyridone 2-position and ultimate hydrolysis of this compound to the 2-S-cysteinyl metabolite; C) formation of the primary amino N-acetyl derivative and subsequent oxidation of this to the corresponding N-glycolate. In each species studied, urine was the primary route of elimination and unchanged amrinone was the major urinary excretion product, the other known pathways being: rat, A and C; dog, A and B; monkey, A.

Administration, Oral↗
PubMedDate not supplied

Dynamics of directional plasticity in the human vertical vestibulo-ocular reflex.

Directional plasticity of the human vestibulo-ocular reflex (VOR) was studied in 10 subjects. The adaptation paradigm coupled 0.25 Hz, 19 degrees/s vertical pitch vestibular rotations with 28 degrees/s horizontal optokinetic oscillations. Electro-oculographic recordings in the dark were taken at 0.05, 0.1, 0.25, 0.5, and 1 Hz pitch rotations before and after training and at 15-minute intervals during 0.25 Hz adaptation. Peak head velocity was kept at 19 degrees/sec for frequencies above 0.1 Hz, while constant amplitude was maintained at +/- 24 degrees for 0.05 and 0.1 Hz. In all subjects, directional training produced slow phase horizontal VOR eye movements that were not present during vertical rotations before adaptation. During the 2-hour training period, the cross-axis VOR gain at 0.25 Hz increased up to 0.16. Adaptive VOR gain was highest at the lowest frequency and reached a tuned peak at the 0.25 Hz training frequency. Cross-axis VOR phase remained around 0 degrees at higher frequencies and lagged at lower frequencies. In all subjects, the cross-axis VOR gain was diminished when subjects were exposed to 0.25 Hz pitch rotations paired with a stationary visual field. The dynamics of the vertical VOR remained constant throughout the experiment. These results are further evidence that the frequency response characteristics of adaptive cross-axis VOR gain are similar in humans and cats, while phase behavior is less complex in humans. The high adaptive gain at low frequencies implicates otolith contributions during cross-axis adaptation.

Adaptation, Physiological↗
PubMedDate not supplied

Phase-shifted direction adaptation of the vestibulo-ocular reflex in cat.

The ability of the vestibulo-ocular reflex (VOR) to alter the phase of the motor output relative to the sensory input is examined. Alert cats were trained for 2 h with 0.25 Hz sinusoidal horizontal vestibular and vertical optokinetic rotational stimuli. In each experiment the optokinetic training stimulus was phase shifted by 0 degree, +45 degrees, -45 degrees, or 90 degrees from the vestibular stimulus. Vertical and horizontal eye movements were measured during horizontal rotations in darkness before and after the training procedure. Phase-advance experiments (+45 degrees) produced an adaptive vertical VOR with a mean phase of +28 degrees. After phase-delay experiments (-45 degrees), the adapted VOR had a mean phase of -19 degrees. The peak adaptive change in VOR gain was at or near the 0.25 Hz training frequency in each experimental group, but the gain depended in a complex manner on the testing frequency and the degree of phase shift of the training stimulus. Training with a 45 degrees phase-delayed optokinetic stimulus produced an adaptive vertical VOR with a gain that was relatively higher at frequencies below the training stimulus than at those that were above. Training with a 45 degrees phase-advanced optokinetic stimulus produced an adaptive vertical VOR with a gain that was higher at frequencies above the training frequency than at those that were below. During training with a phase-shifted optokinetic stimulus, adjustment of the relative efficacies of two neural pathways, a velocity pathway and an integrating pathway, could account for gain dependence on testing frequency and phase shift. This was corroborated by a model of the VOR that incorporates parallel velocity and integrating pathways. Data from 45 degrees phase advances were fit by increasing the gain of the velocity versus integrating pathway, whereas 45 degrees phase delay data were fit by decreasing the gain of the direct versus integrating pathway. The models altered the time constants of either the common oculomotor integrator or the velocity storage mechanism.

Adaptation, Ocular↗