Search PubMed⌕ Search

Biomedical subjects

D L Robinson

Publications and source records attributed to D L Robinson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Alfalfa NADH-dependent glutamate synthase: structure of the gene and importance in symbiotic N2 fixation.

Glutamate synthase (GOGAT), a key enzyme in ammonia (NH+4) assimilation, occurs as two forms in plants: a ferredoxin-dependent form (Fd-GOGAT) and an NADH-dependent form (NADH-GOGAT). These enzymes are encoded by distinct genes as evidenced by their cDNA and deduced amino acid sequences. This paper reports the isolation and characterization of a NADH-GOGAT gene from alfalfa (Medicago sativa L.), the first GOGAT gene to be isolated from a eukaryote. RNase protection and primer extension experiments map the transcription start site of NADH-GOGAT to nearly identical positions. The transcribed region of this gene, 12,214 bp, is comprised of 22 exons separated by 21 introns. The 2.7 kbp region 5' from the translation initiation site confers nodule-specific reporter gene activity when used in a chimeric beta-glucuronidase (GUS) construct and transformed into Lotus corniculatus and Medicago sativa. Both infected and uninfected cells display GUS activity. The abundance of NADH-GOGAT transcripts increases substantially in developing nodules of plants infected with effective rhizobia. However, this increase is not observed when nodules are induced by a variety of ineffective rhizobial strains. Thus, unlike many other plant genes involved in root nodule NH+4 assimilation, high levels of NADH-GOGAT expression are strictly associated with effective nodules indicating that NADH-GOGAT plays a central role in the functioning of effective root nodules. An alfalfa Fd-GOGAT PCR product showing greater than 85% identity to maize Fd-GOGAT was isolated and used to investigate the contribution of this enzyme to NH+4 assimilation in nodules. Fd-GOGAT mRNA was abundant in leaves and cotyledons but was not detected in alfalfa root nodules. Fd-GOGAT in alfalfa does not appear to play a significant role in symbiotic N2 fixation.

Amino Acid Sequence↗
PubMed1995

Clinical presentation of "silent" meningiomas after general anaesthesia.

We present two patients who became unrousable within 48h after general anaesthesia for non-neurosurgical operations; both were found to have frontal meningiomas. Analysis of these and previous reports suggest that several anaesthetic and perioperative factors probably combine to contribute to the accelerated presentation of these previously "silent" tumours, and we recommend that dexamethasone should be administered early in the course of unexplained neurological deterioration after operation.

Aged↗
PubMed1995

Modified saccades evoked by stimulation of the macaque superior colliculus account for properties of the resettable integrator.

1. Models of the saccadic system propose that there is an integration of the pulse signal, and there is good evidence that the integrator is reset gradually (Nichols and Sparks 1994, 1995). Other studies of the superior collicular contribution to the saccadic system have proposed a sensory, not motor, nature for its signal. 2. To test experimentally the resetting of the integrator and the nature of the collicular signal, we electrically stimulated the superior colliculus during periods of fixation and during the course of visually guided saccades. Trains of stimuli which were presented during periods of fixation evoked saccades with fixed vectors. Identical stimulation at the beginning of a visually guided saccade evoked saccades whose direction was rotated and amplitude extended from the fixed vector. The direction of the rotation was opposite that of the visually guided saccade, and the magnitude of this rotation could be as large as 80 degrees. 3. Stimulation which was applied at progressively later times during the visually guided saccade, evoked saccades with progressively smaller rotations and progressively less elongations. The time period during which saccades were modified persisted beyond the end of the visually guided saccade, when the eyes were stationary. Thus, we confirm the previous findings (Nichols and Sparks 1994, 1995; Robinson, 1972), that the end of the saccade is not a period of quiescence within the oculomotor pathways. 4. Our results confirm that the resetting of the integration of the saccade signal is gradual rather than abrupt. Furthermore, these data suggest that the superior colliculus signals a motor error.

Animals↗
PubMed1995

Covert orienting of attention in macaques. II. Contributions of parietal cortex.

1. To understand some of the contributions of parietal cortex to the dynamics of visual spatial attention, we recorded from cortical cells of monkeys performing attentional tasks. We studied 484 neurons in the intraparietal sulcus and adjacent gyral tissue of two monkeys. We measured phasic responses to peripheral visual stimuli while the monkeys attended toward or away from the stimuli or when attention was not controlled. Neurons were tested while the monkeys gazed at a spot of light (simple fixation task), actively attended to a foveal target (foveal attention task), performed a reaction time task (cued reaction time task), made saccadic eye movements to visual targets (saccade task), or responded to a repetitious peripheral target (probability task). 2. In a previous paper we demonstrated that monkeys, like humans, responded more quickly to visual targets when the targets followed briefly flashed visual cues (validly cued targets) (Bowman et al. 1993). It has been hypothesized that the cue attracts attention to its locus and results in faster reaction times (Posner 1980). In the present physiological studies, visual cues consistently excited these neurons when they were flashed in the receptive field. Such activity might signal a shift of attention. Visual targets that fell within the receptive field and that immediately followed the cue evoked relatively weak responses. This response was due to a relative refractory period. 3. Next we tested attentional processes in these tasks that were independent of the visual response to the cue. We placed the cue outside of the receptive field and the target within the receptive field. We found that 23% of these cells had a significant decrease in their firing rate to validly cued targets in their receptive fields under these conditions. Strong responses were evoked by the same target when the cue was flashed in the opposite hemifield (invalidly cued targets). Thus this group of neurons responded best when attention was directed toward the opposite hemifield. 4. For another group of parietal cells (13%) there was an enhanced response to targets in the visual receptive field when the cue was in the same hemifield. For the remaining 64% of the cells there was no significant modulation in this task. 5. The cued reaction time task involved exogenous control of attention; the sensory cue gave spatial and temporal direction to attention. We used several other tasks to test for endogenous control of attention.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Covert orienting of attention in macaques. III. Contributions of the superior colliculus.

1. The present experiments were conducted to study physiological mechanisms in the superior colliculus and their relation to visual spatial attention. We used a cued reaction time task studied in detail previously (Bowman et al. 1993; Posner 1980). Monkeys learned to fixate a spot of light and release a bar when a target light appeared. Cues on the same side as the target (valid cue) were associated with faster reaction times than those on the opposite side (invalid cue). The difference in reaction times is hypothesized to be a measure of attention. 2. A total of 79 neurons within the superficial layers of the superior colliculi of two monkeys were studied. When the cues and targets were positioned so that both were within the visual receptive field, the cues excited the cells, and this produced a refractoriness to the targets for the following 400 ms. Both the ON and OFF responses to the cue were constant under all conditions. 3. These neurons were also tested with the cue just outside of the visual receptive field. This was done to avoid refractory effects from the cue; there was no significant modulation of the response to the target under these conditions. The visual responses of neurons in the intermediate layers of the superior colliculus also responded equivalently under these conditions. 4. When the activity of cells within the foveal representation was compared during the performance of three tasks, there was differential activity. The appearance of the fixation point during the performance of the cued reaction time task led to a strong, transient discharge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Subcortical contributions to head movements in macaques. I. Contrasting effects of electrical stimulation of a medial pontomedullary region and the superior colliculus.

1. These studies were initiated to understand the neural sites and mechanisms controlling head movements during gaze shifts. Gaze shifts are made by saccadic eye movements with and without head movements. Sites were stimulated electrically within the brain stem of awake, trained monkeys relatively free to make head movements to study the head-movement components of gaze shifts. 2. Electrical stimulation in and around the gigantocellular reticular nucleus evoked head movements in the ipsilateral direction. Gaze shifts were never evoked from these sites, presumably because the vestibulo-ocular reflex compensated. The rough topography of this region included large head movements laterally, small movements medially, downward movements from dorsal sites, and upward movements more ventrally. 3. The initial position of the head influenced the magnitude of the elicited movement with larger movements produced when the head was directed to the contralateral side. Attentive fixation was associated with larger and faster head movements when compared with those evoked during spontaneous behavior. 4. The superior colliculus makes a significant contribution to gaze shifts and has been shown to contribute to head movements. Because the colliculus is a major source of afferents to the gigantocellular reticular nucleus, comparable stimulation studies of the superior colliculus were conducted. When the colliculus was excited, shifts of gaze in the contralateral direction were predominant. These were most often accomplished by saccadic eye movements, however, we frequently elicited head movements that had an average latency 10 ms longer than those elicited from the reticular head movement region. Sites evoking head movements tended to be deeper and more caudal than loci eliciting eye movements. Neither the onset latencies, amplitudes, nor peak velocities of head movements and eye movements were correlated. Gaze shifts evoked from the caudal colliculus with the head free were larger than those elicited from the same site with the head fixed. 5. These studies demonstrate that both the superior colliculus and gigantocellular reticular nucleus mediate head movements. The colliculus plays a role in orienting to external events, and so collicular head movements predominantly were associated with gaze shifts, with the eye and head movements uncoupled. The medullary reticular system may play a role in the integration of a wider range of movements. Head movements from the medullary reticular sites probably participate in several forms of head movements, such as those that are related to postural reflexes, started volitionally, and/or oriented to external events.

Animals↗
PubMed1994

Subcortical contributions to head movements in macaques. II. Connections of a medial pontomedullary head-movement region.

1. In the companion article, a variety of head movements were elicited by stimulation in, and adjacent to, the gigantocellular reticular nucleus (Cowie and Robinson 1994). We refer to this area, caudal to the abducens nucleus, as the gigantocellular head movement region. In the present paper, the anatomical connections of this region, as determined by injections of wheat-germ agglutinin conjugated horseradish peroxidase (WGA-HRP), are reported. The majority of efferent and afferent connections were with areas related to head movements. 2. Efferent fibers from the region projected via two paths to the caudal medulla and upper cervical spinal cord. Labeled fibers descended in the anterolateral funiculus of the ipsilateral spinal cord to terminate in lateral parts of the ventral horn. A second pathway descended bilaterally in the medial longitudinal fasciculus to the anterior funiculi and medial portions of the ventral gray. These efferents paralleled the head-movement topography demonstrated physiologically. Other projections included efferents to the interstitial nucleus of Cajal, caudal field H of Forel, paramedian pontine reticular formation, and caudal vestibular nuclei. Other efferent fibers projected to the trigeminal, facial, and hypoglossal nuclei, as well as to the parvocellular reticular field, which contains interneurons for these motor groups. However, no efferent or afferent labeling involved the ocular motor nuclei. 3. Afferents to the gigantocellular head movement region arose mainly from head-movement areas. In all animals, labeled cells were found in the intermediate and deep layers of the caudal superior colliculus. Labeled neurons also were found in the caudal field H of Forel, interstitial nucleus of Cajal, pontine medial tegmentum including the pontine paramedian reticular formation, nucleus subcoeruleus, and vestibular nuclear complex. Caudally, filled cells were located in the parvocellular, magnocellular, dorsal, and ventral reticular nuclei, the supraspinal nucleus, and the upper cervical ventral horn. 4. In one animal, the ipsilateral frontal cortex contained retrogradely labeled neurons. These cells were found in layer V of cortical areas 4 and 6. Other afferent cells were found consistently in the periventricular and periaqueductal gray matter. 5. A control injection into the caudal vestibular nuclear complex showed projections to the gigantocellular reticular formation and labeled cells in the vestibular and parvocellular reticular nuclei. These observations show that the connections of the gigantocellular region are not typical of all head movement sites. 6. These data indicate that the gigantocellular head-movement region has the requisite efferent and afferent connections to function in the subcortical control of head, but not eye, movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Dopamine dependent reaction time deficits in patients with Parkinson's disease are task specific.

This study tested the hypothesis that patients with Parkinson's disease are impaired when they must rely on internal information to generate a response. Choice reaction times of control subjects and patients with Parkinson's disease, on and off their medication, were measured in tasks in which the motor demands were constant but which varied in the degree to which the stimuli held intrinsic information about the required response. A dopaminergic deficit was observed only in the tasks which employed stimuli compatible with the response and not in a task employing stimuli arbitrarily associated with the response. The data do not support the hypothesis that patients are differentially impaired in using internalized stimulus-response relationships.

Adult↗
PubMed1993

Functional contributions of the primate pulvinar.

One of the major tasks facing the central nervous system is choosing which sensory events to use for perception and directed behavior. All organisms live in a rich sensory environment, and it is impossible to attend and respond to everything. Certain brain regions and systems must evaluate sensory signals and then determine which are salient. Based on recent data derived from diverse studies of the pulvinar of primates, it is the hypothesis of this paper that a major role of the pulvinar is to participate in the generation of visual salience, those processes which precede perception and action. This process of salience generation makes use of two broad mechanisms, the suppression of noise and the enhancement of significant signals. Outlined above are experiments which show that the visual activity which might be caused by eye movements is filtered from some pulvinar cells. Visual responses associated with certain directions of gaze are removed. Finally the ability to suppress the activity of distracting visual stimuli is dependent on the integrity of the pulvinar. Conversely, there are neurons within the pulvinar which respond best when animals actively select and thus engender certain stimuli with salience. Modulation of pulvinar functioning with transmitter-related drugs changes performance as if salience is being modulated. Humans and monkeys with destruction of the pulvinar behave as if they too cannot create or evaluate salience. Finally, when salience is demanded of humans by making their visual tasks more demanding, there is an increase in PET activity. The hypothesis here is that the pulvinar functions as an early center for the generation of visual salience. This is similar to the view of striate cortex as an early integration stage for the basic elements of visual processing (Hubel and Wiesel, 1968; Zeki, 1976; Allman et al., 1981). Vision does not take place within the complex microstructure of striate neurons, but all of the essential components are present there, and these are distributed to other cortical areas which construct specific aspects of visual perception. Similarly, regions of the pulvinar contain building blocks for visual/behavioral/oculomotor integration which they distribute to various cortical sites for shifts of attention and other types of response specification. When an organism must determine external visual salience, there are neurons within the pulvinar which signal this. Since the major efferents of these thalamic regions are the visual cortices (Benevento and Rezak, 1976; Lin and Kaas, 1979; Kennedy and Bullier, 1985), our present hypothesis is that these signals are used for the construction of visuomotor and visuo-perceptual states.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Covert orienting of attention in macaques. I. Effects of behavioral context.

1. A task was used by Posner (1980) to measure shifts of attention that occurred covertly, in the absence of an eye movement or other orienting response. This paradigm was used here to assess the nature of covert attentional orienting in monkeys to develop an animal model for neurophysiological studies. Shifts of attention were measurable in monkeys and were consistent across a variety of experimental conditions. 2. The paradigm required that monkeys fixate and release a bar at the appearance of a target, which was preceded by a cue. Reaction times to targets that followed peripheral cues at the same location (validly cued) were significantly faster than those that followed cues in the opposite visual field (invalidly cued). This difference was defined as the validity effect, which as in humans, is used as the measure of a covert attentional shift. 3. When the proportion of validly to invalidly cued targets was decreased, no change was seen in the validity effect of the monkeys. This is in contrast to humans, for whom the ratio of validly to invalidly cued targets affected the magnitude of the validity effect. When 80% of the targets were preceded by cues at the same location, the validity effect was greatest. The effect was reversed when the proportions were reversed. From this result, it is concluded that cognitive processes can affect covert orienting to peripheral cues in humans, whereas in trained monkeys, performance was automatic. 4. To test whether cognitive influences on attention could be demonstrated in the monkey, an animal was taught to use symbolic, foveal signals to covertly direct attention. The magnitude of this validity effect was greater than that obtained with peripheral cues. 5. The effects of motivational and perceptual processes were tested. Although overall reaction times could be modified, the facilitating effects of the cues persisted. This constancy across motivational and perceptual levels supports the notion that the monkeys were performing the task in an automatic way, under the exogenous control of peripheral cues. 6. Most visual cuing has been tested with visual landmarks at the locations of cues and targets. These monkeys were trained with such landmarks, and when tested without them, the attentional effect of the cues was nearly abolished. These data suggest that local visual features can be important for covert orienting. 7. To determine the spatial extent of the effect of the cue, monkeys and humans were tested with four cue-target distances (0-60 degrees).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Live animal measurement of carcass traits: estimation of genetic parameters for beef cattle.

Ultrasound measurements by trained and accredited sonographers on 9,232 Angus, Hereford, and Polled Hereford cattle at an average age of 450 d were used to estimate genetic and environmental (co)variances for weight at scanning (Wt), longissimus muscle area (LMA), longissimus muscle area adjusted to a constant weight of 400 kg (LMAawt), and fat depths at the rump and 12/13 rib sites. Estimated kilograms (ESMkg) and percentage of saleable meat yield (ESM%) were also calculated and analyzed. Subjective muscle scores, available for 2,488 animals, were also included in the analysis. Estimated heritabilities were 46% for Wt, 21% for LMA and LMAawt, 37% for rump fat, 30% for rib fat, 15% for muscle score, 44% for ESMkg, and 36% for ESM%. The two measurements, LMA and LMAawt, had high genetic (.82) and environmental (.91) correlations. The two fat depths were also highly correlated (.86 genetic; .67 environmental). Weight at scanning was moderately correlated with LMA (.45 genetic; .41 environmental). Differences between breeds could not be detected, but some variation in parameter estimates between data sets of the same breed was observed. Environmental correlations between fat depths or muscle score and Wt were approximately .3; genetic correlations were .07 to .12. Subjective muscle score had marginally higher genetic correlations with LMA than with LMAawt (.22 vs .08) but similar environmental correlations (.31 vs .27). Results show that carcass traits measured by ultrasound and predictions of meat yield have genetic variability, are moderately heritable, and that genetic progress based on genetic evaluation by mixed-model analysis can be made.

Adipose Tissue↗
PubMed1993

Transcatheter embolization of an aortocaval fistula caused by residual renal artery stump from previous nephrectomy: a case report.

An arteriovenous fistula between the renal artery and vein is a rare complication of nephrectomy. We report the first case of direct inferior vena cava to renal artery fistula after nephrectomy. In addition, this was the first use of the Amplatz "spider," a vascular obstructing device used to trap coils during transcatheter embolization of a high-flow fistula. The patient's fistula was embolized successfully, with immediate improvement of symptoms and without pulmonary embolization.

Aged↗
PubMed1992

Highly conserved repetitive DNA sequences are present at human centromeres.

Highly conserved repetitive DNA sequence clones, largely consisting of (GGAAT)n repeats, have been isolated from a human recombinant repetitive DNA library by high-stringency hybridization with rodent repetitive DNA. This sequence, the predominant repetitive sequence in human satellites II and III, is similar to the essential core DNA of the Saccharomyces cerevisiae centromere, centromere DNA element (CDE) III. In situ hybridization to human telophase and Drosophila polytene chromosomes shows localization of the (GGAAT)n sequence to centromeric regions. Hyperchromicity studies indicate that the (GGAAT)n sequence exhibits unusual hydrogen bonding properties. The purine-rich strand alone has the same thermal stability as the duplex. Hyperchromicity studies of synthetic DNA variants indicate that all sequences with the composition (AATGN)n exhibit this unusual thermal stability. DNA-mobility-shift assays indicate that specific HeLa-cell nuclear proteins recognize this sequence with a relative affinity greater than 10(5). The extreme evolutionary conservation of this DNA sequence, its centromeric location, its unusual hydrogen bonding properties, its high affinity for specific nuclear proteins, and its similarity to functional centromeres isolated from yeast suggest that this sequence may be a component of the functional human centromere.

Animals↗
PubMed1992

The pulvinar and visual salience.

One of the major problems of living in a rich visual environment is deciding which particular object or location should be chosen for complete processing or attention; that is, deciding which object is most salient at any particular time. The pulvinar has enlarged substantially during evolution, although little has previously been known about its function. Recent studies suggest that the pulvinar contains neurons that generate signals related to the salience of visual objects. This evidence includes: (1) anatomical and physiological observations of visual function; (2) augmented responses in the pulvinar for visual stimuli presented in important contexts; (3) suppression of activity for stimuli presented in irrelevant conditions; (4) thalamic modulation producing behavioral changes in cued attention paradigms; and (5) similar changes with visual distracter tasks.

Animals↗
PubMed1992

Live animal measurement of carcass traits by ultrasound: assessment and accuracy of sonographers.

The establishment and evaluation of an assessment system to accredit sonographers for measuring the carcass traits of subcutaneous fat depths and longissimus muscle area (LMA) on potential breeding animals by real-time ultrasound is described. Repeatability of operators, variation between the animal's left and right sides, and variations in technique were assessed from measurements and repeat measurements of 30 cattle by up to eight operators at three testing sessions. Accuracy of carcass data was determined by repeatability of measurements, variability between measurers, between left and right sides of the carcass, and variation due to handling and dressing procedures. Correlations with carcass data averaged .92 for rump fat, .90 for rib fat, and .87 for LMA. Residual SD averaged .81 mm, .88 mm, and 5.1 cm2. A very experienced sonographer can measure LMA only marginally less accurately than it can be measured on the carcass. In Session 3, the SE between repeat fat measurements for accredited sonographers averaged .43 mm, indicating that fat depths can be measured more accurately, but when comparing measurements from different operators, adjustments may be required for differences in technique, otherwise overall accuracy will be about the same, approximately 1 mm. Scanned rump fat measurements were consistently approximately 20% higher than on the chilled, hanging carcass 24 h after slaughter; after applying the standard correction factor of 1.17, LMA measurements were similar. Scan and carcass rib fat measurements were similar for animals with less than or equal to 10 mm of fat cover, above which carcass measurements tended to be higher.

Accreditation↗
PubMed1991

Visual responses of pulvinar and collicular neurons during eye movements of awake, trained macaques.

1. We recorded from single neurons in awake, trained rhesus monkeys in a lighted environment and compared responses to stimulus movement during periods of fixation with those to motion caused by saccadic or pursuit eye movements. Neurons in the inferior pulvinar (PI), lateral pulvinar (PL), and superior colliculus were tested. 2. Cells in PI and PL respond to stimulus movement over a wide range of speeds. Some of these cells do not respond to comparable stimulus motion, or discharge only weakly, when it is generated by saccadic or pursuit eye movements. Other neurons respond equivalently to both types of motion. Cells in the superficial layers of the superior colliculus have similar properties to those in PI and PL. 3. When tested in the dark to reduce visual stimulation from the background, cells in PI and PL still do not respond to motion generated by eye movements. Some of these cells have a suppression of activity after saccadic eye movements made in total darkness. These data suggest that an extraretinal signal suppresses responses to visual stimuli during eye movements. 4. The suppression of responses to stimuli during eye movements is not an absolute effect. Images brighter than 2.0 log units above background illumination evoke responses from cells in PI and PL. The suppression appears stronger in the superior colliculus than in PI and PL. 5. These experiments demonstrate that many cells in PI and PL have a suppression of their responses to stimuli that cross their receptive fields during eye movements. These cells are probably suppressed by an extraretinal signal. Comparable effects are present in the superficial layers of the superior colliculus. These properties in PI and PL may reflect the function of the ascending tectopulvinar system.

Animals↗