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Biomedical subjects

D A Oakley

Publications and source records attributed to D A Oakley.

At least 19 recordsLinked to original sources
PubMed1992

Evaluation of an automated system for hemoglobin measurement in animals.

In veterinary medicine, PCV determined by centrifugation of blood in a microhematocrit tube is the most common clinical test used to initially assess and monitor anemic and polycythemic animals. In contrast, blood hemoglobin (Hb) concentration, rather than PCV, is generally determined in human patients. One automated system photometrically measures blood Hb concentration after conversion of Hb to azide methemoglobin without dilution and was found to be a simple and accurate instrument for use in human medicine. We evaluated the system for its accuracy in measuring blood Hb concentration in animals by comparing it with standard techniques and for its suitability in veterinary practice. Blood samples, anticoagulated with potassium EDTA, from 78 healthy animals (33 dogs, 17 cats, 13 horses, and 15 cows) and 58 dogs and 4 cats with various blood abnormalities (10 anemia, 11 polycythemia, 21 lipemia, 16 leukocytosis, and 6 icterus) were analyzed. In all species, blood Hb concentration of healthy animals determined by the system was comparable to that measured by standard cyanmethemoglobin methods (ie, an automated counter; rI = 0.987 to 0.998 and a hemoglobin kit, rI = 0.946 to 0.993). The aforementioned system also yielded similar values to those obtained by use of standard methods in anemic, polycythemic, and icteric dogs and cats. Moreover, the system reads the absorbance at 2 wavelengths to correct for turbidity, and therefore, accurately measured Hb concentration in blood samples with severe lipemia (triglycerides concentration > 500 mg/dl) and marked leukocytosis (> 50,000 WBC/microliter), whereas other standard Hb techniques are known to give falsely high results.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The effect of unilateral anteromedial cortex lesions on prey-catching and spatio-motor behaviour in the rat.

The neglect which follows a unilateral lesion of anteromedial cortex in rat was examined using two tasks. In the first task animals had to press the left bar of a two-bar Skinner box for food reward. In the second task animals captured live locusts presented in either their right or left visual field. The results showed that in the Skinner box there was a transitory spatial neglect contralateral to the lesion, which disappeared after 2-3 days. In the prey-catching task animals failed to target or track locusts when they were in the field contralateral to the lesion throughout the 4-day testing period. Capture and consummatory responses were normal when the locust was presented (or moved independently) into the ipsilateral (non-neglected) field. 60 days later the asymmetrical response to locusts in the contralateral field had disappeared.

Animals↗
PubMed1990

Performance on two fixed-interval schedules in the absence of neocortex in rats.

Rats with complete surgical removal of the neocortex (neodecorticates) were trained, with milk as the reinforcer, on a 40-s fixed-interval (FI-40) schedule, then on an FI-120, and finally reexposed to the FI-40. Like controls, neodecorticates developed and appropriately adjusted their postreinforcement pauses and response distributions and showed scallop-type responding on the FI-120 and a positive correlation between running rate and the preceding postreinforcement pause on both FI-40 schedules but not on the FI-120. On some variables neodecorticates reached asymptotic levels of performance more slowly than controls. Extended training on the first FI-40 did not differentially affect neodecorticates' performance. The results suggest that neodecorticates retain a functional timing mechanism.

Animals↗
PubMed1989

Anomalous patterns of response learning and transfer in decorticate rats.

Behavioural flexibility in decorticate rats was examined by testing response transfer in an obstructed alleyway. In the first experiment, rats were trained to push a ball out of a cylindrical alleyway in order to gain access to the goal box. When this 'push' habit was prevented by blocking forward movement of the ball, decorticate rats were much quicker than sham-operated rats in successfully developing the novel clearance response of pulling the ball into the start box. Both groups were subsequently able to reverse effectively between responses. In a second experiment, sham-operated and decorticate rats were first shaped to pull the ball clear from the alleyway, and then required to adopt a push-type clearance response when movement of the ball towards the start box was prevented. Here, the decorticates showed difficulty both in learning to pull the ball out of the alley and in transferring to a push-type clearance response, but having transferred they coped well with subsequent reversals. This asymmetrical pattern of transfer results is not readily attributed to response preference and raises the possibility that, in some situations at least, decorticated animals may show greater behavioural flexibility than had previously been supposed.

Animals↗
PubMed1989

Autoshaping in micrencephalic rats.

An autoshaping procedure in which the illumination of a lever was predictive of food reinforcement was used to compare learning in rats with micrencephaly induced by irradiation on the 16th day of gestation and in sham-irradiated controls. Both groups showed equivalent levels of lever-directed activity, and the micrencephalic animals differentiated as well as the control animals between the predictive lever and a nonpredictive lever. The micrencephalic animals were able to redistribute their lever-directed activity when the significance of the levers was reversed and did so more readily than the control animals. Results support the claim that association learning survives either traumatic or developmental neocortical damage and have implications for remedial procedures following both head injury and developmental cerebral pathology in humans.

Animals↗
PubMed1987

Visual discrimination in the absence of visual cortex.

Normal rats and rats with devascularization lesions ranging from subtotal removals of striate cortex (Area 17) to complete removal of neocortex were trained in a horizontal/vertical stripe discrimination for a liquid reinforcer. Subgroups of animals were identified on the basis of size and location of lesion (with particular reference to striate cortex) as Subtotal, Striate, Posterior and Decorticate. Some animals in all of the lesion groups were able to acquire the discrimination, but there was a direct relationship between lesion size and number of training trials. Those animals which reached criterion on the original discrimination were trained on a second horizontal/vertical discrimination under either transfer or reversal conditions using 'rotated obliques' stimuli. Performance on this second discrimination indicated that animals from all lesion groups had been using visual stimuli based on stripe orientation in the original problem. Members of all lesion groups solved the rotated obliques problem under the transfer condition, though the speed and completeness with which they did so was again inversely related to lesion size. These data show high levels of visual competence in the absence of visual cortex even when stimuli thought to detect form discrimination are used and thus reinforce the view that superior colliculus may be a more significant visual area for the rat than was previously assumed. They also support other observations that animals do not use residual visual capacities without extensive experience and appropriate motivation.

Animals↗
PubMed1986

Colour versus orientation discrimination in severely brain-damaged and normal adults.

Normal adults and adults with severe, diffuse brain damage were tested on a two-choice simultaneous discrimination where either the colour or orientation of stripes on the stimulus cards was the relevant dimension. There was no overall impairment in discrimination learning by the brain-injured subjects. In the normal subjects, however, the discrimination was produced more readily for line orientation than for colour whereas the converse was true for the brain-damaged group. The present data are compared to those obtained in developmental studies and with other types of cerebral pathology.

Adult↗
PubMed1985

Expected and actual behavioural capacity after diffuse reduction in cerebral cortex: a review and suggestions for rehabilitative techniques with the mentally handicapped and head injured.

Expectations of residual function (and of potential therapeutic outcome) after brain damage are important factors in the selection of rehabilitation programmes. Drawing upon reports of what we call here association learning and memory in humans and animals, it is shown that this type of learning remains intact and may be mediated by subcortical brain structures, despite the often severe cognitive blunting which accompanies diffuse cortical brain damage. In retarded humans the application of association learning-based behaviour modification techniques may lead to the development of an adequate behavioural base-line on which to develop cognitive rehabilitation programmes. The implications of potentially valid neuropsychological extrapolations from animals to man are discussed. Finally suggestions are made concerning the interaction between association learning and more cognitive information-processing strategies, and the implications for behaviour modifications with retarded and head injured are considered.

Anencephaly↗
PubMed1975

Role of cortex in Pavlovian discrimination learning.

Two totally neodecorticate rabbits and two groups of normal rabbits were trained on a light-tone differentiation using a Pavlovian nictitating membrane response. The significance of the two stimuli involved in the differentiation was then reversed. Excellent initial differentiations were produced by both decorticates and normals, although there was some evidence of a small retardation of conditional response acquisition in the decorticates in this first stage of the experiment. Under reversal conditions the decorticates extinguished responding to the formerly positive conditional stimulus in fewer trials and produced more complete differentiation performances than normal animals. The decorticates, unlike the normal animals, failed to show a reduction in conditional response onset latencies during either differentiation or reversal training.

Acoustic Stimulation↗
PubMed1975

Backward conditioning in the rabbit (Oryctolagus cuniculus).

Backward conditioning of the nictitating membrane response of rabbits was studied. The prior exposure to unconditional stimulus-conditional stimulus (US-CS) pairings retarded subsequent forward conditioning. Control procedures eliminated latent inhibition and forward safety-signal effects as accounting for the data. The relevance of this report to other recent studies of backward conditioning is discussed.

Acoustic Stimulation↗
PubMed1975

Ontogeny of spontaneous locomotor activity in rabbit, rat, and guinea pig.

Postnatal locomotor activity was investigated in rabbit, rat, and guinea pig. A peak was found in this behavior at 5 days of age in the rabbit and, in confirmation of earlier studies, at 15-20 days in the rat. Neonatal guinea pigs showed no variation in activity levels due to age. The guinea pig is born at an advanced stage of neural maturation in comparison with the rat, and the rabbit is born at an intermediate stage. This difference accounts for the observed variations in postnatal activity profiles if it is assumed that the behavioral peak coincides with the transition from a stage of primarily mesencephalic arousal system maturation to a stage of primarily diencephalic and telencephalic inhibitory system maturation.

Age Factors↗