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Biomedical subjects

R Richardson

Publications and source records attributed to R Richardson.

At least 145 records · Page 8Linked to original sources
PubMed1985

Competition between seminal and exogenous proteinase inhibitors for sites on murine epididymal sperm.

Sixteen proteinase inhibitors were tested for their ability to compete with the natural seminal inhibitor for binding to the surface of murine epididymal sperm. The most effective competitors, 4-methylumbelliferyl-p-quanidinobenzoate (MUGB) and p-nitrophenyl-p-guanidinobenzoate (NPGB), are also effective inhibitors of both murine acrosin and in vitro fertilization of mouse gametes. The data support the suggestion that the inhibition of fertilization by these inhibitors may be effected by their action on the sperm surface rather than binding to enzymes located within the acrosome. Since the surface acceptor molecule recognizes a number of inhibitor types, as well as substrates for such enzymes as trypsin and acrosin, the acceptor's binding site may be similar to the active site on the enzyme.

Animals↗
PubMed1985

Administration of dexamethasone prior to training blocks ACTH-induced recovery of an extinguished avoidance response.

Pretest administration of ACTH has been shown to produce recovery of an extinguished avoidance response. Presumably this effect is found because endogenous ACTH is a component of the original training memory. However, another possible explanation of this finding is that administration of the peptide acts as a novel stimulus that "disinhibits" the extinguished response. In order to test this "disinhibitory" hypothesis of ACTH-induced recovery of an extinguished avoidance response, some subjects were given dexamethasone 2 hr prior to training and extinction. This synthetic glucocorticoid is effective in blocking endogenous release of ACTH. Thus, ACTH should not be a component of the training memory in subjects given dexamethasone prior to training and extinction but would be a relatively novel stimulus condition at testing. Pretest administration of ACTH was found to be effective in alleviating performance deficits induced by extinction only for subjects given saline prior to training and extinction. Administration of ACTH had no effect on the avoidance responding of subjects given dexamethasone. These findings suggest that pretest administration of ACTH affects retrieval processes rather than acts as a disinhibitor.

Adrenocorticotropic Hormone↗
PubMed1984

Stimulus generalization of conditioned taste aversion in rats.

Relatively little information is available regarding the intradimensional stimulus generalization of conditioned taste aversion (CTA). Experiment 1 employed a between-groups generalization test to examine the extent to which conditioned flavor aversion to one sucrose solution generalized to other concentrations of sucrose in adult rats. Evidence of a gradient of aversion was obtained. Because generalization gradients in other tasks have been found to flatten over a retention interval, Experiment 2 investigated the effects of delayed testing (2, 7, or 21 days) upon the slope of the generalization gradient. The generalization gradient flattened at the intervals, suggesting that subjects forgot the specific attributes of the conditioning concentration and avoided generalized stimuli as if they were the original CS. Experiment 3 used a long delay between taste and toxicosis to degrade the associative contingency and found no evidence that the generalization gradients found in the first two experiments could be explained in terms of enhanced neophobia due to poisoning. These findings provide further evidence (cf. A. W. Logue, 1979, Psychological Bulletin, 86, 276-296; M. Domjan, 1980, in J. S. Rosenblatt, R. A. Hinde, C. Beer, & M. Busnel (Eds.), Advances in the study of behavior, Vol. 11, New York: Academic Press) that CTA shares a number of similarities with other learning processes. Further, they illustrate that stimulus forgetting can be detected in a paradigm considered relatively immune to retention loss.

Animals↗
PubMed1984

Nutritional assessment using a microcomputer. 2. Programme evaluation.

Nutritional assessment ideally should be used to determine the nutritional requirements of a patient taking into account his nutritional and metabolic status. It should also be used to monitor a patient's progress and any alteration in requirements. In addition, nutritional assessment should be able to identify groups of patients at risk from the effects of malnutrition. Finally, the parameters used for assessment should be simple, yet effective and readily available to any hospital. A computer program designed by the Nutrition Support Service, Riyadh Armed Forces Hospital, Saudi Arabia and in use for the past 2 years has been evaluated and found to fulfil these criteria.

Journal Article↗
PubMed1983

Alleviation of infantile amnesia in rats by means of a pharmacological contextual state.

Although a number of studies have demonstrated that the relatively rapid rate of forgetting in young rats (i.e., infantile amnesia) can be alleviated by various reminder treatments, the possibility of enhancing retention by other procedures seems largely unexplored. Given the putative importance of contextual cues as sources of memory retrieval, this experiment examined whether the presence of a distinctive pharmacological state at training and testing could override infantile amnesia. Weanling rats were given pentobarbital or saline prior to Pavlovian fear-conditioning. When tested 1 week later, subjects in the same-state drug condition showed better retention than the same-state saline group. This finding extends previous work on memory recovery in young animals by demonstrating alleviation of infantile amnesia without a re-exposure to the CS or UCS during the retention interval.

Animals↗
PubMed1983

Persistence of flavor neophobia as an indicator of state-dependent retention induced by pentobarbital, stress, and estrus.

As fear conditioning paradigms have failed to find state-dependent retention (SDR) in rats dissociated by the estrous state, an attempt was made to establish a paradigm involving the attenuation of flavor neophobia as a more sensitive indicator of SDR. Experiment 1 established that the paradigm did indicate SDR in male rats dissociated by pentobarbital (10 mg/kg). Experiment 2 generalized the utility of the technique by employing an endogenous state, shock-induced stress, as the dissociative state. Having proved to be an indicator of SDR in the first two experiments, the technique was used in Experiment 3 to investigate the possible dissociative characteristics of the estrous state in female rats. Estrus was investigated because, due to the hormonal condition during estrus, it may provide a useful tool in investigating the dissociative aspects of human perimenstrual periodic psychosis. In Experiment 3, using ovariectomized female rats brought into estrus by injection of estrogen and progesterone in a sequence and amount comparable to the natural cycle, estrus was not demonstrated to be dissociative, i.e., did not produce SDR. The implications of these results in relation to perimenstrual periodic psychosis were discussed.

Animals↗
PubMed1983

Anterograde memory loss induced by hypothermia in rats.

In contrast with the extensive animal research on retrograde amnesia, relatively little attention has been given to anterograde amnesia. Moreover, previous studies of anterograde amnesia have not always clearly separated the effects of the anterograde treatment on acquisition from those on retention. Thus, hypothermia-induced anterograde amnesia for a one-trial conditioned fear memory was examined in three experiments. Experiment 1A demonstrated an anterograde disruption of performance in subjects receiving training in the hypothermic state (29 degrees C) and tested 24 hr later. Acquisition of the target memory in animals exposed to hypothermia prior to conditioning was demonstrated in Experiment 1B. Subjects conditioned while in a hypothermic state (29 degrees C) performed similarly to noncooled subjects if tested shortly after conditioning (while still in a hypothermic state), but not 24 hr after conditioning (while in a normothermic state). Experiment 2 shows that the anterograde amnesia effect is temperature dependent. That is, of animals trained at 29 or 33 degrees C, only the more hypothermic group demonstrated deficits in retention when tested 24 hr later. This experiment also attempted, unsuccessfully, to demonstrate recovery of the amnestic memory by administration of a noncontingent footshock prior to testing. Implications of the failure to demonstrate recovery of memory are discussed along with possible mechanisms involved in producing anterograde amnesia.

Animals↗
PubMed1983

Is anterograde amnesia a special case of retrograde amnesia?

In anterograde amnesia, memory loss is obtained for events that occur subsequent to the traumatic insult. But because the effects of an anterograde agent or treatment usually last for minutes, or even hours, after the nominal training event, processing of information may be altered during the postacquisition period as well as during acquisition. Since posttraining manipulations are themselves capable of modulating memory, or inducing retrograde amnesia, the memory loss due to a putative anterograde treatment may instead represent retrograde processes. The present experiment examined this potential source of confounding by using an amnestic treatment that can be quickly reversed after training in order to remove postacquisition effects. Thus, the presence of amnesia would isolate anterograde contributions as the source of loss. For induction of anterograde amnesia, rats were trained while at reduced body temperature (29 degrees C). A rapid rewarming procedure was introduced for some animals immediately after training to ensure that the hypothermic state did not extend into the postacquisition period. Other subjects were rapidly rewarmed 1 hr after training to control for any effects of the rewarming manipulation. Both groups showed severe anterograde amnesia that was indistinguishable from that obtained in the gradually rewarmed controls. These data provide an empirical example of an anterograde-induced memory deficit that is independent of retrograde influences.

Animals↗
PubMed1982

Automated nitrogen-washout methods for infants: evaluated using cats and a mechanical lung.

Infants with respiratory distress syndrome are treated with constant distending pressures to counter atelectasis and increase the functional residual capacity (FRC). However, FRCs are not monitored in these severely ill infants because present methods are impractical. We computerized N2-washout techniques for estimating the lung volume in these infants. The system has been evaluated using 1) a mechanical lung model and 2) small cats with normal and edematous lungs. Comparing the results of measured lung volumes with the fixed mechanical lung volumes yielded a correlation coefficient 0.996 (n=50). Decreasing the N2 gradient between initial N2 concentration and the washout medium from 0.79 to 0.10 did not affect the accuracy or reproducibility of measurements in the mechanical lung. For normal cats, comparing the results of N2-washout measurements of FRC with He-dilution values yielded a correlation coefficient of 0.921 (n=128); results from cats with pulmonary edema yielded a correlation coefficient 0.989 (n=80). We conclude that this computerized system is accurate, reproducible, and clinically acceptable for monitoring infants.

Animals↗
PubMed1982

Modification of reactivated memory through "counterconditioning".

Four experiments using rats were conducted to determine whether a "counterconditioning" procedure would be effective in altering old, but reactivated, memory. The aversiveness of previously established Pavlovian conditioned stimuli was reduced by giving subjects a highly preferred substance (maltose solution) shortly after a brief exposure to the fear cues (Experiments 1 and 2). No evidence of a time-dependent effect was obtained with a 1-hr. delay between reactivation and maltose (Experiment 2). Groups given noncontingent footshocks in lieu of Pavlovian conditioning (whether or not they subsequently received maltose) showed uniformly little aversion to test cues (Experiment 3). This finding suggests that counterconditioning in this paradigm affects associative memory processes. A time-dependent effect of delayed treatment and other evidence that active memory is necessary for counterconditioning were obtained (Experiment 4). These experiments support the notion that in rats as well as in humans, memory is a malleable process susceptible to postacquisition modifications and revealed the potential value of the reactivation paradigm in studying counterconditioning as a model for desensitization.

Animals↗
PubMed1981

Onchocerciasis diagnosis and the probability of visual loss in patients with skin snips negative for Onchocerca volvulus microfilariae.

Two methods have been used to verify the diagnosis of patients living in the onchocerciasis hyperendemic region of Liberia found to have O.v. negative skin snips. The first was based on a histological and an electronmicroscopic examination of the skin to determine whether the characteristic onchocerciasis dermatitis was absent, and to compare the results with age matched subjects having minimal to densely O.v. mf infested skin. The second method involved the skin response of patients with O.v. mf negative skin snips to topically applied DEC. No O.v. mf were found in skin snips serially sectioned and examined histologically from patients in which the results of incubation studies were completely negative. Skin snips from these seemingly O.v. mf negative patients had a dermatitis, whereas no dermatitis was found in skin snips taken from subjects living in nearby nonendemic areas. Patients with O.v. mf positive skin snips responded to DEC applied topically with increased pruritus and a papular rash whose severity was proportionate to the intensity of infestation. Patients with O.v. mf negative skin snips responded to DEC applied topically with increased pruritus and developed either a localized papular rash or widely dispersed papules; confirmation of onchocerciasis in these patients was found in the identification of O.v. mf in histological sections of the papules.

Adolescent↗