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Biomedical subjects

J H Maes

Publications and source records attributed to J H Maes.

12 recordsLinked to original sources
PubMed2001

Contextual dependencies in predictive learning.

Two experiments assessed contextual dependencies in a predictive-learning task. Subjects learned to associate each of four pictorial stimuli with the occurrence or non-occurrence of a specific outcome. Each of these stimuli, the intentional stimuli, was presented against one of two different visual (Experiment 1) or auditory (Experiment 2) context stimuli. These context stimuli were incidental: subjects were not explicitly instructed to pay any attention to them and each of them in isolation was not predictive of the outcome. During acquisition and testing, subjects expressed the expected relationship between intentional stimulus and outcome by an appropriate key press. At test, intentional stimuli were presented either with the same contextual stimulus as also present during acquisition (same trials), or with the other one (switched trials). The response latency was slower on switched trials than on same trials in each experiment, a result extending previous findings on the effect of environmental contextual stimuli on task performance. Results are discussed in the framework of contextual occasion setting and habituation to contextual stimuli.

Adolescent↗
PubMed2001

Effects of acute D-amphetamine and ketamine on the performance of rats in a serial negative patterning procedure.

This study assessed the effects of acute amphetamine and ketamine on the performance of rats in a serial negative patterning procedure. A 5 s auditory target stimulus and a 5 s visual feature cue were each followed by food, but the target stimulus was not followed by food if preceded by the feature. There was a 5 s empty gap between feature termination and target onset in the latter, non-reinforced trials. Thus, the feature functioned as a cue signalling the non-reinforcement of the target. The interval between the feature and the target was varied in the non-reinforced trials following pretreatment with subcutaneous saline, D-amphetamine (0.5 mg/kg) or ketamine (5 mg/kg). The main behaviour measured was visits to the place of food delivery during target presentation. Under saline, the response frequency during the target was lowest when the interval between the feature and the target exactly matched the interval used during training. Either shortening or lengthening the interval enhanced responding. Neither D-amphetamine nor ketamine disturbed this temporal pattern, although D-amphetamine and ketamine non-specifically increased and decreased response frequencies, respectively, in all the trial types. The results are discussed in the framework of the amphetamine and ketamine models of schizophrenia.

Animals↗
PubMed2001

Effects of d-amphetamine on the performance of rats in an animal analogue of the A-X continuous performance test.

Schizophrenia patients subjected to the A-X Continuous Performance Test (A-X CPT) show cognitive deficits that are thought to reflect impaired representation and maintenance of context information. An issue deserving attention is to what extent the acute amphetamine model of schizophrenia also models these cognitive deficits. The present experiment examined the effect of acute d-amphetamine (AMP) on the performance of rats in an animal analogue of the A-X CPT. Subjects first learned to solve an A --> X+, B --> X-, A --> Y- discrimination task, with A and B representing visual features; X and Y designating auditory target stimuli; --> signifying a serial presentation; and + and - referring to food reinforcement and non-reinforcement, respectively. Frequency of food-magazine visits was the dependent measure. After mastering the discrimination, rats received test trials under either saline or 0.5 mg/kg AMP (s.c.). At test, the interval between feature and target presentation was varied; reinforcement contingencies were maintained. AMP significantly impaired performance on the A --> X+/B --> X- discrimination by increasing the response level on B --> X- trials. AMP did not significantly affect performance on the A --> X+/A --> Y- discrimination. However, AMP also increased magazine responding in the absence of the presentation of features and targets. A parsimonious conclusion based on these preliminary results is that acute AMP does not affect processing of context information provided by the visual features in this procedure. It rather has a more non-specific response-enhancing effect, especially with respect to stimuli associated with the delivery of food.

Animals↗
PubMed1997

Conditional control by midazolam and amphetamine in a rapid appetitive discrimination procedure.

The present two experiments examined conditional control by midazolam and amphetamine cues in an appetitive discrimination procedure. In each of two experiments, male Wistar rats were subjected to a small number of two types of training sessions in a conditioning box. During one type of session, a stimulus was consistently followed by food in a magazine, whereas during the other type of session, this very same stimulus was followed by nothing. Groups of rats were injected with either midazolam (0.1 mg/kg, s.c.) or amphetamine (0.5 mg/kg, s.c.), prior to each food-reinforced session, and with saline prior to each food non-reinforced session. Other groups received the reverse treatment. Subsequent non-reinforced test session showed that, in both experiments, only the rats that had been food reinforced in a drug state displayed shorter magazine-response latencies in their previously reinforced than in their previously non-reinforced state, both prior to and during the stimulus. This finding was interpreted as reflecting the joint operation of unconditioned and conditioned drug effects, with the latter being based on occasion setting by the drug cues that was induced by the relatively short discrimination training procedure. The present results parallel those of previous aversive drug-discrimination experiments adopting a similar short discrimination procedure.

Amphetamine↗
PubMed1997

State-dependency of conditioning and extinction of an appetitive response with amphetamine and midazolam.

Rats received a single conditioning session in which unsignaled food pellets were delivered to the food magazine of a training box, followed by a single extinction session without pellet presentations. Groups of rats differed in the drug state induced prior to conditioning and extinction according to a 2 x 2 design using d-amphetamine sulphate (AMP, 0.5 mg/kg, S.C.) and midazolam (MID, 0.1 mg/kg, S.C.). Subsequently, all rats received nonreinforced test sessions under AMP and MID. The dependent measure was the frequency of magazine visits during selected portions of each session. Rats that received extinction in the same drug state as had been present during conditioning did not respond significantly more during the extinction session than rats extinguished in a different drug state. This implies that conditioning was not state dependent. However, during the AMP tests, the rats extinguished under MID responded more under AMP than under MID, whereas the rats extinguished under AMP did not respond differentially during the tests under AMP vs. MID. These results were interpreted as reflecting the joint operation of state-dependent extinction and unconditioned drug effects. As in studies manipulating external contextual stimuli, extinction proved to be more vulnerable to becoming context dependent than conditioning.

Amphetamine↗
PubMed1996

Drug states as modulators of conditioned immobility in a latent discrimination procedure.

Midazolam, amphetamine, and flesinoxan were used in four rat experiments to examine the usefulness of a latent Pavlovian discrimination procedure to assess the discriminative-stimulus, or occasion-setting, properties of drugs. Experiment 1 first assessed the unconditioned effect of each of the drugs on the dependent measure used, which was immobility. Relative to saline, midazolam enhanced immobility, whereas flesinoxan, and especially amphetamine decreased it. In each of the Experiments 2-4, subjects received a limited number of training sessions during which they consistently received a footshock in a distinctive box after a drug but not after saline, or vice versa. Subsequently, non-reinforced test sessions were performed in the drug and saline states in both the conditioning box and a novel box. Relative to the saline state, rats previously shocked under midazolam were less mobile in the conditioning box under midazolam, whereas rats previously not shocked under amphetamine or flesinoxan were more mobile under the drug. The remaining animals did not show differential responding. The response profiles were accounted for in terms of the combined operation of an associative, or occasion-setting, effect and a non-associative effect of the drug-induced states.

Amphetamines↗
PubMed1993

Context conditioning: positive reinforcing effects of various food-related stimuli.

Rats were subjected to context preference tests to investigate the degree to which various manipulations involving food stimuli can be used to appetitively condition contextual cues. One manipulation consisted of placing hungry rats in a context that contained food that they could consume. A second one involved exposure to a context containing food that could only be seen and smelled, without consumption being possible. A third type of manipulation consisted of exposing animals to a context after the consumption of a small meal in the home cage. Finally, hungry, control subjects were merely exposed to a context containing an empty food tray. Preference for the context was only enhanced after the first type of manipulation, indicating that the actual consummatory act constitutes the major source of reinforcement in the present procedure. Olfactory and visual food cues, as well as postingestional aftereffects in isolation, did not function as reinforces.

Animals↗
PubMed1989

Rapid presumptive diagnosis of anaerobic infections in animals by gas-liquid chromatography.

The detection of volatile fatty acids (VFA) by gas chromatography of 85 purulent specimens from abscesses or pyogenic infections in cats, dogs, rodents, and ruminants was compared with the results of bacteriologic culturing, and proved to be a rapid means of presumptively diagnosing anaerobic infections. Of 83 bacteriologically positive specimens, 52 (61%) yielded obligate anaerobes and in 50 specimens, 1 or more VFA (butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, or isocaproic acid) was detected. Forty-six specimens were positive for culturing of anaerobes and for detection of 1 or more of these VFA. By contrast, pus from infections caused by (facultative) aerobic microorganisms contained no VFA or only acetic and/or propionic acid.

Abscess↗
PubMed1984

[A new treatment possibility for dogs with chronic or recurrent pyoderma].

Effective treatment of chronic or recurrent pyodermas in dogs is often found to be difficult. The disease apparently results from a change in the balance between the infecting microorganism: Staphylococcus aureus, and the host. This change in the normal equilibrium could be due to enhanced virulence of the infecting strain of staphylococci, but is more likely to have been caused by host factors such as disturbed non-specific defence mechanisms (of the skin) or malfunction of the immune response, e.g. hypersensitivity. When conventional forms of treatment such as grooming, skin-hygienic measures and antibiotics fail or relapses occur, immunotherapy with a staphylococcal vaccine or toxoid might be considered. In studies with experimental animals it was shown alpha-toxoid was superior to other staphylococcal toxoids or vaccines in preventing skin lesions. Four dogs with deep-seated chronic pyodermas were treated with staphylococcal alpha-toxoid emulsified in Freund's adjuvant. Three of these animals recovered, but because of severe unwanted side-effects, this form of therapy was abandoned. Ten dogs with deep-seated chronic primary pyodermas were treated with a commercially available alpha- and beta-toxoid preparation (Isopyos). Nine of these patients recovered. In two cases, however, relapses occurred several months later, but the symptoms disappeared again after a booster injection. One dog did not respond; its condition deteriorated and it had to be euthanised. As the dogs received toxoid intracutaneously as well as intramuscularly, the positive effect might be due to desensitization of the animals rather than to immunisation.

Animals↗
PubMed1983

The detection of obligate anaerobic bacteria in swine abscesses. A comparison between gas-liquid chromatography and bacteriological culturing methods.

From the 62 swine abscesses examined, 56 yielded positive cultures, of which 38 cases were mixtures of facultative aerobes and obligate anaerobic bacteria (OAB). Only 6 species appeared to be sterile. In all specimens, which yielded OAB, VFA (C4-C6) could be detected by gas-liquid chromatography (GLC). False negatives were not recorded, and only one false positive was found, which might have been due to faulty culture technique, or to the fact that the metabolic markers may persist longer than the OAB themselves. Because current methods to isolate non-sporulating OAB are laborious and not available in most veterinary clinical situations and because there is a need to evaluate the importance of non-sporulating OAB in veterinary medicine, GLC seems to be a useful alternative to culture techniques for detecting the presence of OAB in infectious processes in animals.

Abscess↗
PubMed1983

Warfarin pharmacokinetics in the horse.

The pharmacokinetics of racemic warfarin were studied in 6 adult horses. After IV administration, the plasma concentration of warfarin showed a biphasic decline in time. Analysis of the data, according to 2-compartment kinetics, revealed the following constants: biological half-life was 13.3 hours, apparent volume of distribution was 0.46 L X kg-1, body clearance was 25.3 ml X hour-1 X kg-1. Warfarin was bound (91.5%) to plasma proteins. Unchanged warfarin was not detected in the urine. Absorption from the gastrointestinal tract was almost complete. Concentrations of warfarin in tissue were examined in 4 foals that were given 1 g of warfarin orally 14 hours before they were euthanatized. The concentrations in the kidney were higher than those in plasma (about 2 fold). The hypothrombogenic effect of the acute IV and oral administration of warfarin (0.75 mg/kg of body weight) was noticeable only after 60 hours and lasted for about 30 hours. The effect was weak; the maximum effect was a prolongation of 2.3 s (from 11.5 s to 13.8 s) in thromboplastin time.

Administration, Oral↗