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Biomedical subjects

R Dantzer

Publications and source records attributed to R Dantzer.

At least 163 records · Page 9Linked to original sources
PubMed1990

[Stress, behavior and disease].

For those who have attempted to attach some importance to the problem, the role played by psychological factors in disease usually is reduced to a doctrinal choice between psychoanalytic connotations and a mechanism theory based on the biology of stress. The boundaries of this choice have enormously evolved during these last years and the results of the psychobiologic approach allow us to leave this bipolar quarrel aside. The notion of stress invariably suggests the idea of a common final pathway through which environmental aggression influence the psychological equilibrium and visceral function. This notion is obsolete. Our organism has specific defence mechanisms according to the nature of the aggression. Each of these systems relies on the close relationship existing between visceral reactions and behaviour. They differ, however, by their trigger mechanisms and the somatic and psychic modalities of expression. The exteroceptive defence system is the best known. It is activated by any external aggression susceptible of endangering the animal's (including man) physical or mental being. The behaviour pattern which arises from this reaction depends on the species, but varies according to the possibilities of prevision and control of the aggression. The same is true for their hormonal and autonomous components. In the interoceptive defence system, it is essentially the gastrointestinal components related to acquired gustative aversion that have been studied. Poisoning due to ingestion of spoiled food provokes an aversion to the aliment responsible, based on its organoleptic characteristics. The mechanisms that differ according to whether the aliment can be expelled by vomiting or by acceleration of intestinal transit.(ABSTRACT TRUNCATED AT 250 WORDS)

Aggression↗
PubMed1989

Specific modulation of social memory in rats by cholinomimetic and nootropic drugs, by benzodiazepine inverse agonists, but not by psychostimulants.

The recognition of an unfamiliar juvenile rat by an adult rat has been shown to imply short-term memory processes. In this study the effect of various psychotropic drugs on this investigatory behaviour was examined. The procedure was as follows: an unfamiliar juvenile rat was placed in the home cage of an adult rat for 5 min. The time spent by the adult rat in investigating the juvenile was recorded. The adult rat was then immediately treated with vehicle or test compounds, and was again exposed for 5 min to the same juvenile 2 h later. At this time point vehicle-treated rats no longer recognized the juvenile rat, i.e. the time of investigation was similar to that observed during the first presentation. Arecoline (1 and 3 mg/kg IP), physostigmine (0.05 and 0.1 mg/kg SC), RS86 (0.5 mg/IP) and nicotine (0.125 and 0.5 mg/kg IP) reduced in a dose-dependent fashion the time spent in investigating the juvenile during the second exposure. This result cannot be attributed to nonspecific effects, since it was not observed when a different juvenile was used for the second exposure. The effect of arecoline was reversed by scopolamine, but not by methylscopolamine. Aniracetam reduced investigatory behaviour at the dose of 50 mg/kg IP. FG 7142 (5 mg/kg IP) and beta-CCM (0.4 mg/kg IP) were also active and their effect was reversed by Ro 15-1788. DL-Amphetamine (0.5 and 1 mg/kg IP), nomifensine (1.25-10 mg/kg IP) and strychnine (0.25 and 0.5 mg/kg IP) were ineffective or reduced this behaviour unspecifically.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Stress and immunity: an integrated view of relationships between the brain and the immune system.

The old notion that stress exacerbates the progression of physical illness via its corticosteroid-mediated immunosuppressive effects must be revised. Experimental and clinical studies demonstrate that both laboratory and natural stressors alter the activities of lymphocytes and macrophages in a complex way that depends on the type of immune response, the physical and psychological characteristics of the stressor and the timing of stress relative to the induction and expression of the immune event. The influences of stress on immunity are mediated not only by glucocorticoids but also by catecholamines, endogenous opioids and pituitary hormones such as growth hormone. Sensitivity of the immune system to stress is not simply fortuitous but is an indirect consequence of the regulatory reciprocal influences that exist between the immune system and the central nervous system. The immune system receives signals from the brain and the neuroendocrine system via the autonomic nervous system and hormones and sends information to the brain via cytokines. These connections appear to be part of a long-loop regulatory feedback system that plays an important role in the coordination of behavioral and physiological responses to infection and inflammation.

Animals↗
PubMed1988

Interleukin-1 induces conditioned taste aversion in rats: a possible explanation for its pituitary-adrenal stimulating activity.

To investigate the possible aversive stimulus properties of peripherally administered interleukin 1 (IL-1), rats received two pairings of ingestion of a saccharin solution with various doses of recombinant rat interleukin 1 in a conditioned taste aversion paradigm, using 20 mg/kg lipopolysaccharide endotoxin as a positive control. Rats treated with 1 and 10 micrograms IL-1 showed a dose-dependent reduced preference for saccharin together with dose-dependent impairments in weight gain. Since these effects were obtained within the range of doses that has been previously reported to stimulate the release of ACTH, it is proposed that this last action of IL-1 is likely to be secondary to the aversive effects of IL-1.

Animals↗
PubMed1988

Septal vasopressin modulates social memory in male rats.

Adult male rats that are confronted with a sexually immature conspecific display a dramatic reduction in investigatory behavior upon re-exposure to the same juvenile when this exposure takes place 30 min after the initial exposure, but not when it is delayed by an interval of 2 h. This behavioral change may be used to measure the duration of the memory that the test animal forms of the stimulus animal. Vasopressin injected directly into the lateral septum of adult male rats at a dose of 0.1 ng facilitated this form of memory, whereas local injection of a specific hydrophilic vasopressor antagonist, desGlyNH2d(CH2)5Tyr(Me)AVP, impaired it. These findings suggest that vasopressinergic innervation of the lateral septum may be physiologically involved in the modulation of social memory in male rats.

Animals↗
PubMed1988

Schedule-induced polydipsia experience decreases locomotor response to amphetamine.

To investigate the influence of schedule-induced polydipsia (SIP) on central dopaminergic systems, rats trained in a SIP procedure were challenged with the psychostimulant and dopaminergic agonist, D-amphetamine. In a first experiment, rats that had access to water and developed SIP (SIP-positive) displayed a lower response to amphetamine than rats that had access to water but did not develop SIP (SIP-negative) and rats that had no access to water. There was no difference in the spontaneous activity of these different groups of animals. In a second experiment, SIP-positive rats displayed the same reduced response to amphetamine following only 10 min of SIP drinking. In addition, SIP-positive rats that were tested without access to water during the SIP test displayed an increased locomotor activity both after saline and amphetamine treatments. These results suggest that SIP has stress-reducing properties.

Animals↗
PubMed1988

The propensity for schedule-induced polydipsia is related to differences in conditioned avoidance behaviour and in defense reactions in a defeat test.

In line with previous research showing that animals predisposed to develop schedule-induced polydipsia when submitted to intermittent distribution of food show differential behavioural and neurochemical characteristics, the present experiments investigated the nature of defense reactions to aversive situations in rats that do or do not develop schedule-induced polydipsia. It was found that rats that engage in excessive drinking during intermittent feeding display more rapid active avoidance learning in a 2-way shuttle-box and show less freezing when confronted with an aggressive resident male in a defeat test than those that do not develop schedule-induced polydipsia. These results are consistent with the hypothesis that individual differences in the propensity to exhibit oral consummatory activities in conditions of mild stress are related to the ability to shift behavioural programmes in response to external stimulation.

Aggression↗
PubMed1988

Schedule-induced polydipsia experience decreases plasma corticosterone levels but increases plasma prolactin levels.

To determine the neuroendocrine pattern of response to excessive drinking induced by exposure of rats to an intermittent distribution of food (schedule-induced polydipsia, SIP), the present experiment investigated changes in plasma corticosterone, prolactin and catecholamines in chronically catheterized rats that had developed or not this form of adjunctive behaviour. It was found that rats that engage in excessive drinking displayed decreased plasma levels of corticosterone and increased levels of prolactin during the course of a SIP session. There was, however, no differences between groups in plasma catecholamine levels. The difference observed between SIP-pos and SIP-neg rats were entirely condition-specific, since they disappeared in the absence of access to water.

Animals↗
PubMed1988

Influence of stressor predictability and behavioral control on lymphocyte reactivity, antibody responses and neuroendocrine activation in rats.

The present experiments were designed to study the influence of prediction and control of electric shocks on various aspects of immune function, and the possible intermediate role of glucocorticoid hormones. After two sessions of inescapable footshocks, the reactivity of splenocytes to concanavalin A was reduced by one third. This effect was completely reversed when each shock was preceded by a warning stimulus, even though the adrenocortical response was the same in both conditions. In another experiment, rats were submitted to ten sessions of continuous avoidance in a shuttle-box and a group of yoked animals received the same footshocks without any relationship to their shuttling behavior. Although yoked rats displayed a reduced reactivity of splenocytes to lectins, animals of the avoidance group had a reduced antibody response to sheep erythrocytes. In contrast, no difference was observed in the corticosterone or prolactin response. These data further support the importance of psychological factors on stress-induced changes in immune functions. Furthermore, they demonstrate that various aspects of the immune system are differentially affected by behavioral factors and the results argue against a major role for the adrenocortical system in mediating these changes.

Adaptation, Psychological↗
PubMed1988

Experimental assessment of drug-induced changes in cognitive function: vasopressin as a case study.

Two important forms of cognition are knowledge about internal states and social cognition. Knowledge about internal states is dependent on the ability to discriminate between different classes of visceral sensations and to associate them specifically to distinctive cues. The phenomenon of conditioned taste aversion (CTA) is the best example of this type of knowledge. Many chemicals induce interoceptive changes that can be perceived by animals and give rise not only to subjective sensations but also to causal attributions. However, the possibility that animals are able to discriminate different forms of interoceptive changes in a CTA paradigm has received little attention. Studies of the mechanisms of vasopressin-induced CTA provide evidence that it is the case and that animals are able to classify in different categories sensations related to the vasopressor activity of vasopressin and sensation induced by a prototypical aversive drug, apomorphine. Social cognition involves what individuals know about each other. One of the requirements for social cognition is social recognition, i.e., the ability to identify other individuals and classify them in different categories. Social recognition can be assessed by changes in duration of investigation of another animal when the stimulus animal is presented at different intervals. This form of memory is based on olfactory characteristics of the stimulus animal in rats and it can be enhanced or attenuated by memory-modulating drugs, as demonstrated by experiments with vasopressin.

Cognition↗
PubMed1987

Centrally injected arginine vasopressin (AVP) facilitates social memory in rats.

'Memory' for a juvenile conspecific in male rats can be measured by variation in duration of investigation times when the same juvenile is presented at different intervals. Typically, exposure of an adult male rat to a juvenile results in transient investigatory activity that rapidly declines with repeated exposures at short interexposure intervals (30 min). Longer interexposure intervals (120 min) result in re-investigation with durations similar or greater than the original investigation. Arginine vasopressin (AVP) injected into adult male rats intracerebroventricularly in doses of 0.5-2.0 ng immediately after investigation of the juvenile decreased social investigation of the same juvenile at the long (120 min) interexposure interval. This decrease in investigatory time was similar to that observed after a 30-min interexposure interval in untreated animals. These results support the hypothesis that increasing the availability of AVP in the central nervous system can improve the consolidation of olfactory information and improve conspecific recognition in rats.

Animals↗
PubMed1987

Modulation of social memory in male rats by neurohypophyseal peptides.

Adult male rats spend a great amount of time investigating novel juveniles. In contrast, rats re-exposed to the same juvenile 30 min after the initial exposure display little investigatory behavior. If the re-exposure occurs 2 h later, the juvenile is thoroughly investigated. These results have been interpreted to mean that rats form a transient memory for a particular juvenile. In the present study, memory was enhanced when the initial exposure to the juvenile was followed by another exposure to the same juvenile (retroactive facilitation) and impaired when exposure to the original juvenile was followed by exposure to another juvenile (retroactive interference). Arginine vasopressin had retroactive facilitating effects on social memory and these effects were blocked by the vasopressor antagonist dPTyr(Me)AVP. Moreover, the antagonist had retroactive interfering effects, since it impaired the recognition of a familiar juvenile. Oxytocin shared the same inhibitory pattern of action. These results suggest that neurohypophyseal peptides may have a prepotent role in modulating the mnemonic processing of chemosensory information associated with social interactions.

Animals↗
PubMed1987

Cyclosporine and alpha-interferon do not attenuate morphine withdrawal in rats but do impair thermoregulation.

Immunomodulating drugs as diverse as alpha-interferon and cyclosporine have been reported to attenuate physical signs of morphine withdrawal in rats. On the basis of these results, the immune system has been claimed to be involved in opiate addiction. To assess whether this is the case, the effects of alpha-interferon and cyclosporine were studied on objective signs of morphine withdrawal in morphine-dependent rats. Rats made dependent upon morphine by implantation of a 75-mg morphine pellet were challenged three days later by naloxone (1 mg/kg). Pretreatment with alpha-interferon (150 U/g) or cyclosporine (15 mg/kg) did not attenuate the reduction in body weight or the behavioral suppression induced by naloxone in morphine-dependent rats trained to press a lever for food reinforcement on a fixed-ratio 10 schedule. Alpha-interferon pretreatment blocked the capacity of naloxone to decrease body temperature in these rats and actually induced an hyperthermic response. In contrast, cyclosporine tended to enhance the drop in body temperature induced by naloxone. This last effect was more striking when the rats were placed in a cold room at 3.5 degrees C. Cyclosporine by itself induced a drop in body temperature in normal rats exposed to 3.5 degrees C. These results indicate that alpha-interferon and cyclosporine impair thermoregulation but do not directly interfere with morphine withdrawal signs.

Animals↗
PubMed1987

Changes in serum cortisol reveal functional differences in frustration-induced chain chewing in pigs.

The pituitary-adrenal correlates of oral stereotypes in pigs were studied in two frustration situations of intermittent food distribution in which small amounts of food were given every 4 min (n = 4), and a massed food situation in which the same total amount of food was given in one meal at the beginning of the session (n = 5). Control animals (n = 6) were exposed to intermittent food but without a chain. Both intermittent-food and massed-food pigs developed chain chewing at similarly high rates. Blood samples were taken on days 8 and 21 of the experiment. Serum cortisol decreased between the beginning and the end of session 21 in intermittent-food pigs, but increased in pigs subjected to the massed-food condition. These findings suggest that oral stereotypies elicited by an intermittent schedule of food presentation are not equivalent to those elicited by the massed-food regimen.

Animals↗
PubMed1987

Prediction and control of food rewards modulate endogenous pain inhibitory systems.

Tail-flick latencies were measured in food-deprived rats submitted to various schedules of food reinforcement with experimental and yoked animals differing by the possibility of either predicting the occurrence of food by means of a pre-food signal, controlling its delivery by lever-pressing or developing adjunctive activities (schedule-induced drinking). In the first two cases, yoked animals that could not predict or control food deliveries displayed higher tail-flick latencies at the end of sessions than did experimental animals. In the polydipsia experiment, rats that did not develop schedule-induced drinking had higher tail-flick latencies from the start of the experiment than rats that did develop drinking and for these latter animals, drinking was accompanied by a significant reduction in tail-flick latencies. These results demonstrate that prediction and control over external events modulate the activation of endogenous pain-suppressing systems.

Animals↗
PubMed1987

Corticotropin-releasing factor antagonist blocks stress-induced fighting in rats.

Corticotropin-releasing factor (CRF) has been shown to have potent central nervous system-activating effects when administered intracerebroventricularly (i.c.v.). In the present experiment, this activating effect was exaggerated by use of a stress-motivated behavioral paradigm. Low doses of CRF (0.01 and 0.1 micrograms/rat) administered i.c.v. facilitated stress-induced fighting. More importantly, alpha-helical CRF-(9-41), a CRF antagonist, blocked stress-induced fighting produced by higher levels of stress. These results suggest that CRF in the central nervous system may have a role in mediating behavioral responses to stress.

Aggression↗
PubMed1987

Hypertonic saline mimics the effects of vasopressin on inhibitory avoidance in the rat.

Rats tested in a step-through inhibitory avoidance task were administered hypertonic saline (2 ml of 0.25. 0.5, and 1.0 M intraperitoneally) or arginine vasopressin (1.0, 2.0, and 4.0 micrograms) injected subcutaneously (sc) after the training trial where the rats received a mild footshock (0.2 mA, 3 s). Both hypertonic saline and vasopressin produced significant increases in latency to reenter 24 h later. These treatments failed to increase reentry latencies in animals that received the same procedure but no shock. The facilitation of inhibitory avoidance produced by hypertonic saline was reversed by sc administration of 25 micrograms of the vasopressor (V-1) vasopressin antagonist, dPtyr(Me)AVP. The results suggest that the endogenous release of vasopressin can be behaviorally significant in situations of acute homeostatic challenge.

Animals↗