A preliminary study for identifying olfactory markers of fear in the rat

In stressful situations, many animals release alarm pheromones to warn conspecifics of impending danger. The authors sought to establish experimental conditions for a larger study aimed at identifying alarm pheromones emitted by the rat. They placed rats in a specially designed chamber and exposed them to aversive tactile, visual and acoustic stimuli over the course of a few days. The researchers observed rats' behavior and analyzed air samples taken from their immediate environment under the following conditions: (i) when rats were unstressed; (ii) immediately after rats were exposed to aversive stimuli; and (iii) when rats were left alone in the chamber after being conditioned to fear imminent aversive stimuli. Stressed rats emitted several substances that are known to function as alarm pheromones in insects. When previously unstressed control rats were exposed to these same substances, they had a distinct behavioral fear response.     

Saccharin exposure increases the potency and aversive property of naloxone in drug-naive rats

In naive rats previously given saccharin (0.1%) as the only drinking fluid for 14 days, naloxone produced a conditioned taste aversion at a dose (0.09 mg/kg, SC) that had little or no effect in normal controls. The magnitude of this effect of the saccharin increased between 2 and 7 days after cessation of the treatment. Under these experimental conditions, evidence of an interaction between the saccharin exposure and a naloxone response was also seen with rectal temperature measurements. Therefore, in rats having no history of morphine, previous consumption of saccharin may potentiate various actions of naloxone including its aversive property.     

Ketaset-Rompun extends the effective interstimulus interval in long-trace taste-aversion conditioning in rats

The effect of anesthesia (Ketaset-Rompun) interpolated between the conditioned stimulus (CS) and unconditioned stimulus (US) during long-trace taste-aversion conditioning in rats was examined in three experiments. In Experiment 1, rats that were anesthetized immediately after experiencing a saccharin solution formed a taste aversion at a 3-h interval that typically does not support conditioning, a prolongation effect. Prior experience with the anesthetic eliminated the associability of the aversive consequences of the anesthetic but did not eliminate the anesthetic's prolongation effect. Some evidence was also obtained indicating that LiCl produced an aversion at the 3-h interval in unanesthetized rats if they had experience with the anesthetic prior to conditioning. In Experiment 1a, the interval between prior experience and conditioning was extended from 24 to 96 h. Results demonstrated that the evidence for conditioning at 3 h for unanesthetized subjects in Experiment 1 was not a robust finding. By reversing the role of Ketaset-Rompun (KR) and LiCl as prior experience manipulation and US treatment in Experiment 2, the prolongation effect was shown not to be due to the summation of the aversive properties of the anesthetic and the LiCl. Results were interpreted in terms of a hypothesized metabolic pacemaker.     

A DUAL TASTE FOR SACCHARIN IN THE RAT: II. Taste Change Following Alloxan Injection

It has previously been proposed that saccharin has a dual tasefor the rat, that is has both sweet and aversive componentsto its taste, and that the aversion shown to saccharin by alloxandiabetic rats might be accounted for by the diabetes reducingthe effectiveness of the sweet component. In this study it isshown that the generalization to saccharin of a conditionedaversion to glucose is reduced or eliminated following alloxantreatment suggesting that the sweet component is reduced, andthat the generalization of a conditioned aversion to quinineis enhanced suggesting that the second component of the saccharintaste is quinine-like. ^* Supported by National Research Council of Canada Grant #APO-97     

Long-term retention of a poorly learned saccharin aversion : Evidence for an incubation effect

The retention of a weak conditioned saccharin aversion was tested using independent groups over a 14-day period. The delay between CS (saccharin 0.1 %) and US (LiCl 0.15 M) was 6 hours. Significant variations in the retention function were observed, in particular an improvement of memory - i.e. an incubation effect - over the 14-day period. This result suggests that retention of conditioned taste aversion may share common features with the retention of more classical aversive conditioning.     

Acquisition and extinction of conditioned suppression of a graft-vs-host response in the rat

Injection of rats with cyclophosphamide (CY) after their consumption of a novel saccharin-flavored drinking solution results in a conditioned aversion to saccharin and a conditioned suppression of immune responses. In this study, female Lewis X Brown Norwegian F1 rats were conditioned by pairing saccharin with 50 mg/kg CY. Seven weeks later (day 0), a graft-vs-host response (GvHR) was induced in these animals by injecting splenic leukocytes from Lewis donors into a rear footpad. At this time, some conditioned animals were reexposed to saccharin, the conditioned stimulus. During the 7-wk interval between conditioning and immunization, subgroups of conditioned rats were given 0, 4, 9, or 18 extinction trials (saccharin followed by saline injections). Animals receiving 4, 9, or 18 extinction trials showed a greater preference for saccharin on day 0 than did animals receiving no extinction trials, but these groups did not differ among themselves; all conditioned groups showed a lower preference for saccharin than placebo-treated animals. There was a clear effect of number of extinction trials on the GvHR. Animals receiving 9 or 18 extinction trials did not differ from controls, whereas animals receiving 0 or 4 trials had a milder GvHR than did conditioned rats that were not reexposed to saccharin at the time of immunization. These results confirm a previous report of conditioned suppression of a GvHR, demonstrate that conditioned immunopharmacologic responses are subject to experimental extinction, and indicate that conditioned immunosuppression can be dissociated from conditioned taste aversion.     

Monosodium glutamate and sweet taste: discrimination between the tastes of sweet stimuli and glutamate in rats

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.     

Acute 3rd-ventricular amylin infusion potently reduces food intake but does not produce aversive consequences

In this study, a conditioned taste aversion (CTA) paradigm was used to assess the possibility that 3rd-ventricular (i3vt) administration of the pancreatic hormone amylin produces aversive consequences that secondarily reduce food intake independently of the normal regulation of energy balance. After 1-h daily access to water for 7 days, rats were given 1-h access to a 0.15% saccharin solution, followed immediately by i3vt amylin (100 pmol) in one group (n=7) and i3vt CSF vehicle in another (n=7). As positive control for the formation of a CTA, a third group of seven rats received intraperitonial (i.p.) lithium chloride (LiCl). Saline was given i.p. to a fourth group (n=7) as control for i.p. LiCl. As expected, the LiCl rats exhibited a marked aversion to the saccharin in a subsequent two-bottle intake test. In contrast, although the 100 pmol i3vt amylin dose is substantially higher than that required to reduce food intake, no evidence of a CTA was observed in the rats that had received i3vt amylin. In summary, these data are consistent with the conclusion that acute i3vt amylin infusion does not reduce food intake by producing aversive consequences.     

Acquired Recognition of Chemical Stimuli from Pike,Esox lucius,by Brook Sticklebacks,Culaea inconstans (Osteichthyes,Gasterosteidae)

In this study we test whether brook sticklebacks (Culaea inconstans) can acquire predator recognition through releaser-induced recognition learning, i.e. simultaneous exposure to aversive ('releasing') stimuli and neutral stimuli causing learned aversion to the neutral stimuli. We exposed wild-caught pike-naive brook sticklebacks (collected from a creek containing fathead minnows, Pimephales promelas, but not pike, Esox lucius) to chemical stimuli from pike that were mixed with brook stickleback skin extract, fathead minnow skin extract, or a control of distilled water. In subsequent tests 2 d later, when only pike stimuli were presented, sticklebacks conditioned with stickleback skin extract and fathead minnow skin extract exhibited antipredator behaviour (i.e. increased schooling and movement toward the substrate), while those conditioned with distilled water did not. Sticklebacks conditioned with stickleback skin extract responded to pike with a more intense response, in terms of movement toward the substrate, than those conditioned with fathead minnow skin extract, suggesting that conspecific skin extract may be a stronger stimulus than heterospecific skin extract for learning recognition of predators. To our knowledge this is the first study to demonstrate that an acanthopterygian fish can acquire predator recognition through the pairing of conspecific alarm pheromone with the cue of a predator. Furthermore, our results are the first to demonstrate that fish can acquire predator recognition through the pairing of a heterospecific alarm pheromone with the cue of a predator. These results suggest that brook sticklebacks will benefit by being in close proximity to fathead minnows. Acquired predator recognition has long-term consequences in mediating predator-prey interactions.     

Taste aversion learning induced by delayed swimming activity

The experiment reported here demonstrated that forced swimming endows rats with aversion to a taste solution consumed 30 min before the swimming. The experimental rats were allowed to drink 0.2% sodium saccharin solution, which was followed by a 30-min empty interval, and then a 20-min swimming opportunity in water. Compared with the control rats, which were returned to their home cages after drinking the saccharin, the experimental rats drank a small amount of saccharin solution both in the later sessions of one-bottle training and in the subsequent two-bottle choice (saccharin versus tap water) testing. The delayed swimming procedure was as effective as an immediate swimming procedure, extending the generality of the swimming-induced taste aversion, which we recently discovered with the immediate swimming procedure.     

Radiation-induced taste aversion: effects of radiation exposure level and the exposure-taste interval

Radiation-induced taste aversion has been suggested to possibly play a role in the dietary difficulties observed in some radiotherapy patients. In rats, these aversions can still be formed even when the radiation exposure precedes the taste experience by several hours. This study was conducted to examine whether increasing the radiation exposure level could extend the range of the exposure-taste interval that would still support the formation of a taste aversion. Separate groups of rats received either a 100 or 300 R gamma-ray exposure followed 1, 3, 6, or 24 h later by a 10-min saccharin (0.1% w/v) presentation. A control group received a sham exposure followed 1 h later by a 10-min saccharin presentation. Twenty-four hours following the saccharin presentation all rats received a series of twelve 23-h two-bottle preference tests between saccharin and water. The results indicated that the duration of the exposure-taste interval plays an increasingly more important role in determining the initial extent of the aversion as the dose decreases. The course of recovery from taste aversion seems more affected by dose than by the temporal parameters of the conditioning trial.     

Striatal-Enriched Protein Tyrosine Phosphatase Controls Responses to Aversive Stimuli: Implication for Ethanol Drinking

The STriatal-Enriched protein tyrosine Phosphatase (STEP) is a brain-specific phosphatase whose dysregulation in expression and/or activity is associated with several neuropsychiatric disorders. We recently showed that long-term excessive consumption of ethanol induces a sustained inhibition of STEP activity in the dorsomedial striatum (DMS) of mice. We further showed that down-regulation of STEP expression in the DMS, and not in the adjacent dorsolateral striatum, increases ethanol intake, suggesting that the inactivation of STEP in the DMS contributes to the development of ethanol drinking behaviors. Here, we compared the consequence of global deletion of the STEP gene on voluntary ethanol intake to the consumption of an appetitive rewarding substance (saccharin) or an aversive solution (quinine or denatonium). Whereas saccharin intake was similar in STEP knockout (KO) and wild type (WT) littermate mice, the consumption of ethanol as well as quinine and denatonium was increased in STEP KO mice. These results suggested that the aversive taste of these substances was masked upon deletion of the STEP gene. We therefore hypothesized that STEP contributes to the physiological avoidance towards aversive stimuli. To further test this hypothesis, we measured the responses of STEP KO and WT mice to lithium-induced conditioned place aversion (CPA) and found that whereas WT mice developed lithium place aversion, STEP KO mice did not. In contrast, conditioned place preference (CPP) to ethanol was similar in both genotypes. Together, our results indicate that STEP contributes, at least in part, to the protection against the ingestion of aversive agents.     

Early Learning and the Recognition of Conspecific Cocoons by Carpenter Ants (Camponotus spp.)

Groups of newly-eclosed workers of two carpenter ant species (Camponotus floridanus and C. tortuganus) were reared in the presence of conspecific cocoons, cocoons of the other species, or were kept without cocoons. Groups of older workers (> 20 days), previously exposed to conspecific brood in their natal nest, were familiarized with either conspecific or heterospecific cocoons. After 14 days of exposure, groups were subjected to short-term (5 min) and long-term (10 day) preference tests. Young and older workers retrieved and retained many cocoons of both species, familiar and unfamiliar. However, a pattern of non-exclusive discrimination emerged: (1) Young workers exposed to conspecific cocoons picked up and retrieved conspecifics before unfamiliar heterospecifics, and retained conspecifics longer. (2) Young workers generally required experience with conspecifics to develop this preference, as those exposed to only heterospecifics and those deprived of cocoons were impartial in short-term tests. However, in long-term tests (5–10 days), naive young workers significantly preferred unfamiliar conspecifics. (3) Older workers preferred conspecific cocoons, whether familiar or unfamiliar, in short-term tests, but their tolerance for heterospecifics in the longer term (5 days) could be increased by recent familiarization. In no case did young or older ants significantly prefer familiar heterospecifics to conspecifics. These results confirm a role for early learning in brood recognition by carpenter ants, but suggest that it is less important than in Formica species studied by previous authors.     

Video demonstrations seed alternative problem-solving techniques in wild common marmosets

Studies of social learning and tradition formation under field conditions have recently gained momentum, but suffer from the limited control of socio-ecological factors thought to be responsible for transmission patterns. The use of artificial visual stimuli is a potentially powerful tool to overcome some of these problems. Here, in a field experiment, we used video images of unfamiliar conspecifics performing virtual demonstrations of foraging techniques. We tested 12 family groups of wild common marmosets. Six groups received video demonstrations (footage of conspecifics either pulling a drawer open or pushing a lid upwards, in an ‘artificial fruit’); the other six groups served as controls (exposed to a static image of a conspecific next to the fruit). Subjects in video groups were more manipulative and successful in opening the fruit than controls; they were also more likely to use the technique they had witnessed and thus could serve as live models for other family members. To our knowledge, this is the first study that used video demonstrations in the wild and demonstrated the potent force of social learning, even from unfamiliar conspecifics, under field conditions.     

Behaviorally conditioned suppression of the immune response by antilymphocyte serum

Previous studies have shown that cyclophosphamide, a drug with a broad spectrum of cytotoxic activity and one that produces noxious gastrointestinal side effects, can elicit taste aversion conditioning when paired with a non-immunosuppressive oral stimulus (saccharin) resulting in immunosuppression after subsequent exposure to the paired stimulus (1). The study reported here indicates that rabbit anti-rat lymphocyte serum (ALS) which is selectively cytotoxic for lymphocytes and does not produce sensory side effects can similarly induce taste aversion conditioning of the immune response. Rats were exposed to oral saccharin paired with ALS injection. Upon subsequent reexposure to saccharin alone the immunosuppressive effects of ALS were reenlisted and the primary mixed lymphocyte culture response of conditioned rats to allogeneic lymphocytes was suppressed by 35% compared to controls. The demonstrated influence of psychologic factors on the immune response has far reaching implications, especially to human medicine, and their role in the course of disease and recovery in man demands further investigation.     

An experimental analysis of “empathic” response: Effects of pain reactions of pigeon upon other pigeon's operant behavior.

Suppression of operant behavior by exposure to pain reactions of conspecifics was examined with pigeons. Three groups of pigeons were trained on a VI schedule, and were then exposed to the pain reactions of an adjoining bird to electric shocks. Although every subject showed suppression of responding, the suppression decreased with repeated exposures. Following this assessment, a conditioning group received conditioned suppression training in which the pain reaction of the adjoining bird was the CS and an electric shock was the US; a shock exposure group received the electric shock without any explicit CS; and, a no-shock group did not receive any shock. After these treatments, every group was exposed to the pain reactions of the adjoining bird (test 1). The conditioning group and the shock exposure group showed clear suppression in responding, but the no-shock group did not.The no-shock group then received the shock exposure treatment and the conditioned suppression training succesively, and the shock exposure group received the conditioned suppression training. Results of tests with the pain reaction of the adjoining bird supported the results of the test 1, however, suppression caused by the shock exposure was not so clear in the no-shock group.The present results demonstrated that conspecific behavior can become a CS by conditioned suppression training, and, the behavior to an aversive stimulus can acquire aversive properties for other conspecifics when they have shared the exposure to the same aversive stimulus.     

Taste aversions in the ontogeny of the rat

The characteristics of acquisition and extinction of conditioned taste aversion (CTA) were studied in rats of both sexes and various ages by pairing of saccharin solution consumption with discomfort (LiCl intoxication, rotation). Pairing of saccharin consumption with LiCl in adult rats led to acquisition of CTA, more profound in male rats than in female ones. In rats of both sexes 30 days old, a profound CTA, comparable in intensity with CTA of adult male rats was acquired. In 2 months after acquisition of CTA in adult rats its magnitude did not change, while in rats of the junior group which by that time had reached puberty, CTA was reduced in females and did not change in males. Pairing of saccharin intake and rotation led to acquisition of CTA only in rats 30 days old. The role of external factors in duration of retention of CTA acquired by pairing of saccharin solution consumption with LiCl injection was studied in male and female rats 1 and 3.5 months old. In all cases CTA was extinguished much sooner in home cages than in experimental chambers, and in the elder group sex dimorphism was found: in both situations CTA disappeared sooner in female rats. The obtained data allow to suggest modulating influences of hormonal background and of contextual stimuli on CTA acquisition and retention.     

Female rats show a bimodal preference response to the artificial sweetener sucralose

The preference of female Sprague-Dawley rats for sucralose, a non-nutritive sweetener derived from sucrose, was evaluated in 23 h two-bottle tests with water or saccharin. Overall, the rats displayed weak or no preferences for sucralose (0.25-4 g/l) over water but strong preferences for saccharin (0.5-8 g/l) over water and saccharin (1 g/l) over sucralose (0.5 g/l). The rats also preferred a saccharin + sucrose mixture to sucrose, but sucrose to a sucralose + sucrose mixture. There were marked individual differences in sucralose preferences: about half the rats preferred sucralose to water at some concentrations while most remaining rats avoided sucralose. Both subgroups preferred saccharin to sucralose. Sucralose appears to have an aversive off-taste that reduces its palatability to rats.     

Self-selection of Dietary Threonine in the Rat and the Effect of Taste Stimuli on its Selection

The possible regulation of dietary threonine intake and the effect of a palatable (sodium saccharin) or aversive (quinine sulfate) taste stimulus on the manner of threonine selection were investigated in rats using a self-selection feeding method. Weanling rats were offered the choice of two diets differing only in threonine content for 2 weeks. Both weight gain and food consumption in the rats offered the choice of diets were quite comparable to each other and were the same as those in rats fed one diet containing sufficient threonine. Threonine intake of the self-selecting rats ranged from 0.43 to 1.90% of the food consumed. The threonine concentrations in the plasma and brain of the self-selecting rats increased proportionally with the threonine intake. When rats were offered a choice of two diets containing various amounts of threonine with taste materials, i.e., sodium saccharin or quinine sulfate, neither the dietary threonine nor their growth were ever affected.

These results indicate clearly that rats have an ability to regulate threonine intake to meet their requirement for the l-amino acid, and the threonine selection is not influenced significantly by the dietary addition of palatable or aversive taste materials.     

Information transfer and the facilitation and inhibition of feeding in a schooling fish

Synopsis Recent studies show that fish forage actively when perceived risk is low, but decrease foraging and increase vigilance when perceived risk is high. Isolated juvenile chum salmon,Oncorhynchus keta, were visually exposed to groups of conspecifics engaged in different activities to examine their ability to gain information about foraging opportunity and risk by interpreting conspecific behavior. Isolates ate most when exposed to feeding groups, less when exposed to nonfeedig groups, and least when exposed to alarmed groups. Isolates exposed to alarmed conspecifics also spent more time motionless than did fish exposed to either feeding or nonfeeding conspecifics. These findings indicate that schooling fish gain information by interpreting conspecific behavior, and are consistent with research showing that animals balance the conflicting demands of foraging and vigilance.