Influence of conspecific and predatory Stressors and their associated odors on defensive burying and freezing responses

In Experiment 1, male rats were exposed to either aggressive (i.e., alpha) or nonaggressive conspecific colonies and tested 24 h later, with or without alpha odors, for freezing behavior and burying of a wall prod that had been the source of a brief electric shock. The results indicated that prior defeat experience and the presence of alpha odors alone during testing had no significant effects, but the combination of prior defeat and alpha-odor testing significantly decreased burying and increased freezing behavior. In Experiment 2, we examined the effects of noncontact exposure to a cat, as a predatory Stressor, during subsequent prod-shock tests involving the presence or absence of cat odors. Exposure to a cat failed to disrupt later prod burying and did not produce freezing. However, the presence of cat odors during testing significantly reduced the amount of defensive burying,without resulting in an increment in freezing. In Experiment 3, rats were given 1, 5, or 30 inescapable preshocks in the presence of either cat odors or a hedonically neutral citronella odor and were tested 24 h later for prod burying and freezing with or without these odors. Both the cat and the citronella odors resulted in a significant reduction in burying and an increase in freezing for rats given 5 and 30 preshocks and tested in the presence of these respective conditioned odors. For the groups that were given 5 preshocks, preshock and later testing in the presence of cat odors resulted in significantly less prod burying and more freezing than for rats that were preshocked and tested in the presence of citronella. The findings of these three ethoexperimental studies are discussed in terms of the learned-helplessness theory, the stress-coping-fear-defense (SCFD) theory, and the concept of selective CS-US associability.     

Influence of conspecific stress odors and shock controllability on conditioned defensive burying

In Experiment 1, rats received a session of 80 inescapable tail shocks or no shocks while restrained in a tube. During tests of conditioned defensive burying 24 h later, the bedding of the chamber contained odors from either stressed or nonstressed conspecific donor rats. Following a single prod shock, subjects that had had prior shocks or that were tested with the stress odors spent significantly less time burying the prod, made smaller piles of bedding, and displayed more freezing behavior. The combination of prior shock and stress odors during later testing enhanced these effects. In Experiment 2, a yoked group of rats that was given inescapable shocks, in contrast to a group that had wheel-turn escape training and one that was restrained but not shocked, later showed significantly less burying and more freezing when tested for defensive burying with stress odors present. In both experiments the duration of burying and the heights of piles were positively correlated, and both of these measures were negatively correlated with freezing. The demonstrated capacity of unconditioned stress odors to mediate different degrees of fear, depending upon the controllability of prior shock, is related to other studies of learned helplessness, and the predominance of freezing over burying is discussed in terms of various types of defensive strategies, stimulus-control processes, and the author’s stress-coping-fear-defense (SCFD) theory.     

Effects of conspecific odor on rats’ position and behavior in an open field

When rats were tested in a novel open field, half of which had previously been occupied by a conspecific, they tended to enter the predecessor half first and subsequently spent more time in this half. There was proportionally more sniffing of the floor, sniffing of the air, and grooming in the predecessor half compared with the clean one, and proportionally less ambulating, rearing, and sniffing of the wall. Time spent in the predecessor half was unaffected by whether or not the predecessor had been tested under a relatively stressful condition (strong illumination), but rats tested after a “stressed” conspecific ambulated and reared less and showed more inactivity and thigmotaxis. Predecessor influence may be mediated by qualitative and/or quantitative differences in odor associated with urine traces, an influence that could affect results during routine successive open-field testing.     

Training rats to discriminate between the odors of individual conspecifics

To determine the influence of genetic and microbiological factors in producing individually unique urine odors, we used a go/no-go operant task to assess the ability of eight male Long-Evans rats to discriminate between urine odors from the following pairs of male rats: (1) two outbred Long-Evans rats, (2) individual conventionally housed rats differing genetically only at the major histocompatibility complex (PVG vs. PVG.R1), (3) individual PVG versus PVG.R1 rats born by cesarean section and raised in germfree conditions, and (4) conventionally housed, genetically identical individuals of the PVG or PVG.R1 strains. Discriminable differences were present between the urine odors used in all four tasks. Analysis of the errors to a criterion of 85% correct discrimination responses revealed different learning patterns in each task. When bacteria were not present in genetically different rats (Task 3) and when bacteria were present but there were no genetic differences between rats (Task 4), the discrimination was the most difficult. The easiest discrimination involved the presence of bacteria and a genetic difference at the major histocompatibility complex (Task 2). These results indicate that, although bacteria are not necessary for the production of discriminable odor differences, they do influence the discriminability of the urine odors of rats.     

Taste + odor interactions in compound aversion conditioning

In three experiments with rats, taste + odor interactions in compound aversion conditioning were investigated. In Experiment 1, two odors (0.02% almond and 0.02% orange) were compared on single-element odor aversions, taste (denatonium) potentiated odor aversions, and potentiated odor aversions following taste extinction. Although no odor differences were seen following single-element conditioning, both types of potentiated orange odor aversions were stronger than their almond odor counterparts. These data show that odors of similar conditionability are differentially potentiated by the same taste. To determine whether these differences were due to unique perceptual representations, the effects of elemental extinction or compound extinction on aversions to the compound were investigated in Experiments 2 and 3. In Experiment 2, orange odor extinction weakened responding to the compound significantly more than taste extinction did. In contrast, almond odor extinction and taste extinction produced similar decrements in responding to the compound in Experiment 3. These results suggest that the perceptual representation of these specific taste + odor compounds are different, and they are discussed in regard to configural and within-compound association accounts of potentiation.     

Attractiveness of lactating females' breast odors to neonates

A series of experiments investigated the responses of human infants to olfactory cues produced by lactating females. 2-week-old bottle-feeding girls oriented preferentially to the breast odor (odorized pad) of a nursing woman when paired with such odors from either a nonparturient female or axillary odors from the same lactating female. Responses to axillary odor from a lactating female did not differ from those to a clean (nonodorized) pad. These data indicate that breast odors from lactating females are especially attractive to female infants who are unfamiliar with the stimulus woman and who have had no prior breast-feeding experience.     

The effects of isolation rearing on exploration in the rat

The hypothesis that isolation rearing enhances exploration was tested in two settings which varied the extent to which exploratory behavior would be affected by competing hyperactivity. Experiment 1 measured exploration as contact of a discrete novel stimulus, in terms of bout frequency and duration. Locomotor activity was measured by photocell beam interruption. Isolation-reared rats were hyperactive, showed an increased incidence of exploratory bouts but no differences in duration of exploratory behavior, compared with group-reared controls. Experiment 2 measured, independently, locomotor activity and the preference for a novel environment over a familiar one. Isolation-reared rats, whether male or female, showed enhanced novelty preference compared with controls. No significant differences were found in locomotor activity. The results are discussed in terms of the hyperactivity of isolates interfering with investigative behavior by response incompatibility.     

Odors of individuality originating from the major histocompatibility complex are masked by diet cues in the urine of rats

Male Long-Evans rats were trained to discriminate between the urine odors of two congenic strains of rats (PVG and PVG.R1) in an olfactometer on a go/no-go operant task with water reinforcement. These odor donors differ genetically at only one locus of the major histocompatibility complex (MHC). The ability of the subjects to transfer their training to discriminate between novel individuals of the same MHC strain on the same and different diets was then examined. The subjects correctly generalized their original training to new samples from previously undiscriminated individuals of the same MHC type on the same diet without a significant drop in performance. A change in diet disrupted the perception of the MHC-related odor. In a second experiment, rats were trained to discriminate between the odors of pairs of genetically identical PVG or PVG.R1 rats on different diets and were tested for generalization using the odors of rats of the other strain (PVG.R1 or PVG) maintained on the same diet. Changing the strain of the odor donor did not disrupt the learned discrimination. The results of these two experiments confirm the ability of the MHC to generate constant cues in the urine but also reveal that variable diet cues disrupt the perception of these cues. The relationship between the MHC, diet, and other factors in determining individual odors is discussed.     

Different odors in rats from large and small rewards

Although rats emit different odors in a goalbox upon receipt of unsignaled reward and nonreward, recent studies have failed to find odor differences from unsignaled large and small reward, apparently disconfirming the generalization that frustration-producing manipulations lead to a distinctive emission. Experiment 1 tested the hypothesis that providing discriminative runway signals, permitting subjects to anticipate the large and small rewards, would lead to different odor emissions. Results supported the hypothesis: donor rats emitted odors sufficiently different to provide cues for differential responding in test subjects. However, an attempt to replicate the recent observations on unsignaled rewards suggested that these, too, occasioned goalbox emissions. Therefore, Experiment 2 again gave donors unsignaled large and small reward, but increased the incentive for discrimination in test rats. Test subjects readily discriminated, confirming the conclusion that large and small rewards occasion different emissions even without discriminative signals and supporting a frustration-odor interpretation.     

Persistence of social investigatory behavior in the male rat: Evidence for long-term memory of initial copulatory experience

The duration of active social investigation by sexually mature male rats, following exposure to a novel conspecific, was investigated to assess the influence of former social experience. In Experiments 1 and 2, pretest social isolation of older males with extensive heterosexual experience and of younger males with limited heterosexual experience failed to affect their subsequent persistence in social investigation. Older and sexually experienced rats, however, engaged in significantly less investigatory behavior than did younger, sexually inexperienced males. Experiments 3, 4, and 5 demonstrated that this difference was associated with prior copulatory experience. A single copulatory series with either an intact female or a hormone-primed castrate female effected a significant and sustained decrease in social investigatory behavior. The results are interpreted as demonstrating a form of long-term memory for associations formed during initial copulatory experience.     

The basic tastants in aversion conditioning: Evidence for sensory preconditioning and not potentiation

In Experiment 1, a potentiation paradigm was used to test the relative influence of odor and taste with two 2 basic tastants (i.e., salt and sweet) in conditioned aversion learning. Experiment 1 showed that aversions to tastants (salt or sweet presented in a manner by which it could be tasted) were established only in subjects trained with the tastant, not the odor (i.e., salt or sweet presented in a manner by which it could not be tasted). Experiment 2 demonstrated, with a sensory preconditioning procedure, that the expression of an aversion to tastants was dependent on previous tastant experience prior to odor aversion training. These results suggest that while subjects can smell salt and sweet solutions, these odors are neither sufficient nor necessary for the expression of a conditioned tastant aversion.     

The relationship between locus of odor cues and double-alternation responding in the rat

In two experiments, rats traversed a runway in the presence of odor cues from odor-donor rats (stimulus odor). These odors were established in the start and run sections of a runway. As in previous work, these odors were shown to be influential determinants of behavior There is an indication that odors of reward and nonreward may be different for different rats, and that these different odors can be used to form complex discriminations.     

Visual and olfactory oddity learning in rats: What evidence is necessary to show conceptual behavior?

Experiment 1 involved the use of plastic and wooden objects and trial-unique problems. The rats performed successfully on nonconceptual oddity problems given before and after conceptual training, showing that the testing conditions were suitable, but they showed chance performances on the trial-unique problems. Experiment 2 involved the use of olfactory discriminanda. Five pretraining problems and 300 unique five-trial problems were presented. Two of 3 rats performed better than chance on Trial 2 and on Trials 3–5, but all performed at chance levels on Trial 1 throughout. The data suggest that the rats responded to specific odors on Trials 2–5 following the Trial 1 experience, as opposed to respondingconceptually to the “odd” odor. Had they responded conceptually to odd odors, they should have performed better than chance on Trial 1. These findings and the general logical argument that they support are considered in the context of the numerous inconclusive reports of the use of the oddity concept by nonprimate animals.     

Prolonged exposure to conspecific and predator odors reduces fear reactions to these odors during subsequent prod-shock tests

In Experiment 1, four groups of male rats were given a session as an intruder in either aggressive (i.e., alpha) or nonaggressive colonies of conspecifics and later received either a 2-h exposure to the odors of the alpha colonies or an exposure-control session with the odors of a nonalpha colony. Two additional groups of rats that had been attacked and defeated by alpha residents were later given a 12-h exposure session with alpha-colony odors or nonaipha-control odors. Twenty-four h after the colony-intruder session, all subjects were given a single 6.5-mA shock from a prod with alpha-colony odors present in the bedding of the test chamber. Attacked rats that had been given exposure-control sessions showed significantly less prod burying and greater freezing than nondefeated subjects. This implies that the alpha-colony odors elicited conditioned fear. In contrast, the attacked subjects that had been given a pretest exposure session with alpha-colony odors showed significantly more prod burying and significantly less freezing. This suggests that the alpha-odor exposure resulted in the extinction of fear to these odors. Furthermore, the 12-h exposure to alpha-colony odors was found to be more effective in reducing fear-mediated responses than was the 2-h exposure. In Experiment 2, three groups of rats were exposed to a cat while they were in a protective cage; later they were given a 12-h exposure session with cat odors, a 12-h exposure-control session with no cat odors, or no exposure treatment. Compared with the two control groups, the subjects that were exposed to cat odors showed less freezing during subsequent prod-shock tests in the presence of cat odors, but they did not show prod burying. The reported changes in fear-mediated reactions to the odors of conspecifics and a predator are discussed in terms of both associative and nonassociative processes.     

Reactions of Mongolian gerbils in the presence of urine stimuli

Forty sexually mature Mongolian gerbils served as subjects in a study designed to examine responsiveness to samples of urine. In a two-choice comparison situation in the home cage, each isolated gerbil was tested for amount of time spent with each urine sample during a 3-min period. Male gerbils spent significantly more time with estrus female urine than nonestrus female gerbil urine, and with nonestrus female gerbil urine than with either male gerbil urine or water. Female gerbils did not respond differentially to any of the stimuli. Neither sex discriminated between gerbil and hamster urine of either sex. Results suggest that female gerbil urine communicates sexual identity and, especially, sexual readiness to the male gerbil.     

Attraction to mobile and immobile conspecifics

Male and female laboratory rats invariably investigate a novel conspecific placed in their home cages. In Experiment 1, mature male rats were exposed in their home cages to active and inactive juvenile males. Inactive juveniles were pretreated with haloperidol to induce behavioral stasis in a normally upright, quadrupedal stance. In repeated daily observations, males exposed to active juveniles displayed significantly longer intervals of investigation than did males exposed to inactive juveniles. In Experiment 2, mature males and females were repeatedly exposed to active and inactive castrate females. Males investigated significantly longer than did females, active female castrates were investigated significantly longer than were inactive female castrates, and sex of subject interacted significantly with activity-nonactivity of the social stimulus animal. In Experiment 3, mature males and females were repeatedly exposed to active and inactive castrate males. Males investigated significantly longer than did females, active male castrates were investigated significantly longer than were inactive male castrates, and sex of subject interacted significantly with activity-nonactivity of the social stimulus animal. The results demonstrate that sexual dimorphism in persistence of social investigation may be interpreted as a sex difference in response to normal movement cues of a stimulus complex characterizing a conspecific.     

Aversive conditioning of naturally produced reward and nonreward odors in rats

Past experiments have reported that rats encountering reward (R) or nonreward (N) goal events emit odors that can be utilized as discriminative stimuli for instrumental behavior by conspecifics. In the present study, thirsty male rats were aversively conditioned by ingestional toxicosis to R and N odors, and their suppression of water consumption in the presence of these odors was measured. Thirsty trained donors were placed into chambers containing R or N goal events to generate, respectively, the R or N odors. Test animals were given eight differential conditioning trials (four with one odor as CS+; four with the other as CS?), involving placement into an odorcontaining chamber with water available, followed by a LiCl injection on CS+ trials. Animals tested in their CS+ odor consumed significantly less water than did CS? and control subjects. Both R and N odors were conditioned by aversive means and readily discriminable from each other. This represents the first laboratory demonstration of aversive conditioning of such naturally produced odors, and it suggests that aversive conditioning may be useful in the study of odorous emissions generally. Implications for innate meanings of R and N odors are discussed.     

Reciprocal overshadowing in the discrimination of color-odor compounds by honeybees: Further tests of a continuity model

Honeybees were trained to discriminate between simultaneously presented color-odor compounds, one group with color and odor confounded and a control group with color relevant and odor irrelevant; in subsequent differentially reinforced training with the colors in the absence of the odors, the performance of the two groups was the same (Experiment 1). When, however, response to the colors was measured in a 10-min extinction test, discrimination was found to be poorer after confounded training (Experiment 2), and like results were obtained in an extinction test with the odors after control animals had been trained with odor relevant and color irrelevant, the confounded animals showing poorer discrimination of the odors than the controls (Experiment 3). The results of the first two experiments, in which overshadowing of color by odor was found only with an extinction test, require us to take seriously the possibility that our previous modeling experiments (with probability of correct choice in differentially reinforced training as the measure of performance) may have been insufficiently sensitive to noncontinuity effects. Our first efforts to model extinction suggest, however, that all the results of the present experiments can be understood without sacrifice of the parsimonious independence principle.     

A reexamination of the effects of motivational state on utilization of conspecific odors in the rat

Two previous studies suggested that rats are unable to use conspecifics’ odors when the motivational state of the donor rats is different from their own (Davis et al., 1974; Davis, Prytula, Noble, & Mollenhour, 1976). The effects of motivational conditions on the utilization of such odors were further evaluated in the present study. In Phase 1, test rats were given training either with donors in the same motivational state or with donors in a different state. Differential responses to donors’ odor emissions occurred only when the motivational states of donors and test subjects were the same, thus confirming earlier findings. However, when test subjects’ motivational conditions were changed in Phase 2, discriminations that had been present in Phase 1 were maintained even though the motivational states of these test subjects and their respective donors no longer matched. Thus, any constraint on the rat’s ability to use odors from conspecifics in a different motivational state is not absolute.     

The effects of early rearing conditions upon responses to mirror-image stimulation in domestic chicks and turkeys

Two experiments were performed in which either White Plymouth Rock chicks or domestic turkeys were reared under three maintenance conditions (with a mirror, with a conspecific, or in visual isolation) from Day 1 posthatch until Day 7. On Day 7, the Ss were given a preference test to determine whether they spent more time before a mirror or with another bird. Ss reared with a mirror spent approximately two-thirds of their time in the vicinity of the mirror, whereas socially reared Ss spent approximately two-thirds of their time with an agemate. The social isolates, on the other hand, failed to show a preference for either mirror image of conspecific stimulation. A third experiment evaluated the choice behavior of turkeys socially reared in the presence of a mirror, and revealed that, like the social isolates, these Ss also failed to exhibit a reliable preference. The results are interpreted in terms of the effects of early rearing conditions upon social stimulus preferences.