Discrimination of odors from stressed rats by non-stressed rats

Comparison of earlier reports of rat stress odors is complicated by the many differences in experimental parameters and responses measured. To evaluate whether these stress odors provide a special signal, rats were subjected to different levels of stressful foot-shock in one half of a simple two-compartment test box whilst the other half was clean and unoccupied. The results show that whilst test subjects preferred the half containing odors from non-stressed rats, this preference was decreased by the presence of stress odors to an extent concordant with the level of stressor applied to the odor donors. There were no differences in plasma corticosterone among the odor donors indicating that this hormone is probably not the source of stress odors. Plasma corticosterone levels of the subjects were similar to each other and to the odor donors. Compared to odors from non-stressed rats, stress odors increased the activity of the subjects. The evidence strongly suggests a special signalling function for stress odors although responses to this signal are not stereotyped.     

Olfactory lateralization: odor intensity but not the hedonic estimation is lateralized

An earlier study in humans comparing the olfactory sensitivity of both nostrils revealed a small but significant advantage of the right nostril for detection and for olfactory quality discrimination. However lateralization was not evaluated for the perception of odor intensity and hedonic evaluation (pleasantness/unpleasantness). Thus we investigated lateralization of olfactory intensity and hedonic evaluation in right-handed healthy volunteers (n=186) from the HeDoS-F database (Hedonic Database of Smell-Franconia). For olfactory evaluation the Sniffin' Stick Test was employed with the parameters detection, discrimination, identification and extended by analogue hedonic and intensity rating scales. Over all odors subjects rated the perceived intensity significantly higher following stimulation of the right compared to the left nostril. The analysis of the single odors of the Sniffin' Stick Test consistently confirmed higher intensity ratings for the right compared to the left nostril reaching a statistically significant difference for 10 out of 16 odors. In contrast we found no significant differences between the nostrils for the hedonic estimates over all odors. Differences in odor detection, discrimination and identification did not reach a statistically significant level, but for all these parameters the scores of the right nostril were slightly higher compared to the left nostril. For odor identification, however, a statistical tendency was observed. Based on our results we concluded that olfactory intensity estimates represent the most sensitive parameter of olfactory lateralization.     

Influence of the odorization of the rearing environment on the development of odor-guided behavior in rat pups

The study describes a phenomenon in which attraction of rat pups to artificial odors disappeared after the first week of life. In experiment 1, pups were continually exposed to either: (1) the normal odors present in the litter or (2) the same odors enriched with one of four artificial odors present in the dam's food. Pups were tested daily with the odors of normal or adulterated soiled shavings from their nests. The results show that attraction to the normal test shavings lasted throughout the testing period (PN 1-7). However, pups raised on odorized shavings exhibited an attraction to the artificial odor until day 6 only, not on day 7. In experiment 2, pups were tested with dam's artificially adulterated food. The results show that the artificial odor, and not the food odor, was responsible for the lack of attraction on day 7. Experiment 3 was carried out to determine whether the date on which attraction to artificial odors changed might be specific to postnatal day 7 or whether the duration of odor exposure in test conditions was the important factor. The results suggest that the age of pup is the more important variable.     

Identification of unpleasant odors is independent of age.

The purpose of this study was to investigate (a) the relationship between identification proficiency for specific odors and chronological age and (b) to determine whether the relationships were related to perceived quality (i.e., judgments of familiarity, intensity, and hedonics) of the odor item. Data from 472 subjects (227 men, 245 women) ranging in age from 18 to 79 years were assessed in a cued identification test comprising 16 odors. The results indicated a reliable age effect in overall odor identification performance. Further analyses indicated that the observed age-related deficit was odorant-specific, with some odors being equally well identified across age cohorts and others showing sensitivity to the process of aging. Additional examination regarding the observed age-differential effects across the different odor types indicated that these may be understood according to the pleasantness/upleasantness associated with the odor. Specifically, odors perceived as unpleasant showed age invariance whereas odors rated as pleasant exhibited age sensitivity.     

Effect of food restriction on acquisition and expression of a conditioned odor discrimination in mice

Level of food restriction was manipulated in mice to assess its importance for the acquisition and expression of a conditioned odor discrimination. In training, animals were exposed to odors (either rose or lemon) presented on a piece of filter paper in a pot covered in bedding. For half of the conditioning trials, group paired received one odor (CS+) with sucrose, the unconditioned stimulus (us), under the bedding. For the remaining trials, they received the other odor (CS-) alone. Group CS-alone was also exposed to both odors, but neither odor was paired with sugar on any of the conditioning trials. During training, Group Paired mice that were food-restricted tended to dig more readily and longer in the odors, especially in the CS+ odor, than animals that were not restricted. Both restricted and nonrestricted PAIRED GROUPS dug more in the CS+ than in the CS- by the end of training, but the CS-alone mice dug very little in either. Following training, mice were exposed to both odors simultaneously in a discrimination test. Half the mice in each training food restriction condition were tested under food restriction, and half were not. Only PAIRED animals that were food-restricted in the test expressed an odor discrimination, digging only in the CS+. This occurred regardless of their previous restriction state in training. These data suggest that both food-restricted and nonrestricted mice can acquire an odor discrimination; however, expression of this odor discrimination depends on food restriction.     

Stability of preference for odors after short-term exposure in young spiny mice

The stability of olfactory preferences for artificial odors was studied in young spiny mouse pups (Acomys cahirinus). Subjects aged between 2 and 20 days were exposed to the odor of either cinnamon or cumin for 1.5 hr. The durability of preferences for the familiar versus novel odor was subsequently monitored in a three-choice preference test. The results suggest the existence of a sensitive phase for learning odor characteristics, through simple exposure, between Days 2 and 18 of the pups' postnatal life. The sensitive phase proved not be an “on-off” process, but the strongest effect of exposure to odors took place at about Days 4 and 6. However, the duration of preference for exposed odors was dependent on later experience with the odors during retests. The results point to an unusual plasticity in rapid learning of odors through simple exposure in precocial young spiny mice. © 1993 Johan Wiley & Sons, Inc.     

Olfaction and the "data" memory system in rats

A set of studies was conducted to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radial maze; one of the arms contained a water reward. After training on four or five pairs of odors (20 trials per day), rats learned to discriminate the members of a new pair in 5-10 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the rats learn both positive and negative odors, rather than simply ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Training on 30 pairs did not result in any slowing of subsequent learning, which suggest that the capacity of the memory system for odors is substantial. In a second group of experiments, we tested whether rats distinguish between odors by identifying unshared subcomponents or instead treat odors in a gestalt (i.e., unitary) fashion. Animals trained on three component odors with two in common did not recognize the elements that were unshared when these were presented by themselves. Even when one of the two shared components was combined with the differentiating component into a cue (i.e., two thirds of the original three-component odor), the new cue was treated as a novel odor. However, inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rats assess degree of relatedness from human odors

Despite widespread interest in the evolutionary implications of human olfactory communication, the mechanisms underlying human odor production are still poorly understood. Previous studies have demonstrated that human odor cues are related to variations in the major histocompatibility complex, but it is unclear whether odors are associated with overall genotypic variation. In this study, we investigated whether more closely related humans produce more similar odor cues. To assess objective odor qualities we tested odor similarity using rats in a habituation–discrimination paradigm. Rats were first habituated to a referent human odor and were then presented with two test odors obtained from individuals related in different degrees to the referent. Investigation times for each odor were compared. Because rats investigate novel odors longer than familiar odors, we were able to determine which test odor the rats perceived as more similar to the referent human odor. For six of ten odor donor families, rats investigated the odor of the less closely related individual significantly longer than that of the more closely related individual, and investigation durations were in the expected direction for all families. These results indicate that similarity of human odor cues is associated with degree of genetic relatedness, with more closely related humans producing more similar odor cues. This study supports the hypothesis that odor cues provide information regarding degree of relatedness and may thus affect a wide variety of human behaviors, including kin preferences, nepotism, and mate choice.     

Odor modulation of ventral scent gland marking in the Mongolian gerbil

Gerbil odors were allowed to accumulate in individual home cages for several months in order to provide stable olfactory stimuli that might modulate the number of ventral scent gland marks produced by both male and female Mongolian gerbils. Male marking levels for most test conditions were 2-3 times larger than those in females. In general, the relative patterns of responsiveness to particular odors were similar in both sexes. The number of scent marks in home cages was significantly smaller than the number obtained in clean cages. This suppression was not strongly dependent on the odors emanating from an individual's own ventral gland sebum. Marking levels in the home cages of other gerbils were substantially higher than those seen in the test animal's own cage and were maximal in the home cages of other males. Behaviorally receptive females marked at significantly higher levels in home, clean, and conspecific cages than did nonreceptive females. Conspecific urine odors, especially those from females, increased marking levels significantly over those obtained in home cages. In males, home cage marking was significantly enhanced by the presence of a female. Females, on the other hand, marked at similar levels in home cages whether a potential mating partner was present or not. Both sexes showed significant reductions in marking levels in another's cage if the resident animal was present. These results suggest that when sufficient gerbil-related odors are available to a test animal, its rate of scent-marking is altered, depending on the particular odor environment. Some gerbil-related odors increase marking levels, whereas others decrease marking. Scent-marking then, like other olfactory guided behaviors and odor preferences, is context specific.     

Enrichment to odors improves olfactory discrimination in adult rats

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments.     

The effects of odors from stressed mice on conspecific behavior

Four experiments correlate conspecific reactions to odors from stressed (foot shocked) BALB/cJ mice with the frequency of specific motor activities and taste avoidance. Where behavior was restricted to forward and backward movement in a tube, animals tended to avoid the side where the odors from stressed animals entered. In a more socially complex home cage (3 recipients) a wide variety of behaviors were affected by odors from stressed conspecifics. Animals were alerted by the odor, searched out the source of the odor and showed increases in general activity, rearing, and air sampling. Many of these behaviors habituated with continuous exposure. The major response to odors from stressed animals was to increase "vigilance." A restriction of behavioral opportunities will lead to odor avoidance; however, when the environment permits, the behavioral reaction to odors becomes more complex. These odors failed to produce conditioned taste aversion, suggesting a sensory specificity in the use of these odors.     

The failure to demonstrate avoidance of ventral gland odors in male gerbils (Meriones unguiculatus)

The gerbil's ventral gland secretion has been assumed to play a role in territorial defense. The odor of this secretion should be avoided by males which have recently lost a dominance contest to a male which deposited the odor mark. In two experiments, male gerbils were randomly paired and dichotomized on the basis of dominance status. Twenty-four hours later, they were presented either with the odor of the dominant member of the pair in an otherwise clean open-field, or with the odors of the dominant, a novel male, the subject or an unscented area. There was no indication that the animals differentiated the dominants' odors from the others. In neither case was an odor avoided. Areas containing the odor of conspecifics were marked less frequently than the clean area. These data indicate that conspecific odors were detected, but there was no evidence of a differential response to any of the odors employed.     

The vomeronasal organ is involved in discrimination of individual odors by males but not by females in golden hamsters

The vomeronasal organ (VNO) has a wide variety of functions in terrestrial vertebrates, some of which involve responses to classical pheromones whereas others do not. We examined the role of the VNO in discrimination of individual differences in odors of male and female golden hamsters using a habituation paradigm. Removal of the VNO resulted in elimination of the ability of male hamsters to discriminate between some individually distinctive odors (e.g., flank gland secretion), but not others (e.g., urine). In females, such lesions had no effect. The type of test trial also influenced the results; in test trials employing a single, novel odor, removal of the VNO in males did have an effect but in test trials in which both the novel and the familiar odor were presented, VNO removal had no effect. It is concluded that (a) there is a sex difference in the role of the VNO in the discrimination of individual odors, (b) the role of the VNO in discrimination of individual odors varies from odor to odor, and (c) deficits due to VNO removal are more readily observed in more difficult tasks.     

Olfactory tests as possible probes for detecting and monitoring Alzheimer's disease

One of the characteristics of Alzheimer's disease is the early loss of neurons in pathways involved in processing olfactory information. Olfactory function was assessed in subjects with Alzheimer's disease using a conventional Smell Identification Test and a simple three odor match-to-sample problem. The patients exhibited a diminished capacity to identify common odors but were severely impaired in their ability to use novel odors in a match-to-sample task. Subjects with Parkinson's disease had a severe deficit for identifying common odors with the majority scoring as anosmic. Multiple sclerosis was not accompanied by detectable changes in olfactory functioning. The results of the Alzheimer's group are similar to recent animal studies that have shown lesions of the piriform-entorhinal cortex produce a variety of memory deficits that are particularly acute in tasks involving novel odors.     

Sex differences in olfactory self-recognition

This study investigated sex differences in the ability to recognize one's own body odor accompanied by an attempt to account for variance in this ability by comparing ratings of self-body odor and other odors on a visual analog scale (VAS). Whereas over half (59.4%) of the females were able to identify their own odor, only one out of 18 (5.6%) males were able to recognize their own odor. Females rated their own secretions as significantly lower on a pleasant-positive factor than males rated their own odors (axillary secretions), but there was no difference in ratings between those who could and those who could not identify their own odor. The dimensions tapped by the VAS used in this study do not seem to account for the ability to identify one's own body odors.     

Olfactory experience and the development of odor preference and vaginal marking in female Syrian hamsters

Rodent reproductive behavior relies heavily on odor processing, and evidence suggests that many odor-guided sexual behaviors are shaped by prior experience. We sought to determine if exposure to male odors during development is required for the adult expression of proceptive sexual behavior toward male odors in female Syrian hamsters. Exposure to male odors was restricted in na?ve subjects by removing all male siblings from the litter at three to five days of age. Control litters were also culled, but included equal numbers of male and female pups. As adults, na?ve females displayed investigatory preferences toward male odors in a Y-maze that were comparable to control females; this preference was observed whether contact with the odor stimuli was prevented of allowed. In contrast, na?ve females vaginal scent-marked equally toward male and female volatile odors, suggesting an inability to target behavior toward sexually relevant odors. However, na?ve females marked preferentially toward male odors when allowed to contact the odor stimuli. These results provide evidence for the experience-dependent development of vaginal marking behavior toward volatile components of sexual odors. Furthermore, they suggest that distinct mechanisms regulate the development of odor preferences and vaginal marking behavior in this species.     

Attraction of newborn rabbits to abdominal odors of adult conspecifics differing in sex and physiological state

The present study aimed at assessing the ability of newborn rabbits (1-3 days) to detect and discriminate abdominal odors emitted by adult conspecifics varying in sex and physiological state. Pups were submitted to a two-choice test exclusively based on olfaction, which permitted exposure to conspecifics either during successive or simultaneous presentations. Their orientation toward either of the two stimuli was timed. These behavioral assays revealed that (a) pups display attraction to odors of the abdomen of nonlactating, nonpregnant females and males when pitted against a control stimulus; (b) pups preferred the odor of nonlactating, nonpregnant females when simultaneously presented with the odor of a male; (c) all sexually mature females (virgin, pregnant, or lactating) were attractive to pups; (d) the odor of lactating females was preferred to the odor of either nonlactating, nonpregnant or pregnant females. Thus, from the first day after birth, newborn rabbits are able to olfactorily discriminate conspecifics from cues emitted at the abdominal level and display the strongest attraction to lactating females.     

Effect of odor quality and intensity on conditioned odor aversion learning in the rat

Odor quality and intensity were varied to test the ability of rats to associate odor with an induced illness. Rats were allowed 10 minutes access to water on each of nine days; deodorized air was directed towards each rat's nose while drinking at familiarization and recovery sessions (days 1-5 and 7-8, respectively) and odorized air at treatment and test sessions (days 6 and 9, respectively). Each rat was injected with LiCl following its drinking period on day 6. The difference between the amount of water consumed on day 6 and day 9 gave a measure of the conditioned aversion. Only mild or no aversion occurred with odors of n-butyric acid, benzylamine, cyclohexanone, and n-butanol. Strong conditioned aversions were obtained to odors of triethylamine, 1,4-cineole, and isoamyl acetate, and the degree of aversion increased linearly with the log of odor concentration. The effect of odor quality, intensity and presentation method, and the role of the different chemoreceptor systems in the acquisition of odor aversions are discussed.     

A simple method of olfactory discrimination of urines for the Mongolian gerbil,Meriones unguiculatus

Olfactory discrimination in gerbils can be reliably assessed by measuring changes in rearing toward an odor. After the frequency of rearing stabilizes during a non-odor period, the introduction of a urinary odor through a ceiling aperture quickly produced an increase in rearing frequency and duration. Rearing then habituated during the odor presentation period but recurred at high levels if a new urinary odor was introduced. This pattern of rearing was robust enough to allow for the testing of three urinary odors during a single 24-min test period. Preliminary work suggests that the procedure is equally sensitive with different odors, can be adapted for use with other rodents, and may provide additional information about differential investigation of urinary odors. The simplicity, reliability, and brevity of this method makes it a potentially important tool for olfactory research.     

Ambient odors associated to failure influence cognitive performance in children.

We investigated whether odors can become conditioned to emotionally salient experiences such that when later encountered they influence performance consistent with a previously associated event. To test this hypothesis, 5-year-olds were given the experience of failure/frustration on a cognitive maze in a room scented with fragrance and later given another cognitively challenging test in a different room scented with either the same odor, a different odor, or no odor. Results revealed that subjects who performed the test in the presence of the same odor as the maze task did significantly worse than subjects in any other group. Performance in the different odor and the no odor groups were equivalent. Facial expressions and verbal remarks made during the maze task indicated a predominant display of negative affect. These findings show that odors can become conditioned to experiential states and when later encountered have directional influences on behavior.