Rat's responses to blood and body odors of stressed and non-stressed conspecifics

Male rats were tested in a Y-maze for exploratory responses to odors from stressed and non-stressed rats, and from the blood of stressed and non-stressed rats. Significant differences in activity but not preference were obtained in rats receiving odors from stressed and non-stressed rats. Odors from rats given 5 random, signalled, 2 sec electric shocks over 15 min, significantly increased the activity of receivers, compared to responses elicited by odors from non-stressed animals (Experiment 1). Odors from rats given 12 random, signalled, 2 sec electric shocks over 35 min significantly reduced receivers' activity (Experiment 2). Interestingly, responses of rats to odors from the blood of stressed and non-stressed rats were similar to their responses to odors from stressed and non-stressed rats. It is concluded that responses to these odors depend upon the stressor applied to the odor producing rats. Rats subjected to different stress conditions may change the quality or concentration of the odors they emit and thereby alter the responses of rats receiving the odors.     

Dietary influences in the preferences of pre-weanling Long-Evans rats for the anal excreta of adult males

Male rats which ingest feces of lactating females produce anal excreta which is attractive to pups. This excreta is as attractive as that of lactating females and more attractive than the excreta of males eating a diet of lab chow only. Anal excreta of males which consume feces of lactating females is more attractive to pups than excreta of males that consume feces of nonlactating females. These results suggest that group or colony odors may develop from rats eating feces of other colony members and that infant rats may be more attracted to adults that have an odor which is similar to the maternal odor than adults which have different odors.     

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.     

Corticotropin-releasing factor antagonist attenuates defensive-withdrawal behavior elicited by odors of stressed conspecifics

This study examined the hypothesis that defensive responsiveness induced by threatening stimuli of biological origin is mediated by the action of endogenous corticotropin-releasing factor (CRF). Rats were exposed for 15 min to a large open field containing a small chamber. Twenty-four hours later, rats received intracerebroventricular injections of either vehicle or 20 micrograms of alpha-helical CRF(9-41), a CRF receptor antagonist. After 20 min, rats were reexposed to the open field, which now contained odors of urine and feces from a stressed conspecific. In the reexposure test, vehicle- and antagonist-treated rats withdrew rapidly into the chamber. Antagonist-treated rats, however, emerged subsequently from the chamber to explore the open field as indicated by a significant increase in the number of passages made between the chamber and the open field. Results suggest that central injection of alpha-helical CRF(9-41) reduces the level of fear induced by odors associated with threat. In addition, CRF receptors are implicated in mediating the species-typical display of defensive-withdrawal behavior.     

The role of the medial preoptic area in appetitive and consummatory reproductive behaviors depends on sexual experience and odor volatility in male Syrian hamsters

In Syrian hamsters (Mesocricetus auratus), the expression of reproductive behavior requires the perception and discrimination of sexual odors. The behavioral response to these odors is mediated by a network of ventral forebrain nuclei, including the medial preoptic area (MPOA). The role of MPOA in male copulatory behavior has been well-studied, but less is known about the role of MPOA in appetitive aspects of male reproductive behavior. Furthermore, many previous studies that examined the role of MPOA in reproductive behavior have used large lesions that damaged other nuclei near MPOA or fibers of passage within MPOA, making it difficult to attribute post-lesion deficits in reproductive behavior to MPOA specifically. Thus, the current study used discrete, excitotoxic lesions of MPOA to test the role of this nucleus in opposite-sex odor preference and copulatory behavior in both sexually-naïve and sexually-experienced males. Lesions of MPOA eliminated preference for volatile, opposite-sex odors in sexually-naïve, but not sexually-experienced, males. When males were allowed to contact the sexual odors, however, preference for female odors remained intact. Surprisingly, lesions of MPOA caused severe copulatory deficits only in sexually-naïve males, suggesting previous reports of copulatory deficits following MPOA lesions in sexually-experienced males were not due to damage to MPOA itself. Together, these results demonstrate that the role of MPOA in appetitive and consummatory aspects of reproductive behavior varies with the volatility of the sexual odors and the sexual experience of the male.     

Preferences of pre- and post-weanling long-evans rats for nest odors

Three experiments were conducted on the preferences of infant rats for nest odors. Pre-weanling rats preferred their own nest odor to nests of strange litters and showed low preferences for the nest odors of virgin females. Nest odors of unmated males were investigated less than the pup's own nest odor but more than the odors of virgin females. Male and female rats did not differ in odor preferences. Rats reared with both their dam and sire did not differ in their odor preferences from rats reared with their dam alone when tested at 16–20 days of age, but when tested at 33–38 days of age they showed a greater preference for male odors. Post-weanling rats did not show a preference for the nest odors of lactating females and began to show sex differences in their preferences.     

Ferret odor as a processive stress model in rats: neurochemical, behavioral, and endocrine evidence

Predator odors have been shown to elicit stress responses in rats. The present studies assessed the use of domestic ferret odor as a processive stress model. Plasma corticosterone and adrenocorticotropin hormone levels were higher after 30 min of exposure to ferret odor (fur/skin) but not control odors, ferret feces, urine, or anal gland secretions. Behavioral differences were also found between ferret and the control odors as tested in a defensive withdrawal paradigm. In addition, c-fos messenger RNA expression in several brain areas previously associated with processive stress was significantly higher in ferret odor-exposed rat brains than in control odor-exposed brains. These results suggest that ferret odor produces a reliable unconditioned stress response and may be useful as a processive stress model.     

Ovarian hormones and their role in aggression inhibition among male mice

The role of ovarian steroids in the inhibition of isolation-induced aggression (defined here as fighting or threatening behavior) in male mice was studied, as well as the possibility of interspecies action of mammalian pheromones. Male mice were paired and tested for aggressiveness after being smeared with urine from female mice, rats, rabbits, and humans. Urine from intact and sexually mature animals caused a decrement in aggression, while ovariectomized or sexually immature animals did not produce an aggression inhibiting urine. Urine from ovariectomized animals given injections of estradiol (0.1 mg/day) for 5 days, and other estrogens caused non-aggression. Heavy perfume did not stop aggression, supporting the theory that non-aggression is not the result of simple masking of male odors. Progesterone (1 mg/day for 5 days) was ineffective in inhibiting aggression. An interspecies action of this aggression inhibiting pheromone appears to exist among mice, rats, rabbits, and to some degree, humans.     

Individual odors of rats are discriminable independently of changes in gonadal hormone levels

Male Long-Evans hooded rats were tested for their ability to discriminate between the urine odors from individual outbred Long-Evans rats using the habituation-dishabituation method. There were discriminable differences between the urine odors of two individual intact males, castrated males, estrous/proestrous females, diestrous/metestrous females and ovariectomized females. Thus, individual outbred rats of both sexes can be discriminated on the basis of their urine odors using this technique and discrimination between individuals occurs despite changes in gonadal hormone levels. This suggests that individual recognition is independent of reproductive state and social status although these may influence the production of body odors used for individual discrimination in rats. Individual odors most likely reflect genetic differences between individuals within the outbred strain.     

Transfer of a sex odor discrimination by rats

To test for transfer of a sex odor discrimination, 2 male rats were initially trained to discriminate between the odors of sawdust bedding from a male and female rat and then tested with stimuli from 4 other pairs of male and female rats. Both animals showed strong positive transfer to each of the pairs of test stimuli.     

Rats can discriminate between the urine odors of genetically identical mice maintained on different diets.

Male Long-Evans hooded rats were tested in a habituation-dishabituation procedure for their ability to discriminate between the urine odors of male C57BL/6J mice maintained on two different diets. There were discriminable differences between the urinary odors of two individual mice maintained on different diets. The rats did not dishabituate when presented with urine odors from two individuals on the same diet or two odor samples from the same individual. These results indicate that individual urinary odors of genetically identical mice are influenced by diet. We discuss the hypothesis that diet may act together with genetic differences, commensal bacteria, and hormonal changes to convey olfactory information used for individual recognition.     

Preference for natural odors in rat pups: Implications of a failure to replicate

The results of the present experiment indicate that very minor changes in the diet on which a rat dam is maintained can have profound effects on the attractiveness of her feces to her pups. Rat pups exhibited a strong preference for the odor of feces taken from dams maintained on one sample of Purina Rodent Laboratory Chow No. 5001, but no preference for the odor of the feces of dams maintained on a second sample of the same diet. These data point to the need for very great care in the design of experiments employing, as independent variables, stimuli which are not under direct experimenter control. The results also suggest that experience of a natural odor during ontogeny may not be sufficient for the development of a preference for that odor in young rats.     

The maternal pheromone and brain development in the preweanling rat

Preweanling rats selectively approach and consume pheromone-containing maternal feces. This selectivity suggests that the consumption of maternal feces might be important for the growing pup. Previous research suggested that such feces might promote brain development. A series of experiments was carried out in which pups were denied access to maternal feces. These pups were clearly inferior to control pups in brain growth and neurobehavioral maturation, as well as in the quantity of brain myelin.     

The maternal pheromone and deoxycholic acid in the survival of preweanling rats

Preweanling rats selectively approach and consume pheromone-containing maternal feces. This selectivity suggests that the consumption of maternal feces might be important for the growing pup. We tested the hypothesis that such feces, because of their high deoxycholic acid content, may protect against acute enteritis. A series of experiments was carried out in which pups were denied access to maternal feces. These pups died more often from acute enteritis than control pups. Additional confirmation of the hypothesis was obtained when feces-denied young fed deoxycholic acid showed a significantly lower mortality than feces-denied young fed laboratory chow alone.     

Do odors from different cats induce equivalent unconditioned and conditioned responses in rats?

Since cats are predators of rats and mice, interest in the consequences of exposure to cat-associated odors has increased in the last decade, particularly regarding the development of putative animal models of post-traumatic stress disorder (PTSD). Although in the literature there are some comments on the variability of the effects depending on the individual cat used, there are no reports on this subject. In the present study, we demonstrated, using male Sprague-Dawley rats and cloths impregnated with fur/skin odors from three different cats (one ovariectomized female and two intact males), that the unconditioned endocrine (release of corticosterone) and behavioral (inhibition of activity and avoidance of the cloth area) responses to the presence of the cat odors were statistically significant and similar among the three cats. The conditioned behavioral response to a clean cloth, studied 7 days after the initial exposure to odors, was also evident with the three cats, with minor differences among them. In contrast, only the fur odor from one of the male cats clearly increased anxiety-like behavior in the elevated plus-maze 6 days later. These data indicate that: (i) evaluation of unconditioned and conditioned responses to cat odors does not appear to strongly predict long-lasting increases in anxiety-like behavior; and, therefore, both types of responses are partially dissociated; and (ii) differences among cats mainly affected the induction of long-lasting changes in anxiety-like behavior. The ultimate reasons for these differences are not known, but their characterization is critical for a proper understanding of putative PTSD models.     

High-performance liquid chromatographic assays for a second-generation novel oral iron chelator (APCP363) and their application to pharmacokinetic studies in rats

Sensitive and specific HPLC assays for APCP363 in biological matrices (rat plasma, urine and feces) were developed. The recovery of APCP363 ranged from 81.2 to 99.9% in plasma, from 82.1 to 92.8% in urine, and from 65 to 68% in feces. Standard deviations were below 10% for all analyses. The limits of quantitation were 0.1, 10 and 30 microg/ml in plasma, urine and feces, respectively. The HPLC assays, which are the first reports for APCP363 analysis in biological matrices, have been successfully applied to preliminary pharmacokinetic studies in rats. The stool assay is the first non-radiolabeled method for hydroxypyridinones in feces.     

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.     

Response selectivity of neocortical neurons to specific odors in the rabbit

Odor responses of neocortical neurons in rabbits under light pentobarbital anesthesia were studied in a restricted area in the lateral half of the prefrontal cortex close to the frontal pole. A preevent cumulative sum chart provided a visual display of the change in unit discharge rate following each odor stimulation, and critical levels on each chart provided a visual display of statistical significance. The neocortical neurons studied were activated predominantly by biologically significant odors, such as feces, urine, and dry food. Of those same neurons, 90% failed to respond to pure-chemical odors, and no neurons were found that responded to pure-chemical odors alone. Some neurons responded exclusively to one of the animal-product odors. Some odor-sensitive neurons were affected by electrical stimulation of the mediodorsal thalamic nucleus. Responses to the animal-product odors were observed after ablation of the trigeminal and/or vomeronasal inputs. The responses to these pheromone-like substances are discussed in the context of a central role for odor-sensitive neocortical neurons in cognitive aspects of discrimination of specific odor patterns in the mammals.     

Sensitive period for the acceptance of unpalatable flavors in the presence of a preexposed odor in infant rats

It has been shown that exposure to familiar odors facilitate the acceptance of bitter flavors in preweanling rats, yet it unknown how long this phenomenon persists. This study assessed, in 9- or 15-day-old Wistar rats, the influence of a familiar scent (i.e., lemon) on the intake of and behavioral responsiveness (i.e., mouthing, paw lick, chin rub, head shake, among other taste reactivity responses) elicited by a 0.1% quinine solution. The results showed heightened quinine intake in 9-day-old rats that had been preexposed to the odor, when compared to non-preexposed controls. This result was replicated in Experiment 2, which also documented no alterations in behavioral responsiveness toward quinine in the 9-day-old rats, as a function of the pre-exposure. More importantly, 15-day-old rats exhibited no alterations in intake or behavioral responsiveness toward quinine as a function of odor pre-exposure. These results suggest that the effects of odor pre-exposure upon acceptance of bitter tastes may occur within a sensitive period for the acceptance of bitter food.     

Failure to produce conditioning with low-dose trimethylthiazoline or cat feces as unconditioned stimuli

Trimethylthiazoline (TMT), a derivative of fox feces, has been reported to fail to produce aversive conditioning as an unconditioned stimulus (UCS) when presented in large amounts (I. S. McGregor, L. Schrama, P. Ambermoon, & R. A. Dielenberg, 2002). Experiment I evaluated very low TMT levels that nonetheless produced defensive behaviors in rats during exposure. Although each level (0.01, 0.05, and 0.10 microl TMT) produced significant change in defensiveness, none resulted in significant changes the following day in the absence of TMT. Experiment 2 evaluated cat urine, cat feces, and cat fur/skin odor against a no-odor control. Urine produced no significant changes, but feces and fur/skin odors elicited virtually identical changes in defensive behaviors during exposure. When tested the next day in the absence of odor, the fur/skin odor-exposed group showed significant differences on the same behaviors as during exposure, but the feces-exposed group showed no differences on any measure. Results suggest that lack of conditioning to TMT may relate to the type of predator odor rather than the amount, predator species, or possible lack of odor components in TMT that are present in natural feces. Predator feces may also be less effective as a UCS because they are poorly predictive of the actual presence of the predator, suggesting the need for a reevaluation of UCS functions in aversive conditioning.