Preferences of pre- and post-weanling Long-Evans rats for nest odors

Housing pregnant mice (Mus musculus) in small groups facilitates the development of odor-based homing in offspring

Infant mice (Mus musculus) born to dams housed in isolation throughout pregnancy (IsoPreg) begin differentially approaching homenest bedding over clean bedding on Postnatal Day 6. Offspring of dams housed with 2 other potentially pregnant conspecifics (SocPreg) display such homing behavior on Day 4. Earlier onset of homing reflects facilitated olfactory responsiveness in SocPreg pups, rather than qualitative or quantitative differences in IsoPreg versus SocPreg nest odors, body growth, or motoric capabilities. Exposing pregnant IsoPreg dams to SocPreg bedding also accelerated homing onset in the offspring, though not to the same extent as the full social context. Thus, it appears that the facilitation of homing is mediated through the pregnant dam by a combination of chemical cues and other social stimuli.

Use of ultrasonic vocalizations to assess olfactory detection in mouse pups treated with 3-methylindole

Altricial mammals use olfaction long before the olfactory bulb has reached its anatomically mature state. Indeed, while audition and vision are still not functional, the olfactory system of newborn animals can clearly process distinct odorant molecules. Although several previous studies have emphasized the important role that olfaction plays in early critical functions, it has been difficult to develop a sensitive and reliable test to precisely quantify olfactory ability in pups. One difficulty in determining early sensory capabilities is the rather limited behavioral repertory of neonates. The present study examines the use of ultrasonic vocalizations emitted by isolated rodent pups as a potential index of odor detection in newborn mice. As early as postnatal day 2, mice reliably decrease their emission of ultrasonic calls in response to odor exposure to the bedding of adult male mice but not in response to clean bedding odors or to non-social odorant molecules. A toxin known to damage the olfactory epithelium in adult, the 3-methylindole, impairs the ultrasonic call responses triggered by exposure to male bedding, thus confirming the efficiency of this olfactotoxin on mice pups. The administration of 3-methylindole severely reduced the life expectancy of the majority of subjects. This result is discussed according to the critical role of olfaction in nipple-seeking behavior in mouse pups.

Cholecystokinin receptor antagonists increase the rat pup's preference toward maternal-odor and rug texture

The role of the cholecystokinin (CCK) system in mediating the infant's natural preferences toward maternal-related stimuli was examined by peripheral administration of selective CCK(A) and CCK(B) receptor antagonists (Devazepide and L-365,260, respectively) to 11-12-day-old rats and presenting them with a 3-minute preference test. In Experiment 1, the choice was between two floor textures, rug and plywood; the time spent on the relatively preferred side (rug) was measured. In Experiment 2, the odor of maternal faces emanated from one end of the test arena; time spent near that end was measured. These sensory stimuli were chosen as they represent olfactory and tactile aspects of the dam and nest. Compared to controls, both CCK receptor antagonists selectively increased the time spent on the preferred side, in both experiments, without affecting axillary temperature or locomotor activity. The results suggest that CCK may mediate and attenuate the infant's attraction toward naturally preferred stimuli.

Ontogeny of Home-orienting Behavior in Rat Pups During the First Half of the Lactation Period: Effects of Early Postnatal Protein Malnutrition on Repeated but not Single Testing

The ontogeny of home-orienting behavior was investigated during the first half of the lactation period in postnatally protein malnourished pups using repeated or single testing at 7, 9 and 11 days of life. During the lactation period (21 days) each litter (6 male and 2 female pups) was provided with 16% (control) or 6% (low protein) casein diets. To study home-orienting ability the well-nourished and malnourished pups were divided into two groups: the independent group (single testing), in which the pup was tested only once at 7, 9 or 11 days of age, and the dependent group (repeated testing), in which the same animal was tested once a day at 7, 9 and 11 days of age. Latency to reach the nest bedding, latency to reach the fresh bedding, time spent in the half of the box that contained nest bedding, time spent in the half of the box that contained fresh bedding, and total number of entered sections were recorded in 3 min sessions. Postnatal protein malnutrition significantly impaired the ability (higher latencies) to locate nest bedding in the group of pups repeatedly tested at 7, 9 and 11 days of age. This difference was not found in the group of pups tested just once at 7, 9 or 11 days of age. Both groups showed increased ability to find nest bedding across age. Locomotor activity was similar for well-nourished and malnourished pups in both groups, suggesting that impaired performance to find nest bedding in malnourished pups repeatedly tested at 7, 9 and 11 days of age cannot be attributed to differences in locomotion ability. The results suggest a possible role of spatial learning in the home-orienting behavior when the same pup is repeatedly tested at 7, 9 and 11 days of age as compared with pups tested just once on each of those days. This impairment of spatial learning in response to nest odor in malnourished pups is discussed in terms of its relevance for social behavior in early infancy and adulthood.

Effects of preweanling ethanol odor exposure on ethanol preference

Preweaning exposure to a foreign odor has been shown to alter later responding to that odor. Early experience with ethanol odor may alter not only responding to ethanol odor, but also intake of ethanol solutions. The present study tested the effects of exposure to ethanol odor prior to weaning on ethanol odor preference and ethanol consumption. Sprague-Dawley-derived rats were exposed to the odor of 100% ethanol from postnatal day 1 to 22 in the home cage. An odor preference test was conducted on postnatal day 14 and a two-bottle ethanol intake test was conducted after weaning. In both odor preference and intake tests, animals previously exposed to ethanol odor exhibited a greater preference for ethanol than controls. The results demonstrate that early experience with the odor of ethanol can increase ingestion of ethanol later in life.

The influence of natural preference for tactile stimuli on appetitive learning in rat pups

Stimuli of the same modality tend to be organized along a "natural preference scale." This study examined the ability of six- and nine-day-old rat pups to acquire appetitive learning, when the CS was one of two differently "naturally preferred" tactile stimuli (floor textures: rug and plywood). In Experiment 1, all pups showed a relative natural preference for the rug texture over the plywood texture. Pups conditioned on the plywood texture (exposed to a sibling pup as the US) showed a robust increase in preference for the conditioned texture whereas pups conditioned on the rug texture showed a different and more moderate pattern of acquisition. Developmental differences were found only in extinction of the conditioned response: six-day-old (but not nine-day-old) pups displayed extinction of the response over four trials. Experiment 2 indicated that preexposure to the rug CS prior to conditioning (latent inhibition) did not interfere with the learning process on the rug texture. Two major alternative explanations for the differential learning patterns are discussed: motivational and catecholaminergic influences on learning. The results suggest that natural preferences may modulate early learning and memory processes.

Odor-guided behavior in mammals

The odor-guided behaviors selected for presentation in this paper encompass the major areas of animal behavior, and illustrate the important principal that complex relations exist between odor-guided behaviors, hormonal state, and experiential factors. Clearly, experiences with odors at several life stages results in profound influences upon later behaviors, including those related to eating, mating, fighting, and nesting. Interestingly, only brief social encounters are needed in rats to induce such phenomena as ultrasonic calling to conspecific estrous females or their odors, preferences for estrous over non-estrous odors, and the short-term modification of feeding behaviors. Although the mechanisms behind these intriguing phenomena are poorly understood, it is noteworthy that rats can learn relatively complex concepts on the basis of odors, rivaling even the ability of our own species to learn analogous tasks by visual cues. Despite the fact that close relationships can be demonstrated between odor-guided behaviors and variables such as endocrine state and sexual experience, caution is warranted in assuming that simple causal relations exist between such variables. In normally cycling women, for example, the correlation between olfactory sensitivity and plasma levels of estradiol during the menstrual cycle is relatively high; however, attenuation of the cyclical estradiol fluctuations by oral contraceptives does not eliminate the olfactory fluctuations, suggesting the relation is not causal. In house mice, social experience can override hormonal factors in their odor-guided urine marking and submissive behaviors. Thus, even though androgen titer usually correlates with such measures, a mouse made subordinant in a social encounter will not exhibit scent marking even when its circulating testosterone is maintained at a high level by a silastic implant. Further reason for caution comes from studies that suggest olfactory input influences the endocrine systems of sexually experienced and sexually inexperienced animals in different ways. For example, in sexually experienced male rats, anosmia decreases testosterone and estradiol levels and increases corticosterone levels, whereas in sexually inexperienced ones it has no significant influence on the levels of these steroids. Taken together, such observations suggest that the causal bases of a number of the odor-guided behaviors described in this paper are complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of responsiveness to conspecific scent in house mice: effects of preweaning and postweaning experiences

Responses to male conspecific odors (soiled bedding) presented in an alleyway were compared among five groups of adult male albino house mice with different rearing histories. Both isolated mice that had as pups been fostered onto a rat mother and normally nursed mice that had been group housed since weaning showed reduced attraction to conspecific odor. Preweaning paternal presence, a factor known to affect the development of response to male conspecific scent in rats and gerbils, had no reliable effect with mice.

Home odor preferences in young hares (Lepus capensis syriacus): effects of age and role of maternal presence

The odor preferences of mother-reared and hand-reared young hares between 1-30 days of age were studied. Subjects were exposed daily to three choice tests in which the following pairs of odors were presented: home cage odor (HCO)-neutral odor (NO); HCO-strange cage odor (SCO); SCO-NO. All young strongly preferred their HCO over SCO throughout the 30-day period. HCO was preferred over NO until the age of 20 days, while avoidance of SCO was shown during the first 10 or 20 days. The same experiment conducted on postweaned hares (31-50 days of age) revealed a strong preference for SCO over both HCO and NO. These findings may be interpreted with respect to the natural history of the hare and its unusual mother-young relationship, which, in the wild, is limited to a single daily meeting for nursing. It is suggested that the highly precocial hare recognizes and prefers its home odor independently of any maternal contribution to that odor, possibly relying on odor cues from its own body to return to its nursing site. Other possible advantages of these olfactory preferences, including predation avoidance and facilitation of social relationships, are discussed.

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.

Establishing an "affective scale" for odor preferences of infant rats

To establish an "affective scale" for odor preferences, the scale must indicate aversion as well as attraction to odors. Because the construction of preference scales requires repeated tests with a set of odors, and because exposure to aversive odors may lead to a reduction in the aversiveness of these odors, the effects of repeated exposure to an aversive odor (peppermint) on preferences for this odor were examined. Eighteen-day-old Long-Evans rats were given three preference tests using all pairs of three odors: unscented pine shavings (N), own maternal odors (M), and peppermint odors (P). Before these tests rats were exposed to the test arena and unscented pine shavings or peppermint odor for 0, 1, or 4 days. All rats showed an attraction to their maternal odor and an aversion to peppermint odor, showing the preference scale M greater than N greater than P. Preexposure to peppermint in the test apparatus only slightly reduced the aversion to peppermint odor. The results indicate that scaling procedures will accurately detect odor aversions as well as attractions and that the preference scales are only slightly altered by repeated exposure to odors during the testing period.

Preferences of pre-weanling Long-Evans rats for anal excreta of adult males and females

Long-Evans hooded rat pups were reared with their dam alone, their dam and sire or their dam 12 hrs per day and their sire 12 hrs per day and tested for preferences for anal excreta from adult male and female rats when they were 18 to 20 days of age. In all rearing conditions the anal excreta of the rat's own dam was preferred to that of strange dams and the excreta of both own and strange dams was preferred to that of virgin females. Anal excreta from virgin females was preferred to no odor as was anal excreta of unmated males, strange sires and the rat's own sire. Only rats reared with their dam and sire preferred the odor of their own sire to that of other males. The results suggest that pre-weanling rats may attend to different dimensions of the odors of conspecifics, such as the species odor, maternal odor, and individual odor and that different rearing conditions may influence the odor dimension to which the rat attends.