Effects of in utero odorant exposure on neuroanatomical development of the olfactory bulb and odour preferences

Human babies and other young mammals prefer food odours and flavours of their mother's diet during pregnancy as well as their mother's individually distinctive odour. Newborn mice also prefer the individual odours of more closely related--even unfamiliar--lactating females. If exposure to in utero odorants-which include metabolites from the mother's diet and the foetus's genetically determined individual odour-helps shape the neuroanatomical development of the olfactory bulb, this could influence the perception of such biologically important odours that are preferred after birth. We exposed gene-targeted mice during gestation and nursing to odorants that activate GFP-tagged olfactory receptors (ORs) and then measured the effects on the size of tagged glomeruli in the olfactory bulb where axons from olfactory sensory neurons (OSNs) coalesce by OR type. We found significantly larger tagged glomeruli in mice exposed to these activating odorants in amniotic fluid, and later in mother's milk, as well as significant preferences for the activating odour. Larger glomeruli comprising OSNs that respond to consistently encountered odorants should enhance detection and discrimination of these subsequently preferred odours, which in nature would facilitate selection of palatable foods and kin recognition, through similarities in individual odours of relatives.     

The effects of adaptation on the perception of similar and dissimilar odors

The Pubishers wish to apologise for the inadvertent mis-spellingof Charles J. Wysocki and other errors in the above article,which should be corrected as follows. On Page 471, Table I, the first Number in the second columnshould read 2:6. On page 477, Table II, the results under d-limonene should readas below. On page 481, the NIH grant number to CJW is DC00298.     

Patterns of Urination of a Blind Subterranean Rodent,Spalax ehrenbergi

Urination patterns of blind mole rats of the Spalax ehrenbergi superspecies of Israel were investigated in the laboratory under various conditions in various types of simulated tunnel systems. Behavioral responses to urine in these systems were observed. The results suggest that mole rats do not mark their tunnels or novel areas, either along the tunnel floor by dropping a urine-trail or at the peripheral ends of the tunnel systems. Urination is not a fear response, and the urine does not contain a chemosensory releaser. Intruders respond (e.g. by sniffing, running away, aggressive threat displays etc.) to occupant's urine in a previously occupied system, and some occupants urinate at a border in ‘no-contact’ encounters with a potential intruder. Male and female mole rats seem to use urine to advertise their ownership of resources by placing their sanitation areas in the vicinity of the nest and food store and may advertise their identity and occupancy at borders when there is potential contact with intruders. Likely similarities between urination patterns in the laboratory and in nature are discussed.     

The effects of adaptation on the perception of similar and dissimilar odors

Adaptation among several odors was studied using a multiple-alternative,forced-choice procedure where six concentrations of each odorantand three blanks were presented in a random sequence beforeand after adaptation to each of the odors. Adaptation was expressedin terms of changes in both identification threshold and perceivedintensity. In the first experiment, Galaxolide® (a syntheticisochroman musk) and 5-androst-16-en-3-one (androstenone) showedno cross-adaptation in spite of sharing, for some people, amusky note. In the second experiment, Galaxolide and Thibetolide®(a synthetic macrocyclic musk) showed significant, but asymmetric,cross-adaptation. When Galaxolide was the adapting stimulus,shifts in indentification threshold and magnitude estimatesfor Thibetolide were not significantly different from thoseobtained for Galaxolide, a result consistent with the conclusionthat cross-adaptation was as effective as self-adaptation. WhenThibetolide was the adapting stimulus, shifts in identificationthreshold and magnitude estimates for Galaxolide were significantlyless than those obtained for Thibetolide, suggesting that cross-adaptationwas less effective. This result is puzzling given the perceptualsimilarity of these two musky compounds: subjects did not distinguishbetween them during random presentation. The distinct odorsof amyl acetate (banana) and d-limonene (orange) showed no cross-adaptationin either experiment.     

Preferences of newborn mice for odours indicating closer genetic relatedness: is experience necessary?

Evidence from studies with adult rodents indicates that individual recognition enables distinctions between familiar individuals irrespective of relatedness (but including close kin) and a separate mechanism enables discriminations based on genetic relatedness without prior familiarity. For example, adult mice could assess the extent of their genetic relatedness to unfamiliar individuals using perceptual similarities between their individual odours. The ontogeny of this genetic relatedness assessment mechanism, however, had not been investigated. Here, in two-choice tests, newborn mice differentially preferred odours of more genetically similar lactating females (paternal aunts to unrelated conspecific and conspecific to heterospecific) even without prior direct exposure to adults with the tested genotypes. The results provide a direct demonstration of genetic relatedness assessment abilities in newborns and show that experience with parental odours is not necessary for genetic relatedness distinctions. Future studies will be necessary to determine whether exposure to odours of other foetuses in the womb or littermates shortly after birth affects this genetic relatedness assessment process.     

Individual Odours in Two Chromosomal Species of Blind,Subterranean Mole Rat (Spalax ehrenbergi): Conspecific and Cross-species Discrimination

Mole rats from two chromosomal species (2n = 58 and 2n = 60) of the Spalax ehrenbergi superspecies of Israel were tested to determine whether they were able to discriminate differences in the odour of urine from same-sex individuals of their own and of the other chromosomal species. An habituation-discrimination apparatus was designed for use with these solitary and blind subterranean rodents. Animals habituated to the odour of urine from one individual presented for 10 min at a centre sniffing area in the roof of a 50 cm long Perspex tunnel. The odour of urine from the original donor and from a second individual were presented at two other sniffing areas in the tunnel roof during a 5 min discrimination phase. Significant differences in the time spent investigating the two odours demonstrated successful discrimination between them. The results indicate that male and female mole rats of both species can discriminate between the individual-specific odour cues in urine from pairs of conspecifics and pairs of heterospecific mole rats.     

Individual odour similarities across species parallel phylogenetic relationships in the S. ehrenbergi superspecies of mole-rats

Research using habituation techniques has shown that rodents from the same kin group, population, or species share similarities in their individual odours that covary with shared genetic similarities between them, that is, the closer their genetic relatedness, the more similar their odours. We assessed similarities in individual odours across four sibling species of subterranean mole-rats from the Spalax ehrenbergi superspecies in Israel. Mole-rats were habituated to the urine odour of a same-sex individual from one species then tested with urine odours of individuals from two different species of the superspecies. Subjects treated urine odours of individuals from more closely genetically related species as similar compared with the odours of individuals from a less closely related species, showing that the covariance between odours and genes extends across species. These similarities in odour also paralleled genetic similarities determined by molecular analysis: odours of descendent species were perceived as similar to those of their closest ancestral species, suggesting that some qualities of the odour of the ancestral species persist in the descendent species. It is generally assumed that during speciation incipient species develop species-specific markers, including, for example, odour markers, to facilitate discrimination of conspecifics from close ancestral heterospecifics. Our findings indicate that similarities in odours across species are more salient than species-specific odour markers. Such findings may also have important implications for mechanisms of species recognition. Copyright 2000 The Association for the Study of Animal Behaviour.     

Social Interaction is Necessary for Discrimination between and Memory for Odours of Close Relatives in Golden Hamsters

The role of social experience in recognition of individuals and their odours is not well understood. In a previous study, hamsters discriminated between the odours of their familiar litter mates, but they did not discriminate between the odours of two males or two females from a different litter that were unfamiliar to them. In this paper the role of social experience in discrimination between odours of male litter mates is examined using habituation techniques. Males, tested 1.5–2 mo after separation from their litter mates, discriminated between the flank gland odours of their foster brothers, but they did not discriminate between flank odours from their unfamiliar brothers that had been reared by another mother (Expt. 1). In Expt. 2, adult males did not discriminate between the flank gland odours of two males from a different litter after a week of exposure across a barrier to their sights, sounds, and odours, but subjects did discriminate between the odours of these same males after five brief encounters with them. A month after the encounters, however, subjects no longer discriminated between these odours. In contrast, adult males discriminated between the flank odours of their brothers 9 mo after separation from them (Expt. 3). These results suggest that hamsters must have direct interactions with closely related individuals to discriminate between their odours because the odours of close kin are so similar. Experience with nest mates results in long-lasting memories for their odours.