The human brain is a detector of chemosensorily transmitted HLA-class I-similarity in same- and opposite-sex relations

Studies on subjective body odour ratings suggest that humans exhibit preferences for human leucocyte antigen (HLA)-dissimilar persons. However, with regard to the extreme polymorphism of the HLA gene loci, the behavioural impact of the proposed HLA-related attracting signals seems to be minimal. Furthermore, the role of HLA-related chemosignals in same- and opposite-sex relations in humans has not been specified so far. Here, we investigate subjective preferences and brain evoked responses to body odours in males and females as a function of HLA similarity between odour donor and smeller. We show that pre-attentive processing of body odours of HLA-similar donors is faster and that late evaluative processing of these chemosignals activates more neuronal resources than the processing of body odours of HLA-dissimilar donors. In same-sex smelling conditions, HLA-associated brain responses show a different local distribution in male (frontal) and female subjects (parietal). The electrophysiological results are supported by significant correlations between the odour ratings and the amplitudes of the brain potentials. We conclude that odours of HLA-similar persons function as important social warning signals in inter- and intrasexual human relations. Such HLA-related chemosignals may contribute to female and male mate choice as well as to male competitive behaviour.     

Orientation of European corn borer first instar larvae to synthetic green leaf volatiles

European corn borer (ECB) neonate larvae are capable of orienting towards maize odours and of avoiding spinach odours. We previously reported that maize odours’ attraction was dependent on the stimulus regime. This led us to propose that maize odours could have a repellent or attractive effect depending on their concentration. In this work, we tested this hypothesis by evaluating attraction or avoidance of neonate ECB larvae to four concentrations of each of six single green leaf volatiles (GLVs); these are commonly found in maize and other plants. We found a dose‐dependent effect for all of these GLVs with the exception of 1‐hexyl acetate, which did not elicit any orientation behaviour over the range of concentrations tested. These five GLVs were repellent at high concentrations, while two of them were attractive at a lower concentration. These observations indicate for the first time that plant odours induce different behaviours in ECB neonate larvae depending not only on their chemical identity but also their concentration.     

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.     

Effect of yokukansan on psychophysiological insomnia evaluated using cyclic alternating pattern as an objective marker of sleep instability

In this open-label study using final evaluator blinding, the efficacy of yokukansan (YKS) was evaluated in six psychophysiological insomnia patients using the cyclic alternating pattern (CAP) method. YKS had no influence on objective sleep parameters by the Rechtschaffen & Kales method, but the CAP rate and CAP cycle frequency decreased significantly. In the subjective Visual Analog Scale test, significant improvement was seen in five items: tension, calmness, fatigue, heavy-headedness and lassitude. No adverse reactions were noted. YKS improved sleep quality without influencing sleep structure and showed no adverse reactions, suggesting that YKS is an effective antiinsomnia drug with good tolerability.

     

Extreme sensitivity in an olfactory system

We recorded olfactory-induced cardiac responses to evaluate olfactory response thresholds to behaviourally relevant odours in a moth. Specific antennal receptor neurons enable insects to detect biologically meaningful odours such as sex pheromones and host-plant volatiles. The response threshold values demonstrated here are well below anything earlier reported in any organism. A heart response was triggered by less than six molecules of the most efficient odours hitting the antennae of the insect. The behavioural significance of this extreme sensitivity most likely lies in the creation of awareness and readiness to respond behaviourally at higher concentration levels.     

Physiological and morphological properties of interneurones in the deutocerebrum of male cockroaches which respond to female pheromone

Summary Interneurones in the deutocerebrum of male cockroaches were characterised according to their intracellularly recorded responses to odours of females and to selected food odours. Following physiological characterization the interneurones were stained by the intracellular injection of dye. Some interneurones were characterized by extracellular recording and staining.The intracellular electrodes were either placed in the somata of the interneurones or more usually in neurites between the deutocerebral glomeruli. Such recordings reveal a continuous background of synaptic potentials, and spikes at a variable but low frequency depending upon the individual interneurone. The odours, which were blown over one antenna, were a whole female extract and two purified components of this; Fraction A and a second identical to Periplanone B. Sixteen other food odours were also tested. The interneurones revealed fell into four main groups which responded to: the whole female extract and the two components, to one of the two components preferentially, and to whole female extract but neither of the components. Other interneurones were inhibited by female odours but excited by some food odours. The interneurones with these characteristics which were stained, were principal interneurones with cell bodies in the lateral cluster in the deutocerebrum, branches within the deutocerebrum confined to the macroglomerulus (an enlarged glomerulus found only in adult males), and an axon projecting to the calyces and lobus lateralis protocerebralis of the protocerebrum. The interneurones responding preferentially to Periplanone B had branches throughout the macroglomerulus, but those responding to Fraction A had a more restricted pattern of branching within the macroglomerulus.     

A six-arm olfactometer permitting simultaneous observation of insect attraction and odour trapping

Abstract.  Behavioural assays to study insect attraction to specific odours are tedious, time consuming and often require large numbers of replications. Olfactometer and flight tunnel tests can usually only be conducted with one or two odour sources at a time. Moreover, chemical information on the odour sources has to be obtained in separate analytical studies. An olfactometer was developed in which six odours can be tested simultaneously for their relative attractiveness while during the assays, part of each test odour can be trapped for further analyses. The effectiveness of this six-arm olfactometer was tested by observing the responses of the solitary endoparasitoid Cotesia marginiventris (Cresson) to host-induced odours from young maize plants. For statistical analyses, we used log-linear models were adapted to account for overdispersion and possible positional biases. Female wasps responded extremely well in tests where they were offered a single odour source, as well as in tests with multiple choices. The responses of wasps released in groups were the same as those released individually and it was found that females did not attract or repel each other, but males preferred arms in which females had been released. Dose–response tests with varying numbers of plants or host larvae on plants revealed that the wasps responded in a dose-related manner, thus showing that the system is well suited to measure relative preference. The clear choices of the insects amongst six possibilities provided substantial statistical power. Gas chromatographic analyses of sampled air revealed clean and effective odour trapping, which largely facilitates the comparison of results from behavioural assays with the actual blends of volatiles that were emitted by the various odour sources. Advantages and disadvantages compared to other methods are discussed.     

The influence of olfactory enrichment on the behaviour of captive black-footed cats,Felis nigripes

The value of olfactory enrichment for captive-housed animals is now well recognised. Large cats have been shown to benefit from the introduction of odours to their captive environment, but to date the effect of odour introduction on the behaviour of small cats remains unknown. This study investigated the behaviour of six zoo-housed black-footed cats, Felis nigripes, in response to four odours (no odour [control], nutmeg, catnip and body odour of prey) introduced individually on cloths into the animals’ pens over a period of 5 days. It was hypothesised that the cats’ behaviour would differ significantly between the control and experimental odours and that interest in the experimental odours would wane over time. All of the experimental odours influenced the cats’ behaviour, resulting in an increase in the amount of time that the animals spent in active behaviours, i.e. moving (average increase of 8.3%), grooming (average increase of 5.9%), exploring the cloth (average increase of 10.9%) and exploring the pen (average increase of 9.2%). The experimental odours also resulted in a decrease in the amount of time that the cats spent in sedentary behaviours, i.e. standing (average decrease of 2.8%), sitting (average decrease of 5.2%) and resting (average decrease of 25.9%). Nutmeg exerted less of an effect on the cats’ behaviour than catnip or odour of prey. The cats’ response to all of the experimental odours waned over the course of the 5-day observation period, suggesting that the animals habituated to the stimuli. The results highlight the potential for odour to be employed as a method of environmental enrichment for small captive-housed felids, if presented in an appropriate manner.     

Kin recognition in golden hamsters: evidence for kinship odours

Differential treatment of kin and non-kin has been well documented, but much remains unclear about how kin are recognized. If kin are recognized by a phenotype-matching mechanism, there must be a correlation between genetic relatedness and the similarity of cues used for recognition. A habituation technique was used with golden hamsters,Mesocricetus auratus, to investigate the relative similarity of the odour quality of flank gland secretions from siblings and unrelated individuals. Hamsters discriminated between the odours of their own, same-sex siblings but also treated these odours as similar compared to odours of non-siblings (experiment 1). They did not discriminate between the flank gland odours of unfamiliar siblings from another family (experiment 2). They also did not discriminate between the flank gland odours of unfamiliar, paternal half-siblings from another family (experiment 3). These results indicate that subjects perceived odours from genetically similar individuals as similar and provide evidence for kinship odour cues. The discrimination between the flank gland odours of subjects’ own siblings, however, indicates that hamsters learn the subtle differences between the odours of their close kin, probably through experience with siblings in the nest. When only volatile components from flank gland secretions were available to subjects (experiment 4), they again discriminated between the odours of their own siblings, suggesting that the volatile components from the flank gland secretion were sufficient for recognition of individual litter-mates.     

Female body odour is a potential cue to ovulation

Human body odours have been reported to influence female mate choice. Women prefer the odours of immunocompatible men and, during their fertile period, judge the body odours of men with symmetrical bodies--which is indicative of genetic quality--as sexy and pleasant. The reproductive success of men largely depends on mating with fertile women, but it is not known whether men can detect a woman's fertile period. We asked women who had regular menstrual cycles and who were not using hormonal contraceptives to wear a T-shirt for three consecutive nights during their late follicular (ovulatory) phase and another T-shirt during the luteal (non-ovulatory) phase of their menstrual cycle. Male raters judged the odours of T-shirts worn during the follicular phase as more pleasant and sexy than odours from T-shirts worn during the luteal phase. The odour differences between the follicular and luteal phases did not dissipate quickly over time as male raters were able to detect and judge follicular phase body odours as more pleasant and sexy than the odours from the luteal phase even after the T-shirts were kept at room temperature for one week. These findings suggest that ovulation may not be concealed and that men could use ovulation-linked odours in their mate selection.     

Behavioural development of conspecific odour preferences in bank voles,Clethrionomys glareolus

Biological odours of conspecifics are known to have strong influences on behavioural interaction in bank voles Clethrionomys glareolus. This experiment tested two hypotheses. (1) Olfactory cues from familiar and unfamiliar mature opposite-sex conspecifics differ in their attractiveness to males and females, and their behavioural reactions change with age. (2) A genetically based mechanism is involved in female recognition of kin.In a two-choice preference test, prepubertal males and females were more attracted to familiar than to unfamiliar odours of opposite-sex conspecifics, as manifested by more time spent sniffing familiar voles. As the young reached sexual maturity they shifted their odour preferences. Mature males and females preferred the novel odour of unrelated opposite-sex conspecifics to that of relatives. The results of experiments testing the second hypothesis indicate that females use a genetically based mechanism to recognise their kin. Young and mature females were able to recognise the odour of their biological but socially unknown fathers, and showed the same pattern of behaviour as females in previous experiments.The possible biological functions of kin recognition in bank voles are discussed.     

Olfactory responses of seed wasps Megastigmus pinus Parfitt and Megastigmus rafni Hoffmeyer (Hym., Torymidae) to host-tree odours and some monoterpenes

Megastigmus pinus and Megastigmus rafni are able to colonize the seed cones in eight different species of Abies in Denmark. Olfactory responses of M. pinus females from Abies alba and Abies procera seeds and of M. rafni females from A. alba and Abies grandis seeds to odours of different host-trees cones, needles and pure alpha-pinene and limonene were studied in a Y tube Plexiglas olfactometer. The odours of young cones significantly influenced the behaviour of females. The results obtained in experiments with cones from different trees indicate the occurrence of biotypes depending on the host tree within the M. pinus and M. rafni species. Megastigmus pinus females from A. procera cones preferred the cone odours of A. procera and were significantly repelled by the cone odours of other possible host trees. Megastigmus pinus females from A. alba cones preferred A. alba cone odour but were not indifferent to A. procera cones. This suggests that the M. pinus population in A. alba apparently originates from the A. procera population. Megastigmus rafni from A. grandis cones preferred only A. grandis cone odours. Megastigmus rafni females from A. alba cones preferred A. alba cone odour but were also significantly attracted by A. grandis cone odours. This probably indicates that the M. rafni population living in A. alba originates from the A. grandis population. Neither M. pinus nor M. rafni responded to the odours of the host-tree needles or alpha-pinene. The limonene odour significantly acted as a repellent to both seed chalcid species, independent of the origin-tree.     

Individual odours and mate recognition in the prairie vole,Microtus ochrogaster

A habituation-discrimination technique was used to demonstrate that male and female prairie voles can discriminate individual differences in the odours of soiled shavings and urine from male and female conspecifics. A second experiment, employing a Y-maze, showed that females significantly preferred the odours of their mate over those of either another mated male or an unmated male. Males preferred their mate's odours to those of other mated females but showed no significant preference between the odours of their mate and those of a virgin female. A third experiment demonstrated that, over a 10-h period, females built nests and/or stayed preferentially on the side of a Y-maze containing their mate's odours. Likewise, males preferentially built nests in their mate's side compared to the side containing odours from a virgin female. However, although the same trend was present when mate odours were paired with odours from another mated female, the preference was not statistically significant. Taken as a whole, these results indicate that mate recognition may be an important of individually distinctive odours in this species.     

Influence of gonadal hormones on odours emitted by male meadow voles (Microtus pennsylvanicus).

Free-living male meadow voles (Microtus pennsylvanicus) emit odours that are attractive to females at the beginning, but not at the end, of the breeding season. The effect of gonadal hormones on female-attractant cues was examined in males born and reared in long (14 h light day-1) and short (10 h light day-1) photoperiods that simulate daylengths in the breeding and nonbreeding seasons, respectively. Gonadectomy affected the attractant properties of odours emitted by long photoperiod, but not short photoperiod, males. Long photoperiod females preferred odours of intact rather than those of gonadectomized long photoperiod males, and odours of gonadectomized long photoperiod males rather than those of intact short photoperiod males. Females did not show a preference between the odours of intact and castrated short photoperiod males. Gonadal hormone replacement in males affected female responses to the odours emitted by long photoperiod, but not short photoperiod, gonadectomized males. Long photoperiod females did not display a preference between odours of intact long photoperiod males and gonadectomized long photoperiod males treated with testosterone or oestradiol. We conclude that in spring and summer gonadal hormones increase attractiveness of male odours; this effect may require aromatization of testosterone to oestradiol. Substrates that control attractiveness of odour cues in male voles appear to be unresponsive to androgens during the nonbreeding season.     

Group relatedness and kin discrimination in honey bees Apis mellifera L.

In addressing problems concerning kin discrimination and the evolutionary significance of inclusive fitness in highly eusocial insects, the genetic relatedness between groups, such as individuals belonging to the same patriline within colonies, is of interest. Based on the definitions for individual genetic relationship, several new measurements of group relatedness are derived and their genetical meaning is discussed. In a metabolic bioassay for the documentation of kin discrimination, carbon dioxide production was used to quantify reactions of groups of honey bees to volatile odours of other groups. Worker test groups, which had not experienced their hive environment, were able to discriminate between related and unrelated groups of workers within and between colonies. Test groups responded in a similar way to odours of genotypically mixed groups with related and unrelated workers and to the odours of pure groups of the less related subgroup. Thus, the reaction to group odours that function as discrimination labeles is not a linear response as predicted by an additive gestalt odour model. Since experienced bees collected from the colony could not discriminate between the various patrilines, the observed phenomenon resembles nest mate recognition rather than within-colony kin recognition.     

Scent-marking behaviour in response to conspecific odours by the rat, Rattus norvegicus

The scent-marking behaviour of male and female rats in response to conspecific odours was investigated in two experiments. The results of the first experiment indicated that exposure to conspecific odours generally led to an increase in marking rates. However, no sex differences were found, and large differences in marking responses according to the sex of the odour donor were only found for dioestrous females. These results do not suggest that the primary function of scent-marking in this species is sexual. In the second experiment, odour sources differed not only in the sex of the donor, but also in their relative familiarity to the animal being tested. This experiment showed that males marked more in response to odours from familiar (non-related) females. Females did not differ significantly on measures of marking but did display greater interest in odours from unfamiliar males. The results are discussed in relation to possible functions of marking in this species.     

The attractiveness of different odour sources from the fruit–host complex on Leptopilina boulardi, a larval parasitoid of frugivorous Drosophila spp.

In parasitoid insects, successful offspring development depends on the female’s ability to find a suitable host. Specific recognition is often based on responses to olfactory cues, but their source and nature have rarely been determined. –This paper deals with the recognition of odours involved in host location by Leptopilina boulardi[Barbotin, Carton & Kelner-Pillault] (Hymenoptera: Eucoilidae), a larval parasitoid of Drosophila species that develops in mature fruits. The nature and origin of volatile stimuli recognized among odours of the host–fruit complex, and the effect of learning on this recognition, were investigated. Oriented responses to these odours were observed in a four-armed olfactometer and were analysed with the observer software (Noldus Information Technology). Fruit odours alone (banana and pear) were not spontaneously attractive to naive parasitoids, whereas naturally-infested bananas were highly attractive. The attraction was related to the odour that adult Drosophila left on the substrate but not to Drosophila oviposition activity or larval development. A synergism between some fruit odours (banana and pear) and the odour left by adult Drosophila on damp filter paper was observed. However, when testing a non-fruit substrate (mushroom), no synergism was observed. Thus, female L. boulardi may innately recognize host–food substrate odours associated with odours from the adult stage of their host. In addition, an oviposition experience on an infested banana allows L. boulardi females to memorise the fruit odour itself through associative learning. The adaptive significance of this process is discussed.     

Perceptual and neural olfactory similarity in honeybees

The question of whether or not neural activity patterns recorded in the olfactory centres of the brain correspond to olfactory perceptual measures remains unanswered. To address this question, we studied olfaction in honeybees Apis mellifera using the olfactory conditioning of the proboscis extension response. We conditioned bees to odours and tested generalisation responses to different odours. Sixteen odours were used, which varied both in their functional group (primary and secondary alcohols, aldehydes and ketones) and in their carbon-chain length (from six to nine carbons).The results obtained by presentation of a total of 16 × 16 odour pairs show that (i) all odorants presented could be learned, although acquisition was lower for short-chain ketones; (ii) generalisation varied depending both on the functional group and the carbon-chain length of odours trained; higher generalisation was found between long-chain than between short-chain molecules and between groups such as primary and secondary alcohols; (iii) for some odour pairs, cross-generalisation between odorants was asymmetric; (iv) a putative olfactory space could be defined for the honeybee with functional group and carbon-chain length as inner dimensions; (v) perceptual distances in such a space correlate well with physiological distances determined from optophysiological recordings of antennal lobe activity. We conclude that functional group and carbon-chain length are inner dimensions of the honeybee olfactory space and that neural activity in the antennal lobe reflects the perceptual quality of odours.     

Olfactory memory capacity of the cricket Gryllus bimaculatus

Olfactory learning in insects is a useful model for studying neural mechanisms underlying learning and memory, but memory storage capacity for olfactory learning in insects has not been studied. We investigate whether crickets are capable of simultaneously memorizing seven odour pairs. Fourteen odours were grouped into seven A/B pairs, and crickets in one group were trained to associate A odours with water reward and B odours with saline punishment for all the seven pairs. Crickets in another group were trained with the opposite stimulus arrangement. Crickets in all the groups exhibited significantly greater preference for the odours associated with water reward for all the seven odour pairs. We conclude that crickets are capable of memorizing seven odour pairs at the same time.