Search

We recorded the electrophysiological responses of individual olfactory receptor neurons in sensilla trichodea on the antennae of adult arctiid moths, Utetheisa ornatrix, to stimulation with volatiles associated with both sexes. All trichoid sensilla contain at least two receptor neurons, each with distinct action potential amplitudes and waveforms, that respond dichotomously to male and female odors. Although, neither female neuron responds to extracts of coremata or the male-produced pheromone hydroxydanaidal, they do respond in a gender-specific manner to the volatiles emanating from whole pupae, hemolymph, thoracic froth, and adult animals of several ages. Thoracic froth, which contains pyrrolizidine alkaloids, is thought to play a role in defense. Froth from moths reared on diets, with or without added pyrrolizidine alkaloids, were equally effective in eliciting gender-specific patterns of response. Male trichoid receptor neurons respond to these same materials with similar patterns of activation. These receptor neurons provide information about substances, which we have termed "gender odors," that are persistently emitted by nearby animals. These substances do not appear to be the same as those already known to be involved in defense or the sexual dialog between individuals.

Explorations of the qualitative and quantitative differences between the odors of pemenone (PEM), androstenone (AND) and isovaleric acid (IVA) show that they share a number of common perceptual characteristics. Among these are similarities in their odor quality and relative intensity ratings. PEM is also an efficient cross-adaptor and modulator of a subject's AND sensitivity. Here we evaluate the reciprocal efficacy of AND adaptation to alter the perceived intensity and quality of PEM, IVA and AND. Twenty-three people, including both those osmic and allosmic (n = 11) for the putrid odor quality of PEM, were tested. Following training in odor quality and intensity rating techniques, subjects sampled a selected substance for 2 min to obtain adaptation and then reported quality and intensity ratings for the three test stimuli. There was significant self-adaptation by PEM and IVA in all subjects, but self-adaptation by AND was only observed in the PEM-osmic subjects. AND did not cross-adapt PEM or IVA to any significant extent. Collectively, these results contrast with our earlier study in which PEM was an efficient cross-adaptor of AND. Here, AND was no more efficient than the control as an adapting substance for PEM, despite significant self-adaptation of PEM by itself. This lack of reciprocity in the effectiveness of PEM and AND as cross-adapters is not related to differences in odor intensity, as the PEM and AND concentrations were adjusted for each subject to elicit comparable intensity reports. These results support the notion that PEM, AND and IVA share certain perceptual characteristics, but interact differentially with three or more sets of perceptual channels that are now thought to result in a putrid odor quality.

The validity of the odor quality reports given by naive human subjects is often questionable. On the one hand, social conventions can influence the labeling of odorants, especially those that have putrid or uncommon odor qualities, and on the other, semantic differences exist for odor descriptors among individuals. We are interested in the individual differences in the quality reports elicited by two nominally putrid odorants, androstenone (AND) and pemenone (PEM). Here we sought to establish empirical support for the individual differences previously obtained in studies of their odor quality, using a nonverbal, semantic-free method of classification. Undergraduate volunteers sniffed a moderate concentration (390 microM) of PEM, rated its intensity, and provided a verbal odor descriptor. The subjects were then classified as PEM osmic (n = 42) if the quality report was putrid (rancid, urinous, sweaty), allosmic (n = 23), if the quality was nonputrid, and anosmic (n = 39) if no odor was detected. The subjects then sorted 15 odorants matched for intensity, five selected from each of three nominal odor quality types, into as many odor groups as they wished, as long as each group contained all of the compounds with similar odors. The number of times each odorant was paired with another was used as data for an independent multidimensional scaling with ALSCAL, for each class of subject. Three-dimensional solutions showed that this nonverbal, semantic-free scaling method produced odor classifications consistent with those found when each class of subject reported odor qualities from a defined list of quality descriptors. Cluster analysis of the MDS coordinates revealed that these solutions also retained the individual odor quality differences thought to be characteristic of osmic, allosmic and anosmic subjects.

The responses elicited by olfactory stimuli may be modified throughout an organism's life. For example, Wysocki et al. found that regular presentations of 5a-androst-16-en-3-one (androstenone) to anosmic subjects resulted in a graded increase in the perceived intensity of this substance in about half of their subjects (Wysocki et al., 1989). The increased sensitivity they observed appeared to be specific to the exposed odorant and was presumed to occur only in anosmic subjects. Here, we continue our explorations of the individual differences in olfactory capabilities among subjects initially classified by their ability to detect and identify the odor of the diastereoisomeric ketone, cis-4-(4'-t-butylcyclo-hexyl)-4-methyl-2-pentanone (pemenone) which shares with androstenone a pronounced urine-sweaty odor. We asked if regular pemenone exposure enhances the sensitivity of human subjects to pemenone, androstenone, isovaleric acid, or phenylethyl alcohol and, if shifts in threshold occurred, were they specific to particular odorants and classes of subject? Detection thresholds for the four substances were determined before and after 7-8 weeks of regular, biweekly, exposure to pemenone (n = 18 subjects) or a control substance (22 subjects). Significant decreases in threshold were seen in the experimental group, relative to the control group, for androstenone, but not for the other compounds evaluated. Neither gender nor initial pemenone osmicity significantly affected the frequency of subjects with enhanced sensitivity. These findings show that a subject's sensitivity to one odorant can be enhanced by exposure to another, chemically distinct compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation techniques have traditionally been employed in sensory physiology and psychology to characterize afferent pathways and to dissect the quantitative and, to a lesser degree, the qualitative aspects of perception. We continue to explore the individual differences in olfactory capabilities among subjects initially classified by their ability to detect and identify the diastereoisomeric ketone, cis-4-(4'-t-butylcyclohexyl)-4-methyl-2-pentanone (pemenone) which shares with 5 alpha-androst-16-en-3-one (androstenone) a pronounced urine-sweaty odor. Our previous studies of these and other compounds for which specific anosmias were said to exist revealed significant relationships between intensity scores and a corresponding clustering of the odor quality descriptors used to characterize these materials by subjects judged to be specifically anosmic for the urinous note. Here, we attempt to dissect the web of interactions which give rise to individual differences in perceived odor quality by evaluating the effects of self- and cross-adaptation on the intensity and quality reports elicited by pemenone, androstenone and four other odors in 18 human subjects including both pemenone-osmic and non-osmic (n = 6) individuals. Intensity and quality ratings for the six compounds were obtained before and after an adaptation sequence in which subjects sniffed a test odorant, pemenone or the diluent. For each odorant, intensity ratings under the different adapting conditions were compared by ANOVA. Self-adaptation was universal but cross-adaptation by pemenone was only found in the intensity ratings of androstenone. The intensity ratings of isovaleric acid, which shares the urinous note with pemenone and androstenone, were unaffected by pemenone adaptation. Most of the subjects judged to be osmic still reported a urinous odor quality for androstenone and isovaleric acid following pemenone adaptation. Except for shifts to the no-odor category, adaptation did not significantly alter the odor quality reports of osmic or non-osmic individuals. This suggests that the odor quality reports engendered by these substances are multidimensional and that compounds which share the same odor quality label may interact with different perceptual channels.

Receptive female Syrian hamsters were significantly attracted to the odors of other hamsters but not to odors obtained from certain foods. Estrous female attraction scores were larger in response to male Syrian flank gland sebum (SMFG) than to estrous hamster vaginal discharge (HVD) obtained from either Syrian (SHVD) or Turkish (THVD) hamsters. On Day 3 of their estrous cycle, nonreceptive Syrian hamsters were significantly attracted to food-related odors but not to the odors of other hamsters (SMFG, SHVD, or THVD).

Multicomponent pheromone systems are the rule in many species. As our knowledge about the number and kinds of different chemical compounds actually employed in the communication system of a particular species has increased, so too has our appreciation for the level of neurobiological complexity that must underlie these capabilities. The supposition that mixtures are differentially processed in the nervous system arises most easily when biologically relevant materials are evaluated, either singly or in multicomponent blends, with modern behavioral assay techniques. It is becoming increasingly clear that this increase in the chemical and behavioral complexity of a particular communication system must be paralleled by an increase in the efficiency of the physiological mechanisms employed for the neural encoding of behaviorally relevant odor compounds and blends. Here we review several studies that have examined the electrical activity elicited in primary olfactory receptor neurons when they are stimulated with mixtures of odorants. Particular attention is given to the responses elicited in a subset of the individual pheromone-sensitive sensilla on the antennae of male cabbage looper moths (Trichoplusia ni). Electrophysiological responses to single- and multiple-component stimuli, each drawn from among the seven known behaviorally active compounds for this insect, were obtained at several different stimulus intensities. Both (Z)7-dodecenyl acetate and (Z)7-dodecenol were effective stimuli for both of the receptor neurons found in one of the two classes of pheromone-sensitive sensilla, even at relatively low stimulus intensities (0.0005 micrograms). Dodecyl acetate, although behaviorally active, did not significantly excite either of these receptor neurons. However, when mixed with either of the unsaturated components, it significantly enhanced the receptor neuron's response to its appropriate parent compound only in the middle range of stimulus intensities. A mixture of all three components did not show this enhancement and at the middle range of intensities actually elicited reduced responses when compared to those elicited by appropriate amounts of any of the one- and two-component stimuli evaluated. Thus, some blends elicited electrical responses from primary olfactory receptor neurons that were not readily predicted from a knowledge of the receptor neurons' response to individual components.

Estrous hamster vaginal discharge (HVD) contains both volatile and nonvolatile chemical signals which collectively elicit both male attraction to females and male mating behavior. These two aspects of normal sexual behavior are differentially affected by lesions involving afferents of the main and the accessory olfactory systems. The results of lesions that involve the main olfactory system suggest that it provides information primarily concerning those volatile components of HVD that normally signal the presence of a female. Lesions restricted to the accessory olfactory system do not impair a male's interest in or relative preference for HVD but do significantly interfere with subsequent stages of sexual behavior by reducing the amount of mating obtained upon exposure to HVD. Stimulation of the accessory olfactory system by nonvolatile components of HVD has thus been implicated in the production of mating behavior. In these experiments, male hamsters were attracted to female odor and engaged in significant amounts of mating behavior with surrogate females when only the volatile components of HVD were available to them. These behaviors were further enhanced when both volatile and nonvolatile components of HVD were provided. Lesion studies of the afferents involved reinforce the hypothesis that the main olfactory system is preferentially involved with processing those volatile chemical signals in HVD that denote female attractiveness whereas the accessory olfactory system is preferentially involved with processing those chemical signals, both volatile and nonvolatile, that evoke subsequent steps in male sexual behavior.