Induction of olfactory receptor sensitivity in mice.

Repeated exposure to olfactory ligands (odorants) increased peripheral olfactory sensitivity in mice. For two unrelated ligands, androstenone and isovaleric acid, induction of olfactory sensitivity was odorant-specific and occurred only in inbred strains that initially had low sensitivity to the exposure odorant. These data demonstrate stimulus-induced plasticity in a sensory receptor cell, suggesting a form of stimulus-controlled gene expression. Induction with two unrelated odorants implies that olfactory induction is a general phenomenon that may occur in a large fraction of the human population.

Access of urinary nonvolatiles to the mammalian vomeronasal organ.

Guinea pigs were allowed to investigate urine that contained rhodamine, a nonvolatile fluorescent dye. Guinea pigs given free access to dyed urine exhibited fluorescence in their vomeronasal and septal organs but not on their olfactory epithelium. Fluorescence was not seen when unadulterated urine was presented. Thus compounds of low volatility, which do not reach the olfactory epithelium, may stimulate the vomeronasal system and provide information that is normally not provided by gustation or olfaction.

Recognition of H-2 types in relation to the blocking of pregnancy in mice.

Inbred BALB/c females were mated and subsequently exposed in a divided cage to "stimulus" males or females whose H-2 type was similar or dissimilar to the stud male's. The incidence of pregnancy blocking was considerably higher when stud and stimulus males differed in H-2 type than when they did not. Similar results were obtained with urine samples of H-2 identical and nonidentical males. Females exposed after mating to other females whose H-2 type differed from the stud male, under the same experimental conditions, also showed an appreciable incidence of pregnancy block. It is therefore concluded that chemosensory recognition of H-2 types affects the reproductive hormonal status of the pregnant female.

Analyses of volatile organic compounds from human skin.

BACKGROUND: Human skin emits a variety of volatile metabolites, many of them odorous. Much previous work has focused upon chemical structure and biogenesis of metabolites produced in the axillae (underarms), which are a primary source of human body odour. Nonaxillary skin also harbours volatile metabolites, possibly with different biological origins than axillary odorants. OBJECTIVES: To take inventory of the volatile organic compounds (VOCs) from the upper back and forearm skin, and assess their relative quantitative variation across 25 healthy subjects. METHODS: Two complementary sampling techniques were used to obtain comprehensive VOC profiles, viz., solid-phase microextraction and solvent extraction. Analyses were performed using both gas chromatography/mass spectrometry and gas chromatography with flame photometric detection. RESULTS: Nearly 100 compounds were identified, some of which varied with age. The VOC profiles of the upper back and forearm within a subject were, for the most part, similar, although there were notable differences. CONCLUSIONS: The natural variation in nonaxillary skin odorants described in this study provides a baseline of compounds we have identified from both endogenous and exogenous sources. Although complex, the profiles of volatile constituents suggest that the two body locations share a considerable number of compounds, but both quantitative and qualitative differences are present. In addition, quantitative changes due to ageing are also present. These data may provide future investigators of skin VOCs with a baseline against which any abnormalities can be viewed in searching for biomarkers of skin diseases.

Neurobehavioral evidence for the involvement of the vomeronasal system in mammalian reproduction.

Jacobson's organ of the vomeronasal system is found in every order of mammals with the possible exception of Cetacea. The equivocal evidence claiming a vestigial or absent organ in humans is reviewed. Based upon anatomical considerations, the sensory epithelium of Jacobson's organ is one of five possible sensory components within the nasal cavity. Many methods designed to test the role of olfaction (sensu strictu) in physiology and behavior do not discriminate among the possible systems. Therefore, erroneous conclusions may have been drawn from the results of intervention experiments. The central neuroanatomical projections of the vomeronasal and olfactory systems are different and relatively independent of each other. The vomeronasal system reciprocally communicates with central areas concerned with reproductive events. On the other hand, the olfactory system may subserve individual maintenance tasks (e.g., feeding). As a periscope from the diencephalon, the vomeronasal system may monitor exogenous hormones, "pheromones".

Hand preference and age in the United States.

A survey of 1,177,507 U.S. men and women between the ages of 10 and 86 included questions regarding hand preference for writing and throwing. Three effects were observed. Individuals with at least some left motoric bias comprised a smaller percent of the population with advancing age. This finding provides large-scale confirmation of a previously described phenomenon. Among sinistrals, concordance for writing and throwing was 2.2 times as prevalent as left-writing with right-throwing, and 4.1 times as prevalent as right-writing with left-throwing. These sinistral subpopulations displayed distinct and stable prevalence prior to age 50 and changing patterns of prevalence subsequent to age 50. The results confirm a decrease with age in the prevalence of sinistrality, but indicate that age-specific rates of mixed- and left-handedness are distinct. The implications for hypotheses regarding age-related change in the prevalence of sinistrality are discussed.

Extinction of response to urine odor as a consequence of vomeronasal organ removal in male guinea pigs.

It has been found that removal of the vomeronasal chemoreceptor organ (VNO) in male guinea pigs disrupted investigatory responses to conspecific odors but this disruption was time-dependent; immediately following surgery, behavior appeared almost normal, whereas several months following surgery, animals became very unresponsive to conspecific odor. It was hypothesized that in the absence of a functional VNO, the main olfactory system (MOS) was capable of maintaining response to conspecific odor but that this response extinguished following repeated exposures. However, postsurgical change in the central nervous system, unrelated to exposure to the bioassay, remained a possible explanation. In order to separate these hypotheses, the VNO was surgically removed in two groups of animals (A and B), and a third group (C) experienced sham surgery. Beginning 3 weeks following surgery, males in Groups A and C were given two standard urine-response tests/week for 24 weeks. Initiation of testing of Group B animals was delayed until Week 15 following surgery. Results indicated that (a) responses of Group A declined relative to those of Group C, (b) at the first postsurgical test, Group B was as responsive to urine as Group C and much more responsive than Group A and (c) a decline in responses for Group B occurred during tests after Week 15. The data therefore strongly supported the extinction hypothesis. The MOS is capable of eliciting a high level of investigatory behavior in response to female urine odors, but in the absence of the VNO, this response wanes, perhaps due to a loss of reinforcing properties associated with VNO stimulation.

Consequences of removing the vomeronasal organ.

In the last decade, research in our laboratories has focused on the effects of deafferentation of the mammalian chemosensory vomeronasal organ (VNX). Many different assays have been conducted and the results of some are briefly reviewed in this contribution, including the effects of VNX on neuroanatomical assessments using histochemistry (lectin binding) and immunohistochemistry (LHRH), male mouse and prairie vole ultrasonic vocalizations and hormone surges in response to cues from females, male mouse courtship and sexual behavior, territorial marking and inter-male aggression, the production of a puberty-altering substance found in mice, activation of reproduction in female voles (who generally do not exhibit estrous cycles) and maternal behaviors by female mice, including aggression directed toward intruder males. In some instances, the otherwise detrimental effects of VNX can be overcome by experience prior to deafferentation, especially in assays that are dependent upon expressions of behavior. In other situations, experience may have little impact on amelioration of the effects of VNX. The essential conclusions of this work focus our attention on reproductive physiology and behavior and a role for the vomeronasal organ in the perception of pheromones that modulate these functions.

Spatiotemporal masking in pure olfaction.

In olfaction, it is not possible to determine which nostril is being stimulated, i.e., lateralize, when a pure olfactory substance, e.g., phenylethyl alcohol or vanillin, is administered into one nostril, and, simultaneously, an odorless, solvent blank into the contralateral nostril. We subjected volunteers to extensive training, with feedback on each trial, in an attempt to determine whether it was possible, in these well-trained subjects, to overcome this apparent impossibility. We failed to obtain any evidence to support the notion that a pure olfactory stimulus could be lateralized when the odorant and blank were presented simultaneously. The task, however, became simple when the odorant and the blank entered each nostril sequentially. We investigated, using a two-channel olfactometer, temporal parameters that enabled such discrimination. We controlled the duration of odorant and blank air puffs, as well as their mutual timing, to determine the threshold stimulus onset-disparity, i.e., the interval between stimulus onset and blank onset, that resulted in an inability to lateralize. Latencies shorter than the threshold interval would be perceived as simultaneous stimulation. We determined that the onset interval was between 200 and 400 ms, depending on the duration of the stimuli (a shorter interval was noted for stimuli of 150-ms duration relative to 300- and 450-ms stimuli). This was also true when two odorants were applied, rather than an odorant and a blank, and the subject was instructed to focus on the sequence of odorant delivery and side of stimulation. The temporal onset threshold was the same for lateralization and for order of stimulation. Whether the olfactory system per se mediates this discrimination or whether inputs from olfaction and chemesthesis, via trigeminal free nerve endings stimulated by air-stream onset, combine to allow this discrimination has yet to be determined.

Removal of the vomeronasal organ disrupts the activation of reproduction in female voles.

The reproductive system of female prairie voles remains quiescent in the absence of stimulation from males; however, chemosignals from males are capable of at least partially activating female reproduction. In other species, the vomeronasal system mediates some of the reproductive responses of females to males. We found that surgical removal of the vomeronasal organ (VNX) from adult female prairie voles impeded reproductive activation in response to pairing with stud males: ovarian and uterine weights of VNX females paired with stud males for 24 or 60 hours were significantly less than those of normal (NORMAL) or sham-operated (SHAM) females. Furthermore, 8 of 9 NORMAL, 10 of 13 SHAM, but only 4 of 9 VNX females paired with stud males for 60 hours mated. VNX females, however, were still able to use chemosensory cues to locate food. Behavioral observations of females encountering stud males were similar for VNX, SHAM and NORMAL females. We conclude that vomeronasal chemoreception may be a primary component of reproductive activation in female prairie voles, presumably by mediating neuroendocrine responses to chemosignals.

FOS immunoreactivity after exposure to conspecific or heterospecific urine: where are chemosensory cues sorted?

Female prairie voles (Microtus ochrogaster) typically require an intact vomeronasal system and exposure to a chemical signal found in urine from male prairie voles to induce uterine growth necessary for reproduction. Urine from male mice (Mus musculus) does not contain an effective cue for activation of female vole reproduction: after 4 days of exposure to stimuli, voles exposed to urine from female or water had still uteri whereas voles exposed to urine from male voles had large uteri. The initial response to urine from male voles included neuronal activity in the vomeronasal system as indicated by FOS immunocytochemistry. Stimuli (urine from a male vole or a male mouse, or water) were painted on the nose of naive female voles 1 h before sacrifice. Female voles exposed to urine from male voles had more FOS-immunoreactive cells in the accessory olfactory bulb than voles exposed to mouse urine or to water. We conclude that exposure to urine from male voles stimulates the vomeronasal pathway (as measured by FOS immunoreactivity) and induces uterine growth in female voles, whereas exposure to urine from male mice (or water) does not. This suggests that some degree of functional specificity of the clinical cue is determined at or before the accessory olfactory bulb, perhaps in the expression of specific receptors within the vomeronasal organ, rather than entirely within the central nervous system.

Odorant exposure increases olfactory sensitivity: olfactory epithelium is implicated.

Exposure-induced shifts in sensitivity to odors may involve peripheral and/or central components of the olfactory system. The ability to disconnect the olfactory epithelium from the bulbs provides a unique opportunity to examine how odorant exposure affects each component. In one experiment, odor thresholds were established for either amyl acetate or androstenone. The mice were then exposed for 10 days to the same test odorant for which a threshold was obtained. After exposure, sensitivity to the odorant increased relative to preexposure levels. The mice then underwent bilateral olfactory nerve transection (BNX). When both groups of mice were tested 45-50 days after recovery from surgery and return of olfactory function, increased sensitivity to the exposed odorant persisted; however, 121-203 days after surgery, sensitivity returned to preexposure levels. Another experiment was similar to the first except that mice were exposed to an odorant, either amyl acetate or androstenone, for 10 days beginning 1 day after BNX or sham surgery. When the mice were tested 45-50 days after surgery, sensitivity to the exposed odorant was increased relative to preexposure levels, whereas sensitivity to the nonexposed odorant remained at preexposure levels. Although further work is needed to determine the precise mechanism(s) underlying shifts in sensitivity to odors, these studies provide additional evidence for peripheral involvement in exposure-induced sensitization to odorants and demonstrate the remarkable capacity of the olfactory system to maintain or even regain sensitivity after injury.

Vomeronasal organ removal and female mouse aggression: the role of experience.

Removal of the vomeronasal organ (VNX) from female mice had little effect upon fecundity, nest building and pup retrieval. Surprisingly, VNX significantly affected aggression by lactating females. Normally, lactating females will attack and fight intruders placed into the home cage, especially if the intruder is an unfamiliar male. In Experiment 1, we determined that VNX prior to sexual experience totally eliminated this type of aggression. Intact females were highly aggressive, but much more so to unfamiliar than to familiar males. Copulation prior to surgery did not ameliorate the effects of VNX; again, none of the VNX females were aggressive (Experiment 2). In Experiment 3, attacks and fights by previously aggressive primiparous females also were eliminated or significantly suppressed following VNX. Even when the testing occurred later during the postpartum period and for extended periods of time, this same suppression of aggression held following VNX. We conclude that aggression by lactating female mice is under strict mediation by chemosignals detected by the vomeronasal organ.

Vomeronasal organ and social factors affect urine marking by male mice.

Adult CF-1 male mice cohabited for 15 days with three different females (EXPERIENCED) or remained physically isolated (INEXPERIENCED) prior to removal of their vomeronasal organs (VNX) or a SHAM procedure. Subjects were tested one month after surgery for urine marking in response to a stimulus male, a stimulus female, or no stimulus animal on the opposite side of a screened partition. VNX males exhibited a significant reduction in urine marking compared to SHAM males. EXPERIENCED VNX males deposited urine in amounts that were intermediate to SHAMs and INEXPERIENCED VNX males. These results suggest that deficits in urine marking behavior that result from loss of vomeronasal chemoreception may be ameliorated by prior sexual and/or social experience with females.

Mediation of male mouse urine marking and aggression by the vomeronasal organ.

The effects of vomeronasal organ removal (VNX) on male mouse urine marking and aggressive behaviors were investigated. In three different stimulus conditions VNX male marking rates were about half that of sham-operated males. Aggressive behavior was tested by pairing males with male-urine-swabbed castrate males. Only 1 of the 12 VNX males displayed normal levels of fighting behavior and 6 did not initiate any fights during the aggression tests. These results indicate that normal male aggressive and urine marking behaviors are dependent on the presence of an intact vomeronasal system for their expression.

Behavioral responses of male guinea pigs to conspecific chemical signals following neonatal vomeronasal organ removal.

Following vomeronasal organ removal or sham surgery at 4-7 days of age, male guinea pigs were tested for responsiveness to conspecific chemical uses as infants and again as adults. In the first experiment, vocalizations in response to soiled home cage bedding and male bedding were monitored twice prior to surgery and twice weekly for four weeks. Home cage cues elicited more vocalizations than did male bedding in both groups; however, there was no effect of vomeronasal organ removal. When tested as adults in a second experiment, animals without vomeronasal organs exhibited depressed investigative responsiveness and vocalizations to female genital smears. The data from the first experiment fail to indicate a role for the vomeronasal organ in infantile response to conspecific odor. However, the second experiment demonstrates that adult responses to similar odors are substantially depressed by an absence of the vomeronasal organ.

Mouse vomeronasal organ: effects on chemosignal production and maternal behavior.

Adult male mice excrete a urinary chemosignal that accelerates puberty in females, whereas group-housed female mice excrete a urinary chemosignal that delays puberty in young females. We found that: (1) the excretion of the puberty-acceleration chemosignal by males persisted in the absence of the vomeronasal organs and (2) the puberty-delay chemosignal was not present in the urine of group-housed females whose vomeronasal organs had been surgically removed (VNX), but was present in the urine of group-housed females subjected to sham surgery (SHAM). These results suggest that in males, vomeronasal chemoreception does not affect the excretion of the puberty-acceleration chemosignal, but that in females, the vomeronasal organ receives chemosignals that influence the excretion of the puberty-delay chemosignal. Additionally, we found no difference between SHAM and VNX females in rates of conception, litter size, pup growth, pup recognition, or maternal behavior, indicating that normal maternal processes are expressed in the absence of an intact accessory olfactory system.

An ephemeral pheromone of female house mice: perception via the main and accessory olfactory systems.

Two experiments examined the chemosensory modalities by which males detect an ephemeral sex pheromone in the freshly voided urine of female mice. Experiment 1 examined the interaction of deafferenting the accessory olfactory system (vomeronasal organ removal) and subsequent sexual experience upon ultrasonic vocalizations by male mice to freshly voided female urine. In general, sexually experienced males vocalized substantially more than sexually naive males. In addition, males possessing a vomeronasal organ vocalized slightly more than those without. Nonetheless, a functioning vomeronasal organ clearly was not essential for vocalizing to fresh female urine. Experiment 2 examined the effects of deafferenting the main olfactory system (ZnSO4 nasal irrigation) and/or the accessory olfactory system (vomeronasal removal) in sexually experienced males. Males with both olfactory systems functioning vocalized at high levels to fresh urine, while males with only one functioning system vocalized at intermediate levels. Males with neither system functioning did not vocalize at all to fresh urine. In contrast, when female mice themselves served as stimuli, all groups of males vocalized at high levels. We conclude that adult male mice can detect the ephemeral pheromone via either the main olfactory system or the accessory olfactory system. However, vocalizations to the female herself can be mediated by other sensory systems as well.

The vomeronasal organ: primary role in mouse chemosensory gender recognition.

Four experiments were conducted to determine the chemosensory modality that supports ultrasonic courtship vocalizations by male mice to females and to chemosignals from females. Both removal of the olfactory bulbs (Experiment 1) and removal of the vomeronasal organ (Experiments 2-4) produced similar deficits in the pattern of ultrasonic vocalizations elicited by conspecifics or their odors. Removal of the vomeronasal organ did not impair the ability to locate food buried under cage shavings. These results are consistent with the notion that the analysis of food related odors is subserved by olfaction and that vocalizations to sex chemosignals are elicited primarily by stimulation of the vomeronasal organ/accessory olfactory bulb. Removal of the vomeronasal organ did not induce seminal vesicle regression or lower plasma immunoreactive testosterone levels (Experiment 2) nor was an attempt to restore vocalizations with exogenous testosterone successful (Experiment 4). Thus the altered vocalization pattern following removal of the vomeronasal organ does not appear to arise as a motivational deficit mediated by androgens. Experiments 2 and 3 demonstrated that, in the absence of the vomeronasal organ, stimulation of other sensory systems can, to some extent, maintain the male's tendency to vocalize more to females or their odors than to males or their odors. However, this responsiveness to females may rely upon additional behavioral cues. Previous experience also plays a considerable role in the response to chemosensory gender cues by males who lack their vomeronasal organs. Removal of the vomeronasal organ prior to adult heterosexual encounters (Experiment 3) virtually eliminated the male's responsiveness to either anesthetized females or their chemosignals. Hence males require adult heterosexual experience with a functioning vomeronasal organ before other chemosensory systems acquire the ability to mediate gender recognition as measured by ultrasonic vocalizations.

Chemoinvestigatory and sexual behavior of male guinea pigs following vomeronasal organ removal.

The vomeronasal organs of male guinea pigs were removed (VNX; n = 10) or males experienced sham surgery (Sham; n = 10). Subsequently a battery of chemosensory tests of investigatory responsiveness to conspecific urine was conducted. Additionally, male subjects were paired with female conspecifics for short and long periods and social and sexual behaviors were monitored. VNX males exhibited a depression in urine investigation and this depression became more profound following repeated testing and/or the passage of time. By 6.3 months following surgery, investigatory responsiveness to urine was practically eliminated. Maintenance of responsiveness to urine odors may require reinforcing input through the accessory olfactory system. In contrast to these effects on responsiveness to odors, VNX and Sham males were indistinguishable in their social and sexual behavior. These data indicate that male guinea pigs without a VNO: (1) Exhibit a depression of investigation of urine odors which is time dependent and which may involve an extinction-like process; (2) continue to discriminate classes of urine (e.g., urine from male vs urine from female conspecifics); and (3) exhibit normal sexual behavior. The vomeronasal organ in the male domestic guinea pig is apparently critical for the maintenance of normal responsiveness to sex odors but, in its absence, other sensory systems are capable of maintaining normal sexual behavior under conditions of laboratory testing.