N. Jay Bean

Carbon disulfide: a semiochemical mediating socially-induced diet choice in rats.

Gas chromatography/mass spectrometry revealed the presence of both carbon disulfide (CS2) and carbonyl sulfide (COS) on rat breath. Behavioral experiments indicated that rats exposed to an unfamiliar diet moistened with CS2, like rats exposed to an unfamiliar diet placed on the fur of an anesthetized rat, subsequently exhibited enhanced preference for the unfamiliar diet. Rats in experimental groups: (a) interacted for 30 min with a wad of cotton batting powdered with one of two unfamiliar foods (either Diet A or Diet B) and moistened with a dilute, aqueous CS2 solution, (b) ate Diets A and B in succession and finally, (c) were injected with LiCl. In a subsequent choice between Diets A and B, these rats exhibited a preference for whichever of the foods had been present on the cotton batting during (a). Rats in control groups were treated identically to those in experimental groups, except that the diet-coated cotton batting to which they were exposed was moistened with distilled water rather then CS2 solution. Rats in control groups were not affected in their later diet choice by the food present on the cotton batting during (a). These data are consistent with the hypothesis that CS2 is a semiochemical that mediates social influence on diet selection in rats.

Olfactory and vomeronasal mediation of ultrasonic vocalizations in male mice

The effects of deafferentation of the vomeronasal, olfactory or both systems of male mice on ultrasonic vocalizations in response to a male or female stimulus were analyzed. Regardless of the technique used, disruption of the vomeronasal system led to consistent reductions in ultrasonic vocalizations. Each animal receiving vomeronasal tract cuts, bulbectomies or a combined treatment of vomeronasal tract transection and intranasal flush with ZnSO4 markedly suppressed responding to the stimulus animals. Animals treated with intranasal ZnSO4 alone or those receiving control procedures continued to respond to the female stimulus animals at rates similar to pretreatment. These results indicate that the vomeronasal system is directly involved in the perception of female mouse chemosignals and, hence, mediates the males responses to these signals.

Taxon-specific differences in responsiveness to capsaicin and several analogues: correlates between chemical structure and behavioral aversiveness

The present set of experiments was designed to explore avian insensitivity to capsaicin. Based upon a molecular model of avian chemosensory repellency, we hypothesized that structural modifications of the basic capsaicin molecule, which is itself not aversive to birds, might produce aversive analogues. To this end, European starlings (Sturnus vulgaris) and Norway rats (Rattus norvegicus) were given varied concentrations of synthetic capsaicin and four analogues (methyl capsaicin, veratryl amine, veratryl acetamide, vanillyl acetamide) in feeding and drinking tests. The results agreed with a model that we are developing to describe the chemical nature of avian repellents. Synthetic capsaicin and vanillyl acetamide were not repellent to birds, owing to the presence of an acidic phenolic OH group. Conversely, veratryl acetamide was aversive, due to the basic nature of this compound. For rats, repellent effectiveness among compounds was reversed: synthetic capsaicin was the best repellent while veratryl acetamide was the worst. We speculate that this taxonomic reversal may reflect basic differences in trigeminal chemoreception. In any case, it is clear that chemical correlates of mammalian repellents are opposite to those that predict avian repellency.

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.

Effects of medial preoptic lesions on male mouse ultrasonic vocalizations and copulatory behavior.

In male mice, lesions in the medial preoptic area (MPA) reduced the proportion of animals showing mounting behavior but failed to abolish ano-genital exploration of the female. The lesions did not effect the amount of 70 kHz ultrasound elicited by intact females or by soiled bedding obtained from female-occupied cages. These results suggest components of male sexual behavior are mediated by neural systems outside the MPA.

Testosterone implants alter the frequency range of zebra finch songs

To investigate whether changes in testosterone alter the frequency range in which a zebra finch produces song, we assigned male zebra finches to two groups, one of which received testosterone implants and the other empty silastic capsule implants. We then recorded songs up to 52 weeks after the surgery and measured frequency changes in the fundamental frequencies of arbitrarily chosen harmonic stacks in the songs of birds in either group. We found statistically significant decreases after 5 weeks in the songs of the testosterone-treated birds. No changes were found in the fundamental frequencies of the control group. The frequency change remained after the apparent effects of the testosterone implants ended. These data show that high levels of testosterone can lower the frequencies of elements in zebra finch songs.

Hormonal regulation of chemosignal-stimulated precopulatory behaviors in male housemice (Mus musculus)☆

Five experiments examined the hormonal regulation of the precopulatory reproductive behavior of male housemice of two genotypes (DBA/2J inbreds and C57BL/6J X AKR/J hybrids). The two precopulatory behaviors examined were preferences for female urinary odors and ultrasonic courtship vocalizations to anesthetized females. The preferences were then used to make inferences about odor attractiveness. Gonadally intact hybrid males were highly attracted to the airborne urinary odors of female mice but were either indifferent to, or exhibited less attraction to, male urinary odors. Castration decreased male attraction to female odor such that castrated males were equally attracted to male and female odors. Normal levels of attraction could be maintained in castrated hybrid males by Silastic implants of either testosterone or estradiol. While Silastic implants of dihydrotestosterone (DHT) were also effective in maintaining attraction in hybrids, this hormone was ineffective in inbreds. The effectiveness of estradiol, DHT, and testosterone in maintaining attraction following castration was paralleled in castrated hybrids by the effects of these hormones in maintaining courtship vocalizations to females. In contrast to the genotype-specific effects of DHT upon behavior, DHT was effective in both genotypes in maintaining seminal vesicle weight. Estradiol, on the other hand, which was quite effective in maintaining both precopulatory behaviors in hybrids, had little effect upon seminal vesicle weight. Thus these experiments dissociate the behavioral effects of steroids from their effects upon peripheral morphology. We suggest that testosterone can activate precopulatory behaviors following either aromatization or 5-alpha reduction but that genetic variability somehow gives rise to strain differences in DHT responsiveness.

The Mammalian Vomeronasal System: Its Role in Learning and Social Behaviors

Over the past several years, we have conducted behavioral work with mice and guinea pigs to define the functions of the mammalian vomeronasal system. This chapter will review the status of some of our ongoing research by summarizing the results of experiments designed to determine the role of the vomeronasal system in chemosensory investigation of female guinea pig urine by male guinea pigs, male mouse reproductive behavior, aggression among mice, and chemosensory-evoked ultrasonic vocalizations in mice. We will show that the vomeronasal system appears to be critical for maintaining certain behaviors; in its absence, chemosensory-mediated responses diminish or extinguish. Hence, we suggest that stimulation of the vomeronasal system is itself inherently rewarding. We will also demonstrate that deafferentation of the vomeronasal system neonatally or prior to experience is more detrimental to an animal than deafferentation subsequent to experience and will propose that the importance of stimuli detected by chemosensory systems other than the vomeronasal system, most likely olfaction, is learned during social encounters. These learned cues can later elicit behaviors in the absence of a functional vomeronasal system.

70-kHz vocalizations by male mice do not inhibit aggression in lactating mice

Two experiments investigated the relationship between adult male 70-kHz vocalizations and aggression by lactating female mice (Mus domesticus). Intact, vocalizing males, surgically devocalized males, and naturally nonvocalizing males were used to assess the effects of high frequency vocalizations on maternal aggression. The emission of high frequency vocalizations promoted aggressive behavior by the females. In both experiments, lactating females attacked the vocalizing males more rapidly and showed a higher incidence of aggressive behaviors toward these males than they did to the nonvocalizing male. We suggest that these vocalizations are only one of many situational cues that the female uses to determine her final behavioral response.

Development of chemosensory attractants for white-tailed deer ( Odocoileus virginianus)

White-tailed deer (Odocoileus spp.) overpopulate many areas of the United States. Browse damage to agricultural crops, forest regeneration and landscaping can be severe. Human and animal health also are threatened by Lyme disease, which is spread by the deer tick (Ixodes dammini). Although sterilants to reduce and/or slow the growth of deer populations and vaccines against Lyme disease may soon become available, efficient and economical techniques to inoculate large numbers of deer have not been developed. Oral baits represent one promising possibility. In experiment 1, salt blocks and several olfactory lures were evaluated as potential lures for use in deer baits. Plain salt blocks were attractive and odour stimuli such as acorn, apple and peanut butter significantly enhanced effectiveness. Apple was the best stimulus in an old field; peanut butter and acorn were the best stimuli in a bottomland habitat. In experiment 2, blocks of minerals, salt, molasses, and mineral-molasses were presented; all were scented with apple extract. Mineral blocks were the most attractive, followed by salt blocks and mineralmolasses blocks; molasses blocks were the least attractive. In experiment 3, mixtures of apple, acorn and peanut butter extracts were presented with mineral blocks. None of the combinations was more attractive than the others and none was more attractive than mineral blocks presented with apple extract only.