Roles of the main olfactory and vomeronasal systems in the detection of androstenone in inbred strains of mice

We investigated the role of the main olfactory and accessory olfactory systems （MOS and AOS respectively） in the detection of androstenone. We used the following experimental approaches： behavioral, surgical removal of the vomeronasal organ （VNX） followed by histochemical verification and Fos immunohistochemistry. Using a Y-maze paradigm we estimated sensitivity of NZB/B1NJ and CBA/J mice to androstenone. CBA mice were 2,000-fold more sensitive to androstenone than NZB mice. VNX caused a 4-tol6-fold decrease in sensitivity to androstenone in highly-sensitive CBA mice, but did not affect thresholds in NZB mice. Results indicate the involvement of the MOS and AOS in the detection of androstenone. We observed a specific pattern of Fos-positive cells in the main olfactory bulb of CBA mice but not in NZB mice subsequent to exposure of mice to androstenone; the compound activated cells in the accessory olfactory bulb in both strains of mice, indicating the involvement of the vomeronasal organ. Patterns of Fos-positive cells in the vomeronasal organ were recorded subsequent to exposure to androstenone. Fos-positive receptor cells in the vomeronasal organ of CBA and NZB mice were different, in CBA mice Fos-positive cells were noted in both the basal and apical zones, however, in NZB mice activation was observed only in the apical zone [Current Zoology 56 （6）： 813-818, 2010].

Heat,sight and scent:multiple cues influence foraging site selection by an ambush-foraging snake Hoplocephalus bungaroides(Elapidae)

Most mobile organisms respond to multiple cues when selecting habitat types,and laboratory experiments that manipulate only single cues may fail to reveal the true complexity of habitat-selection behaviour.In south-eastern Australia,broad-headed snakes Hoplocephalus bungaroides(Elapidae)lie in wait under sun-warmed rocks to ambush velvet geckos Oedura leseuerii(Gekkonidae).Previous laboratory work has shown that both the geckos and the snakes actively select hotter rather than colder rocks,and that the snakes actively select rocks scented by geckos.We manipulated rock temperature and the presence of two types of cues from geckos(chemical and visual information)to clarify the causal basis for foraging site selection by the juveniles of this snake.When given a choice between cold lizard-scented rocks and hot unscented rocks,our captive snakes gave a higher priority to lizard scent than to temperature.The snakes also selected shelter-sites that provided visual as well as scent cues from lizards,rather than shelter-sites with scent cues alone.Thus,although broad-headed snakes show a direct preference for hotter rather than colder rocks in the laboratory,their choice of foraging site in the field may also be influenced by the presence of scent cues from prey.Our laboratory results suggest that habitat selection by broad-headed snakes may be more complex than has been suggested by previous single-factor laboratory trials.

Histological Architecture of the Nasal Region in Rana chensinensis

The nasal region of Rana chensinensis is divided into the nasal capsules and nasal cavities. In this study, we investigated the adult histological structure of the nasal capsules and nasal cavities in the frog R. chensinensis under the microscope. We found that an eminentia olfactoria is present in this frog and the presence of the eminentia olfactoria may be connected to a terrestrial life style. The double staining method using alcian blue and alizarin red showed that the septomaxilla, the most important bone associated with the olfactory capsules, is an intramembranous bone in R. chensinensis. The opening of the nasolacrimal duct showed a close proximity to the apertura nasalis externa. The presence of the nasolacrimal duct in the olfactory region may be an adaptation to a terrestrial environment. The function of the vomeronasal and olfactory organs is discussed in the paper.

Vomeronasal organ lesion disrupts social odor recognition, behaviors and fitness in golden hamsters

Most studies support the viewpoint that the vomeronasal organ has a profound effect on conspecific odor recog­nition,scent marking and mating behavior in the golden hamster(Mesocricetus auratus).However,the role of the vomeronasal organ in social odor recognition,social interaction and fitness is not well understood.There­fore,we conducted a series of behavioral and physiological tests to examine the referred points in golden ham­ster.We found that male hamsters with vomeronasal organ lesion showed no preference between a predator odor(the anal gland secretion of the Siberian weasels(Mustela sibirica)and putative female pheromone components(myristic acid and palmitic acid),but were still able to discriminate between these 2 kinds of odors.In behavior­al tests of anxiety,we found that vomeronasal organ removal causes female hamsters to spend much less time in center grids and to cross fewer center grids and males to make fewer crossings between light and dark boxes than sham-operated controls.This indicates that a chronic vomeronasal organ lesion induced anxious responses in females.In aggressive behavioral tests,we found that a chronic vomeronasal organ lesion decreased agonistic behavior in female hamsters but not in males.The pup growth and litter size show no differences between the 2 groups.All together,our data suggested that vomeronasal organ ablation disrupted the olfactory recognition of social chemosignals in males,and induced anxiety-like and aggressive behavior changes in females.However,a vomeronasal organ lesion did not affect the reproductive capacity and fitness of hamsters.Our studies may have important implications concerning the role of the vomeronasal organ in golden hamsters and also in rodents.

Molecular and evolutionary analyses of formyl peptide receptors suggest the absence of VNO-specific FPRs in primates

Formyl peptide receptors (FPRs) were observed to expand in rodents and were recently suggested as candidate vomeronasal chemo-sensory receptors. Since vomeronasal chemosensory receptors usually underwent positive selection and evolved concordantly with the vomeronasal organ (VNO) morphology, we surveyed FPRs in primates in which VNO morphology is greatly diverse and thus it would provide us a clearer view of VNO-FPRs evolution. By screening available primate genome sequences, we obtained the FPR repertoires in representative primate species. As a result, we did not find FPR family size expansion in primates. Further analyses showed no evolution-ary force variance between primates with or without VNO structure, which indicated that there was no functional divergence among pri-mates FPRs. Our results suggest that primates lack the VNO-specific FPRs and the FPR expansion is not a common phenomenon in mammals outside rodent lineage, regardless of VNO complexity.

Ontogenetic shift in response to prey-derived chemical cues in prairie rattlesnakes Crotalus viridis viridis

Snakes often have specialized diets that undergo a shift from one prey type to another depending on the life stage of the snake. Crotalus viridis viridis （prairie rattlesnake） takes different prey at different life stages, and neonates typically prey on ectotherms, while adults feed almost entirely on small endotherms. We hypothesized that elevated rates of tongue flicking to chemical stimuli should correlate with particular prey consumed, and that this response shifts from one prey type to another as in- dividuals age. To examine if an ontogenetic shift in response to chemical cues occurred, we recorded the rate of tongue flicking for 25 neonate, 20 subadult, and 20 adult （average SVL = 280.9, 552, 789.5 mm, respectively） wild-caught C. v. viridis to chemi- cal stimuli presented on a cotton-tipped applicator; water-soluble cues from two ectotherms （prairie lizard, Sceloporus undulatus, and house gecko, Hemidactylusfrenatus）, two endotherms （deer mouse, Peromyscus maniculatus and lab mouse, Mus musculus）, and water controls were used. Neonates tongue flicked significantly more to chemical cues of their common prey, S. undulatus, than to all other chemical cues; however, the response to this lizard＇s chemical cues decreased in adult rattlesnakes. Subadults tongue flicked with a higher rate of tongue flicking to both S. undulatus and P. maniculatus than to all other treatments, and adults tongue flicked significantly more to P. maniculatus than to all other chemical cues. In addition, all three sub-classes demonstrated a greater response for natural prey chemical cues over chemical stimuli of prey not encountered in the wild （M. musculus and H. frenatus）. This shift in chemosensory response correlated with the previously described ontogenetic shifts in C. v. viridis diet. Be-cause many vipers show a similar ontogenetic shift in diet and venom composition, we suggest that this shift in prey cue dis- crimination is likely a general phenomenon among viperid snakes.

Chemosensory response in stunted prairie rattlesnakes Crotalus viridis viridis

Rattlesnakes use chemical stimuli in ambush site selection and for relocation of envenomated prey through atrike-induced chemosensory searching. Shifts in responsiveness to prey chemicals have been documented in many snakes, and often correlate with prey commonly taken as snakes increase in age and size as well as geographical locations of the species. For instance, neonate rattlesnakes that prey primarily on ectotherms responded most strongly to chemical cues of commonly taken lizard prey, whereas adult rattlesnakes that prey primarily on small mammals responded significantly to chemical cues of com- monly taken rodents. In the current study, 11 Prairie Rattlesnakes Crotalus viridis viridis which were classified as large neonates based on measures of snout-vent length （SVL） and body mass, yet chronologically were at or near adulthood, were tested for their responsiveness to chemical extracts of natural and non-natural prey items. Although the snakes had eaten only neonate lab mice （Mus musculus）, they responded significantly more to chemical cues of natural prey items and particularly to chemical cues of prey normally taken by subadults （Peromyscus mice and Sceloporus lizard）. These results suggest that ontogenetic shifts in re- sponsiveness to natural prey chemical cues are innately programmed and are not based on body size or feeding experience in C. v. viridis. This does not imply, however, that growth and experience are without effects, especially with novel prey or rare prey that have experienced recent population expansion [Current Zoology 59 （2）： 175-179, 2013].

Male pheromones and their reception by females are co-adapted to affect mating success in two subspecies of brown rats

Pheromonal communication plays a key role in the sociosexual behavior of rodents.The coadaptation between pheromones and chemosensory systems has been well illustrated in insects but poorly investigated in rodents and other mammals.We aimed to investigate whether coadaptation between male pheromones and female reception might have occurred in brown rats Rattus norve-gicus.We recently reported that major urinary protein(MUP)pheromones are associated with male mating success in a brown rat subspecies,R.n.humiliatus(Rnh).Here,we discovered that MUPs were less polymorphic and occurred at much lower concentrations in males of a parapatric subspecies,R.n.caraco(Rnc),than in Rnh males,and found no association between pheromones and paternity success.Moreover,the observation of Rnc males that experienced chronic dyadic encounters and established dominance-submission relationships revealed that the dominant males achieved greater mating success than the subordinate males,but their MUP levels did not differ by social status.These findings suggest that male mating success in Rnc rats is related to social rank rather than to pheromone levels and that low concentration of MUPs might not be a reliable signal for mate choice in Rnc rats,which is different from the findings obtained in Rnh rats.In addition,compared with Rnh females,Rnc females exhibited reduced expression of pheromone receptor genes,and a lower number of vomeronasal receptor neurons were activated by MUP pheromones,which imply that the female chemosensory reception of pheromones might be structurally and functionally coadapted with male pheromone signals in brown rats.