Approach/Avoidance Behavior to Novel Objects is Correlated with the Serotonergic and Dopaminergic Systems in the Brown Rat (Rattus norvegicus)

The brown rat (Rattus norvegicus) is known to show three types of behavioral responses to novel objects. Whereas some rats are indifferent to novel objects, neophobic and neophilic rats show avoidance and approach behavior, respectively. Here, we compared the dopaminergic, serotonergic, and noradrenergic systems immunohistochemically among these rats. Trapped wild rats and laboratory rats were first individually exposed to the novel objects in their home cage. Wild rats were divided into neophobic and indifferent rats depending on their behavioral responses. Similarly, laboratory rats were divided into neophilic and indifferent rats. Consistent with the behavioral differences, in the paraventricular nucleus of the hypothalamus, Fos expression in corticotropin-releasing hormone-containing neurons was higher in the neophobic rats than in the indifferent rats. In the anterior basal amygdala, the neophobic rats showed higher Fos expression than the indifferent rats. In the posterior basal amygdala, the neophobic and neophilic rats showed lower and higher Fos expressions than the indifferent rats, respectively. When we compared the neuromodulatory systems, in the dorsal raphe, the number of serotonergic neurons and Fos expression in serotonergic neurons increased linearly from neophobic to indifferent to neophilic rats. In the ventral tegmental area, Fos expression in dopaminergic neurons was higher in the neophilic rats than in the indifferent rats. These results demonstrate that approach/avoidance behavior to novel objects is correlated with the serotonergic and dopaminergic systems in the brown rat. We propose that the serotonergic system suppresses avoidance behavior while the dopaminergic system enhances approach behavior to novel objects.

Naloxone increases conditioned fear responses during social buffering in male rats

Social buffering is the phenomenon in which the presence of an affiliative conspecific mitigates stress responses. We previously demonstrated that social buffering completely ameliorates conditioned fear responses in rats. However, the neuromodulators involved in social buffering are poorly understood. Given that opioids, dopamine, oxytocin and vasopressin play an important role in affiliative behaviour, here, we assessed the effects of the most well-known antagonists, naloxone (opioid receptor antagonist), haloperidol (dopamine D2 receptor antagonist), atosiban (oxytocin receptor antagonist) and SR49059 (vasopressin V1a receptor antagonist), on social buffering. In Experiment 1, fear-conditioned male subjects were intraperitoneally administered one of the four antagonists 25 min prior to exposure to a conditioned stimulus with an unfamiliar non-conditioned rat. Naloxone, but not the other three antagonists, increased freezing and decreased walking and investigation as compared with saline administration. In Experiment 2, identical naloxone administration did not affect locomotor activity, anxiety-like behaviour or freezing in an open-field test. In Experiment 3, after confirming that the same naloxone administration again increased conditioned fear responses, as done in Experiment 1, we measured Fos expression in 16 brain regions. Compared with saline, naloxone increased Fos expression in the paraventricular nucleus of the hypothalamus and decreased Fos expression in the nucleus accumbens shell, anterior cingulate cortex and insular cortex and tended to decrease Fos expression in the nucleus accumbens core. Based on these results, we suggest that naloxone blocks social buffering of conditioned fear responses in male rats.

Mass, Spectroscopy, and Two-Neutron Decay of ^{16}Be

The structure and decay of the most neutron-rich beryllium isotope, ^{16}Be, has been investigated following proton knockout from a high-energy ^{17}B beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground (J^{π}=0^{+}) and first excited (2^{+}) state, with E_{x}=1.31(6)  MeV. The mass excess of ^{16}Be was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^{+} level presents a far more diffuse neutron-neutron distribution.

An appeasing pheromone ameliorates fear responses in the brown rat (Rattus norvegicus)

The brown rat (Rattus norvegicus) is one of the major animals both in the laboratory and in urban centers. Brown rats communicate various types of information using pheromones, the chemicals that mediate intra-species communication in minute amounts. Therefore, analyses of pheromones would further our understanding of the mode of life of rats. We show that a minute amount of 2-methylbutyric acid (2-MB) released from the neck region can ameliorate fear responses both in laboratory rats and in wild brown rats. Based on these findings, we conclude that 2-MB is an appeasing pheromone in the brown rat. A better understanding of rats themselves would allow us to perform more effective ecologically based research on social skills and pest management campaigns with low animal welfare impacts, which might contribute to furthering the advancement of science and improving public health.

Glutamatergic Projections from the Posterior Complex of the Anterior Olfactory Nucleus to the Amygdala Complexes

Social buffering is a phenomenon where stress responses are ameliorated by an affiliative conspecific. Our previous findings suggest that the posterior complex of the anterior olfactory nucleus (AOP) is well positioned to participate in the neural mechanisms underlying social buffering. However, the lack of anatomical information prevents us from further estimating the role of the AOP. Here, we obtained anatomical information regarding the AOP in male rats. In Experiment 1 (n = 5), among 4',6-diamidino-2-phenylindole-positive cells in the AOP, the proportion of glutamic acid decarboxylase 67 (GAD67)-positive cells was 13.8% ± 1.2%. In Experiment 2 (n = 5), among the cells that were labeled by a retrograde tracer injected into the basolateral complex of the amygdala (BLA), the proportion of GAD67-positive cells was 18.6% ± 0.8%. In Experiment 3 (n = 5), we demonstrated the existence of cells that were labeled by the retrograde tracer injected into the posterior part of the medial amygdala (MeP), mostly into the ventral part of the MeP. In addition, the proportion of GAD67-positive cells among the tracer-labeled cells was 21.7% ± 1.7%. In Experiment 4 (n = 3), the retrograde tracers were injected into the BLA and MeP, mostly into the ventral part of the MeP. The proportion of double-labeled cells among the tracer-labeled cells was 2.1% ± 1.2%. Taken together, these results suggest that the AOP is predominantly composed of glutamatergic neurons. In addition, the AOP sends mutually independent glutamatergic-predominant projections to the BLA and MeP.

Parallel Olfactory Systems Synergistically Activate the Posteroventral Part of the Medial Amygdala Upon Alarm Pheromone Detection in Rats

In rats, a mixture of hexanal and 4-methylpentanal is a main component of the alarm pheromone. When detected by the main olfactory system (MOS) and the vomeronasal system, respectively, they activate the anterior part of the bed nucleus of the stria terminalis (BNSTa). Therefore, the information from the two olfactory systems is expected to be integrated before being transmitted to the BNSTa. To specify the integration site, we examined Fos expression in 16 brain regions in response to water (n = 10), hexanal (n = 9), 4-methylpentanal (n = 9), the mixture (n = 9), or the alarm pheromone (n = 9) in male rats. The posteroventral part of the medial amygdala showed increased Fos expression to hexanal and 4-methylpentanal. The expression was further increased by the mixture. Therefore, this region is suggested as the integration site. In addition, the BNSTa, paraventricular nucleus of the hypothalamus, and anteroventral, anterodorsal, and posterodorsal parts of the medial amygdala were suggested to be located downstream of the integrated site because only the mixture increased Fos expression. We suggest that the posterolateral part of the cortical amygdala is upstream of the integration site in the MOS because all stimuli increased Fos expression. The posterior part of the bed nucleus of the stria terminalis and posteromedial part of the cortical amygdala were suggested as being located upstream in the vomeronasal system because 4-methylpentanal and the mixture increased Fos expression. These results provide information about the neural pathway underlying the alarm pheromone effects.

Why are predator cues in the field not more evocative? A ‘real world’ assay elicits subtle, but meaningful, responses by wild rodents to predator scents

Mismatches between highly-standardized laboratory predatory assays and more realistic environmental conditions may lead to different outcomes. Understanding rodents’ natural responses to predator scents is important. Thus, field studies on the same and related species are essential to corroborate laboratory findings to better understand the contexts and motivational drives that affect laboratory responses to predator scents. However, there are too few field assays to enable researchers to study factors that influence these responses in genetically variable populations of wild rodents. Therefore, we placed laboratory-style chambers and remote-sensing devices near multiple colonies of two species of wild mice (Apodemus agrarius and Apodemus flavicollis) to test dual-motivational drives (appetitive and aversive) in a ‘familiar’, yet natural environment. A highly-palatable food reward was offered daily alongside scents from coyotes, lions, rabbits, and both wet and dry controls. In all but two instances (n = 264), animals entered chambers and remained inside for several minutes. Animals initiated flight twice, but they never froze. Rather, they visited chambers more often and stayed inside longer when predatory scents were deployed. The total time spent inside was highest for lion urine (380% longer than the dry control), followed by coyote scent (75% longer), dry control and lastly, herbivore scents (no difference). Once inside the chamber, animals spent more time physically interacting with predatory scents than the herbivore scent or controls. Our findings support the common assumption that rodents fail to respond as overtly to predatory scents in the field compared to what has been observed in the laboratory, possibly due to their varying motivational levels to obtain food. More time spent interacting with scents in the field was likely a function of ‘predator inspection’ (risk assessment) once subjects were in a presumed safe enclosure. We conclude this sort of chamber assay can be useful in understanding the contexts and motivational drives inherent to field studies, and may help interpret laboratory results. Our results also suggest more attention should be given to subtle behaviors such as scent inspection in order to better understand how, and when, environmental stimuli evoke fear in rodents.

The strain of unfamiliar conspecifics affects stress identification in rats

Humans show distinct social behaviours when we evaluate an individual as being a member of the same group and recognize social similarity to the individual. One example is more accurate identification of emotion in that individual. Our previous studies proposed that rats recognize social similarity to certain strains of unfamiliar rats. It is therefore possible that the strain of unfamiliar conspecifics affects stress identification in rats. Wistar subject rats were allowed to explore a pair of unfamiliar Wistar, Sprague-Dawley (SD), Long-Evans (LE), or Fischer344 (F344) stimulus rats. To induce differences in stress, one of the stimulus rats had received foot shocks immediately before the test. It was found that the subjects showed biased interaction towards the shocked Wistar and SD stimulus rats, but not toward the shocked LE or F344 stimulus rats. Subsequent experiments confirmed that the biased interaction towards the shocked Wistar and SD stimulus rats was driven by stress in these stimulus rats. In addition, the lack of biased interaction towards the shocked LE and F344 stimulus rats did not appear to be due to procedural reasons. The experiment using LE subject rats further confirmed that the shocked LE stimulus rats emitted distress signals. These results suggested that Wistar rats could identify stress in unfamiliar Wistar and SD rats, but not in unfamiliar LE or F344 rats. Therefore, rats appear to recognize social similarity to certain unfamiliar strains of rats.

Mapping of c-Fos expression in the medial amygdala following social buffering in male rats

Social buffering is the phenomenon in which an affiliative conspecific (associate) ameliorates stress responses of a subject. We previously found that social buffering in Wistar subject rats is induced if the strain of the associate is Wistar or a strain derived from Wistar rats. In the present study, we assessed the possible role of medial amygdala (Me) in this strain-dependent induction of social buffering. The subjects were exposed to the conditioned stimulus (CS) that had been paired or unpaired with a foot shock either alone, with an unfamiliar Wistar associate, or with an unfamiliar Fischer 344 (F344) associate. We found that the Wistar associates, but not F344 associates, ameliorated increased freezing and Fos expression in the paraventricular nucleus of the hypothalamus and lateral amygdala caused by the CS. In addition, Fos expression in the posterior complex of the anterior olfactory nucleus and lateral intercalated cell mass of the amygdala was increased simultaneously. These results suggest that Wistar associates, but not F344 associates, induced social buffering. In the Me, we did not find any differences associated with stress responses or amelioration of stress responses. In contrast, a comparison among the unpaired subjects found that the Wistar associates, but not F344 associates, increased exploratory behavior and Fos expression in the posteroventral subdivision of the Me (MePV). Based on these results, we propose that the MePV is involved in the recognition of social similarity with the associates. Taken together, the present study provides information about the possible role of Me in social buffering.

Rats and the COVID-19 pandemic: considering the influence of social distancing on a global commensal pest

Rats contaminate foods and spread pathogens. Thus, changes in rat populations have consequences for society, especially in densely-populated cities. Following widespread social distancing and lockdown measures to curtail SARS-CoV-2, worldwide media outlets reported increased sightings of rats. To document possible changes in rat populations, we: (i) examined public service requests in the 6 years before, and during, ‘lockdown’ in New York City; (ii) used spatial analyses to identify calls in proximity to food service establishments (FSE); and (iii) surveyed pest-management companies. Over 6 years prior to the pandemic, we found a consistent moderate spatial association (r = 0.35) between FSE and rat-related calls. During the early stages of the pandemic, the association between rat reports and food services did not decrease as would be expected by restaurant closures, but instead modestly increased (r = 0.45). There was a 29.5% decrease in rat reports, overall. However, hotspot analysis showed that new reports were highly localized, yet absent in several industrial areas they were previously observed in, potentially masking a higher proportion of calls in neighborhoods near closed restaurants. Additionally, 37% of pest management companies surveyed reported that, unlike previous years, 50–100% of requests were from new clients and addresses. The finding that hotspots remained nearby dense clusters of restaurants does not support the common narrative that rats moved long distances. Rather, our results are consistent with rats finding nearby alternative food resources. Tracking these dynamics as the COVID-19 pandemic abates will be an important step to identifying how rats respond to society returning to normal activity patterns.

Social distancing measures differentially affected rats in North America and Tokyo

Because rats are commensal organisms that depend on human activities for food, shifts in human behavior will have pronounced effects on local rat populations. In the spring of 2020, social distancing measures were implemented globally to curtail the spread of SARS-CoV-2. This presented a unique opportunity to obtain information regarding the immediate effects of shifts in human behavior on rat populations in a variety of countries. In response to increased sightings of rats in the USA that were reported in American media, we analyzed the changes in the number of public service calls in Tokyo, Japan. We found that the number of calls increased after the implementation of social distancing measures, suggesting that rat sightings had also increased in Tokyo. We then surveyed the changes in the business activities of pest management professionals in the USA, Canada, and Tokyo. We found that the activities were increased in 50 to 60% of the respondents from the USA and Canada. In contrast, 60 to 70% of the respondents from Tokyo answered that their activities were not changed. These results implied that, following the implementation of social distancing measures, rat infestations increased in North America, but not in Tokyo. The survey also suggested that roof rats were considered to be the predominant rodent species in Tokyo. This may account for the limited infestations in Tokyo because roof rats are more sedentary than brown rats. Taken together, our findings suggest that social distancing measures differentially affected rat populations in North America and Tokyo.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10340-021-01405-z.

Rats do not consider all unfamiliar strains to be equivalent

Humans show distinct social behaviours when we recognise social similarity in opponents that are members of the same social group. However, little attention has been paid to the role of social similarity in non-human animals. In the Wistar subject rats, the presence of an unfamiliar Wistar rat mitigated stress responses, suggesting the importance of social similarity in this stress-buffering phenomenon. We subsequently found that the presence of unfamiliar Sprague-Dawley (SD) or Long-Evans (LE) rats, but not an unfamiliar Fischer 344 (F344) rat, similarly mitigated stress responses in the subject rats. It is therefore possible that the subject rats recognised social similarity to unfamiliar SD and LE rats. In this study, we demonstrated that the Wistar subject rats were capable of categorizing unfamiliar rats based on their strain, and that the Wistar subjects showed a preference for unfamiliar Wistar, SD, and LE rats over F344 rats. However, the subject rats did not show a preference among Wistar, SD, and LE rats. In addition, the results were not due to an aversion to F344 rats, and preference was not affected when anaesthetised rats were presented to the subject rats. The findings suggested that rats recognise social similarity to certain unfamiliar strains of rats.

Quasifree Neutron Knockout Reaction Reveals a Small s-Orbital Component in the Borromean Nucleus ^{17}B

A kinematically complete quasifree (p,pn) experiment in inverse kinematics was performed to study the structure of the Borromean nucleus ^{17}B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 1s_{1/2} and 0d_{5/2} orbitals, and a surprisingly small percentage of 9(2)% was determined for 1s_{1/2}. Our finding of such a small 1s_{1/2} component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in ^{17}B. The present work gives the smallest s- or p-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of s or p orbitals is not a prerequisite for the occurrence of a neutron halo.

Surface Localization of the Dineutron in ^{11}Li

The formation of a dineutron in the ^{11}Li nucleus is found to be localized to the surface region. The experiment measured the intrinsic momentum of the struck neutron in ^{11}Li via the (p,pn) knockout reaction at 246  MeV/nucleon. The correlation angle between the two neutrons is, for the first time, measured as a function of the intrinsic neutron momentum. A comparison with reaction calculations reveals the localization of the dineutron at r∼3.6  fm. The results also support the density dependence of dineutron formation as deduced from Hartree-Fock-Bogoliubov calculations for nuclear matter.

Existence of wild brown rats (Rattus norvegicus) that are indifferent to novel objects

Exposure to novel objects typically evokes avoidance behavior in wild animals, which is called neophobia. We previously found that wild brown rats (Rattus norvegicus) that were trapped in a park in downtown Tokyo, Japan, exhibited neophobia. We also found that this behavior was accompanied by the activation of the basolateral complex of the amygdala (BLA). Previous studies have suggested that genetic factors are the primary determinants of neophobia. Since rats in cities form populations with distinct genetic characteristics, it is reasonable to assume that wild rats caught at different locations in urban centers will exhibit different levels of neophobia. Here we assessed the intensity of neophobia in wild rats trapped at a wholesale market in Tokyo. Although we performed exactly the same experiment in which neophobia was observed in wild rats trapped at the park, the presence of novel objects did not affect the behaviors of wild rats trapped at the market. Conversely, laboratory rats showed approach and exploratory behaviors as seen in the previous study, suggesting that the experiment was performed appropriately. Compared to the laboratory rats, the lack of behavioral changes in the wild rats was accompanied by fewer Fos immunoreactive cells in the BLA. In addition, the numbers of Fos immunoreactive cells in the bed nucleus of the stria terminalis and ventromedial hypothalamus were similar between the two types of rats. The results demonstrated the existence of wild rats that were indifferent to novel objects.

Mapping of a New Deformation Region around ^{62}Ti

We performed the first direct mass measurements of neutron-rich scandium, titanium, and vanadium isotopes around the neutron number 40 at the RIKEN RI Beam Factory using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ^{58-60}Sc, ^{60-62}Ti, and ^{62-64}V were measured for the first time. The experimental results show that the two-neutron separation energies in the vicinity of ^{62}Ti increase compared to neighboring nuclei. This shows that the masses of Ti isotopes near N=40 are affected by the Jahn-Teller effect. Therefore, a development of Jahn-Teller stabilization appears below the Cr isotopes, and the systematics in Sc, Ti, and V isotopes suggest that ^{62}Ti is located close to the peak of the Jahn-Teller effect.

Social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats

The presence of an affiliative conspecific reduces stress responses to a wide variety of stimuli, which is termed "social buffering." We previously reported that social buffering in male rats ameliorated behavioral responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). In addition, subjects that experienced social buffering did not show stress responses when re-exposed to the CS the next day in the absence of an accompanying rat. However, the mechanisms underlying this enhancement of between-session extinction are poorly understood. In Experiment 1, we compared corticosterone levels at 0, 10, and 15 min after extinction training. Subjects that experienced social buffering had lower corticosterone levels than subjects that trained alone at the end of extinction training. However, corticosterone levels at 10 and 15 min after training were not affected by the experience of social buffering. These results suggest that a lower level of corticosterone during extinction training had an important role in the enhancement of extinction. To directly assess this, in Experiment 2, we manipulated the corticosterone level during extinction training. We found that a subcutaneous injection of corticosterone before extinction training blocked the enhancement of extinction by social buffering. These results demonstrate that the enhancement is caused by a low level of corticosterone during the training. Taken together, we suggest that social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats.

Prevalence of 17 feline behavioral problems and relevant factors of each behavior in Japan

Undesirable behaviors exhibited by cats are regarded as feline behavioral problems. Like canine behavioral problems, feline behavioral problems are commonly reported by owners. Thus, in order to advise cat owners appropriately, veterinarians, particularly general veterinary practitioners, are encouraged to have sufficient knowledge of these problems. However, in ordinary Japanese homes, only a small number of feline behavioral problems have been investigated in terms of prevalence and relevant factors. Comprehensive survey data may improve understanding of feline behavioral problems. In the present study, we distributed an online survey including general information and questions about 17 feline behaviors which can be problematic for owners, to investigate: (1) the prevalence of feline behavioral problems, (2) the most common behavioral problems, and (3) relevant factors for each behavior. We collected 1,376 valid responses. Among all cats, 75.7% exhibited at least one behavioral problem. “Pica” and “Showing fear while on the examination table” were the most frequently reported behavioral problems. To identify factors related to the expression of each behavior, we conducted multiple logistic regression analyses, with the presence of behaviors as objective variables and cats’ general information as explanatory variables. Age, sex, breed, number of cats in the household, and type of residence were each associated with more than one behavior. The present study revealed the prevalence of 17 feline behavioral problems in Japanese homes and relevant factors of each behavior. These findings will help veterinarians understand and address feline behavioral problems.

Novel objects elicit greater activation in the basolateral complex of the amygdala of wild rats compared with laboratory rats

Wild animals tend to avoid novel objects that do not elicit clear avoidance behaviors in domesticated animals. We previously found that the basolateral complex of the amygdala (BLA) and dorsal bed nucleus of the stria terminalis (dBNST) were larger in trapped wild rats compared with laboratory rats. Based on these findings, we hypothesized that the BLA and/or dBNST would be differentially activated when wild and laboratory rats showed different avoidance behaviors towards novel objects. In this study, we placed novel objects at one end of the home cage. We measured the time spent in that half of the cage and expressed the data as a percentage of the time spent in that region with no object placement. We found that this percentage was lower in the wild rats compared with the laboratory rats. These behavioral differences were accompanied by increased Fos expression in the BLA, but not in the dBNST, of the wild rats. These results suggest that wild rats show greater BLA activation compared with laboratory rats in response to novel objects. We also found increased Fos expression in the paraventricular nucleus of the hypothalamus, ventral BNST, and ventromedial hypothalamus, but not in the central amygdala of wild rats. Taken together, our data represent new information regarding differences in behavioral and neural responses towards novel objects in wild vs. laboratory rats.

The lateral intercalated cell mass of the amygdala is activated during social buffering of conditioned fear responses in male rats

The presence of an affiliative conspecific reduces stress responses to a wide variety of stimuli. This phenomenon is termed "social buffering". We previously found that the presence of another Wistar rat (associate) suppressed activation of the lateral amygdala (LA) and ameliorated stress responses to an auditory conditioned stimulus (CS) in a fear-conditioned Wistar subject rat. Subsequent analyses suggested that activation of the posterior complex of the anterior olfactory nucleus (AOP) is responsible for the suppression of the LA. However, it remains unclear how the AOP suppresses the LA. To clarify this issue, a fear-conditioned Wistar subject was exposed to the CS either alone or with a Wistar associate. We also prepared a fear-conditioned Wistar subject that was tested with a Fischer344 (F344) associate as an additional control because F344 associates do not induce social buffering. We found that the presence of a Wistar associate induced a reduction of behavioral responses and Fos expression in the paraventricular nucleus of the hypothalamus (PVN) of the subject. Although Fos expression in the AOP was increased, the expression was not biased towards the GABAergic cells. In addition, Fos expression in the lateral intercalated cell mass of the amygdala (lITC) was increased. In contrast, the presence of a F344 associate did not affect Fos expression in subjects' PVN or lITC, whereas behavioral responses were slightly reduced. These results suggest that the lITC was activated during social buffering. Based on these findings, we propose that the AOP indirectly suppresses the LA by activating the lITC.

Prevalence of 25 canine behavioral problems and relevant factors of each behavior in Japan

Undesirable behaviors exhibited by dogs are called canine behavioral problems. Behavioral problems are common among dogs kept in ordinary homes; hence, veterinarians need to have sufficient knowledge of these problems, so as to advise owners. Among dogs kept in ordinary Japanese homes, only a few behaviors have been investigated regarding prevalence and relevant factors. To improve understanding of behavioral problems, a comprehensive survey is crucial. In this study, we distributed an online survey including general information and questions about 25 canine behaviors that can become problematic to owners, to investigate (1) the prevalence of behavioral problem, (2) the most common behavioral problems, and (3) the relevant factors of each behavior. We collected 2,050 valid responses. Among all dogs, 86.0% exhibited at least one behavioral problem. “Barking at noises inside the house”, “Barking at unfamiliar visitors”, and “Pica” were the most frequent behavioral problems. To reveal those factors related to the expression of each behavior, we performed multiple logistic regression analyses, with the presence of behaviors as objective variables and dogs’ general information as explanatory variables. Breed, age, the presence of other dogs in the household, sex, neutering status, source of acquisition, and type of residence were associated with 19, 16, 5, 4, 4, 4, and 1 behaviors, respectively. This study revealed the prevalence of 25 canine behavioral problems in Japan and relevant factors of each behavior. Our findings will be useful for veterinarians in advising owners about preventing behavioral problems.

A dyad shows mutual changes during social buffering of conditioned fear responses in male rats

The presence of an affiliative conspecific reduces stress responses to a wide variety of stimuli. This phenomenon is termed "social buffering". We previously found that the presence of another naïve rat (associate) reduced conditioned fear responses to an auditory conditioned stimulus in a conditioned subject rat. Although we subsequently conducted a series of studies to examine behavioral, physiological, and neural changes during social buffering in the conditioned subject, the changes in the associate remained unclear. Therefore, in the present study, we investigated the behavioral and neural changes in the associate. Fear-conditioned and non-conditioned rats were re-exposed to the conditioned stimulus with an associate placed in the same enclosure (Experiment 1) or separated by a wire-mesh partition (Experiment 2). In Experiment 1, the associate exhibited increased anogenital contact and allo-grooming, which were accompanied by increased c-Fos expression in the paraventricular nucleus of the hypothalamus and central amygdala. These results suggest that the subject and associate mutually affected each other during social buffering. In contrast, in Experiment 2, we found only a difference in the time course of investigation between associates tested with the conditioned and non-conditioned subjects. These results suggest that the associate was unable to acquire a sufficient amount of signal from the conditioned subject behind the wire-mesh partition necessary to show clear changes in behavior and c-Fos expression. Taken together, the current findings suggest that a dyad shows mutual changes during social buffering of conditioned fear responses in male rats.

Magic Nature of Neutrons in ^{54}Ca: First Mass Measurements of ^{55-57}Ca

We perform the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number 34 at the RIKEN Radioactive Isotope Beam Factory by using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ^{55-57}Ca are determined for the first time to be -18650(160), -13510(250), and -7370(990)  keV, respectively. We examine the emergence of neutron magicity at N=34 based on the new atomic masses. The new masses provide experimental evidence for the appearance of a sizable energy gap between the neutron 2p_{1/2} and 1f_{5/2} orbitals in ^{54}Ca, comparable to the gap between the neutron 2p_{3/2} and 2p_{1/2} orbitals in ^{52}Ca. For the ^{56}Ca nucleus, an open-shell property in neutrons is suggested.

Structural differences in the brain between wild and laboratory rats (Rattus norvegicus): Potential contribution to wariness

Wild animals typically exhibit defensive behaviors in response to a wider range and/or a weaker intensity of stimuli compared with domestic animals. However, little is known about the neural mechanisms underlying "wariness" in wild animals. Wild rats are one of the most accessible wild animals for experimental research. Laboratory rats are a domesticated form of wild rat, belonging to the same species, and are therefore considered suitable control animals for wild rats. Based on these factors, we analyzed structural differences in the brain between wild and laboratory rats to elucidate the neural mechanisms underlying wariness. We examined wild rats trapped in Tokyo, and weight-matched laboratory rats. We then prepared brain sections and compared the basolateral complex of the amygdala (BLA), the bed nucleus of the stria terminalis (BNST), the main olfactory bulb and the accessory olfactory bulb. The results revealed that wild rats exhibited larger BLA, BNST and caudal part of the accessory olfactory bulb compared with laboratory rats. These results suggest that the BLA, BNST, and vomeronasal system potentially contribute to wariness in wild rats.

Comparative studies of social buffering: A consideration of approaches, terminology, and pitfalls

KIYOKAWA, Y. and HENNESSY, M.B. Comparative studies of social buffering: A consideration of approaches, terminology, and pitfalls…NEUROSCI BIOBEHAV REV XXX-XXX, .- Over the past decades, there has been an increasing number of investigations of the impact of social variables on neural, endocrine, and immune outcomes. Among these are studies of "social buffering"-or the phenomenon by which affiliative social partners mitigate the response to stressors. Yet, as social buffering studies have become more commonplace, the variety of approaches taken, definitions employed, and divergent results obtained in different species can lead to confusion and miscommunication. The aim of the present paper, therefore, is to address terminology and approaches and to highlight potential pitfalls to the study of social buffering across nonhuman species. We review and categorize variables currently being employed in social buffering studies and provide an overview of responses measured, mediating sensory modalities and underlying mechanisms. It is our hope that the paper will be useful to those contemplating examination of social buffering in the context of their own research.

Two strains of roof rats as effective models for assessing new-object reaction

Wild animals generally avoid even small and harmless novel objects and/or familiar objects moved to a novel position, which is termed “new-object reaction”. Although new-object reaction appears to be a biologically important characteristic for animals, little progress has been made in understanding the neural mechanisms underlying new-object reaction. One reason might be the lack of effective experimental animals. Two strains of roof rats (Sj and Og strains) were established from wild roof rats caught in Shinjuku, Tokyo and one of the Ogasawara Islands, respectively, by a Japanese pest control company. Based on the rat caregivers’ informal observations, we conducted behavioral and anatomical tests to assess the validity of Sj and Og strains for the analyses of new-object reaction. In Experiment 1, the Sj strain showed reduced food consumption compared with the Og strain when food was provided in a novel way, suggesting that the Sj strain had a stronger avoidance of novel objects compared with the Og strain. Experiment 2 demonstrated that the basolateral complex of the amygdala and bed nucleus of the stria terminalis in experimental Sj rats had a larger percentage area compared with that of experimental Og rats, indicating these nuclei might be involved in the difference observed in avoidance of novel objects between the strains. Taken together, the present study suggests that Sj and Og strains are effective experimental animals for assessing new-object reaction.

Social Odors: Alarm Pheromones and Social Buffering

In this chapter, I describe 2 types of olfactory communication in rats, which appear to arouse anxiety and relief, respectively. In alarm pheromonal communication, rats release 4-methylpentanal and hexanal from their perianal region when they are stressed. These molecules activate the anxiety circuit, including the bed nucleus of the stria terminalis, when 4-methylpentanal and hexanal are simultaneously detected by the vomeronasal system and the main olfactory system, respectively. Consequently, recipient rats show a variety of anxiety responses, depending on the threatening stimuli. In appeasing olfactory communication, non-stressed rats release an appeasing olfactory signal, which is detected by the main olfactory system of other rats. When detected, this olfactory signal suppresses activation of the basolateral complex of the amygdala and, as a result, ameliorates stress responses elicited by an auditory conditioned stimulus during social buffering phenomenon. Because social buffering appears to be based on affinity and attachment to accompanying animals, the appeasing olfactory signal may arouse relief in rats. A definition of social buffering is also proposed as we still have no set definition for the term social buffering yet.

The right central amygdala shows greater activation in response to an auditory conditioned stimulus in male rats

Pavlovian fear conditioning is an experimental procedure in which a conditioned stimulus (CS) acquires an ability to elicit fear responses. This type of conditioning depends on the basolateral complex of the amygdala (BLA) and/or central amygdala (CeA). We previously found that rats showed reduced fear responses to an auditory CS when they were subjected to a pre-training chemical lesion of the entire right amygdala as compared with the left amygdala. Based on this finding, we hypothesize that the BLA and/or CeA in the right hemisphere will be more strongly activated by an auditory CS than those in the left hemisphere. To test this hypothesis, we re-exposed fear-conditioned and non-conditioned rats to an auditory CS 1 day after fear conditioning. We assessed Fos expression in the BLA and CeA in each hemisphere. We found that fear-conditioned subjects showed fear responses, such as increased freezing and decreased walking, as well as increased Fos expression in the BLA and CeA. When we compared Fos expression between hemispheres, Fos expression in the CeA, but not the BLA, was greater in the right hemisphere compared with the left hemisphere. These results suggest that the right CeA is more strongly activated by the auditory CS.

The strain of an accompanying conspecific affects the efficacy of social buffering in male rats

Social buffering is a phenomenon in which stress in an animal is ameliorated when the subject is accompanied by a conspecific animal(s) during exposure to distressing stimuli. We previously reported that in male Wistar rats, the presence of another Wistar rat mitigates conditioned fear responses to an auditory conditioned stimulus (CS). Subsequent analyses revealed several characteristics of this social buffering of conditioned fear responses. However, information regarding the specificity of accompanying conspecifics is still limited. In the present study, we assessed whether rats of other strains could induce social buffering in Wistar rats. When a fear-conditioned Wistar subject was re-exposed to the CS alone, we observed increased freezing and decreased investigation and walking, as well as elevated corticosterone levels. The presence of a Wistar, Sprague-Dawley, or Long-Evans rat blocked these responses, suggesting that social buffering was induced by these strains of rats. In contrast, a Fischer 344 rat did not induce social buffering in the Wistar subject. We further found that an inbred Lewis rat induced social buffering whereas a Brown Norway rat, a strain that has been established independently from Wistar rats, did not. These results suggest that the difference in origin, rather than the inbred or outbred status of the associate rat, seemed to account for the lack of social buffering induced by the F344 rats. Based on these findings, we conclude that strains of an accompanying conspecific can affect the efficacy of social buffering in rats.

Social buffering ameliorates conditioned fear responses in female rats

The stress experienced by an animal is ameliorated when the animal is exposed to distressing stimuli along with a conspecific animal(s). This is known as social buffering. Previously, we found that the presence of an unfamiliar male rat induced social buffering and ameliorated conditioned fear responses of a male rat subjected to an auditory conditioned stimulus (CS). However, because our knowledge of social buffering is highly biased towards findings in male subjects, analyses using female subjects are crucial for comprehensively understanding the social buffering phenomenon. In the present studies, we assessed social buffering of conditioned fear responses in female rats. We found that the estrus cycle did not affect the intensity of the rats' fear responses to the CS or their degree of vigilance due to the presence of a conspecific animal. Based on these findings, we then assessed whether social buffering ameliorated conditioned fear responses in female rats without taking into account their estrus cycles. When fear conditioned female rats were exposed to the CS without the presence of a conspecific, they exhibited behavioral responses, including freezing, and elevated corticosterone levels. By contrast, the presence of an unfamiliar female rat suppressed these responses. Based on these findings, we conclude that social buffering can ameliorate conditioned fear responses in female rats.

Temporary inactivation of the anterior part of the bed nucleus of the stria terminalis blocks alarm pheromone-induced defensive behavior in rats

Rats emit an alarm pheromone in threatening situations. Exposure of rats to this alarm pheromone induces defensive behaviors, such as head out behavior, and increases c-Fos expression in brain areas involved in the mediation of defensive behaviors. One of these brain areas is the anterior bed nucleus of the stria terminalis (aBNST). The goal of the present study was to investigate if pharmacological inactivation of the aBNST by local microinjections of the GABA_A receptor-agonist muscimol modulates alarm pheromone-induced defensive behaviors. We first established the behavioral paradigm of alarm pheromone-induced defensive behaviors in Sprague-Dawley rats in our laboratory. In a second experiment, we inactivated the aBNST, then exposed rats to one of four different odors (neck odor, female urine, alarm pheromone, fox urine) and tested the effects of the aBNST inactivation on the behavior in response to these odors. Our data show that temporary inactivation of the aBNST blocked head out behavior in response to the alarm pheromone. This indicates that the aBNST plays an important role in the mediation of the alarm pheromone-induced defensive behavior in rats.

Social buffering suppresses fear-associated activation of the lateral amygdala in male rats: behavioral and neurophysiological evidence

In social mammals, the presence of an affiliative conspecific reduces stress responses, a phenomenon referred to as “social buffering.”In a previous study, we found that the presence of a conspecific animal ameliorated a variety of stress responses to an aversive conditioned stimulus (CS), including freezing and Fos expression in the lateral amygdala (LA) of male rats. Although these findings suggest that the presence of a conspecific animal suppresses neural activity in the LA, direct neurophysiological evidence of suppressed activity in the LA during social buffering is still lacking. In the present study, we analyzed freezing behavior and local field potentials in the LA of fear-conditioned rats in response to the CS, in the presence or absence of a conspecific. After auditory aversive conditioning, the CS was presented to the conditioned rats in the presence or absence of a conspecific animal, on 2 successive days. The presence of a conspecific animal significantly decreased the mean peak amplitudes of auditory evoked field potentials, gamma oscillations (25–75 Hz) and high frequency oscillations (100–300 Hz) in the LA. Furthermore, magnitudes of these neural responses positively correlated with freezing duration of the fear-conditioned rats. The results provide the first electrophysiological evidence that social buffering suppresses CS-induced activation in the LA, which consequently reduces conditioned fear responses.

Neural correlates underlying naloxone-induced amelioration of sexual behavior deterioration due to an alarm pheromone

Sexual behavior is suppressed by various types of stressors. We previously demonstrated that an alarm pheromone released by stressed male Wistar rats is a stressor to other rats, increases the number of mounts needed for ejaculation, and decreases the hit rate (described as the number of intromissions/sum of the mounts and intromissions). This deterioration in sexual behavior was ameliorated by pretreatment with the opioid receptor antagonist naloxone. However, the neural mechanism underlying this remains to be elucidated. Here, we examined Fos expression in 31 brain regions of pheromone-exposed rats and naloxone-pretreated pheromone-exposed rats 60 min after 10 intromissions. As previously reported, the alarm pheromone increased the number of mounts and decreased the hit rate. In addition, Fos expression was increases in the anterior medial division (BNSTam), anterior lateral division (BNSTal) and posterior division (BNSTp) of the bed nucleus of the stria terminalis, parvocellular part of the paraventricular nucleus of the hypothalamus, arcuate nucleus, dorsolateral and ventrolateral periaqueductal gray, and nucleus paragigantocellularis (nPGi). Fos expression was decreased in the magnocellular part of the paraventricular nucleus of the hypothalamus. Pretreatment with naloxone blocked the pheromone-induced changes in Fos expression in the magnocellular part of the paraventricular nucleus of the hypothalamus, ventrolateral periaqueductal gray, and nPGi. Based on these results, we hypothesize that the alarm pheromone deteriorated sexual behavior by activating the ventrolateral periaqueductal gray-nucleus paragigantocellularis cluster and suppressing the magnocellular part of the paraventricular nucleus of the hypothalamus (PVN) via the opioidergic pathway.

Social buffering reduces male rats' behavioral and corticosterone responses to a conditioned stimulus

In social species, the presence of an affiliative same-sex conspecific ameliorates acute stress responses in threatening conditions. We previously found that the presence of an unfamiliar male rat separated by a wire mesh barrier blocks the behavioral responses and Fos expression in the paraventricular nucleus of the hypothalamus (PVN) in a male subject rat that had previously been exposed to an auditory conditioned stimulus (CS) paired with foot shocks. Based on the Fos expression in the PVN, we hypothesized that the presence of a conspecific ameliorated the hypothalamic-pituitary-adrenal (HPA) axis activation and induced social buffering of conditioned fear responses. The direct evidence for this hypothesis, however, is still lacking. To clarify this point, we exposed fear-conditioned and non-conditioned subjects to the CS either alone or with a conspecific separated by a wire mesh barrier. When the fear-conditioned subject alone was re-exposed to the CS, it exhibited increased freezing, decreased sniffing, and elevated corticosterone levels. In contrast, the presence of the conspecific suppressed these behavioral and HPA axis responses to a level similar to those observed in the non-conditioned subjects. These results suggest that the presence of a conspecific suppressed the behavioral responses and HPA axis activation to the CS. The present results provide direct evidence for the existence of social buffering of conditioned fear responses in male rats.

Physical interaction is not necessary for the induction of housing-type social buffering of conditioned hyperthermia in male rats

In social animals, housing with conspecific animals after a stressful event attenuates the subsequent adverse outcomes due to the event, and this has been called housing-type social buffering. We have previously found that housing-type social buffering attenuates the enhancement of hyperthermia and Fos expression in the paraventricular nucleus of the hypothalamus that occurs in response to an aversive conditioned stimulus in male rats. Here, we analyzed the role of physical interactions during social housing in the induction of housing-type social buffering. When a fear-conditioned subject was alone after the conditioning and then exposed to the conditioned stimulus, it showed behavioral, autonomic, and neural stress responses. However, social housing, during which physical interactions were prevented by wire mesh, attenuated these autonomic and neural stress responses, as has been seen in previous studies. These results suggested that physical interaction was not necessary for the induction of housing-type social buffering. With this social cohabitation model, we then found that social cohabitation increased Fos expression in the posterior complex of the anterior olfactory nucleus of the fear-conditioned subject. Social cohabitation also increased Fos expression in 11 brain regions, including the prefrontal cortex, the nucleus accumbens, the bed nucleus of the stria terminalis, and the medial, lateral, basal, and cortical amygdala. These results provide information about the neural mechanisms that induce housing-type social buffering.

Alarm pheromone is detected by the vomeronasal organ in male rats

It is widely known that a stressed animal releases specific pheromones, possibly for alarming nearby conspecifics. We previously investigated an alarm pheromone in male rats and found that this alarm pheromone evokes several responses, including increases in the defensive and risk assessment behaviors in a modified open-field test, and enhancement of the acoustic startle reflex. However, the role of the vomeronasal organ in these pheromone effects remains unclear. To clarify this point, vomeronasal organ-excising or sham surgeries were performed in male rats for use in 2 experimental models, after which they were exposed to alarm pheromone. We found that the vomeronasal organ-excising surgery blocked the effects of this alarm pheromone in both the modified open-field test and acoustic startle reflex test. In addition, the results of habituation/dishabituation test and soybean agglutinin binding to the accessory olfactory bulb suggested that the vomeronasal organ-excising surgery completely ablated the vomeronasal organ while preserving the functioning of the main olfactory system. From the above results, we showed that the vomeronasal organ plays an important role in alarm pheromone effects in the modified open-field test and acoustic startle reflex test.

Association of puppies' behavioral reaction at five months of age assessed by questionnaire with their later 'Distraction' at 15 months of age, an important behavioral trait for guide dog qualification

Guide dogs help visually impaired persons both physically and psychologically. More than half of all candidate dogs do not qualify, mainly for behavioral reasons. Improved training efficacy is desirable, and earlier prediction of qualification-related traits would be beneficial. In a previous study, we identified 'Distraction', assessed during the training period, as an important behavioral trait for judging the qualification of guide dogs at the Japan Guide Dog Association. As a second step, we aimed to develop an index that can predict during the puppy period. In this study, candidate guide dogs, 5-month-old Labrador retrievers, were assessed by puppy raisers using a newly developed questionnaire that consisted of 20 items. The same dogs were assessed later, at 15 months, by trainers to determine 'Distraction'. In principal components analysis, nine items, including excitability toward strangers, initiative while out for a walk, and exploration, composed the first principal component (PC1). When we compared PC1 points with 'Distraction' points, the two categories were positively correlated (n=110, r(s)=0.31, P=0.0009). Although the accuracy of the questionnaire should be increased, the results of the present study suggest that it may be possible to assess and predict 'Distraction', which is associated with disqualification for guide dogs, early in the puppy-raising period.

Risk factors for canine tail chasing behaviour in Japan

The aim of this study was to investigate the risk factors for tail chasing behaviour that occurs when a dog spins in tight circles to chase its tail, sometimes biting it. The behaviour is a sign of canine compulsive disorder (CD). A questionnaire about tail chasing behaviour and general information about the animals was used to collect data on seven breeds of pet dogs. The data were gathered at a dog event and at veterinary practices. To determine which variables were associated with tail chasing behaviour, stepwise multiple regression analyses were performed. Regardless of cohort, 'breed' and 'source of acquisition' were significantly associated with tail chasing behaviour. Using a chi-square test, the association between 'source of acquisition' and the behaviour was examined separately in two breeds (Shiba inu and Dachshund) that had the largest number of individuals chasing their tails accompanied by biting and/or growling at them. This factor showed a significant and consistent association across the two breeds. With respect to the risk factors of 'breed' and 'source of acquisition', high percentages of Shiba inu and dogs originating from pet stores were included in the group chasing their tails with biting and/or growling. The results suggest that distinct risk factors exist for tail chasing behaviour and such factors appear to be regulated by both genetics and the environment.

Pretreatment with CP-154526 blocks the modifying effects of alarm pheromone on components of sexual behavior in male, but not in female, rats

We previously demonstrated that an alarm pheromone released from male donor Wistar rats evoked several physiological and behavioral responses in recipient rats. However, the pheromone effects on social behavior were not analyzed. In the present study, we examined whether the alarm pheromone affects sexual behavior in male or female rats. When a pair of male and female subjects was exposed to the alarm pheromone during sexual behavior, the ejaculation latency was elongated, the number of mounts was increased, and the hit rate (number of intromissions/number of mounts and intromissions) was decreased in the male subject. In contrast, female sexual behavior was not affected by the alarm pheromone. When we exposed only the male or female subject of the pair to the pheromone just before sexual behavior, the results were similar: the pheromone effects were evident in male, but not in female, subjects. In addition, when we pretreated with corticotropin-releasing factor (CRF) antagonist (CP-154526) before exposing the male subject to the alarm pheromone, the pheromone effects were attenuated in a dose-dependent manner. These results indicate that the alarm pheromone modifies male, but not female, components of sexual behavior and that CRF participates in the effects.