Density-induced social stress alters oxytocin and vasopressin activities in the brain of a small rodent species

In need of a specific antibody against the oxytocin receptor for neuropsychiatric research: A KO validation study

Antibodies are one of the most utilized tools in biomedical research. However, few of them are rigorously evaluated, as there are no accepted guidelines or standardized methods for determining their validity before commercialization. Often, an antibody is considered validated if it detects a band by Western blot of the expected molecular weight and, in some cases, if blocking peptides result in loss of staining. Neither of these approaches are unquestionable proof of target specificity. Since the oxytocin receptor has recently become a popular target in neuropsychiatric research, the need for specific antibodies to be used in brain has arisen. In this work, we have tested the specificity of six commercially available oxytocin receptor antibodies, indicated by the manufacturers to be suitable for Western blot and with an available image showing the correct size band (45-55 KDa). Antibodies were first tested by Western blot in brain lysates of wild-type and oxytocin receptor knockout mice. Uterus tissue was also tested as control for putative differential tissue specificity. In brain, the six tested antibodies lacked target specificity, as both wild-type and receptor knockout samples resulted in a similar staining pattern, including the expected 45-55 KDa band. Five of the six antibodies detected a selective band in uterus (which disappeared in knockout tissue). These five specific antibodies were also tested for immunohistochemistry in uterus, where only one was specific. However, when the uterine-specific antibody was tested in brain tissue, it lacked specificity. In conclusion, none of the six tested commercial antibodies are suitable to detect oxytocin receptor in brain by either Western blot or immunohistochemistry, although some do specifically detect it in uterus. The present work highlights the need to develop standardized antibody validation methods, including a proper negative control, in order to grant quality and reproducibility of the generated data.

Long-term monitoring of cycles in Clethrionomys rutilus in the Yukon boreal forest

Baseline studies of small rodent populations in undisturbed ecosystems are rare. We report here 50 years of monitoring and experimentation in Yukon of a dominant rodent species in the North American boreal forest, the red-backed vole Clethrionomys rutilus. These voles breed in summer, weigh 20-25 g, and reach a maximum density of 20 to 25 per ha. Their populations have shown consistent 3-4-year cycles for the last 50 years with the only change being that peak densities averaged 8/ha until 2000 and 18/ha since that year. During the last 25 years, we have measured food resources, predator numbers, and winter weather, and for 1-year social interactions, to estimate their contribution to changes in the rate of summer increase and the rate of overwinter decline. All these potential limiting factors could contribute to changes in density, and we measured their relative contributions statistically with multiple regressions. The rate of winter decline in density was related to both food supply and winter severity. The rate of summer increase was related to summer berry crops and white spruce cone production. No measure of predator numbers was related to winter or summer changes in vole abundance. There was a large signal of climate change effects in these populations. There is no density dependence in summer population growth and only a weak one in winter population declines. None of our results provide a clear understanding of what generates 3-4-year cycles in these voles, and the major missing piece may be an understanding of social interactions at high density.

Ultrasound-Induced Prenatal Stress: New Possibilities for Modeling Mental Disorders

The development of animal models of mental disorders is an important task since such models are useful for studying the neurobiological mechanisms of psychopathologies and for trial of new therapeutic drugs. One way to model pathologies of the nervous system is to impair fetal neurodevelopment through stress of the pregnant future mother, or prenatal stress (PS). The use of variable frequency ultrasound (US) in rodents is a promising method of imitating psychological stress, to which women in modern society are most often subjected. The aim of our study was to investigate the effect of PS induced by exposure to variable frequency ultrasound (US PS) throughout the gestational period on the adult rat offspring, namely, to identify features of behavioral alterations and neurochemical brain parameters that can be associated with certain mental disorders in humans, to determine the possibility of creating a new model of psychopathology. Our study included a study of some behavioral characteristics of male and female rats in the elevated plus maze, open-field test, object recognition test, social interaction test, sucrose preference test, latent inhibition test, Morris water maze, forced swimming test, acoustic startle reflex, and prepulse inhibition tests. We also determined the activity of the serotonergic, dopaminergic, and noradrenergic neurotransmitter systems in the hippocampus and frontal cortex by HPLC-ED. Concentration of norepinephrine, dopamine, DOPAC, serotonin, and HIAA, as well as DOPAC/dopamine and HIAA/serotonin ratios were determined. A correlation analysis of behavioral and neurochemical parameters in male and female rats was performed based on the data obtained. The results of the study showed that US PS altered the behavioral phenotype of the rat offspring. US PS increased the level of anxious behavior, impaired orientation-research behavior, increased grooming activity, decreased the desire for social contacts, shifted behavioral reactions from social interaction to interaction with inanimate objects, impaired latent inhibition, and decreased the startle reflex. US PS activated the serotonergic, dopaminergic, and noradrenergic neurotransmitter systems of the rat frontal cortex and hippocampus. A correlation between neurochemical and behavioral parameters was revealed. Our study showed that US PS leads to a certain dysfunction on behavioral and neurochemical levels in rats that is most closely associated with symptoms of schizophrenia or autism. We hypothesize that this could potentially be an indicator of face validity for a model of psychopathology based on neurodevelopmental impairment.

Geographic Variation in Organ Size in a Toad (Duttaphrynus melanostictus)

Adaptive evolution is the process by which organisms change their morphological, physiological and biochemical characteristics to adapt to different environments during long-term natural selection. Especially, researching variation in organ size can provide important insights into morphological adaptation in amphibians. In this study, we comparatively studied differences in organ sizes (heart, lungs, liver, gallbladder, kidneys, spleen, digestive tract, testes and brain) among five geographical populations of the Asian common toad Duttaphrynus melanostictus. Our results revealed significant variations in the size of these nine specific organs among the populations. Notably, we observed a significant positive correlation between the relative size of the testes and latitude and/or altitude. However, no correlation was found between the relative size of the heart and the length of the digestive tract with altitude across populations, respectively, contradicting Hesse's rule and the digestion theory. These findings suggest that our study does not provide substantial theoretical support for the adaptive evolution of organ size in this particular toad species, but rather contributes to the understanding of the evolution and adaptations of species' different environmental conditions. Further research is warranted to delve deeper into the factors influencing organ size in amphibian populations.

Gut Microbiota is Associated with Aging-Related Processes of a Small Mammal Species under High-Density Crowding Stress

Humans and animals frequently encounter high-density crowding stress, which may accelerate their aging processes; however, the roles of gut microbiota in the regulation of aging-related processes under high-density crowding stress remain unclear. In the present study, it is found that high housing density remarkably increases the stress hormone (corticosterone), accelerates aging-related processes as indicated by telomere length (in brain and liver cells) and DNA damage or inflammation (as revealed by tumor necrosis factor-α and interleukin-10 levels), and reduces the lifespan of Brandt's vole (Lasiopodomys brandtii). Fecal microbiota transplantation from donor voles of habitats with different housing densities induces similar changes in aging-related processes in recipient voles. The elimination of high housing density or butyric acid administration delays the appearance of aging-related markers in the brain and liver cells of voles housed at high-density. This study suggests that gut microorganisms may play a significant role in regulating the density-dependent aging-related processes and subsequent population dynamics of animals, and can be used as potential targets for alleviating stress-related aging in humans exposed to high-density crowding stress.

Providing or receiving alloparental care promote partner preference and alter central oxytocin and dopamine systems in adult mandarin voles

Juveniles of cooperative breeding species usually remain in the natal area and provide care to younger siblings, a behavior considered one form of alloparenting in the natural condition. Previous studies have demonstrated the effects of providing or receiving alloparental care on adult behaviors, including anxiety-like behavior, social interaction, and parental behavior, but little is known about the influences on species-typical bonding behaviors, such as pair-bond formation. In this study, we explored this concept using socially monogamous mandarin voles (Lasiopodomys mandarinus). As the oxytocin (OT) and dopamine systems are involved in alloparental and pair-bonding behaviors, we also examined the levels of central OT and tyrosine hydroxylase (TH), as well as OT receptor (OTR) and dopamine D1-type and D2-type receptors (D1R and D2R) mRNA expression in the nucleus accumbens (NAcc) and amygdala to investigate the underlying mechanisms. Our results show that mandarin voles providing alloparental care to younger siblings displayed facilitation of partner preference formation, lower levels of OT expression in the paraventricular nucleus of the hypothalamus (PVN) and lateral hypothalamus (LH), and increased OTR and D2R mRNA expression in the NAcc compared to controls. Individuals receiving alloparental care also demonstrated facilitation of partner preference formation in adult voles. Additionally, alloparental care enhanced OT expression in the PVN, anterior medial preoptic nucleus (MPOAa), medial amygdala (MeA), and TH expression in the ventral tegmental area (VTA) and zona incerta (ZI). Furthermore, males displayed decreased D1R mRNA expression in the NAcc, whereas females showed slightly increased D2R expression in the amygdala. These results demonstrate that providing or received alloparental care can promote partner preference formation in monogamous species and that these changes are associated with altered OT and dopamine levels and their receptors in specific brain regions.

Effects of Group Size on Behavior, Reproduction, and mRNA Expression in Brains of Brandt's Voles

For social animals, a moderate group size is greatly important to maintain their reproductive success. However, the underlying neurobiological mechanism of group size on behavior and reproduction has rarely been investigated. In this study, we examined the effects of group size (1, 2, 4 pairs of adult male and female voles raised per cage) on behavior and reproduction. Meanwhile, the mRNA expression of stress and reproduction response-related genes in male brains was detected. We found that Brandt's voles (Lasiopodomys brandtii) in the large-sized group fight more severely than those in the small-sized group. Meanwhile, male voles were more anxious than females. The average number of embryos and litters per female in the medium-sized group was significantly higher than that of large-sized group. In male voles, stress- or reproduction-response mRNA expressions were more related to final group size or final density due to death caused by fighting. Our results indicated that a moderate group size was beneficial to the reproductive output of Brandt's voles. Our study highlights the combined effects of stress- or reproduction-related gene expression or behavior in regulating the fitness of voles with different group sizes.

Gut microbiota is associated with the effect of photoperiod on seasonal breeding in male Brandt's voles (Lasiopodomys brandtii)

BACKGROUND

Seasonal breeding in mammals has been widely recognized to be regulated by photoperiod, but the association of gut microbiota with photoperiodic regulation of seasonal breeding has never been investigated.

RESULTS

In this study, we investigated the association of gut microbiota with photoperiod-induced reproduction in male Brandt's voles (Lasiopodomys brandtii) through a long-day and short-day photoperiod manipulation experiment and fecal microbiota transplantation (FMT) experiment. We found photoperiod significantly altered reproductive hormone and gene expression levels, and gut microbiota of voles. Specific gut microbes were significantly associated with the reproductive hormones and genes of voles during photoperiod acclimation. Transplantation of gut microbes into recipient voles induced similar changes in three hormones (melatonin, follicle-stimulating hormone, and luteinizing hormone) and three genes (hypothalamic Kiss-1, testicular Dio3, and Dio2/Dio3 ratio) to those in long-day and short-day photoperiod donor voles and altered circadian rhythm peaks of recipient voles.

CONCLUSIONS

Our study firstly revealed the association of gut microbiota with photoperiodic regulation of seasonal breeding through the HPG axis, melatonin, and Kisspeptin/GPR54 system. Our results may have significant implications for pest control, livestock animal breeding, and human health management. Video Abstract.

Relationship between brain size and digestive tract length support the expensive-tissue hypothesis in Feirana quadranus

The brain is among the most energetically costly organs in the vertebrate body, while the size of the brain varies within species. The expensive-tissue hypothesis (ETH) predicts that increasing the size of another costly organ, such as the gut, should compensate for the cost of a small brain. Here, the ETH was tested by analyzing the relationship between brain size variation and digestive tract length in a Swelled-vented frog (Feirana quadranus). A total of 125 individuals across 10 populations ranging from 586 to 1,702 m a.s.l. from the Qinling-Daba Mountains were sampled. With the increase in altitude, the brain size decreases and the digestive tract length increases. Different brain regions do not change their relative size in a consistent manner. The sizes of telencephalon and cerebellum decrease with the increase in altitude, while the olfactory nerve increases its size at high altitudes. However, the olfactory bulb and optic tectum have no significant relationship with altitude. After controlling for snout-vent length (SVL), a significant negative correlation could be found between brain size and digestive tract length in F. quadranus. Therefore, the intraspecific variation of brain size follows the general patterns of ETH in this species. The results suggest that annual mean temperature and annual precipitation are environmental factors influencing the adaptive evolution of brain size and digestive tract length. This study also suggests that food composition, activity times, and habitat complexity are the potential reasons driving the adaptive evolution of brain size and digestive tract length.

Geographical variation of organ size in Andrew’s toad (Bufo andrewsi)

Phenotypic variation of morphological and physiological traits is assumed to be generated from spatial heterogeneity in environments, and it has been regarded as an important concern domain in evolutionary biology. Organs display markedly size variation among populations along environmental gradients and this variation is associated with changes in oxygen supply and energy demands. Here, we investigated geographical variation in the relative size of organs (i.e., brain, heart, lung, gallbladder, livers, spleen, kidneys, and digestive tract) among 14 populations of Andrew’s toad (Bufo andrewsi) transcending an elevational range from 864 to 2,367 m, and spanning 8° latitude. We found that although the relative sizes of the eight specific organs varied significantly among populations, none organ size was affected by altitude and latitude. However, based on the combined the new data and published data we found a negative relationship between the relative size of the heart and latitude, contrasting to the Hesse’s rule. We also found that the relative size of livers was positively linked to latitude, suggesting that more energy demands and intakes due to slower metabolism in high latitude shaped the evolution of larger livers.

Gut microbiota reflect the crowding stress of space shortage, physical and non-physical contact in Brandt's voles (Lasiopodomys brandtii)

Density-dependence plays a critical role in behavior and population regulation of small mammals, which is likely mediated by hormones and gut microbiota. High density-induced crowding effects often cause a combination of various social stresses including space shortage, physical contact and non-physical contact, but their distinct effects on gut microbiota in animals have not been investigated. In this study, we examined the crowding effects of space shortage and physical or non-physical contact stress on serum corticosterone and gut microbiota of Brandt's voles in both laboratory and field conditions. Our results demonstrated that the space shortage stress showed a more predominant impact on serum corticosterone and gut microbiota of voles than physical or non-physical contact stress; the crowding effects of non-physical contact stress became stronger in high density conditions, while physical contact stress was stronger in a larger group without density effects. High density or group size treatments under both laboratory and semi-natural enclosure conditions significantly increased the relative abundance of key differential taxa, including Bacteroidetes, TM7, S24_7, Streptococcus, and Lactobacillus; while high density or group size treatments decreased the relative abundance of Firmicutes, Staphylococcaceae, Bacteroides, Faecalibacterium, and Adlercreutzia. Our study suggests that high density-induced space shortage and physical contact or non-physical contact stress may play a significant role in behavior and population regulation through altering gut microbiota in small mammals. Our results may also have significant implications in rodent control or health management for livestock.

Population variation alters aggression-associated oxytocin and vasopressin expressions in brains of Brandt's voles in field conditions

Density-dependent change in aggressive behavior contributes to the population regulation of many small rodents, but the underlying neurological mechanisms have not been examined in field conditions. We hypothesized that crowding stress and aggression-associated oxytocin (OT) and arginine vasopressin (AVP) in specific regions of the brain may be closely related to aggressive behaviors and population changes of small rodents. We analyzed the association of OT and AVP expression, aggressive behavior, and population density of Brandt’s voles in 24 large semi-natural enclosures (0.48 ha each) in Inner Mongolia grassland. We tested the effects of population density on the OT/AVP system and aggressive behavior by experimentally manipulating populations of Brandt’s voles in the grassland enclosures. High density was positively and significantly associated with more aggressive behavior, and increased expression of mRNA and protein of AVP and its receptor, but decreased expression of mRNA and protein of OT and its receptor in specific brain regions of the voles. Our study suggests that changes in OT/AVP expression are likely a result of the increased psychosocial stress that these voles experience during overcrowding, and thus the OT/AVP system can be used as indicators of density-dependent stressors in Brandt’s voles.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

Evolution of stress responses refine mechanisms of social rank

Social rank functions to facilitate coping responses to socially stressful situations and conditions. The evolution of social status appears to be inseparably connected to the evolution of stress. Stress, aggression, reward, and decision-making neurocircuitries overlap and interact to produce status-linked relationships, which are common among both male and female populations. Behavioral consequences stemming from social status and rank relationships are molded by aggressive interactions, which are inherently stressful. It seems likely that the balance of regulatory elements in pro- and anti-stress neurocircuitries results in rapid but brief stress responses that are advantageous to social dominance. These systems further produce, in coordination with reward and aggression circuitries, rapid adaptive responding during opportunities that arise to acquire food, mates, perch sites, territorial space, shelter and other resources. Rapid acquisition of resources and aggressive postures produces dominant individuals, who temporarily have distinct fitness advantages. For these reasons also, change in social status can occur rapidly. Social subordination results in slower and more chronic neural and endocrine reactions, a suite of unique defensive behaviors, and an increased propensity for anxious and depressive behavior and affect. These two behavioral phenotypes are but distinct ends of a spectrum, however, they may give us insights into the troubling mechanisms underlying the myriad of stress-related disorders to which they appear to be evolutionarily linked.

Density-induced social stress alters oxytocin and vasopressin activities in the brain of a small rodent species

It is known that social stress could alter oxytocin (OT) and arginine‐vasopressin (AVP) expression in specific regions of brains which regulate the aggressive behavior of small rodents, but the effects of density‐induced social stress are still unknown. Brandt's voles (Lasiopodomys brandtii) are small herbivores in the grassland of China, but the underlying neurological mechanism of population regulation is still unknown. We tested the effects of housing density of Brandt's voles on OT/AVP system with physical contact (allowing aggression) and without physical contact (not allowing aggression) under laboratory conditions. Then, we tested the effects of paired‐aggression (no density effect) of Brandt's voles on OT/AVP system under laboratory conditions. We hypothesized that high density would increase aggression among animals which would then increase AVP but reduce OT in brains of animals. Our results showed that high housing density induced more aggressive behavior. We found high‐density‐induced social stress (with or without physical contact) and direct aggression significantly increased expression of mRNA and protein of AVP and its receptor, but decreased expression of mRNA and protein of OT and its receptor in specific brain regions of voles. The results suggest that density‐dependent change of OT/AVP systems may play a significant role in the population regulation of small rodents by altering density‐dependent aggressive behavior.