Examination of the role of adrenergic receptor stimulation in the sensitization of neuroinflammatory-based depressive-like behavior in isolated Guinea pig pups.

Early-life attachment disruption appears to sensitize neuroinflammatory signaling to increase later vulnerability for stress-related mental disorders, including depression. How stress initiates this process is unknown, but studies with adult rats and mice suggest sympathetic nervous system activation and/or cortisol elevations during the early stress are key. Guinea pig pups isolated from their mothers exhibit an initial active behavioral phase characterized by anxiety-like vocalizing. This is followed by inflammatory-dependent depressive-like behavior and fever that sensitize on repeated isolation. Using strategies that have been successful in adult studies, we assessed whether sympathetic nervous system activity and cortisol contributed to the sensitization process in guinea pig pups. In Experiment 1, the adrenergic agonist ephedrine (3 or 10 mg/kg), either alone or with cortisol (2.5 mg/kg), did not increase depressive-like behavior or fever during initial isolation the following day as might have been expected to if this stimulation was sufficient to account for the sensitization process. In Experiment 2, both depressive-like behavior and fever sensitized with repeated isolation, but beta-adrenergic receptor blockade with propranolol (10 or 20 mg/kg) did not affect either of these responses or their sensitization. The high dose of propranolol did, however, reduce vocalizing. These results suggest sympathetic nervous system activation is neither necessary nor sufficient to induce the presumptive neuroinflammatory signaling underlying sensitization of depressive-like behavioral or febrile responses in developing guinea pigs. Thus, processes mediating sensitization of neuroinflammatory-based depressive-like behavior following early-life attachment disruption in this model appear to differ from those previously found to underlie neuroinflammatory priming in adults.

Family first! Influence of parental investment in Guinea pigs (Cavia porcellus) prosocial choices.

Literature often assumed that prosocial behaviours (behaviours that benefit others with or without a cost for the actor) would have evolved many species to improve the effectiveness of parental care (Decety and Cowell 2014). While this hypothesis is rarely questioned at a phylogenetic scale, it was never tested at an individual scale to the best of our knowledge. Therefore, we chose to study the impact of effective parental care on prosociality by comparing the prosocial tendencies of Guinea pigs before mating, during mating and after parturition. We conducted Prosocial Choice Tests on three groups of Guinea pigs (males, multiparous females, and nulliparous females). Subjects had to choose between three options: a prosocial option (subject and recipient being rewarded), a selfish option (only subject was rewarded), and a null option (no reward). Our results showed high prosociality towards their mating partner and their young both in male and in female subjects. Males became selfish towards other males after parturition. Among other interesting results, we found a direct reciprocity phenomenon. We also highlighted an ability in our subjects to consider both the identity and relationship shared with the recipient, such as tolerance (enhancing prosociality), dominance rank (being tested with a dominant recipient increasing selfish responses), and its behaviour (begging calls eliciting prosociality, while threatening ones decreasing it), to choose an option. These findings suggested that prosociality could be modulated by many factors and that the constraints and stakes induced by breeding would highly influence prosocial strategies.

Hot crabs with bold choices: Temperature has little impact on behavioural repeatability in Caribbean hermit crabs.

An animal's boldness is generally considered to be influenced by genetic and developmental factors. However, abiotic factors such as temperature have profound effects on the physiology of ectothermic animals, and thus can influence the expression and measurement of this behavioural trait. We examined the relationship between temperature and behaviour in the Caribbean hermit crab (Coenobita clypeatus) using field and lab experiments. Crabs captured in the sun were bolder than crabs captured in the shade, even when measured at a common temperature, which led to bold crabs experiencing higher microhabitat temperatures. In laboratory housed conditions, crabs demonstrated highly repeatable boldness behaviours at all temperatures, and as temperature increased, the mean behavioural latencies decreased across all individuals. Bolder crabs do not seem to rely on an innately higher thermal preference, since there was no association between boldness behaviours and thermal preference in the laboratory. Instead, bolder crabs seem to exploit more open, riskier habitats than shyer crabs. Our results highlight the complex interplay between physiological and ecological factors influencing the behaviour of a widespread and ecologically important ectothermic animal.

Repetitive nociceptive stimulation elicits complex behavioral changes in Hirudo: evidence of arousal and motivational adaptations.

Appropriate responses to real or potential damaging stimuli to the body (nociception) are critical to an animal's short- and long-term survival. The initial goal of this study was to examine habituation of withdrawal reflexes (whole-body and local shortening) to repeated mechanical nociceptive stimuli (needle pokes) in the medicinal leech, Hirudo verbana, and assess whether injury altered habituation to these nociceptive stimuli. While repeated needle pokes did reduce shortening in H. verbana, a second set of behavior changes was observed. Specifically, animals began to evade subsequent stimuli by either hiding their posterior sucker underneath adjacent body segments or engaging in locomotion (crawling). Animals differed in terms of how quickly they adopted evasion behaviors during repeated stimulation, exhibiting a multi-modal distribution for early, intermediate and late evaders. Prior injury had a profound effect on this transition, decreasing the time frame in which animals began to carry out evasion and increasing the magnitude of these evasion behaviors (more locomotory evasion). The data indicate the presence in Hirudo of a complex and adaptive defensive arousal process to avoid noxious stimuli that is influenced by differences in internal states, prior experience with injury of the stimulated areas, and possibly learning-based processes.

Automatically annotated motion tracking identifies a distinct social behavioral profile following chronic social defeat stress.

Severe stress exposure increases the risk of stress-related disorders such as major depressive disorder (MDD). An essential characteristic of MDD is the impairment of social functioning and lack of social motivation. Chronic social defeat stress is an established animal model for MDD research, which induces a cascade of physiological and behavioral changes. Current markerless pose estimation tools allow for more complex and naturalistic behavioral tests. Here, we introduce the open-source tool DeepOF to investigate the individual and social behavioral profile in mice by providing supervised and unsupervised pipelines using DeepLabCut-annotated pose estimation data. Applying this tool to chronic social defeat in male mice, the DeepOF supervised and unsupervised pipelines detect a distinct stress-induced social behavioral pattern, which was particularly observed at the beginning of a novel social encounter and fades with time due to habituation. In addition, while the classical social avoidance task does identify the stress-induced social behavioral differences, both DeepOF behavioral pipelines provide a clearer and more detailed profile. Moreover, DeepOF aims to facilitate reproducibility and unification of behavioral classification by providing an open-source tool, which can advance the study of rodent individual and social behavior, thereby enabling biological insights and, for example, subsequent drug development for psychiatric disorders.

Towards experimental models of delirium utilizing zebrafish.

Delirium is an acute neuropsychiatric condition characterized by impaired behavior and cognition. Although the syndrome has been known for millennia, its CNS mechanisms and risk factors remain poorly understood. Experimental animal models, especially rodent-based, are commonly used to probe various pathogenetic aspects of delirium. Complementing rodents, the zebrafish (Danio rerio) emerges as a promising novel model organism to study delirium. Zebrafish demonstrate high genetic and physiological homology to mammals, easy maintenance, robust behaviors in various sensitive behavioral tests, and the potential to screen for pharmacological agents relevant to delirium. Here, we critically discuss recent developments in the field, and emphasize the developing utility of zebrafish models for translational studies of delirium and deliriant drugs. Overall, the zebrafish represents a valuable and promising aquatic model species whose use may help understand delirium etiology, as well as develop novel therapies for this severely debilitating disorder.

Histone acetyltransferases and external demands influence task switching in Temnothorax ants.

In social hymenopterans, workers specialize in different tasks. Whether a worker nurses the brood or forages is influenced by the responsiveness for task-related cues which in turn is determined by gene expression. Task choice is dynamic and changes throughout a worker's life, e.g. with age or in response to increased demands for certain tasks. Behavioural switches require the ability to adjust gene expression but the mechanisms regulating such transcriptional adaptations remain elusive. We investigated the role of histone acetylation in task specialization and behavioural flexibility in Temnothorax longispinosus ants. By inhibiting p300/CBP histone acetyltransferases (HAT) and manipulating colony composition, we found that HAT inhibition impairs the ability of older workers to switch to brood care. Yet, HAT inhibition increased the ability of young workers to accelerate their behavioural development and switch to foraging. Our data suggest that HAT in combination with social signals indicating task demands play an important role in modulating behaviour. Elevated HAT activity may contribute to keeping young brood carers from leaving the nest, where they would be exposed to high mortality. These findings shed light on the epigenetic processes underlying behavioural flexibility in animals and provide insight into the mechanisms of task specialization in social insects.

The role of photobehaviour in sponge larval dispersal and settlement.

Deciphering the behavioural ecology of adult (sessile) sponges is challenging. However, their motile larval stages afford opportunities to investigate how behaviour contributes to dispersal and selection of habitat. Light is a fundamental cue contributing to larval sponge dispersal where photoreceptive cells contribute to this process. But how universal is light as a cue to sponge larval dispersal and settlement? Behavioural choice experiments were used to test the effect of light on dispersal and settlement behaviours. Larvae of the tropical sponge species Coscinoderma mathewsi, Luffariella variabilis, Ircinia microconnulosa, and Haliclona sp., from deep (12-15 m) and shallower-water habitats (2-5 m), were used in experiments. Dispersal experiments provided a light-gradient-choice where light represented light attenuation with depth. Light treatments included white light and the spectral components of red and blue light. Settlement experiments comprised a choice between illuminated and shaded treatments. Fluorescence microscopy was used to establish the presence of fluorescent proteins associated with posterior locomotory cilia. Deeper-water species, C. mathewsi and I. microconnulosa discriminate light spectral signatures. Both species changed dispersal behaviour to light spectra as larvae aged. For C. mathewsi positive phototaxis to blue light changed to photophobic responses (all light treatments) after six hours and behaviours in I. microconnulosa changed from positive to negative phototaxis (white light) after six hours. L. variabilis, also a deeper-water species, was negatively phototactic to all light treatments. Larvae from the shallow-water species, Haliclona sp., moved towards all light wavelengths tested. There was no effect of light on settlement of the shallow-water Haliclona sp., but larvae in all three deeper-water species showed significantly higher settlement in shaded treatments. Fluorescence microscopy showed discrete fluorescent bands contiguous to posterior tufted cilia in all four species. These fluorescent bands may play a contributory role in larval photobehaviour.

Assessing the exploratory profile of two zebrafish populations: Influence of anxiety-like phenotypes and independent trials on homebase-related parameters and exploration.

Anxiety is a protective behavior when animals face aversive conditions. The open field test (OFT) is used to assess the spatio-temporal dynamics of exploration, in which both homebase formation and recognition of environmental cues may reflect habituation to unfamiliar conditions. Because emotional- and affective-like states influence exploration patterns and mnemonic aspects, we aimed to verify whether the exploratory behaviors of two zebrafish populations showing distinct baselines of anxiety differ in two OFT sessions. Firstly, we assessed the baseline anxiety-like responses of short fin (SF) and leopard (LEO) populations using the novel tank test (NTT) and light-dark test (LDT) in 6-min trials. Fish were later tested in two consecutive days in the OFT, where the spatial occupancy and exploratory profile were analyzed for 30 min. In general, LEO showed pronounced diving behavior and scototaxis in the NTT and LDT, respectively, in which an "anxiety index" corroborated their exacerbated anxiety-like behavior. In the OFT, the SF population spent less time to establish the homebase in the 1st trial, while only LEO showed a markedly reduction in the latency to homebase formation in the 2nd trial. Both locomotion and homebase-related activities were decreased in the 2nd trial, in which animals also revealed increased occupancy in the center area of the apparatus. Moreover, we verified a significant percentage of homebase conservation for both populations, while only SF showed reduced the number of trips and increased the average length of trips. Principal component analyses revealed that distinct factors accounted for total variances between trials for each population tested. While homebase exploration was reduced in the 2nd trial for SF, an increased occupancy in the center area and hypolocomotion were the main factors that contribute to the effects observed in LEO during re-exposure to the OFT. In conclusion, our novel data support the homebase conservation in zebrafish subjected to independent OFT sessions, as well as corroborate a population-dependent effect on specific behavioral parameters related to exploration.

Father's care uniquely influences male neurodevelopment.

Mammalian infants depend on parental care for survival, with numerous consequences for their behavioral development. We investigated the epigenetic and neurodevelopmental mechanisms mediating the impact of early biparental care on development of alloparenting behavior, or caring for offspring that are not one's own. We find that receiving high parental care early in life leads to slower epigenetic aging of both sexes and widespread male-specific differential expression of genes related to synaptic transmission and autism in the nucleus accumbens. Examination of parental care composition indicates that high-care fathers promote a male-specific increase in excitatory synapses and increases in pup retrieval behavior as juveniles. Interestingly, females raised by high-care fathers have the opposite behavioral response and display fewer pup retrievals. These results support the concept that neurodevelopmental trajectories are programmed by different features of early-life parental care and reveal that male neurodevelopmental processes are uniquely sensitive to care by fathers.

Involvement of Serotonergic Projections from the Dorsal Raphe to the Medial Preoptic Area in the Regulation of the Pup-Directed Paternal Response of Male Mandarin Voles.

Male mammals display different paternal responses to pups, either attacking or killing the young offspring, or contrastingly, caring for them. The neural circuit mechanism underlying the between-individual variation in the pup-directed responsiveness of male mammals remains unclear. Monogamous mandarin voles were used to complete the present study. The male individuals were identified as paternal and infanticidal voles, according their behavioral responses to pups. It was found that the serotonin release in the medial preoptic area (MPOA), as well as the serotonergic neuron activity, significantly increased upon licking the pups, but showed no changes after attacking the pups, as revealed by the in vivo fiber photometry of the fluorescence signal from the 5-HT 1.0 sensor and the calcium imaging indicator, respectively. It was verified that the 5-HTergic neural projections to the MPOA originated mainly from the ventral part of the dorsal raphe (vDR). Furthermore, the chemogenetic inhibition of serotonergic projections from the vDR to the MPOA decreased the paternal behaviors and shortened the latency to attack the pups. In contrast, the activation of serotonergic neurons via optogenetics extended the licking duration and inhibited infanticide. Collectively, these results elucidate that the serotonergic projections from the vDR to the MPOA, a previously unrecognized pathway, regulate the paternal responses of virgin male mandarin voles to pups.

Maternal Chronic Ultrasound Stress Provokes Immune Activation and Behavioral Deficits in the Offspring: A Mouse Model of Neurodevelopmental Pathology.

Neurodevelopmental disorders stemming from maternal immune activation can significantly affect a child's life. A major limitation in pre-clinical studies is the scarcity of valid animal models that accurately mimic these challenges. Among the available models, administration of lipopolysaccharide (LPS) to pregnant females is a widely used paradigm. Previous studies have reported that a model of 'emotional stress', involving chronic exposure of rodents to ultrasonic frequencies, induces neuroinflammation, aberrant neuroplasticity, and behavioral deficits. In this study, we explored whether this model is a suitable paradigm for maternal stress and promotes neurodevelopmental abnormalities in the offspring of stressed females. Pregnant dams were exposed to ultrasound stress for 21 days. A separate group was injected with LPS on embryonic days E11.5 and E12.5 to mimic prenatal infection. The behavior of the dams and their female offspring was assessed using the sucrose test, open field test, and elevated plus maze. Additionally, the three-chamber sociability test and Barnes maze were used in the offspring groups. ELISA and qPCR were used to examine pro-inflammatory changes in the blood and hippocampus of adult females. Ultrasound-exposed adult females developed a depressive-like syndrome, hippocampal overexpression of GSK-3ß, IL-1ß, and IL-6 and increased serum concentrations of IL-1ß, IL-6, IL-17, RANTES, and TNFα. The female offspring also displayed depressive-like behavior, as well as cognitive deficits. These abnormalities were comparable to the behavioral changes induced by LPS. The ultrasound stress model can be a promising animal paradigm of neurodevelopmental pathology associated with prenatal 'emotional stress'.

Boldness is not associated with dynamic performance capacity in hermit crabs.

Boldness, the way an individual reacts to risk, is a commonly studied personality trait in animals. Consistent among-individual differences in startle response durations (latency to recover from a startling stimulus) are frequently assumed to reflect variation in boldness. An alternative explanation is that these latencies are not directly driven by variation in responses to information on risk, but by underlying differences in dynamic performance capacities. Here we investigate this possibility by analysing relationships between locomotory speed, a measure of whole-body dynamic performance capacity in hermit crabs, and startle response duration, a repeatable latency measure used as an index of boldness. Individuals differed in mean startle response duration, in the consistency of their startle responses, in their reaction norms across repeated observations, and mean startle responses increased with crab mass. However, there were no relationships between startle responses and locomotory speed. This indicates that startle responses do not reflect underlying performance capacities and suggests that they provide insight into differences in how individuals respond to risky situations. Since similar latencies are used as measures of boldness in other animals, we suggest that potential relationships between apparent boldness and performance capacity should be tested.

Sex differences in socioemotional behavior and changes in ventral hippocampal transcription across aging in C57Bl/6J mice.

Socioemotional health is positively correlated with improved cognitive and physical aging. Despite known sex differences in socioemotional behaviors and the trajectory of aging, the interactive effects between sex and aging on socioemotional outcomes are poorly understood. We performed the most comprehensive assessment of sex differences in socioemotional behaviors in C57Bl/6J mice across aging to date. Compared to males, females exhibited decreased anxiety-like behavior and social preference but increased social recognition. With age, anxiety-like behavior, cued threat memory generalization, and social preference increased in both sexes. To investigate potential neural mechanisms underlying these behavioral changes, we analyzed transcriptional neuropathology markers in the ventral hippocampus and found age-related changes in genes related to activated microglia, angiogenesis, and cytokines. Sex differences emerged in the timing, direction, and magnitude of these changes, independent of reproductive senescence in aged females. Interestingly, female-specific upregulation of autophagy-related genes correlated with age-related behavioral changes selectively in females. These novel findings reveal critical sex differences in trajectories of ventral hippocampal aging that may contribute to sex- and age-related differences in socioemotional outcomes.

Maternal infection during pregnancy aggravates the behavioral response to an immune challenge during adolescence in female rats.

Prenatal and early postnatal infection have been associated with changes in microglial activity and the development of psychiatric disorders. Here, we investigated the effect of prenatal immune activation and postnatal immune challenge, alone and combined, on behavior and microglial cell density in female Wistar rats. Pregnant rats were injected with poly I:C to induce a maternal immune activation (MIA). Their female offspring were subsequently exposed to a lipopolysaccharide (LPS) immune challenge during adolescence. Anhedonia, social behavior, anxiety, locomotion, and working memory were measured with the sucrose preference, social interaction, open field, elevated-plus maze, and Y-maze test, respectively. Microglia cell density was quantified by counting the number of Iba-1 positive cells in the brain cortex. Female MIA offspring were more susceptible to the LPS immune challenge during adolescence than control offspring as demonstrated by a more pronounced reduction in sucrose preference and body weight on the days following the LPS immune challenge. Furthermore, only the rats exposed to both MIA and LPS showed long-lasting changes in social behavior and locomotion. Conversely, the combination MIA and LPS prevented the anxiety induced by MIA alone during adulthood. MIA, LPS, or their combination did not change microglial cell density in the parietal and frontal cortex of adult rats. The results of our study suggest that the maternal immune activation during pregnancy aggravates the response to an immune challenge during adolescence in female rats.

Does social motivation mitigate fear caused by a sudden sound in horses?

Living in a herd has multiple advantages for social species and is a primary survival strategy for prey. The presence of conspecifics, identified as a social buffer, may mitigate the individual stress response. Social isolation is, therefore, particularly stressful for horses, which are gregarious animals. However, they are not equally vulnerable to separation from the group. We tested whether more and less socially dependent horses and independent individuals would differ in their responses to novel and sudden sounds occurring in two contexts: non-social and social motivation. Twenty warmblood horses were first exposed to two social tests: to evaluate the level of social dependence (rate of restless behaviour; social isolation) and the quantity and the quality of interactions in which they were involved (stay on a paddock). Two fear audio tests were then performed to compare the responses to sudden sounds while feeding (non-social motivation; control trial) and while moving towards the herd (social motivation; experimental trial). Socially dependent horses showed more pronounced avoidance behaviour and needed much more time to resume feeding during the control trial. Hence, dependent individuals appeared to be more fearful. However, during an experimental trial, horses of both groups tended to ignore the sound or paid only limited attention to the stimulus, continuing to move forward towards their conspecifics. Thus, social motivation may mitigate fear caused by a frightening stimulus and make fearful and dependent horses more prone to face a potentially stressful event. This finding should be taken into account in horse training and management.

Temperature change exerts sex-specific effects on behavioural variation.

Temperature is a key factor mediating organismal fitness and has important consequences for species' ecology. While the mean effects of temperature on behaviour have been well-documented in ectotherms, how temperature alters behavioural variation among and within individuals, and whether this differs between the sexes, remains unclear. Such effects likely have ecological and evolutionary consequences, given that selection acts at the individual level. We investigated the effect of temperature on individual-level behavioural variation and metabolism in adult male and female Drosophila melanogaster (n = 129), by taking repeated measures of locomotor activity and metabolic rate at both a standard temperature (25°C) and a high temperature (28°C). Males were moderately more responsive in their mean activity levels to temperature change when compared to females. However, this was not true for either standard or active metabolic rate, where no sex differences in thermal metabolic plasticity were found. Furthermore, higher temperatures increased both among- and within-individual variation in male, but not female, locomotor activity. Given that behavioural variation can be critical to population persistence, we suggest that future studies test whether sex differences in the amount of behavioural variation expressed in response to temperature change may result in sex-specific vulnerabilities to a warming climate.

Data repurposing from digital home cage monitoring enlightens new perspectives on mouse motor behaviour and reduction principle.

In this longitudinal study we compare between and within-strain variation in the home-cage spatial preference of three widely used and commercially available mice strains-C57BL/6NCrl, BALB/cAnNCrl and CRL:CD1(ICR)-starting from the first hour post cage-change until the next cage-change, for three consecutive intervals, to further profile the circadian home-cage behavioural phenotypes. Cage-change can be a stressful moment in the life of laboratory mice, since animals are disturbed during the sleeping hours and must then rapidly re-adapt to a pristine environment, leading to disruptions in normal motor patterns. The novelty of this study resides in characterizing new strain-specific biological phenomena, such as activity along the cage walls and frontality, using the vast data reserves generated by previous experimental data, thus introducing the potential and exploring the applicability of data repurposing to enhance Reduction principle when running in vivo studies. Our results, entirely obtained without the use of new animals, demonstrate that also when referring to space preference within the cage, C57BL/6NCrl has a high variability in the behavioural phenotypes from pre-puberty until early adulthood compared to BALB/cAnNCrl, which is confirmed to be socially disaggregated, and CRL:CD1(ICR) which is conversely highly active and socially aggregated. Our data also suggest that a strain-oriented approach is needed when defining frequency of cage-change as well as maximum allowed animal density, which should be revised, ideally under the EU regulatory framework as well, according to the physiological peculiarities of the strains, and always avoiding the "one size fits all" approach.

A Lightweight Drive Implant for Chronic Tetrode Recordings in Juvenile Mice.

In vivo electrophysiology provides unparalleled insight into the sub-second-level circuit dynamics of the intact brain and represents a method of particular importance for studying mouse models of human neuropsychiatric disorders. However, such methods often require large cranial implants, which cannot be used in mice at early developmental time points. As such, virtually no studies of in vivo physiology have been performed in freely behaving infant or juvenile mice, despite the fact that a better understanding of neurological development in this critical window would likely provide unique insights into age-dependent developmental disorders such as autism or schizophrenia. Here, a micro-drive design, surgical implantation procedure, and post-surgery recovery strategy are described that allow for chronic field and single-unit recordings from multiple brain regions simultaneously in mice as they age from postnatal day 20 (p20) to postnatal day 60 (p60) and beyond, a time window roughly corresponding to the human ages of 2 years old through to adulthood. The number of recording electrodes and final recording sites can be easily modified and expanded, thus allowing flexible experimental control of the in vivo monitoring of behavior- or disease-relevant brain regions across development.