Playful handling by caretakers reduces fear of humans in the laboratory rat

Utilizing synthetic training data for the supervised classification of rat ultrasonic vocalizations

Murine rodents generate ultrasonic vocalizations (USVs) with frequencies that extend to around 120 kHz. These calls are important in social behaviour, and so their analysis can provide insights into the function of vocal communication, and its dysfunction. The manual identification of USVs, and subsequent classification into different subcategories is time consuming. Although machine learning approaches for identification and classification can lead to enormous efficiency gains, the time and effort required to generate training data can be high, and the accuracy of current approaches can be problematic. Here, we compare the detection and classification performance of a trained human against two convolutional neural networks (CNNs), DeepSqueak (DS) and VocalMat (VM), on audio containing rat USVs. Furthermore, we test the effect of inserting synthetic USVs into the training data of the VM CNN as a means of reducing the workload associated with generating a training set. Our results indicate that VM outperformed the DS CNN on measures of call identification, and classification. Additionally, we found that the augmentation of training data with synthetic images resulted in a further improvement in accuracy, such that it was sufficiently close to human performance to allow for the use of this software in laboratory conditions.

Effects of reduced kinematic and social play experience on affective appraisal of human-rat play in rats

BACKGROUND

Play is a common and developmentally important behaviour in young mammals. Specifically in Norway rats (Rattus norvegicus), reduced opportunity to engage in rough-and-tumble (RT) play has been associated with impaired development in social competence. However, RT play is a complex behaviour having both a kinematic aspect (i.e., performing complex 3D manoeuvres during play fights) and a social aspect (interacting with a playful partner). There has been little research so far on disentangling the two aspects in RT play, especially on how these two aspects affect the affective appraisal of the intense physical contact during play.

RESULTS

To examine the developmental effects of kinematic and social play reduction on affective appraisal in rats, we subjected male Long-Evans rats from 21 days old to RT play experience that was reduced either kinematically (through playing in a low ceiling environment) or socially (through playing with a less playful Fischer-344 rat). Starting at 35 days, we measured their production of positively (50-kHz) and negatively (22-kHz) valenced ultrasonic vocalisations (USVs) in a 2-min standardised human-rat play procedure that mimicked the playful sequences of nape contact, pinning, and belly stimulation ('tickling') for ten days. We hypothesised that the rats with kinematically or socially reduced play would perceive the 'tickling' less positively and thus emit positive ultrasonic vocalisations at lower rates compared to control rats with non-reduced play experience. Our results confirmed that each of the treatments reduced play differently: while the kinematic reduction abolished playful pinnings entirely, the social reduction decreased the pinnings and made play highly asymmetric. During the tickling procedure, rats mostly produced 50 kHz USV, indicating that they appraised the procedure as positive. There was a wide inter individual variance and high individual consistency in rats' USV responses to 'tickling'. Crucially, neither the kinematically nor the socially reduced play experience affected either type of USV production when rats were 'tickled'.

CONCLUSIONS

This finding indicates that the ability to appraise play-like interactions as positive remains unaffected even when the kinematic or the social aspect of play experience was substantially curtailed.

Effect of chronic handling and social isolation on emotion and cognition in adolescent rats

Adolescence is a critical period of establishing social relations through social interactions that affect the emotional development associated with stress responses, anxiety, depression, and cognitive development. We investigated the behavioral and neurobiological changes induced by handling and social isolation in adolescent rats to determine social interaction effects. Rats were randomly divided into groups and used as a control, a handling, and a social isolation group. After 12 weeks, the handling group showed a significant increase in mobility in the open field test and in tryptophan hydroxylase expression in the dorsal raphe nucleus, as well as significantly reduced immobility times in the forced swim test, compared to the control group (p < 0.05). The social isolation group, in contrast, showed a significant increase in immobility times in the forced swim test and in glucocorticoid and SIRT1 expression in the hippocampus, as well as a significant reduction in mobility in the open field test and in escape latency times in the passive avoidance test, compared to the control group (p < 0.05). The present results show that while handling did not improve cognitive function, it reduced anxiety and lowered depression levels; social isolation, in contrast, significantly impaired the animals' stress response, anxiety and depression levels, and cognitive function. Our findings indicate that handling and social isolation have a strong effect on adolescents' emotional and cognitive development into healthy adults.

Leveraging Social Learning to Enhance Captive Animal Care and Welfare

From ants to zebras, animals are influenced by the behavior of others. At the simplest level, social support can reduce neophobia, increasing animals’ exploration of novel spaces, foods, and other environmental stimuli. Animals can also learn new skills more quickly and more readily after observing others perform them. How then can we apply animals’ proclivity to socially learn to enhance their care and welfare in captive settings? Here, I review the ways in which animals (selectively) use social information, and propose tactics for leveraging that to refine the behavioral management of captive animals: to enhance socialization techniques, enrichment strategies, and training outcomes. It is also important to consider, however, that social learning does not always promote the uniform expression of new behaviors. There are differences in animals’ likelihood to seek out or use socially provided information, driven by characteristics such as species, rank, age, and personality. Additionally, social learning can result in inexact transmission or the transmission of undesirable behaviors. Thus, understanding when, how, and why animals use social information is key to developing effective strategies to improve how we care for animals across settings and, ultimately, enhance captive animal welfare.

The Effect of Gentle Handling on Depressive-Like Behavior in Adult Male Mice: Considerations for Human and Rodent Interactions in the Laboratory

Environmental factors play a significant role in well-being of laboratory animals. Regulations and guidelines recommend, if not require, that stressors such as bright lighting, smells, and noises are eliminated or reduced to maximize animal well-being. A factor that is often overlooked is handling and how researchers interact with their animals. Researchers, lab assistants, and husbandry staff in animal facilities may use inconsistent handling methods when interacting with rodents, but humans should be considered a part of the animal's social environment. This study examined the effects of different handling techniques on depressive-like behavior, measured by the Porsolt forced swim test, in adult C57BL/6J male mice. The same two researchers handled the mice in a gentle, aggressive, or minimal (control) fashion over approximately two weeks prior to testing. The results demonstrated a beneficial effect of gentle handling: gentle handling reduced swimming immobility in the forced swim test compared to mice that were aggressively or minimally handled. We argue that gentle handling, rather than methodical handling, can foster a better relationship between the handlers and rodents. Although handling is not standardized across labs, consistent gentle handling allows for less challenging behavioral testing, better data collection, and overall improved animal welfare.

The 24/7 approach to promoting optimal welfare for captive wild animals

We have an ethical responsibility to provide captive animals with environments that allow them to experience good welfare. Husbandry activities are often scheduled for the convenience of care staff working within the constraints of the facility, rather than considering the biological and psychological requirements of the animals themselves. The animal welfare 24/7 across the lifespan concept provides a holistic framework to map features of the animal's life cycle, taking into account their natural history, in relation to variations in the captive environment, across day and night, weekdays, weekends, and seasons. In order for animals to have the opportunity to thrive, we argue the need to consider their lifetime experience, integrated into the environments we provide, and with their perspective in mind. Here, we propose a welfare assessment tool based upon 14 criteria, to allow care staff to determine if their animals' welfare needs are met. We conclude that animal habitat management will be enhanced with the use of integrated technologies that provide the animals with more opportunities to engineer their own environments, providing them with complexity, choice and control.

Rat tickling: A systematic review of applications, outcomes, and moderators

Introduction

Rats initially fear humans which can increase stress and impact study results. Additionally, studying positive affective states in rats has proved challenging. Rat tickling is a promising habituation technique that can also be used to model and measure positive affect. However, current studies use a variety of methods to achieve differential results. Our objective was to systematically identify, summarize, and evaluate the research on tickling in rats to provide direction for future investigation. Our specific aims were to summarize current methods used in tickling experiments, outcomes from tickling, and moderating factors.

Methods

We systematically evaluated all articles about tickling identified from PubMed, Scopus, Web of Science, and PsychInfo. Our inclusion criteria were publication in a peer-reviewed journal and collection of original, empirical data on rats using the handling method of tickling. One researcher extracted information from each article. Bias was assessed by 2 investigators using the SYRCLE bias assessment tool.

Results

We identified 32 articles (56 experiments) published in peer-reviewed journals about rat tickling for inclusion. A wide variety of strains, sexes, and ages of rats were included. The most common method used for tickling was cycling through 15 seconds of tickling and 15 seconds of rest for 2 minutes for 3 to 5 days. Experiments with a control for tickling (N = 22) showed that tickling increases positive vocalization, approach behavior, decreases anxiety measures, improves handling, and in some cases decreases stress hormones. Tickling juvenile, individually housed rats with a trait predisposition to respond more positively to tickling, results in the most positive outcomes. Methods to reduce bias were insufficiently reported.

Conclusions

We conclude that tickling is a promising method for improving rat welfare and investigating positive affect. However, the establishment of tickling best practices is essential as the outcomes from tickling can be moderated by several factors.

Context-dependent individual differences in playfulness in male rats

Play has been proposed as an indicator of positive emotions and welfare in higher vertebrates. This study investigated playfulness in male rats by exploring its consistency across motivational states (with/without prior short social isolation) and two age points at early and late adolescence. Twenty-four male Lister Hooded rats housed in cages of four underwent two play tests: conspecific Play-in-Pairs and Tickling by the experimenter, which were compared with play in the home cage and basal anxiety levels. Play-in-Pairs measures were consistent across age and motivational states, and were independent from anxiety. Positively valenced vocalizations in the Tickling test were also consistent across age, yet were negatively related to anxiety. Play-in-Pairs and Tickling play contexts, as well as social and solitary play types, were unrelated. Therefore, this study supports the existence of consistent individual differences in playfulness in rats, and suggests that different play contexts and types represent motivationally distinct systems.

Are 50-kHz calls used as play signals in the playful interactions of rats? II. Evidence from the effects of devocalization

During playful interactions, juvenile rats emit many 50-kHz ultrasonic vocalizations, which are associated with a positive affective state. In addition, these calls may also serve a communicative role - as play signals that promote playful contact. Consistent with this hypothesis, a previous study found that vocalizations are more frequent prior to playful contact than after contact is terminated. The present study uses devocalized rats to test three predictions arising from the play signals hypothesis. First, if vocalizations are used to facilitate contact, then in pairs of rats in which one is devocalized, the higher frequency of pre-contact calling should only be present when the intact rat is initiating the approach. Second, when both partners in a playing pair are devocalized, the frequency of play should be reduced and the typical pattern of playful wrestling disrupted. Finally, when given a choice to play with a vocal and a non-vocal partner, rats should prefer to play with the one able to vocalize. The second prediction was supported in that the frequency of playful interactions as well as some typical patterns of play was disrupted. Even though the data for the other two predictions did not produce the expected findings, they support the conclusion that, in rats, 50-kHz calls are likely to function to maintain a playful mood and for them to signal to one another during play fighting.