Increased latencies to respond in a judgment bias test are not associated with pessimistic biases in rats

Evaluation of miRNA as Biomarkers of Emotional Valence in Pigs

Simple Summary

It is widely recognized that the assessment of animal welfare should include measures of positive emotional (affective) state. Existing behavioral and physiological indicators of a positive affective state frequently lack sensitivity, objectivity or are unsuitable in a production environment. Therefore, there is a need to develop new approaches to accurately and objectively measure a positive emotional state in animals, including novel molecular markers such a miRNA. These biomarkers must be measurable in the peripheral circulation and provide an accurate account of the physiological and molecular activity in regions of the brain associated with emotional processing. Further, such markers require validation against established behavioral and physiological indices. Here we investigated the efficacy of circulating miRNA as biomarkers of emotional state in the pig.

Abstract

The ability to assess the welfare of animals is dependent on our ability to accurately determine their emotional (affective) state, with particular emphasis being placed on the identification of positive emotions. The challenge remains that current physiological and behavioral indices are either unable to distinguish between positive and negative emotional states, or they are simply not suitable for a production environment. Therefore, the development of novel measures of animal emotion is a necessity. Here we investigated the efficacy of microRNA (miRNA) in the brain and blood as biomarkers of emotional state in the pig. Female Large White × Landrace pigs (n = 24) were selected at weaning and trained to perform a judgment bias test (JBT), before being exposed for 5 weeks to either enriched (n = 12) or barren housing (n = 12) conditions. Pigs were tested on the JBT once prior to treatment, and immediately following treatment. MiRNA and neurotransmitters were analyzed in blood and brain tissue after euthanasia. Treatment had no effect on the outcomes of the JBT. There was also no effect of treatment on miRNA expression in blood or the brain (FDR p > 0.05). However, pigs exposed to enriched housing had elevated dopamine within the striatum compared to pigs in barren housing (p = 0.02). The results imply that either (a) miRNAs are not likely to be valid biomarkers of a positive affective state, at least under the type of conditions employed in this study, or (b) that the study design used to modify affective state was not able to create differential affective states, and therefore establish the validity of miRNA as biomarkers.

Symposium review: Scientific assessment of affective states in dairy cattle

Affective states, which refer to feelings or emotions, are a key component of animal welfare, but these are also difficult to assess. Drawing upon a body of theoretical and applied work, we critically review the scientific literature on the assessment of affective states in animals, drawing examples where possible from research on dairy cattle, and highlighting the strengths and weaknesses of scientific methods used to assess affective states in animals. We adopt the "valence/arousal" framework, describing affect as a 2-dimensional space (with valence referring to whether an experience is positive or negative, and arousal referring to the intensity of the experience). We conclude that spontaneous physiological and behavioral responses typically reflect arousal, whereas learned responses can be valuable when investigating valence. We also conclude that the assessment of affective states can be furthered using mood assessments and that the use of drug treatments with known emotional effects in humans can be helpful in the assessment of specific affective states in animals.

Pain-Induced Pessimism and Anhedonia: Evidence From a Novel Probability-Based Judgment Bias Test

Judgment bias tests (JBTs) use responses to ambiguous stimuli to infer emotional states in animals. However, with repeated testing, animals can learn to recognize the previously ambiguous stimuli rendering the test less effective. We describe a novel approach to this problem. Calves (n = 9) were trained in a spatial discrimination task to associate five locations with a specific probability of reward/punishment (Positive: 100%/0%; Near-Positive: 75%/25%; Middle: 50%/50%; Near-Negative: 25%/75%; Negative: 0%/100%). As predicted, calves showed increased latencies to touch locations that had higher probabilities of punishment and lower probabilities of reward. To validate our methodology for detecting mood changes, we followed calves in the hours after routine hot-iron disbudding, a time when animals were likely experiencing post-operative inflammatory pain. At 6 h after disbudding, when inflammatory pain was likely to peak, calves expressed increased approach latencies to the Positive, Near-Positive and Middle locations. These results suggest that calves perceived the value of the reward as being lower (i.e., anhedonia) or had lower expectations of positive outcomes (i.e., pessimism). When re-tested at 22 and 70 h after disbudding, we found no evidence of pessimism or anhedonia (i.e., latencies had returned to baseline). We conclude that our probability-based judgment bias task can detect pain-induced mood changes.

Technology or ecology? New tools to assess cognitive judgement bias in mice

Cognitive judgement bias tests have become important new tools for the assessment of animal emotions. They allow for the inference of an animal's emotional state based on ambiguous cue interpretations. As mice are the predominantly used animal model for cognitive and behavioural neuroscience, research in this field would considerably benefit from the development of suitable judgement bias tests for this species. Against this background, we aimed to implement two different active choice cognitive judgement bias paradigms for mice in a methodological study. For this purpose, two experiments were conducted: in experiment I, an automated, vision-based touchscreen technique was applied, allowing for the direct translation of tasks from rodents to humans and vice versa. Experiment II comprised a task relying on more ecologically relevant cues in form of tunnels of different lengths. While the touchscreen task was characterized by automation-related advantages such as the possibility to present many trials per session and a high convenience for the experimenter, the tunnel task was learned faster by the mice. In both tests, however, the response to the trained and ambiguous conditions resulted in a graded curve, the basic requirement for proving task validity. Thus, both the translational touchscreen task as well as the ecologically more relevant tunnel task could successfully be implemented and provide new tools for the future assessment of cognitive judgement biases in mice.

Oestrous phase cyclicity influences judgment biasing in rats

The identification of cognitive bias has become an important measure of animal welfare. Negative cognitive biases develop from a tendency for animals to process novel information pessimistically. Judgment-bias testing is the commonplace methodology to detect cognitive biases. However, concerns with these methods have been frequently-reported; one of which being the discrepancy between male and female cognitive expression. The current study assessed the factors of social status and oestrus, to investigate whether oestrous cycle rotation, or subordination stress encouraged an increase in pessimistic responses. Female Sprague-Dawley rats (n = 24) were trained on an active-choice judgment bias paradigm. Responses to the ambiguous probe were recorded as optimistic or pessimistic. Oestrous phase was determined by assessing vaginal cytology in stained vaginal cell smears. Rats in the dioestrous phase and those rats considered to be subordinate demonstrated an increased percentage of pessimistic responses. However, no interaction between these factors was observed. This suggests that oestrous cyclicity can influence the judgment biases of female animals; a previously unreported finding. On this basis, researchers should be encouraged to account for both oestrous phase cyclicity and social status as an additional fixed effect in study design.