Correction: Do multiple experimenters improve the reproducibility of animal studies?

[This corrects the article DOI: 10.1371/journal.pbio.3001564.].

Do multiple experimenters improve the reproducibility of animal studies?

The credibility of scientific research has been seriously questioned by the widely claimed "reproducibility crisis". In light of this crisis, there is a growing awareness that the rigorous standardisation of experimental conditions may contribute to poor reproducibility of animal studies. Instead, systematic heterogenisation has been proposed as a tool to enhance reproducibility, but a real-life test across multiple independent laboratories is still pending. The aim of this study was therefore to test whether heterogenisation of experimental conditions by using multiple experimenters improves the reproducibility of research findings compared to standardised conditions with only one experimenter. To this end, we replicated the same animal experiment in 3 independent laboratories, each employing both a heterogenised and a standardised design. Whereas in the standardised design, all animals were tested by a single experimenter; in the heterogenised design, 3 different experimenters were involved in testing the animals. In contrast to our expectation, the inclusion of multiple experimenters in the heterogenised design did not improve the reproducibility of the results across the 3 laboratories. Interestingly, however, a variance component analysis indicated that the variation introduced by the different experimenters was not as high as the variation introduced by the laboratories, probably explaining why this heterogenisation strategy did not bring the anticipated success. Even more interestingly, for the majority of outcome measures, the remaining residual variation was identified as an important source of variance accounting for 41% (CI95 [34%, 49%]) to 72% (CI95 [58%, 88%]) of the observed total variance. Despite some uncertainty surrounding the estimated numbers, these findings argue for systematically including biological variation rather than eliminating it in animal studies and call for future research on effective improvement strategies.

'Ten Years After'-a long-term settlement and bioerosion experiment in an Arctic rhodolith bed (Mosselbukta, Svalbard).

Rhodolith beds and bioherms formed by ecosystem engineering crustose coralline algae support the northernmost centres of carbonate production, referred to as polar cold-water carbonate factories. Yet, little is known about biodiversity and recruitment of these hard-bottom communities or the bioeroders degrading them, and there is a demand for carbonate budgets to include respective rates of polar carbonate build-up and bioerosion. To address these issues, a 10-year settlement and bioerosion experiment was carried out at the Arctic Svalbard archipelago in and downslope of a rhodolith bed. The calcifiers recorded on experimental settlement tiles (56 taxa) were dominated by bryozoans, serpulids and foraminiferans. The majority of the bioerosion traces (30 ichnotaxa) were microborings, followed by attachment etchings and grazing traces. Biodiversity metrics show that calcifier diversity and bioerosion ichnodiversity are both elevated in the rhodolith bed, if compared to adjacent aphotic waters, but these differences are statistically insignificant. Accordingly, there were only low to moderate dissimilarities in the calcifier community structure and bioerosion trace assemblages between the two depth stations (46 and 127 m), substrate orientations (up- and down-facing) and substrate types (PVC and limestone), in that order of relevance. In contrast, surface coverage as well as the carbonate accretion and bioerosion rates were all significantly elevated in the rhodolith bed, reflecting higher abundance or size of calcifiers and bioerosion traces. All three measures were highest for up-facing substrates at 46 m, with a mean coverage of 78.2% (on PVC substrates), a mean accretion rate of 24.6 g m-2   year-1 (PVC), and a mean bioerosion rate of -35.1 g m-2  year-1 (limestone). Differences in these metrics depend on the same order of factors than the community structure. Considering all limestone substrates of the two platforms, carbonate accretion and bioerosion were nearly in balance at a net rate of -2.5 g m-2  year-1 . A latitudinal comparison with previous settlement studies in the North Atlantic suggests that despite the harsh polar environment there is neither a depletion in the diversity of hard-bottom calcifier communities nor in the ichnodiversity of grazing traces, attachment etchings and microborings formed by organotrophs. In contrast, microborings produced by phototrophs are strongly depleted because of limitations in the availability of light (condensed photic zonation, polar night, shading by sea ice). Also, macroborings were almost absent, surprisingly. With respect to carbonate production, the Svalbard carbonate factory marks the low end of a latitudinal gradient while bioerosion rates are similar or even higher than at comparable depth or photic regime at lower latitudes, although this might not apply to shallow euphotic waters (not covered in our experiment), given the observed depletion in bioeroding microphytes and macroborers. While echinoid grazing is particularly relevant for the bioerosion in the rhodolith bed, respective rates are far lower than those reported from tropical shallow-water coral reefs. The slow pace of carbonate production but relatively high rates of bioerosion (both promoted by low carbonate supersaturation states in Arctic waters), in concert with high retention of skeletal carbonates on the seafloor and no calcite cements forming in open pore space created by microborers, suggest a low fossilisation potential for polar carbonates, such as those formed in the Mosselbukta rhodolith beds.

Impact of three commonly used blood sampling techniques on the welfare of laboratory mice: Taking the animal's perspective.

Laboratory mice are the most frequently used animals in biomedical research. In accordance with guidelines for humane handling, several blood sampling techniques have been established. While the effects of these procedures on blood quality and histological alterations at the sampling site are well studied, their impact on the animals' welfare has not been extensively investigated. Therefore, our study aimed to compare three commonly used blood sampling techniques regarding their effects on different indicators of animal welfare, including physiological and behavioural response stress parameters, including pain measures, home-cage behaviour and nest-building as well as exploratory activity and neophobia. Male C57BL/6J mice were subjected to a single blood collection from either the vena facialis, the retrobulbar sinus or the tail vessel, or were allocated to the respective control treatment. While all blood sampling techniques led to an acute increase in plasma corticosterone levels, the response was strongest in animals that underwent sampling from the vena facialis and the retrobulbar sinus. Similar results were observed when the time-course of adrenocortical activity was monitored via corticosterone metabolites from faecal samples. Blood collection from the vena facialis and the retrobulbar sinus also decreased exploration of novel stimuli, resulted in decreased nest-building activity and induced higher scores in the Mouse Grimace Scale. Moreover, locomotor activity and anxiety-related behaviour were strongly affected after facial vein bleeding. Interestingly, tail vessel bleeding only induced little alterations in the assessed physiological and behavioural parameters. Importantly, the observed effects in all treatment groups were no longer detectable after 24 hours, indicating only short-term impacts. Thus, by also taking the animal's perspective and comprehensively assessing the severity of the particular sampling procedures, the results of our study contribute to Refinement within the 3R concept and allow researchers to objectively select the most appropriate and welfare-friendly blood sampling technique for a given experiment.

Social experiences during adolescence affect anxiety-like behavior but not aggressiveness in male mice.

Adolescence has lately been recognized as a key developmental phase during which an individual's behavior can be shaped. In a recent study with male mice varying in the expression of the serotonin transporter, escapable adverse social experiences during adolescence led to decreased anxiety-like behavior and increased exploratory and aggressive behavior compared to throughout beneficial experiences. Since in this study some behavioral tests took place with a delay of one week after the last social experiences have been made, it was not clear whether the observed effects really reflected the consequences of the experienced different social environments. To test this, the present study focused on the direct effects of beneficial and adverse social experiences on aggressiveness and anxiety-like behavior in C57BL/6J mice. In contrast to the previous study, behavioral testing took place immediately after the last social experiences had been made. Interestingly, whereas individuals from an escapable adverse environment showed significantly lower levels of anxiety-like and higher levels of exploratory behavior than animals from a beneficial environment, aggressive behavior was not affected. From this, we conclude that different social experiences during adolescence exert immediate effects on anxiety-like but not aggressive behavior in male mice.

The Unexpected Effects of Beneficial and Adverse Social Experiences during Adolescence on Anxiety and Aggression and Their Modulation by Genotype.

Anxiety and aggression are part of the behavioral repertoire of humans and animals. However, in their exaggerated form both can become maladaptive and result in psychiatric disorders. On the one hand, genetic predisposition has been shown to play a crucial modulatory role in anxiety and aggression. On the other hand, social experiences have been implicated in the modulation of these traits. However, so far, mainly experiences in early life phases have been considered crucial for shaping anxiety-like and aggressive behavior, while the phase of adolescence has largely been neglected. Therefore, the aim of the present study was to elucidate how levels of anxiety-like and aggressive behavior are shaped by social experiences during adolescence and serotonin transporter (5-HTT) genotype. For this purpose, male mice of a 5-HTT knockout mouse model including all three genotypes (wildtype, heterozygous and homozygous 5-HTT knockout mice) were either exposed to an adverse social situation or a beneficial social environment during adolescence. This was accomplished in a custom-made cage system where mice experiencing the adverse environment were repeatedly introduced to the territory of a dominant opponent but had the possibility to escape to a refuge cage. Mice encountering beneficial social conditions had free access to a female mating partner. Afterwards, anxiety-like and aggressive behavior was assessed in a battery of tests. Surprisingly, unfavorable conditions during adolescence led to a decrease in anxiety-like behavior and an increase in exploratory locomotion. Additionally, aggressive behavior was augmented in animals that experienced social adversity. Concerning genotype, homozygous 5-HTT knockout mice were more anxious and less aggressive than heterozygous 5-HTT knockout and wildtype mice. In summary, adolescence is clearly an important phase in which anxiety-like and aggressive behavior can be shaped. Furthermore, it seems that having to cope with challenge during adolescence instead of experiencing throughout beneficial social conditions leads to reduced levels of anxiety-like behavior.

Diet-induced obesity resistance of adult female mice selectively bred for increased wheel-running behavior is reversed by single perinatal exposure to a high-energy diet.

Female mice from independently bred lines previously selected over 50 generations for increased voluntary wheel-running behavior (S1, S2) resist high energy (HE) diet-induced obesity (DIO) at adulthood, even without actual access to running wheels, as opposed to randomly bred controls (CON). We investigated whether adult S mice without wheels remain DIO-resistant when exposed - via the mother - to the HE diet during their perinatal stage (from 2 weeks prior to conception until weaning on post-natal day 21). While S1 and S2 females subjected to HE diet either perinatally or from weaning onwards (post-weaning) resisted increased adiposity at adulthood (as opposed to CON females), they lost this resistance when challenged with HE diet during these periods combined over one single cycle of breeding. When allowed one-week access to wheels (at week 6-8 and at 10 months), however, tendency for increased wheel-running behavior of S mice was unaltered. Thus, the trait for increased wheel-running behavior remained intact following combined perinatal and post-weaning HE exposure, but apparently this did not block HE-induced weight gain. At weaning, perinatal HE diet increased adiposity in all lines, but this was only associated with hyperleptinemia in S lines irrespective of gender. Because leptin has multiple developmental effects at adolescence, we argue that a trait for increased physical activity may advance maturation in times of plenty. This would be adaptive in nature where episodes of increased nutrient availability should be exploited maximally. Associated disturbances in glucose homeostasis and related co-morbidities at adulthood are probably pleiotropic side effects.

Oxytocin microinjected into the central amygdaloid nuclei exerts anti-aggressive effects in male rats.

We recently demonstrated that acute and chronic intracerebroventricular enhancement of brain OXT levels induces potent anti-aggressive and pro-social explorative effects during social challenges. However, the exact anatomical location in the brain where OXT exerts its action is still elusive. In the present study, we targeted two critical brain areas, i.e. the central amygdala (CeA) and the dorsal raphe (DR), both containing high levels of OXT receptors (OXTRs) and constituting important nodes of the neural circuitry related to aggression. Behavioral effects of local micro-infusion of OXT and OXTR antagonist, L368.899, (alone and combined) were evaluated in resident male rats during confrontations with an unfamiliar male intruder. Our results show that OXT microinjected into the CeA markedly reduced resident's offensive behavior and facilitated social exploration, without affecting other non-aggressive behaviors. The receptor specificity of the behavioral effects was verified when a micro-infusion of a selective OXTR antagonist nullified the changes. Pharmacological blockade of CeA OXTRs per se was without clear behavioral effects suggesting that endogenous OXT within the CeA does not play a major inhibitory role on offensiveness. Anatomical specificity was also supported by the absence of relevant behavioral effects when OXT was microinjected into more medial sub-regions of the amygdala. Likewise, within the DR neither OXT nor OXTR exerted significant effects on offensive aggression, while microinjection of the 5-HT1A autoreceptor agonist in this region significantly suppressed aggression. In conclusion, our results point at the CeA as an important brain site of action for the anti-aggressive and pro-social explorative effects induced by exogenous enhancement of brain OXT levels.

Chronic enhancement of brain oxytocin levels causes enduring anti-aggressive and pro-social explorative behavioral effects in male rats.

Oxytocin (OXT) has been implicated in the regulation of social behaviors, including intermale offensive aggression. Recently, we showed that acute enhancement of brain OXT levels markedly suppressed offensive aggression and increased social exploration in resident rats confronted with an intruder in their home territory. Moreover, a different responsivity to the exogenous OXTergic manipulation was observed among individuals based on their baseline aggression. In this study we aimed at evaluating the behavioral response to chronically enhancing or attenuating central OXT levels, and at scrutinizing whether the trait-aggression moderates the treatment-induced behavioral changes. To this end, resident male wild-type Groningen rats were continuously (via osmotic minipumps) intracerebroventricularly infused with synthetic OXT or a selective OXT receptor (OXTR) antagonist for 7days. Changes in behavior were assessed performing a resident-intruder test before and at the end of the treatment period, as well as after 7days of withdrawal. Chronic infusion of OXT was found to selectively suppress aggression and enhance social exploration. Chronic blockage of OXTRs instead increased introductory aggressive behavior (i.e. lateral threat), yet without affecting the total duration of the aggression. The magnitude of the anti-aggressive changes correlated positively with the level of baseline aggression. Interestingly, OXT-induced behavioral changes persisted 7days after cessation of the treatment. In conclusion, these findings provide further evidence that enhanced functional activity of the central OXTergic system decreases social offensive aggression while it increases social explorative behavior. The data also indicate that chronically enhancing brain OXT levels may cause enduring anti-aggressive and pro-social explorative behavioral effects.