Experiments done in Black-6 mice: what does it mean?

A practical guide for the husbandry of cave and surface invertebrates as the first step in establishing new model organisms

While extensive research on traditional model species has significantly advanced the biological sciences, the ongoing search for new model organisms is essential to tackle contemporary challenges such as human diseases or climate change, and fundamental phenomena including adaptation or speciation. Recent methodological advances such as next-generation sequencing, gene editing, and imaging are widely applicable and have simplified the selection of species with specific traits from the wild. However, a critical milestone in this endeavor remains the successful cultivation of selected species. A historically overlooked but increasingly recognized group of non-model organisms are cave dwellers. These unique animals offer invaluable insights into the genetic basis of human diseases like eye degeneration, metabolic and neurological disorders, and basic evolutionary principles and the origin of adaptive phenotypes. However, to take advantage of the beneficial traits of cave-dwelling animals, laboratory cultures must be established-a practice that remains extremely rare except for the cavefish Astyanax mexicanus. For most cave-dwelling organisms, there are no published culturing protocols. In this study, we present the results of our multi-year effort to establish laboratory cultures for a variety of invertebrate groups. We have developed comprehensive protocols for housing, feeding, and husbandry of cave dwellers and their surface relatives. Our recommendations are versatile and can be applied to a wide range of species. Hopefully our efforts will facilitate the establishment of new laboratory animal facilities for cave-dwelling organisms and encourage their greater use in experimental biology.

Genetic background determines synaptic phenotypes in Arid1b-mutant mice

ARID1B, a chromatin remodeler, is strongly implicated in autism spectrum disorders (ASD). Two previous studies on Arid1b-mutant mice with the same exon 5 deletion in different genetic backgrounds revealed distinct synaptic phenotypes underlying the behavioral abnormalities: The first paper reported decreased inhibitory synaptic transmission in layer 5 pyramidal neurons in the medial prefrontal cortex (mPFC) region of the heterozygous Arid1b-mutant (Arid1b+/-) brain without changes in excitatory synaptic transmission. In the second paper, in contrast, we did not observe any inhibitory synaptic change in layer 5 mPFC pyramidal neurons, but instead saw decreased excitatory synaptic transmission in layer 2/3 mPFC pyramidal neurons without any inhibitory synaptic change. In the present report, we show that when we changed the genetic background of Arid1b+/- mice from C57BL/6 N to C57BL/6 J, to mimic the mutant mice of the first paper, we observed both the decreased inhibitory synaptic transmission in layer 5 mPFC pyramidal neurons reported in the first paper, and the decreased excitatory synaptic transmission in mPFC layer 2/3 pyramidal neurons reported in the second paper. These results suggest that genetic background can be a key determinant of the inhibitory synaptic phenotype in Arid1b-mutant mice while having minimal effects on the excitatory synaptic phenotype.

Sex-specific variations in spatial reference memory acquisition: Insights from a comprehensive behavioral test battery in C57BL/6JRj mice

Sex differences in declarative memory are described in humans, revealing a female or a male advantage depending on the task. Specifically, spatial memory (i.e., spatial navigation) is typically most efficient in men. This sexual dimorphism has been replicated in male rats but not clearly in mice. In this study, sex differences in spatial memory were assessed in thirty-six C57BL/6 J mice (Janvier Labs; i.e., C57BL/6JRj mice), a widely used mouse substrain. Both male and female mice (12 weeks-old) were subjected to standard behavioral paradigms: the elevated plus maze, the open field test, the novel object and place tests, the forced swimming test, and the water maze test for spatial navigation. Across assessment, no sex differences were found in measures of locomotor activity, emotional and behavioral responses, and object and place recognition memories. In the water maze, male mice were faster in learning the platform location in the reference memory training and used more spatial strategies during the first training days. However, both sexes reached a similar asymptotic performance and performed similarly in the probe trial for long-term memory consolidation. No sex differences were found in the cued training, platform inversion sessions, or spatial working memory sessions. Hippocampal expression of the brain-derived neurotrophic factor was similar in both sexes, either in basal conditions or after performing the behavioral training battery. Importantly, female mice were not more variable than males in any measure analyzed. This outcome encourages the investigation of sex differences in animal models and the usefulness of including female mice in behavioral research.

How stra(i)nge are your controls? A comparative analysis of metabolic phenotypes in commonly used C57BL/6 substrains

In recent years, insufficiently characterised controls have been a contributing factor to irreproducibility in biomedical research including neuroscience and metabolism. There is now a growing awareness of phenotypic differences between the C57BL/6 substrains which are commonly used as control animals. We here investigated baseline metabolic characteristics such as glucose regulation, fasted serum insulin levels and hepatic insulin signalling in five different C57BL/6 substrains (N, J, JOla, JRcc) of both sexes, obtained from two commercial vendors, Charles River Laboratories (Crl) and Envigo (Env). Our results indicate systematic and tissue-specific differences between substrains, affected by both vendor and sex, in all parameters investigated, and not necessarily mediated by the presence of the NntC57BL/6J mutation. Not only were there differences between 6J and 6N as expected, all three 6J substrains exhibited different profiles, even from the same breeder. Two distinct metabolic profiles were identified, one in which low insulin levels resulted in impaired glucose clearance (6JCrl; both sexes) and the other, where sustained elevations in fasted basal insulin levels led to glucose intolerance (male 6JRccEnv). Further, 6JRccEnv displayed sex differences in both glucose clearance and hepatic insulin signalling markers. In comparison, the two 6N substrains of either sex, irrespective of vendor, did not exhibit considerable differences, with 6NCrl animals presenting a good choice as a healthy baseline 'control' for many types of experiments. Overall, our data emphasise the importance of selecting and characterising control subjects regarding background, sex, and supplier to ensure proper experimental outcomes in biomedical research.

Cyfip2 allelic variation in C57BL/6J and C57BL/6NJ mice alters free-choice ethanol drinking but not binge-like drinking or wheel-running activity

BACKGROUND

Since the origin of the C57BL/6 (B6) mouse strain, several phenotypically and genetically distinct B6 substrains have emerged. For example, C57BL/6J mice (B6J) display greater voluntary ethanol consumption and locomotor response to psychostimulants and differences in nucleus accumbens synaptic physiology relative to C57BL/6N (B6N) mice. A non-synonymous serine to phenylalanine point mutation (S968F) in the cytoplasmic FMR1-interacting protein 2 (Cyfip2) gene underlies both the differential locomotor response to cocaine and the accumbal physiology exhibited by these substrains. We examined whether Cyfip2 allelic variation underlies B6 substrain differences in other reward-related phenotypes, such as ethanol intake and wheel-running activity.

METHODS

We compared voluntary ethanol consumption, wheel-running, and binge-like ethanol drinking in male and female B6J and B6NJ mice. When substrain differences were observed, additional experiments were performed in two novel mouse models in which the B6N Cyfip2 mutation was either introduced (S968F) into the B6J background or corrected (F968S) via CRISPR/Cas9 technology.

RESULTS

B6J consumed significantly more ethanol than B6NJ and allelic variation in Cyfip2 contributed substantially to this substrain difference. In contrast, B6NJ displayed significantly more daily wheel-running than B6J, with Cyfip2 allelic variation playing only a minor role in this substrain difference. Lastly, no substrain differences were observed in binge-like ethanol drinking.

CONCLUSIONS

These results contribute to the characterization of behavior-genetic differences between B6 substrains, support previous work indicating that free-choice and binge-like ethanol drinking are dependent on partially distinct genetic networks, and identify a novel phenotypic difference between B6 substrains in wheel-running activity.

Delay eyeblink conditioning performance and brain-wide c-Fos expression in male and female mice

Delay eyeblink conditioning has been extensively used to study associative learning and the cerebellar circuits underlying this task have been largely identified. However, there is a little knowledge on how factors such as strain, sex and innate behaviour influence performance during this type of learning. In this study, we used male and female mice of C57BL/6J (B6) and B6CBAF1 strains to investigate the effect of sex, strain and locomotion in delay eyeblink conditioning. We performed a short and a long delay eyeblink conditioning paradigm and used a c-Fos immunostaining approach to explore the involvement of different brain areas in this task. We found that both B6 and B6CBAF1 females reach higher learning scores compared to males in the initial stages of learning. This sex-dependent difference was no longer present as the learning progressed. Moreover, we found a strong positive correlation between learning scores and voluntary locomotion irrespective of the training duration. c-Fos immunostainings after the short paradigm showed positive correlations between c-Fos expression and learning scores in the cerebellar cortex and brainstem, as well as previously unreported areas. By contrast, after the long paradigm, c-Fos expression was only significantly elevated in the brainstem. Taken together, we show that differences in voluntary locomotion and activity across brain areas correlate with performance in delay eyeblink conditioning across strains and sexes.

Norecopa: A global knowledge base of resources for improving animal research and testing

There are good ethical, legal and scientific reasons for ensuring that our use of animals in research and testing is limited to the lowest number of animals, and that those which are used are treated as humanely as possible, while at the same time providing reliable, reproducible and translatable data which is adequately reported. Unfortunately, there is widespread evidence that there is room for improvement in all these areas. This paper describes the Norecopa website, which offers links to global resources which can be used to resolve these issues. Much of the website content is linked to the PREPARE guidelines for planning any research or testing which appears to need animals. Attention to detail on all steps of the pathway from early planning to manuscript submission should lead to better science, improved animal welfare, and fewer health and safety accidents. This will also minimize the chances of manuscript rejection due to inadequate planning, avoiding a waste of human resources and animal lives.

Metabolic differences and differentially expressed genes between C57BL/6J and C57BL/6N mice substrains

C57BL/6J (B6J) and C57BL/6N (B6N) mice are the most frequently used substrains in C57BL/6 (B6) inbred mice, serving as physiological models for in vivo studies and as background strains to build transgenic mice. However, the differences in metabolic phenotypes between B6J and B6N mice are not coherent, and genotypic differences in metabolically important tissues have not been well studied. The phenotypic differences between B6J and B6N substrains have often been attributed to the role of the nicotinamide nucleotide transhydrogenase (Nnt) gene, whereby B6J has a spontaneous missense mutation of Nnt. Nevertheless, phenotypic differences between the two cannot be explained by Nnt mutations alone, especially in metabolic traits. Therefore, we aimed to investigate the genetic cause of the phenotypic differences between B6J and B6N mice. Determining consistent genetic differences across multiple tissues involved in metabolic traits such as subcutaneous and visceral white adipose tissues, brown adipose tissue, skeletal muscle, liver, hypothalamus, and hippocampus, may help explain phenotypic differences in metabolism between the two substrains. We report candidate genes along with comparative data on body weight, tissue weight, blood components involved in metabolism, and energy balance of B6J and B6N mice. Insulin degrading enzyme, adenylosuccinate synthase 2, and ectonucleotide triphosphate diphosphohydrolase 4 were highly expressed in B6J mice compared with those in B6N mice, and Nnt, WD repeat and FYVE domain containing 1, and dynein light chain Tctex-type 1 were less expressed in B6J mice compared with those in B6N mice in all seven tissues. Considering the extremely wide use of both substrains and their critical importance in generating transgenic and knock-out models, these findings guide future research across several interrelated fields.

C57BL/6N mice show a sub-strain specific resistance to the psychotomimetic effects of ketamine

Repeated administration of subanesthetic doses of ketamine is a model of psychosis-like state in rodents. In mice, this treatment produces a range of behavioral deficits, including impairment in social interactions and locomotion. To date, these phenotypes were described primarily in the Swiss and C3H/HeHsd mouse strains. A few studies investigated ketamine-induced behaviors in the C57BL/6J strain, but to our knowledge the C57BL/6N strain was not investigated thus far. This is surprising, as both C57BL/6 sub-strains are widely used in behavioral and neuropsychopharmacological research, and are de facto standards for characterization of drug effects. The goal of this study was to determine if C57BL/6N mice are vulnerable to develop social deficits after 5 days withdrawal from sub-chronic ketamine treatment (5 days, 30 mg/kg, i.p.), an experimental schedule shown before to cause deficits in social interactions in C57BL/6J mice. Our results show that sub-chronic administration of ketamine that was reported to cause psychotic-like behavior in C57BL/6J mice does not induce appreciable behavioral alterations in C57BL/6N mice. Thus, we show that the effects of sub-chronic ketamine treatment in mice are sub-strain specific.

Laboratory Codes in Nomenclature and Scientific Communication (Advancing Organism Nomenclature in Scientific Communication to Improve Research Reporting and Reproducibility)

Laboratory registration codes, also known as laboratory codes or lab codes, are a key element in standardized laboratory animal and genetic nomenclature. As such they are critical to accurate scientific communication and to research reproducibility and integrity. The original committee on Mouse Genetic Nomenclature published nomenclature conventions for mice genetics in 1940, and then conventions for inbred strains in 1952. Unique designations were needed, and have been in use since the 1950s, for the sources of animals and substrains, for the laboratories that identified new alleles or mutations, and then for developers of transgenes and induced mutations. Current laboratory codes are typically a 2- to 4-letter acronym for an institution or an investigator. Unique codes are assigned from the International Laboratory Code Registry, which was developed and is maintained by ILAR in the National Academies (National Academies of Sciences Engineering and Medicine and previously National Academy of Sciences). As a resource for the global research community, the registry has been online since 1997. Since 2003 mouse and rat genetic and strain nomenclature rules have been reviewed and updated annually as a joint effort of the International Committee on Standardized Genetic Nomenclature for Mice and the Rat Genome and Nomenclature Committee. The current nomenclature conventions (particularly conventions for non-inbred animals) are applicable beyond rodents, although not widely adopted. Ongoing recognition, since at least the 1930s, of the research relevance of genetic backgrounds and origins of animals, and of spontaneous and induced genetic variants speaks to the need for broader application of standardized nomenclature for animals in research, particularly given the increasing numbers and complexities of genetically modified swine, nonhuman primates, fish, and other species.

Importing genetically altered animals: ensuring quality

The reproducibility of research using laboratory animals requires reliable management of their quality, in particular of their genetics, health and environment, all of which contribute to their phenotypes. The point at which these biological materials are transferred between researchers is particularly sensitive, as it may result in a loss of integrity of the animals and/or their documentation. Here, we describe the various aspects of laboratory animal quality that should be confirmed when sharing rodent research models. We also discuss how repositories of biological materials support the scientific community to ensure the continuity of the quality of laboratory animals. Both the concept of quality and the role of repositories themselves extend to all exchanges of biological materials and all networks that support the sharing of these reagents.

The development of nonalcoholic steatohepatitis is subjected to breeder dependent variation in guinea pigs

Variability in disease development due to differences in strains and breeders constitutes a substantial challenge in preclinical research. However, the impact of the breeder on non-alcoholic steatohepatitis (NASH) is not yet fully elucidated. This retrospective study investigates NASH development in guinea pigs from Charles River or Envigo fed a high fat diet (20% fat, 15% sucrose, 0.35% cholesterol) for 16 or 24/25 weeks. Charles River animals displayed more severe NASH, with higher steatosis (p < 0.05 at week 16), inflammation (p < 0.05 at both week), fibrosis (p < 0.05 at week 16) and disease activity (p < 0.05 at both weeks). Accordingly, alanine and aspartate aminotransferase were increased at week 24/25 (p < 0.01). Hepatic expression of inflammatory (Ccl2, Cxcl8) and fibrotic (Pdgf, Serpine1, Col1a1) genes was also increased (p < 0.05). Differences were observed in healthy chow (4% fat, 0% sucrose, 0% cholesterol) fed animals: Envigo animals displayed higher relative liver weights (p < 0.01 at both weeks), liver cholesterol (p < 0.0001 at week 24/25) and aspartate aminotransferase (p < 0.05 at week 16), but lower levels of alkaline phosphatase (p < 0.0001 at week 24/25). These findings accentuates the importance of the breeder and its effect on NASH development and severity. Consequently, this may affect reproducibility, study comparison and limit the potential of developing novel therapies.

Inflammatory responses of C57BL/6NKorl mice to dextran sulfate sodium-induced colitis: comparison between three C57BL/6 N sub-strains

Background

Inflammatory bowel disease (IBD), including both Crohn’s disease and ulcerative colitis, are chronic human diseases that are challenging to cure and are often unable to be resolved. The inbred mouse strain C57BL/6 N has been used in investigations of IBD as an experimental animal model. The purpose of the current study was to compare the inflammatory responsiveness of C57BL/6NKorl mice, a sub-strain recently established by the National Institute of Food and Drug Safety Evaluation (NIFDS), with those of C57BL/6 N mice from two different sources using a dextran sulfate sodium (DSS)-induced colitis model.

Results

Male mice (8 weeks old) were administered DSS (0, 1, 2, or 3%) in drinking water for 7 days. DSS significantly decreased body weight and colon length and increased the colon weight-to-length ratio. Moreover, severe colitis-related clinical signs including diarrhea and rectal bleeding were observed beginning on day 4 in mice administered DSS at a concentration of 3%. DSS led to edema, epithelial layer disruption, inflammatory cell infiltration, and cytokine induction (tumor necrosis factor-α, interleukin-6, and interleukin-1β) in the colon tissues. However, no significant differences in DSS-promoted abnormal symptoms or their severity were found between the three sub-strains.

Conclusions

These results indicate that C57BL/6NKorl mice responded to DSS-induced colitis similar to the generally used C57BL6/N mice, thus this newly developed mouse sub-strain provides a useful animal model of IBD.

Meta-analysis of light and circadian timekeeping in rodents

We conducted a meta-analysis of papers published over the past half-century (1964-2017) that quantified the phase-shifting effects of timed light exposure on rodent locomotor rhythms. Descriptive statistics were tabulated in order to explore the extent to which these studies were generalizable across species, sex, age, circadian timing, and light sources. Attempts at understanding photic resetting were primarily targeted at younger male animals, with particular emphases placed on characterizing the pacemaker systems of C57BL/6 mice and Syrian hamsters during the parts of their subjective night most sensitive to delivery of white-fluorescent light. With subsequent analyses restricted to these rodent models, we then assessed the relationship between luminous exposure (via broadspectrum emission) and phase-shifting through a series of linear regressions. Monotonically increasing illuminance-response functions were noted at most circadian times surveyed. In the aggregate, our results show that previous research conducted on light's regulation of circadian timekeeping has been skewed in design with respect to several important biological variables. This bias might limit translation of phototherapy-relevant data to women and older individuals.

Substrains matter in phenotyping of C57BL/6 mice

The inbred mouse strain C57BL/6 has been widely used as a background strain for spontaneous and induced mutations. Developed in the 1930s, the C57BL/6 strain diverged into two major groups in the 1950s, namely, C57BL/6J and C57BL/6N, and more than 20 substrains have been established from them worldwide. We previously reported genetic differences among C57BL/6 substrains in 2009 and 2015. Since then, dozens of reports have been published on phenotypic differences in behavioral, neurological, cardiovascular, and metabolic traits. Substrains need to be chosen according to the purpose of the study because phenotypic differences might affect the experimental results. In this paper, we review recent reports of phenotypic and genetic differences among C57BL/6 substrains, focus our attention on the proper use of C57BL/6 and other inbred strains in the era of genome editing, and provide the life science research community wider knowledge about this subject.

Chronic fluoxetine treatment impairs motivation and reward learning by affecting neuronal plasticity in the central amygdala

BACKGROUND AND PURPOSE

The therapeutic effects of fluoxetine are believed to be due to increasing neuronal plasticity and reversing some learning deficits. Nevertheless, a growing amount of evidence shows adverse effects of this drug on cognition and some forms of neuronal plasticity.

EXPERIMENTAL APPROACH

To study the effects of chronic fluoxetine treatment, we combine an automated assessment of motivation and learning in mice with an investigation of neuronal plasticity in the central amygdala and basolateral amygdala. We use immunohistochemistry to visualize neuronal types and perineuronal nets, along with DI staining to assess dendritic spine morphology. Gel zymography is used to test fluoxetine's impact on matrix metalloproteinase-9, an enzyme involved in synaptic plasticity.

KEY RESULTS

We show that chronic fluoxetine treatment in non-stressed mice increases perineuronal nets-dependent plasticity in the basolateral amygdala, while impairing MMP-9-dependent plasticity in the central amygdala. Further, we illustrate how the latter contributes to anhedonia and deficits of reward learning. Behavioural impairments are accompanied by alterations in morphology of dendritic spines in the central amygdala towards an immature state, most likely reflecting animals' inability to adapt. We strengthen the link between the adverse effects of fluoxetine and its influence on MMP-9 by showing that behaviour of MMP-9 knockout animals remains unaffected by the drug.

CONCLUSION AND IMPLICATIONS

Chronic fluoxetine treatment differentially affects various forms of neuronal plasticity, possibly explaining its opposing effects on brain and behaviour. These findings are of immediate clinical relevance since reported side effects of fluoxetine pose a potential threat to patients.

Improving reproducibility in animal research by splitting the study population into several 'mini-experiments'

In light of the hotly discussed 'reproducibility crisis', a rethinking of current methodologies appears essential. Implementing multi-laboratory designs has been shown to enhance the external validity and hence the reproducibility of findings from animal research. We here aimed at proposing a new experimental strategy that transfers this logic into a single-laboratory setting. We systematically introduced heterogeneity into our study population by splitting an experiment into several 'mini-experiments' spread over different time points a few weeks apart. We hypothesised to observe improved reproducibility in such a 'mini-experiment' design in comparison to a conventionally standardised design, according to which all animals are tested at one specific point in time. By comparing both designs across independent replicates, we could indeed show that the use of such a 'mini-experiment' design improved the reproducibility and accurate detection of exemplary treatment effects (behavioural and physiological differences between four mouse strains) in about half of all investigated strain comparisons. Thus, we successfully implemented and empirically validated an easy-to-handle strategy to tackle poor reproducibility in single-laboratory studies. Since other experiments within different life science disciplines share the main characteristics with the investigation reported here, these studies are likely to also benefit from this approach.

Affective Disruption During Forced Ethanol Abstinence in C57BL/6J and C57BL/6NJ Mice

BACKGROUND

In alcohol-dependent individuals, acute alcohol withdrawal results in severe physiological disruption, including potentially lethal central nervous system hyperexcitability. Although benzodiazepines successfully mitigate such symptoms, this treatment does not significantly reduce recidivism rates in postdependent individuals. Instead, persistent affective disturbances that often emerge weeks to months after initial detoxification appear to play a significant role in relapse risk; however, it remains unclear whether genetic predispositions contribute to their emergence, severity, and/or duration. Interestingly, significant genotypic and phenotypic differences have been observed among distinct C57BL/6 (B6) substrains, and, in particular, C57BL/6J (B6J) mice have been found to reliably exhibit higher voluntary ethanol (EtOH) intake and EtOH preference compared to several C57BL/6N (B6N)-derived substrains. To date, however, B6 substrains have not been directly compared on measures of acute withdrawal severity or affective-behavioral disruption during extended abstinence.

METHODS

Male and female B6J and B6NJ mice were exposed to either a 7-day chronic intermittent EtOH vapor (CIE) protocol or to ordinary room air in inhalation chambers. Subsequently, blood EtOH concentrations and handling-induced convulsions were evaluated during acute withdrawal, and mice were then tested weekly for affective behavior on the sucrose preference test, light-dark box test, and forced swim test throughout 4 weeks of (forced) abstinence.

RESULTS

Despite documented differences in voluntary EtOH intake between these substrains, we found little evidence for substrain differences in either acute withdrawal or long-term abstinence between B6J and B6NJ mice.

CONCLUSIONS

In B6J and B6NJ mice, both the acute and long-term sequelae of EtOH withdrawal are dependent on largely nonoverlapping gene networks relative to those underlying voluntary EtOH drinking.

Inbred lab mice are not isogenic: genetic variation within inbred strains used to infer the mutation rate per nucleotide site

For over a century, inbred mice have been used in many areas of genetics research to gain insight into the genetic variation underlying traits of interest. The generalizability of any genetic research study in inbred mice is dependent upon all individual mice being genetically identical, which in turn is dependent on the breeding designs of companies that supply inbred mice to researchers. Here, we compare whole-genome sequences from individuals of four commonly used inbred strains that were procured from either the colony nucleus or from a production colony (which can be as many as ten generations removed from the nucleus) of a large commercial breeder, in order to investigate the extent and nature of genetic variation within and between individuals. We found that individuals within strains are not isogenic, and there are differences in the levels of genetic variation that are explained by differences in the genetic distance from the colony nucleus. In addition, we employ a novel approach to mutation rate estimation based on the observed genetic variation and the expected site frequency spectrum at equilibrium, given a fully inbred breeding design. We find that it provides a reasonable per nucleotide mutation rate estimate when mice come from the colony nucleus (~7.9 × 10⁻⁹ in C3H/HeN), but substantially inflated estimates when mice come from production colonies.

C57BL/6 substrain differences in formalin-induced pain-like behavioral responses

Substantial evidence from preclinical models of pain suggests that basal and noxious nociceptive sensitivity, as well as antinociceptive responses to drugs, show significant heritability. Individual differences to these responses have been observed across species from rodents to humans. The use of closely related C57BL/6 inbred mouse substrains can facilitate gene mapping of acute nociceptive behaviors in preclinical pain models. In this study, we investigated behavioral differences between C57BL/6 J (B6 J) and C57BL/6 N (B6 N) substrains in the formalin test, a widely used tonic inflammatory pain model, using a battery of pain-related phenotypes, including reflexive tests, nesting, voluntary wheel running, sucrose preference and anxiety-like behavior in the light/dark test at two different time points (1-h and 24-h). Our results show that these substrains did not differ in reflexive thermal and mechanical responses at the 1-h time point. However, B6 N substrain mice showed increased sensitivity to spontaneous pain-like behaviors. In addition, B6 N substrain continued to show higher levels of mechanical hypersensitivity compared to controls at 24-h. indicating that mechanical hypersensitivity is a more persistent pain-related phenotype induced by formalin. Finally, no sex differences were observed in our outcome measures. Our results provide a comprehensive behavioral testing paradigm in response to an inflammatory agent for future mouse genetic studies in pain.

Boldness in Male and Female Zebrafish (Danio rerio) Is Dependent on Strain and Test

Differences in selection pressure in nature and labs have profound effects on zebrafish strains. The widely used AB strain of zebrafish has been domesticated over several decades. Recently, there has been an upsurge in the availability of genetically modified lines, e.g., the spiegeldanio (spd), which has a mutation in the fibroblast growth factor receptor 1a (fgfr1a) gene. This mutant strain (fgfr1a) has previously been reported to be bolder than fish of the Tübingen strain, from which it was generated. Our knowledge on behavioral differences between different zebrafish strains, relative to wild-caught zebrafish, is limited. In the present study we compare behaviors related to interpretation of boldness in male and female offspring (F1) of wild-caught fish, AB and fgfr1a ^-/- zebrafish. A second aim of the study was to compare the behavior of fish from these strains when tested in different behavioral assays, i.e., shelter seeking, novel tank diving and scototaxis tests. The results demonstrate that behavioral variation exists both within and between the strains, but interpretation of boldness reveals a complex pattern in which behavior differs between strains but is also related to sex and test. Therefore, a careful assessment of various strains of fish using both males and females is warranted in order to strengthen interpretation of results. This is especially important in studies where zebrafish are used as model organisms for human conditions as well as studies evaluating the effects of pharmacological or toxicological substances on behavior.

High-throughput analysis of vocalizations reveals sex-specific changes in Fmr1 mutant pups

There have been several reports that individuals with Fragile X syndrome (FXS) and animal models of FXS have communication deficits. The present study utilized two different call classification taxonomies to examine the sex-specificity of ultrasonic vocalization (USV) production on postnatal day (PD8) in the FVB strain of Fmr1 knockout (KO) mice. One classification protocol requires the investigator to score each call by hand, while the other protocol uses an automated algorithm. Results using the hand-scoring protocol indicated that male Fmr1 KO mice exhibited longer calls (P = .03) than wild types on PD8. Male KOs also produced fewer complex, composite, downward, short and two-syllable call-types, as well as more frequency steps and chevron call-types. Female heterozygotes exhibited no significant changes in acoustic or temporal aspects of calls, yet showed significant changes in call-type production proportions across two different classification taxonomies (P < .001). They exhibited increased production of harmonic and frequency steps calls, as well as fewer chevron, downward and short calls. According to the second high-throughput analysis, female heterozygotes produced significantly fewer single-type and more multiple-type syllables, unlike male KOs that showed no changes in these aspects of syllable production. Finally, we correlated both scoring methods and found a high level of correlation between the two methods. These results contribute further knowledge of sex differences in USV calling behavior for Fmr1 heterozygote and KO mice and provide a foundation for the use of high-throughput analysis of neonatal USVs.