GluA1 AMPAR subunit deletion reduces the hedonic response to sucrose but leaves satiety and conditioned responses intact

Evidence-based comparative severity assessment in young and adult mice

In animal-based research, welfare assessments are essential for ethical and legal reasons. However, accurate assessment of suffering in laboratory animals is often complicated by the multidimensional character of distress and pain and the associated affective states. The present study aimed to design and validate multidimensional composite measure schemes comprising behavioral and biochemical parameters based on a bioinformatics approach. Published data sets from induced and genetic mouse models of neurological and psychiatric disorders were subjected to a bioinformatics workflow for cross-model analyses. ROC analyses pointed to a model-specific discriminatory power of selected behavioral parameters. Principal component analyses confirmed that the composite measure schemes developed for adult or young mice provided relevant information with the level of group separation reflecting the expected severity levels. Finally, the validity of the composite measure schemes developed for adult and young mice was further confirmed by k-means-based clustering as a basis for severity classification. The classification systems allowed the allocation of individual animals to different severity levels and a direct comparison of animal groups and other models. In conclusion, the bioinformatics approach confirmed the suitability of the composite measure schemes for evidence-based comparative severity assessment in adult and young mice. In particular, we demonstrated that the composite measure schemes provide a basis for an individualized severity classification in control and experimental groups allowing direct comparison of severity levels across different induced or genetic models. An online tool (R package) is provided, allowing the application of the bioinformatics approach to severity assessment data sets regardless of the parameters or models used. This tool can also be used to validate refinement measures.

Metabolic hormones mediate cognition

Recent biochemical and behavioural evidence indicates that metabolic hormones not only regulate energy intake and nutrient content, but also modulate plasticity and cognition in the central nervous system. Disruptions in metabolic hormone signalling may provide a link between metabolic syndromes like obesity and diabetes, and cognitive impairment. For example, altered metabolic homeostasis in obesity is a strong determinant of the severity of age-related cognitive decline and neurodegenerative disease. Here we review the evidence that eating behaviours and metabolic hormones-particularly ghrelin, leptin, and insulin-are key players in the delicate regulation of neural plasticity and cognition. Caloric restriction and antidiabetic therapies, both of which affect metabolic hormone levels can restore metabolic homeostasis and enhance cognitive function. Thus, metabolic hormone pathways provide a promising target for the treatment of cognitive decline.

Comparative Severity Assessment of Genetic, Stress-Based, and Pharmacological Mouse Models of Depression

The use of animals in neurosciences is pivotal to gaining insights into complex functions and dysfunctions of behavior. For example, various forms of physical and/or psychological stress are inherent to various animal models for psychiatric disorders, e.g., depression. Regarding animal welfare, it would be mandatory to use models that inflict the least amount of stress necessary to address the underlying scientific question. This study compared the severity of different approaches to induce depression in mice: mutagenesis in GluA1 knockout, immobilization stress, and stress-induction via stress hormone treatment. While genetic alterations potentially represent a lifelong burden, the temporary intervention only affects the animals for a limited time. Therefore, we used home cage-based behavioral and physiological parameters, including nest building, burrowing, body weight, and fecal corticosterone metabolites, to determine the well-being of male and female mice. In addition, we performed an evidence-based estimate of severity using a composite score for relative severity assessment (RELSA) with this data. We found that even though restraint stress and supplementation of corticosterone in the diet both aimed at depression-related precipitating stress effects, the latter affected the well-being much stronger, especially in females. Restraint leads to less noticeable well-being impairments but causes depression-associated anhedonic behavior. Mice of both sexes recovered well from the stress treatment. GluA1 KO and their littermates showed diminished well-being, comparable to the immobilization experiments. However, since this is a lifelong condition, this burden is not reversible and potentially accumulative. In line with the 3Rs (Replacement, Reduction, and Refinement), the process of choosing the most suitable model should ideally include an evidence-based severity assessment to be able to opt for the least severe alternative, which still induces the desired effect. Promoting refinement, in our study, this would be the restraint stress.

Development of behavioral patterns in young C57BL/6J mice: a home cage-based study

Evidence exists that behavioral patterns only stabilize once mice reach adulthood. Detailed information about the course of behavioral patterns is of particular relevance for neuroscientific research and for the assessment of cumulative severity in genetically modified mice. The analysis considered five age groups focusing on behavioral assessments in the animals’ familiar home cage environment during the adolescence phase. We confirmed age- and sex-specific differences for several of the behavioral parameters and fecal corticosterone metabolites. Interestingly, an age-dependent decline in saccharin preference was detected in female mice. Regardless of sex, relevant levels of burrowing activity were only observed during later developmental phases. The development of nest complexity following the offer of new material was affected by age in female mice. In female and male mice, an age-dependency was evident for wheel running reaching a peak at P 50. A progressive increase with age was also observed for Open field activity. The data sets provide guidance for behavioral studies and for development of composite measure schemes for evidence-based severity assessment in young mice. Except for the burrowing test, the different behavioral tests can be applied in different age groups during post-weaning development. However, age- and sex-specific characteristics need to be considered.

Cucurbitacin IIa: A review of phytochemistry and pharmacology

Cucurbitacin IIa was first found in plants and it belongs to tetracyclo triterpenoids. It is one of the most important active components in cucurbitaceae plants. Studies have found that cucurbitacin IIa has a variety of pharmacological effects, such as antitumor, antiinflammatory, antibacterial, antihepatitis B virus, inhibition of human immunodeficiency virus replication, and antidepressant effect. However, the underlying mechanisms, intracellular targets, and structure-activity relationships of cucurbitacin IIa remain to be completely elucidated. This review summarizes the current advances concerning the phytochemistry and pharmacology of cucurbitacin IIa. Electronic databases such as PubMed, Web of Science, Google Scholar, Science Direct, and CNKI were used to find relevant information about cucurbitacin IIa using keywords such as "Cucurbitacin IIa," "Pharmacology," and "Phytochemistry." These pharmacological effects involve the actin cytoskeleton aggregation, the regulation of JAK2/STAT3, ERBB-MAPK, CaMKII α/CREB/BDNF signal pathways, as well as the regulation of survivin, caspases, and other cell cycles, apoptosis, autophagy-related cytokines, and kinases. It has high development and use value.

The GluA1 AMPAR subunit is necessary for hedonic responding but not hedonic value in female mice

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GluA1 containing AMPA receptors are necessary for palatability responses to sucrose.

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Mice lacking GluA1 showed were sensitive to changes in the hedonic value of sucrose.

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This suggests that GluA1 is necessary for hedonic responding but not hedonic value.

The GluA1 subunit of the AMPA receptor has been implicated in anhedonia. Mice that lack GluA1 (Gria1 knockout mice) show reduced lick cluster size, a measure of palatability in feeding behaviour. This deficit may reflect a role for GluA1 in encoding the hedonic value of palatable substances or instead a role for GluA1 in the behavioural expression of hedonic value. We tested the role of GluA1 in hedonic value by assessing sensitivity to changes in the rewarding property of sucrose as a consequence of negative/positive contrast effects in female mice. During training, on half of the days consumption of a flavour (CS+) mixed with 4% sucrose was preceded by consumption of 1% sucrose (positive contrast). On the other half of days consumption of a different flavour (CS–) mixed with 4% sucrose was preceded by consumption of 16% sucrose (negative contrast). In the test session both wild-type, controls and Gria1 knockout mice consumed more of the CS+ flavour than the CS– flavour. While Gria1 knockout mice showed reduced lick cluster sizes, both genotypes made larger lick clusters for the CS+ flavour than the CS– flavour suggesting that the CS+ was more palatable than the CS–. A follow up experiment in normal mice demonstrated that the negative contrast procedure resulted in a conditioned reduction of palatability of the CS– in comparison to an associatively neutral, novel flavour. The results failed to demonstrate a role for GluA1 in hedonic value suggesting that, instead, GluA1 is necessary for hedonic responding.

Licking microstructure and hedonic changes after flavour preference learning in rats

Pairing a neutral flavour conditioned stimulus (CS) with a nutrient reward will create a learned preference for that CS. Prior studies suggest that this is accompanied by an increase in the hedonic value of the CS, although the reliability of this effect is yet to be fully established. Here, flavour CS+s were mixed with either 16% sucrose or maltodextrin (with control CS-s mixed with 2% solutions of the same carbohydrate). While a reliable preference for the CS+ was seen in every case, and there was a learned increase in lick cluster size when all conditions were considered together, this difference was significant in only one experimental condition considered alone. A meta-analysis of these results and similar published licking microstructure analysis studies found that the Cohen's d_av effect size for changes in licking microstructure after flavour preference learning was 0.16. This is far smaller than the effect sizes reported when assessing learned hedonic changes in flavour preference based on other test or training methods. Although this confirms that flavour preference learning produces hedonic changes in the cue flavours, the analysis of licking microstructure with training based on voluntary consumption of CS and unconditioned stimulus (US) compounds may be an insensitive means of assessing such effects.

A biphasic reduction in a measure of palatability following sucrose consumption in mice

Consumption of foods results in a transient reduction in hedonic value that influences the extent and nature of feeding behavior. The time course of this effect, however, is poorly specified. In an initial experiment, using an analysis of the microstructure of licking in mice we found that consumption of sucrose led to a rapid reduction in lick cluster size, a measure of palatability, which recovered after 10 min, but reemerged 60 min after initial consumption. We then replicated the finding that lick cluster size is reduced after 60 min, but not 10 min, under conditions in which a number of potential behavioural confounds were removed. In Experiment 2 the effect was replicated using a between-subjects design that ruled out the possibility that the effect was a specific consequence of the within-subjects procedures used in the first experiment, in which mice may have come to expect sucrose at different time points within the feeding session. While Experiments 1 and 2 confounded the time between periods of access to sucrose with time since the start of the feeding session, this confound was removed in Experiment 3, and, similar to the previous experiments, it was found that a second reduction in palatability occurred after 60 min. Therefore, the effect was dependent only on the time since the previous exposure to sucrose, demonstrating that sucrose consumption initiates a biphasic reduction in palatability. The reduction in lick cluster size after 60 min was not typically accompanied by a reduction in consumption suggesting that the more slowly developing reduction in the palatability measure was not simply a consequence of post-ingestive satiety. The cause of the biphasic change is not yet clear, and may reflect independent processes or the consequence of a single process that initiates multiple changes in palatability over time.

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Recent consumption of a palatable food results in a reduction in palatability.

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The time course of recovery of palatability after sucrose consumption was tested.

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Palatability was measured using the mean lick cluster size.

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Recent consumption of sucrose resulted in a biphasic change in lick cluster size.