Aim
Aging is thought to coincide with gradual and progressive changes in brain function and behavior over the lifetime. Our previous meta‐analytic study reported age‐related behavioral changes from ...young to middle age in male C57BL/6J mice. However, the previous study had some limitations that could affect the generalizability of the findings because of the potential influence of genetic and environmental factors on behavior, in addition to a lack of information regarding the behaviors of old‐aged mice. Here, to investigate age‐related behavioral changes from young to old age in mice, we analyzed the behaviors of male C57BL/6J mice from four different age groups (8, 47, 73, and 99 weeks of age at the beginning of the experiment) from a colony that had been maintained in a genetically controlled condition based on The Jackson Laboratory's Genetic Stability Program in an environmentally controlled animal facility.
Methods
We used a battery of behavioral tests, including the light/dark transition, open field, elevated plus maze, hot plate, social interaction, rotarod, three‐chamber social approach, prepulse inhibition, Porsolt forced swim, T‐maze, Barnes maze, tail suspension, and fear‐conditioning tests.
Results
Some behavioral changes occurred between young and middle age, and further changes in various behaviors were observed in old age. Decreased locomotor activity and increased anxiety‐like behavior were found in old‐aged mice compared to those in young and middle‐aged mice in the light/dark transition test. Similarly, an age‐dependent decrease in locomotor activity was observed in the open field test and the elevated plus maze test, while there was an age‐dependent increase in the time spent in the center area in the open field test and there were no significant differences among age groups in behavioral measures of anxiety in the elevated plus maze test. Decreases in motor performance and the auditory startle response were found in middle‐aged mice compared to those in young mice. Similar behavioral changes and increased pain sensitivity, decreased social novelty preference, reduced working and spatial memory, and impaired cued fear memory were observed in old‐aged mice compared to those in young mice. Prepulse inhibition was higher in middle‐aged mice than in young and old‐aged mice. Age‐related changes in depression‐related behavior were dependent on the type of test and the test time period.
Conclusions
This study generally confirmed our previous report regarding age‐related behavioral changes from young to middle age and expanded the previous observations by examining the behaviors of old‐aged mice. Our results show age‐related changes in a wide range of behaviors in mice from young to old age. Most behaviors showed gradual changes with advancing age, but some types of behaviors, such as vertical activity, prepulse inhibition, and depression‐related behavior, did not show unidirectional changes with age. These findings provide basic information about the behavioral characteristics of young, middle‐aged, and aged male C57BL/6J mice.
This study reports age‐related changes in a wide range of behaviors in male C57BL/6J mice from young to old age. The findings provide basic information about the behavioral characteristics of young, middle‐aged, and aged male C57BL/6J mice.
The elevated plus maze test is a widely used test for assessing anxiety-like behavior and screening novel therapeutic agents in rodents. Previous studies have shown that a variety of internal factors ...and procedural variables can influence elevated plus maze behavior. Although some studies have suggested a link between behavior and plasma corticosterone levels, the relationships between them remain unclear. In this study, we investigated the effects of experience with a battery of behavioral tests, the wall color of the closed arms, and illumination level on the behavior and plasma corticosterone responses in the elevated plus maze in male C57BL/6J mice. Mice were either subjected to a series of behavioral tests, including assessments of general health and neurological function, a light/dark transition test, and an open field test, or left undisturbed until the start of the elevated plus maze test. The mice with and without test battery experience were allowed to freely explore the elevated plus maze. The other two independent groups of naïve mice were tested in mazes with closed arms with different wall colors (clear, transparent blue, white, and black) or different illumination levels (5, 100, and 800 lx). Immediately after the test, blood was collected to measure plasma corticosterone concentrations. Mice with test battery experience showed a lower percentage of open arm time and entries and, somewhat paradoxically, had lower plasma corticosterone levels than the mice with no test battery experience. Mice tested in the maze with closed arms with clear walls exhibited higher open arm exploration than mice tested in the maze with closed arms with black walls, while there were no significant differences in plasma corticosterone levels between the different wall color conditions. Illumination levels had no significant effects on any measure. Our results indicate that experience with other behavioral tests and different physical features of the maze affect elevated plus maze behaviors. Increased open arm time and entries are conventionally interpreted as decreased anxiety-like behavior, while other possible interpretations are considered: open arm exploration may reflect heightened anxiety and panic-like reaction to a novel situation under certain conditions. With the possibility of different interpretations, the present findings highlight the need to carefully consider the test conditions in designing experiments and drawing conclusions from the behavioral outcomes in the elevated plus maze test in C57BL/6J mice.
Lactate has diverse roles in the brain at the molecular and behavioral levels under physiological and pathophysiological conditions. This study investigates whether lysine lactylation (Kla), a ...lactate-derived post-translational modification in macrophages, occurs in brain cells and if it does, whether Kla is induced by the stimuli that accompany changes in lactate levels. Here, we show that Kla in brain cells is regulated by neural excitation and social stress, with parallel changes in lactate levels. These stimuli increase Kla, which is associated with the expression of the neuronal activity marker c-Fos, as well as with decreased social behavior and increased anxiety-like behavior in the stress model. In addition, we identify 63 candidate lysine-lactylated proteins and find that stress preferentially increases histone H1 Kla. This study may open an avenue for the exploration of a role of neuronal activity-induced lactate mediated by protein lactylation in the brain.
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•Neural excitation increases lactate levels and lysine lactylation in the brain•Social defeat stress increases brain lactate and lactylation levels chronically•Stress-associated neural excitation stimulates histone H1 lactylation•The increased histone H1 lactylation is correlated with decreased social behavior
Hagihara et al. find that lysine lactylation in brain cells is regulated by systemic changes in lactate levels, neural excitation, and social defeat stress. Sixty-three lactylated proteins are identified in the mouse brain. They provide evidence for lactylation in the brain and its regulation by neural-activity-induced lactate.
Prepulse inhibition (PPI) is the suppression of a startle reflex response to a startle stimulus that occurs when a weak prepulse stimulus precedes the startle stimulus. PPI is measured to assess ...sensorimotor gating across species, including humans and rodents. Reduced PPI, which is thought to reflect dysfunction of sensorimotor gating, is reported in patients with psychiatric disorders, such as schizophrenia, bipolar disorder, and post-traumatic stress disorder (PTSD), and in animal models of these disorders. Individual differences in basal startle reactivity occur even in a genetically homogenous group of animals; however, there is limited information regarding whether basal levels of the startle response are associated with variations in PPI levels. Here, to explore the relationship between an acoustic startle response (ASR) and PPI, we performed a meta-analysis of data obtained from more than 1300 C57BL/6J male mice on the influence of an ASR to 110- and 120-dB startle stimuli on the PPI levels of the ASR at 74- and 78-dB prepulse intensities. Examination of scatter plots of the ASR amplitudes and PPI levels followed by correlation analyses indicated that there is no simple linear relationship between the two measures; when mice were divided into three groups on the basis of their startle amplitudes, there were positive correlations between the amplitude of the ASR to the 110-dB stimulus and PPI levels in a group of mice that showed lower ASR amplitudes among the genetically homogenous group, whereas no significant correlations were identified in groups of mice that showed intermediate and higher ASR amplitudes. As indicated by the correlation analysis, the lowest responders to the 110-dB stimulus exhibited lower levels of PPI than the intermediate or higher responders. In contrast, for the 120-dB stimulus, a negative correlation was identified between the amplitude of the ASR to the 120-dB stimulus and the PPI levels in the groups of mice that showed intermediate or higher ASR amplitudes. Lower and intermediate responders showed higher levels of PPI than higher responders to the 120-dB stimulus. These findings suggest that basal startle reactivity may affect PPI levels in male C57BL/6J mice, thus representing one potential confounding factor that may confuse the interpretation of PPI results. These findings emphasize the importance of careful examination of startle reactivity to ensure a reliable assessment of PPI.
Aims
Restraint stress is one of the most widely used experimental methods for generating rodent models of stress‐induced neuropsychiatric disorders, such as depression and anxiety. Although various ...types of restraint apparatuses have been used to expose animals to stress, the magnitudes of the effects of stress exposure via different types of restraint apparatuses on physiology and behavior have not been compared in the same environment. Here, we investigated the effects of stress exposure via two types of restraint apparatuses on body weight, locomotor activity, anxiety‐ and depression‐related behaviors, and plasma corticosterone levels in mice.
Methods
Adult male BALB/cAJcl mice were restrained by placing them in either a well‐ventilated plastic conical tube or a tapered plastic film envelope for 6 hours per day for 10 or 21 consecutive days. Mice were weighed during and after the stress period and were subjected to a battery of behavioral tests, including light/dark transition, open field, elevated plus maze, Porsolt forced swim, tail suspension, and sucrose preference tests, starting on the day after the last stress session. Plasma corticosterone levels were measured in another cohort of mice on the 1st and the 21st stress sessions and after the Porsolt forced swim test.
Results
Exposure to repeated stress via the two above mentioned types of restraint apparatuses caused body weight loss, heightened locomotor activity, altered immobility during forced swim, and increased plasma corticosterone levels, and some of these results differed between the restraint stress protocols. Film‐restraint–stressed mice had significantly lower body weights than tube‐restraint–stressed mice. Film‐restraint–stressed mice exhibited significantly higher or lower immobility during forced swim than tube‐restraint–stressed mice, depending on the test time. Additionally, the stress‐induced increase in plasma corticosterone levels was found to be higher in film‐restraint–stressed mice than in tube‐restraint–stressed mice.
Conclusion
Our results indicate that film‐restraint stress has more pronounced effects on body weight, depression‐related behavior, and corticosterone response than tube‐restraint stress in mice. These findings may help guide which restraint stress procedures to use, depending on the objectives of a given study, in generating animal models of stress‐induced neuropsychiatric disorders.
This study investigated the effects of stress exposure via two types of restraint apparatuses, a well‐ventilated plastic conical tube and a tapered plastic film envelope, on body weights, behaviors, and plasma corticosterone levels in male BALB/cAJcl mice. Film‐restraint stress had more pronounced effects on body weight, depression‐related behavior, and corticosterone response than tube‐restraint stress, which may help guide which restraint stress procedures to use in generating animal models of stress‐induced disorders.
Pregnancy and lactation are characterized by dramatic changes in the endocrine system and brain in mammalian females. These changes, with stress before pregnancy, are potential risk factors for the ...development of postpartum depression (PPD). A valid animal model of PPD is needed to understand the neurobiological basis of the depressive state of females. To explore a mouse model of PPD, we first assessed anxiety-like and depression-related behaviors in nulliparous (virgin), nonlactating primiparous, and lactating primiparous females in four inbred strains of mice (C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl). Pups from the nonlactating female group were removed one day after parturition to examine the effects of physical interaction with pups on the postpartum behaviors. Second, we investigated the additional effects of prepregnancy stress (restraint stress for 6 h/day for 21 days) on postpartum behaviors in the BALB/cAJcl strain. We found that females of the two BALB/c substrains showed decreased locomotor activity and increased anxiety-like and depression-related behaviors compared with females of the two C57BL/6 substrains. Behavioral differences were also observed between the two substrains of each strain. Additionally, pregnancy- and lactation-dependent behavioral differences were found in some strains: lactating BALB/cAJcl females traveled shorter distance than the females of the other reproductive state groups, while nonlactating and lactating BALB/cAJcl and C57BL/6J females showed increased depression-related behavior compared with nulliparous females. Lactating BALB/cAJcl and C57BL/6JJcl females exhibited decreased sucrose preference or anhedonia-like behavior compared with nulliparous and nonlactating females, although these results did not reach statistical significance after correction for multiple testing. An additional independent experiment replicated the marked behavioral changes in lactating BALB/cAJcl females. Moreover, increased anxiety-like behavior was observed in lactating BALB/cAJcl females that experienced prepregnancy stress. These results suggest genetic contributions to the regulation of anxiety-like and depression-related behaviors in female mice. Furthermore, this study suggests that pregnancy and lactation cause decreased locomotor activity and increased depression-related behaviors, which was consistently found in our results, and that prepregnancy stress enhances anxiety-like behavior in the BALB/cAJcl strain. The inbred strain of female mice may be used as a potential model of PPD to further study the genetic and neurobiological mechanisms underlying the development of this disorder.
The contextual and cued fear conditioning test is one of the behavioral tests that assesses the ability of mice to learn and remember an association between environmental cues and aversive ...experiences. In this test, mice are placed into a conditioning chamber and are given parings of a conditioned stimulus (an auditory cue) and an aversive unconditioned stimulus (an electric footshock). After a delay time, the mice are exposed to the same conditioning chamber and a differently shaped chamber with presentation of the auditory cue. Freezing behavior during the test is measured as an index of fear memory. To analyze the behavior automatically, we have developed a video analyzing system using the ImageFZ application software program, which is available as a free download at http://www.mouse-phenotype.org/. Here, to show the details of our protocol, we demonstrate our procedure for the contextual and cued fear conditioning test in C57BL/6J mice using the ImageFZ system. In addition, we validated our protocol and the video analyzing system performance by comparing freezing time measured by the ImageFZ system or a photobeam-based computer measurement system with that scored by a human observer. As shown in our representative results, the data obtained by ImageFZ were similar to those analyzed by a human observer, indicating that the behavioral analysis using the ImageFZ system is highly reliable. The present movie article provides detailed information regarding the test procedures and will promote understanding of the experimental situation.
Throughout life, new neurons are continuously added to the dentate gyrus. As this continuous addition remodels hippocampal circuits, computational models predict that neurogenesis leads to ...degradation or forgetting of established memories. Consistent with this, increasing neurogenesis after the formation of a memory was sufficient to induce forgetting in adult mice. By contrast, during infancy, when hippocampal neurogenesis levels are high and freshly generated memories tend to be rapidly forgotten (infantile amnesia), decreasing neurogenesis after memory formation mitigated forgetting. In precocial species, including guinea pigs and degus, most granule cells are generated prenatally. Consistent with reduced levels of postnatal hippocampal neurogenesis, infant guinea pigs and degus did not exhibit forgetting. However, increasing neurogenesis after memory formation induced infantile amnesia in these species.
The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission. Mice genetically deficient in 5-HTT expression have been used to study the physiological ...functions of 5-HTT in the brain and have been proposed as a potential animal model for neuropsychiatric and neurodevelopmental disorders. Recent studies have provided evidence for a link between the gut-brain axis and mood disorders. However, the effects of 5-HTT deficiency on gut microbiota, brain function, and behavior remain to be fully characterized. Here we investigated the effects of 5-HTT deficiency on different types of behavior, the gut microbiome, and brain c-Fos expression as a marker of neuronal activation in response to the forced swim test for assessing depression-related behavior in male 5-HTT knockout mice. Behavioral analysis using a battery of 16 different tests showed that 5-HTT-/- mice exhibited markedly reduced locomotor activity, decreased pain sensitivity, reduced motor function, increased anxiety-like and depression-related behavior, altered social behavior in novel and familiar environments, normal working memory, enhanced spatial reference memory, and impaired fear memory compared to 5-HTT+/+ mice. 5-HTT+/- mice showed slightly reduced locomotor activity and impaired social behavior compared to 5-HTT+/+ mice. Analysis of 16S rRNA gene amplicons showed that 5-HTT-/- mice had altered gut microbiota abundances, such as a decrease in Allobaculum, Bifidobacterium, Clostridium sensu stricto, and Turicibacter, compared to 5-HTT+/+ mice. This study also showed that after exposure to the forced swim test, the number of c-Fos-positive cells was higher in the paraventricular thalamus and lateral hypothalamus and was lower in the prefrontal cortical regions, nucleus accumbens shell, dorsolateral septal nucleus, hippocampal regions, and ventromedial hypothalamus in 5-HTT-/- mice than in 5-HTT+/+ mice. These phenotypes of 5-HTT-/- mice partially recapitulate clinical observations in humans with major depressive disorder. The present findings indicate that 5-HTT-deficient mice serve as a good and valid animal model to study anxiety and depression with altered gut microbial composition and abnormal neuronal activity in the brain, highlighting the importance of 5-HTT in brain function and the mechanisms underlying the regulation of anxiety and depression.
Aim
Capric acid (also known as decanoic acid or C10) is one of the fatty acids in the medium‐chain triglycerides (MCTs) commonly found in dietary fats. Although dietary treatment with MCTs is ...recently of great interest for the potential therapeutic effects on neuropsychiatric disorders, the effects of oral administration of C10 on behavior remain to be examined. This study investigated acute and chronic effects of oral administration of C10 on locomotor activity and anxiety‐like and depression‐related behaviors in adult male C57BL/6J mice.
Methods
To explore the acute effects of C10 administration, mice were subjected to a series of behavioral tests in the following order: light/dark transition, open field, elevated plus maze, Porsolt forced swim, and tail suspension tests, 30 minutes after oral gavage of either vehicle or C10 solution (30 mmol/kg dose in Experiment 1; 0.1, 0.3, 1.0, 3.0 mmol/kg doses in Experiment 2). Next, to examine chronic effects of C10, mice repeatedly administered with either vehicle or C10 solution (0.3, 3.0 mmol/kg doses per day, for 21 days, in Experiment 3) were subjected to behavioral tests without oral administration immediately before each test.
Results
The mice administrated with the high dose of C10 (30 mmol/kg) showed lower body weights, shorter distance traveled, and more anxiety‐like behavior than vehicle‐treated mice, and the results reached study‐wide statistical significance. The C10 administration at a lower dose of 0.3 mmol/kg had no significant effects on body weights and induced nominally significantly longer distance traveled than vehicle administration. Repeated administration of C10 at a dose of 3.0 mmol/kg for more than 21 days caused lower body weights and decreased depression‐related behavior, although the behavioral differences did not reach study‐wide significance.
Conclusions
Although these results suggest dose‐dependent effects of oral administration of capric acid on locomotor activity and anxiety‐like and depression‐related behaviors, further study will be needed to replicate the findings and explore the underlying brain mechanisms.
Repeated oral administration of the medium‐chain fatty acid, capric acid, decreased depression‐related behavior in C57BL/6J mice. This study suggests that capric acid exerts an antidepressant effect.
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