Sex differences in the timing behavior performance of 3xTg-AD and wild-type mice in the peak interval procedure

Apathy-like behaviour in tau mouse models of Alzheimer's disease and frontotemporal dementia

Apathy is the most common behavioural and psychological symptom in Alzheimer's disease (AD) and other neurodegenerative diseases including frontotemporal dementia (FTD) and Parkinson's disease (PD). In patients, apathy can include symptoms of loss of motivation, initiative, and interest, listlessness, and indifference, flattening of emotions, absence of drive and passion. Researchers have later refined this to a reduction in goal direct behaviours. In animals, specific symptoms of apathy-like behaviour have been modelled including goal directed or nest-building behaviour which are seen as indicative of proxies for motivation and daily activities. In the present study a nest-building protocol was established using four different inbred mouse strains (CD1, BALB/c, C57Bl/6J, C3H) before assessing AD and FTD tau transgenic mice of Line 1 (L1) and Line 66 (L66) in this paradigm. Female mice aged 5 - 6 months were assessed in the home cage over a period of 7 days with nest-building behaviour scored by three independent experimenters at intervals of 1-, 2- and 7-days post nestlet introduction. Inbred mouse strains displayed different levels of nesting behaviour. BALB/c mice were more proficient than CD1 and C3H mice, while all strains displayed similar nest-building behaviour by day 7. In the tau mouse models, L66 presented with impaired nesting compared to wild-type on days 1 and 2 (not day 7), whereas L1 performed like wild-type on all days. Anhedonia measured in a sucrose preference test was only observed in L66. Anhedonia and low nesting scores in L66 mice are indicative of apathy-like phenotypes. Differences evident between the L1 and L66 tau transgenic mouse models are likely due to the different human tau species expressed in these mice.

The effects of noise exposure on hippocampal cognition in C57BL/6 mice via transcriptomics

BACKGROUND

Noise is an important environmental stressor in the industrialized world and has received increasing attention in recent years. Although epidemiological research has extensively demonstrated the relationship between noise and cognitive impairment, the specific molecular mechanisms and targets remain to be fully explored and understood.

METHODS

To address this issue, 5-month-old C57BL/6 mice were divided into two groups, with one group exposed to white noise at 98 dB. The effects of noise on cognition in mice were investigated through molecular biology and behavioral experiments. Subsequently, transcriptomic sequencing of the hippocampus in both groups of mice was performed and enrichment analysis of differentially expressed genes (DEGs) was conducted using KEGG and GO databases. Furthermore, LASSO analysis was used to further narrow down the relevant DEGs, followed by enrichment analysis of these genes using KEGG and GO databases. The DEGs were further validated by rt-qPCR.

RESULTS

Following noise exposure, the hippocampus levels of inflammation-related factors increased, the phosphorylation of Tau protein increased, the postsynaptic density protein decreased, the number of Nissl bodies decreased, and cell shrinkage in the hippocampus increased. Moreover, the behavioral experiments manifest characteristics indicative of a decline in cognitive.A total of 472 DEGs were identified through transcriptomic analysis, and seven relevant genes were screened by the LASSO algorithm, which were further validated by PCR to confirm their consistency with the omics results.

CONCLUSION

In conclusion, noise exposure affects cognitive function in mice through multiple pathways, and the omics results provide new evidence for the cognitive impairment induced by noise exposure.

Imbalance of multiple neurotransmitter pathways leading to depression-like behavior and cognitive dysfunction in the triple transgenic mouse model of Alzheimer disease

Depression is among the most frequent psychiatric comorbid conditions in Alzheimer disease (AD). However, pharmacotherapy for depressive disorders in AD is still a big challenge, and the data on the efffcacy of current antidepressants used clinically for depressive symptoms in patients with AD remain inconclusive. Here we investigated the mechanism of the interactions between depression and AD, which we believe would aid in the development of pharmacological therapeutics for the comorbidity of depression and AD. Female APP/PS1/Tau triple transgenic (3×Tg-AD) mice at 24 months of age and age- and sex-matched wild-type (WT) mice were used. The shuttle-box passive avoidance test (PAT) were implemented to assess the abilities of learning and memory, and the open field test (OFT) and the tail suspension test (TST) were used to assess depression-like behavior. High-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was used to detect the level of neurotransmitters related to depression in the hippocampus of mice. The data was identified by orthogonal projections to latent structures discriminant analysis (OPLS-DA). Most neurotransmitters exert their effects by binding to the corresponding receptor, so the expression of relative receptors in the hippocampus of mice was detected using Western blot. Compared to WT mice, 3×Tg-AD mice displayed significant cognitive impairment in the PAT and depression-like behavior in the OFT and TST. They also showed significant decreases in the levels of L-tyrosine, norepinephrine, vanillylmandelic acid, 5-hydroxytryptamine, and acetylcholine, in contrast to significant increases in 5-hydroxyindoleacetic acid, L-histidine, L-glutamine, and L-arginine in the hippocampus. Moreover, the expression of the alpha 1a adrenergic receptor (ADRA1A), serotonin 1 A receptor (5HT1A), and γ-aminobutyric acid A receptor subunit alpha-2 (GABRA2) was significantly downregulated in the hippocampus of 3×Tg-AD mice, while histamine H3 receptor (H3R) expression was significantly upregulated. In addition, the ratio of phosphorylated cAMP-response element-binding protein (pCREB) and CREB was significantly decreased in the hippocampus of 3×Tg-AD mice than WT mice. We demonstrated in the present study that aged female 3×Tg-AD mice showed depression-like behavior accompanied with cognitive dysfunction. The complex and diverse mechanism appears not only relevant to the imbalance of multiple neurotransmitter pathways, including the transmitters and receptors of the monoaminergic, GABAergic, histaminergic, and cholinergic systems, but also related to the changes in L-arginine and CREB signaling molecules.

Sex similarities and dopaminergic differences in interval timing

Rodent behavioral studies have largely focused on male animals, which has limited the generalizability and conclusions of neuroscience research. Working with humans and rodents, we studied sex effects during interval timing that requires participants to estimate an interval of several seconds by making motor responses. Interval timing requires attention to the passage of time and working memory for temporal rules. We found no differences between human females and males in interval timing response times (timing accuracy) or the coefficient of variance of response times (timing precision). Consistent with prior work, we also found no differences between female and male rodents in timing accuracy or precision. In female rodents, there was no difference in interval timing between estrus and diestrus cycle stages. Because dopamine powerfully affects interval timing, we also examined sex differences with drugs targeting dopaminergic receptors. In both female and male rodents, interval timing was delayed after administration of sulpiride (D2-receptor antagonist), quinpirole (D2-receptor agonist), and SCH-23390 (D1-receptor antagonist). By contrast, after administration of SKF-81297 (D1-receptor agonist), interval timing shifted earlier only in male rodents. These data illuminate sex similarities and differences in interval timing. Our results have relevance for rodent models of both cognitive function and brain disease by increasing represenation in behavioral neuroscience.

A behavioral timing intervention upregulates striatal serotonergic markers and reduces impulsive action in adult male mice

Many studies support the hypothesis that time-based interventions reduce impulsive behavior in rodents. However, few studies have directly assessed 1) how such interventions affect impulsive action rather than impulsive choice, 2) if intervention effects differ by sex, and 3) how time-based interventions affect neurochemistry in regions mediating decision-making and reward. Thus, we assessed how a fixed-interval (FI) intervention initiated during late adolescence and extending into adulthood affected dopaminergic and serotonergic analytes in the frontal cortex and striatum and subsequent impulsive action in adult male and female mice. Beginning on postnatal day (PND) 45, mice were either trained on a progressive series of FI schedules (FI 20, 40, & 60 s) or remained in the home cage. Following the intervention, increases in striatal serotonergic analytes were found in FI-exposed males and females (n = 8/sex/group) with few changes found in the frontal cortex. Impulsive action was assessed in the remaining mice (n = 10/sex/group) using a fixed-ratio waiting-for-reward (FR-wait) task in which completion of an FR-25 component initiated a "free" pellet component in which pellets were delivered at increasing intervals according to a fixed delay increment that varied across sessions. Responses reset the additive delay and initiated a new FR-25 component. FI-exposed males, but not females, showed fewer delay resets and no-wait resets relative to control mice. Importantly, FI-exposure did not affect discrimination reversal performance in either sex. These data suggest that time-based interventions may reduce impulsive action in addition to impulsive choice perhaps with increased male sensitivity. Additionally, time-based interventions appear to operate through striatal serotonergic augmentation.

Bioinformatics analysis of diagnostic biomarkers for Alzheimer's disease in peripheral blood based on sex differences and support vector machine algorithm

Background

The prevalence of Alzheimer's disease (AD) varies based on gender. Due to the lack of early stage biomarkers, most of them are diagnosed at the terminal stage. This study aimed to explore sex-specific signaling pathways and identify diagnostic biomarkers of AD.

Methods

Microarray dataset for blood was obtained from the Gene Expression Omnibus (GEO) database of GSE63060 to conduct differentially expressed genes (DEGs) analysis by R software limma. Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene set enrichment analysis (GSEA) were conducted. Immune checkpoint gene expression was compared between females and males. Using CytoHubba, we identified hub genes in a protein–protein interaction network (PPI). Then, we evaluated their distinct effectiveness using unsupervised hierarchical clustering. Support vector machine (SVM) and ten-fold cross-validation were used to further verify these biomarkers. Lastly, we confirmed our findings by using another independent dataset.

Results

A total of 37 female-specific DEGs and 27 male-specific DEGs were identified from GSE63060 datasets. Analyses of enrichment showed that female-specific DEGs primarily focused on energy metabolism, while male-specific DEGs mostly involved in immune regulation. Three immune-checkpoint-relevant genes dysregulated in males. In females, however, these eight genes were not differentially expressed. SNRPG, RPS27A, COX7A2, ATP5PO, LSM3, COX7C, PFDN5, HINT1, PSMA6, RPS3A and RPL31 were regarded as hub genes for females, while SNRPG, RPL31, COX7C, RPS27A, RPL35A, RPS3A, RPS20 and PFDN5 were regarded as hub genes for males. Thirteen hub genes mentioned above was significantly lower in both AD and mild cognitive impairment (MCI). The diagnostic model of 15-marker panel (13 hub genes with sex and age) was developed. Both the training dataset and the independent validation dataset have area under the curve (AUC) with a high value (0.919, 95%CI 0.901–0.929 and 0.803, 95%CI 0.789–0.826). Based on GSEA for hub genes, they were associated with some aspects of AD pathogenesis.

Conclusion

DEGs in males and females contribute differently to AD pathogenesis. Algorithms combining blood-based biomarkers may improve AD diagnostic accuracy, but large validation studies are needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-022-00252-x.

Not All Mice Are Created Equal: Interval Timing Accuracy and Scalar Timing in 129, Swiss-Webster, and C57BL/6 Mice

Many species, including humans, show both accurate timing − appropriate time estimation in the seconds to minutes range − and scalar timing − time estimation error varies linearly with estimated duration. Behavioral paradigms aimed at investigating interval timing are expected to evaluate these dissociable characteristics of timing. However, when evaluating interval timing in models of neuropsychiatric disease, researchers are confronted with a lack of adequate studies about the parent (background) strains, since accuracy and scalar timing have only been demonstrated for the C57BL/6 strain of mice (Buhusi, Aziz, Winslow, Carter, Swearingen, & Buhusi (2009) Behav. Neurosci., 123, 1102–1113). We used a peak-interval (PI) procedure with three intervals − a protocol in which other species, including humans, demonstrate accurate, scalar timing − to evaluate timing accuracy and scalar timing in three strains of mice frequently used in genetic and behavioral studies: 129, Swiss-Webster (SW), and C57BL/6. C57BL/6 mice showed accurate, scalar timing, while 129 and SW mice showed departures from accuracy and/or scalar timing. Results suggest that the genetic background/strain of the mouse is a critical variable for studies investigating interval timing in genetically engineered mice. Our study validates the PI procedure with multiple intervals as a proper technique, and the C57BL/6 strain as the most suitable genetic background to date for behavioral investigations of interval timing in genetically engineered mice modeling human disorders. In contrast, studies using mice in 129, SW, or mixed-background strains should be interpreted with caution, and thorough investigations of accuracy and scalar timing should be conducted before a less studied strain of mouse is considered for use in timing studies.

Abnormal whisker movements in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease is the most frequent form of dementia in elderly people. The triple transgenic (3xTg-AD) mouse model of Alzheimer's Disease is important in biomedical research as these mice develop both neuropathological and behavioural phenotypes. However, their behavioural phenotype is variable, with findings depending on the specific task, as well as the age and sex of the mice. Whisker movements show motor, sensory and cognitive deficits in mouse models of neurodegenerative disease. Therefore, we examined whisker movements in 3, 12.5 and 17-month-old female 3xTg-AD mice and their B6129S/F2 wildtype controls. Mice were filmed using a high-speed video camera (500 fps) in an open arena during a novel object exploration task. Genotype and age differences were found in mice exploring the arena prior to object contact. Prior to whisker contact, the 3-month-old 3xTg-AD mice had smaller whisker angles compared with the wildtype controls, suggesting an early motor phenotype in these mice. Pre-contact mean angular position at 3 months and whisking amplitude at 17 months of age differed between the 3xTg-AD and wildtype mice. During object contact 3xTg-AD mice did not reduce whisker spread as frequently as the wildtype mice at 12.5 and 17 months, which may suggest sensory or attentional deficits. We show that whisker movements are a powerful behavioural measurement tool for capturing behavioural deficits in mouse models that show complex phenotypes, such as the 3xTg-AD mouse model.

Mice expressing P301S mutant human tau have deficits in interval timing

Interval timing is a key executive process that involves estimating the duration of an interval over several seconds or minutes. Patients with Alzheimer's disease (AD) have deficits in interval timing. Since temporal control of action is highly conserved across mammalian species, studying interval timing tasks in animal AD models may be relevant to human disease. Amyloid plaques and tau neurofibrillary tangles are hallmark features of AD. While rodent models of amyloid pathology are known to have interval timing impairments, to our knowledge, interval timing has not been studied in models of tauopathy. Here, we evaluate interval timing performance of P301S transgenic mice, a widely studied model of tauopathy that overexpresses human tau with the P301S mutation. We employed an interval timing task and found that P301S mice consistently underestimated temporal intervals compared to wild-type controls, responding early in anticipation of the target interval. Our study indicating timing deficits in a mouse tauopathy model could have relevance to human tauopathies such as AD.

A Signal Detection Analysis of Olfactory Learning in 12-Month-Old 5xFAD Mice

Although Alzheimer’s disease is most often studied in terms of memory impairments, olfactory dysfunction begins in the early stages. We tested olfactory learning, sensitivity, and response bias using signal detection methods in 12-month-old male and female 5xFAD mice and their wildtype controls in the operant olfactometer. Odor detection was not reduced in the 5xFAD mice, but learning was, which was worse in female 5xFAD mice than in males. Female mice were more conservative in their response strategy. Signal detection analysis allows us to discriminate between cognitive and sensory deficits of male and female mouse models of AD.

Auditory sensory deprivation induced by noise exposure exacerbates cognitive decline in a mouse model of Alzheimer's disease

Although association between hearing impairment and dementia has been widely documented by epidemiological studies, the role of auditory sensory deprivation in cognitive decline remains to be fully understood. To address this issue we investigated the impact of hearing loss on the onset and time-course of cognitive decline in an animal model of Alzheimer's disease (AD), that is the 3×Tg-AD mice and the underlying mechanisms. We found that hearing loss induced by noise exposure in the 3×Tg-AD mice before the phenotype is manifested caused persistent synaptic and morphological alterations in the auditory cortex. This was associated with earlier hippocampal dysfunction, increased tau phosphorylation, neuroinflammation, and redox imbalance, along with anticipated memory deficits compared to the expected time-course of the neurodegenerative phenotype. Our data suggest that a mouse model of AD is more vulnerable to central damage induced by hearing loss and shows reduced ability to counteract noise-induced detrimental effects, which accelerates the neurodegenerative disease onset.

Similar attention and performance in female and male CD1 mice in the peak procedure

Inaccurate and distorted timing are associated with neurodegenerative disorders such as Alzheimer's disease and schizophrenia in humans, which generates interest in the discovery and understanding of the factors behind such timing difficulties. Timing research in mice has taken an important role, because the availability of genetically-altered strains allows establishing the causal role of specific genes on such neurodegenerative disorders. Nevertheless, few studies have considered mice's sex and some have found sex differences in timing, although results are not yet conclusive. We tested female and male CD1 mice, an outbred strain not yet studied in a peak procedure. By varying the percentage of peak trials and the presence of a gap and/or a distractor in the tests, we found no sex differences in accuracy, precision, or attention. Both females and males followed a stop-clock strategy after distractor and gap + distractor trials. This suggests that both male and female CD1 mice may be exposed to a peak procedure to study factors associated to neurotoxicology or neurogenesis.

Alzheimer's pathogenic mechanisms and underlying sex difference

AD is a neurodegenerative disease, and its frequency is often reported to be higher for women than men: almost two-thirds of patients with AD are women. One prevailing view is that women live longer than men on average of 4.5 years, plus there are more women aged 85 years or older than men in most global subpopulations; and older age is the greatest risk factor for AD. However, the differences in the actual risk of developing AD for men and women of the same age is difficult to assess, and the findings have been mixed. An increasing body of evidence from preclinical and clinical studies as well as the complications in estimating incidence support the sex-specific biological mechanisms in diverging AD risk as an important adjunct explanation to the epidemiologic perspective. Although some of the sex differences in AD prevalence are due to differences in longevity, other distinct biological mechanisms increase the risk and progression of AD in women. These risk factors include (1) deviations in brain structure and biomarkers, (2) psychosocial stress responses, (3) pregnancy, menopause, and sex hormones, (4) genetic background (i.e., APOE), (5) inflammation, gliosis, and immune module (i.e., TREM2), and (6) vascular disorders. More studies focusing on the underlying biological mechanisms for this phenomenon are needed to better understand AD. This review presents the most recent data in sex differences in AD-the gateway to precision medicine, therefore, shaping expert perspectives, inspiring researchers to go in new directions, and driving development of future diagnostic tools and treatments for AD in a more customized way.

Spatial Memory and Gut Microbiota Alterations Are Already Present in Early Adulthood in a Pre-clinical Transgenic Model of Alzheimer's Disease

The irreversible and progressive neurodegenerative Alzheimer’s disease (AD) is characterized by cognitive decline, extracellular β-amyloid peptide accumulation, and tau neurofibrillary tangles in the cortex and hippocampus. The triple-transgenic (3xTg) mouse model of AD presents memory impairment in several behavioral paradigms and histopathological alterations from 6 to 16 months old. Additionally, it seems that dysbiotic gut microbiota is present in both mouse models and patients of AD at the cognitive symptomatic stage. The present study aimed to assess spatial learning, memory retention, and gut microbiota alterations in an early adult stage of the 3xTg-AD mice as well as to explore its sexual dimorphism. We evaluated motor activity, novel-object localization training, and retention test as well as collected fecal samples to characterize relative abundance, alpha- and beta-diversity, and linear discriminant analysis (LDA) effect size (LEfSe) analysis in gut microbiota in both female and male 3xTg-AD mice, and controls [non-transgenic mice (NoTg)], at 3 and 5 months old. We found spatial memory deficits in female and male 3xTg-AD but no alteration neither during training nor in motor activity. Importantly, already at 3 months old, we observed decreased relative abundances of Actinobacteria and TM7 in 3xTg-AD compared to NoTg mice, while the beta diversity of gut microbiota was different in female and male 3xTg-AD mice in comparison to NoTg. Our results suggest that gut microbiota modifications in 3xTg-AD mice anticipate and thus could be causally related to cognitive decline already at the early adult age of AD. We propose that microbiota alterations may be used as an early and non-invasive diagnostic biomarker of AD.

Timing behavior in genetic murine models of neurological and psychiatric diseases

How timing behavior is altered in different neurodevelopmental and neurodegenerative disorders is a contemporary research question. Genetic murine models (GMM) that offer high construct validity also serve as useful tools to investigate this question. But the literature on timing behavior of different GMMs largely remains to be consolidated. The current paper addresses this gap by reviewing studies that have been conducted with GMMs of neurodevelopmental (e.g. ADHD, schizophrenia, autism spectrum disorder), neurodegenerative disorders (e.g., Alzheimer's disease, Huntington's disease) as well as circadian and other mutant lines. The review focuses on those studies that specifically utilized the peak interval procedure to improve the comparability of findings both within and between different disease models. The reviewed studies revealed timing deficits that are characteristic of different disorders. Specifically, Huntington's disease models had weaker temporal control over the termination of their anticipatory responses, Alzheimer's disease models had earlier timed responses, schizophrenia models had weaker temporal control, circadian mutants had shifted timed responses consistent with shifts in the circadian periods. The differences in timing behavior were less consistent for other conditions such as attention deficit and hyperactivity disorder and mutations related to intellectual disability. We discuss the implications of these findings for the neural basis of an internal stopwatch. Finally, we make methodological recommendations for future research for improving the comparability of the timing behavior across different murine models.

The Peak Interval Procedure in Rodents: A Tool for Studying the Neurobiological Basis of Interval Timing and Its Alterations in Models of Human Disease

Animals keep track of time intervals in the seconds to minutes range with, on average, high accuracy but substantial trial-to-trial variability. The ability to detect the statistical signatures of such timing behavior is an indispensable feature of a good and theoretically-tractable testing procedure. A widely used interval timing procedure is the peak interval (PI) procedure, where animals learn to anticipate rewards that become available after a fixed delay. After learning, they cluster their responses around that reward-availability time. The in-depth analysis of such timed anticipatory responses leads to the understanding of an internal timing mechanism, that is, the processing dynamics and systematic biases of the brain's clock. This protocol explains in detail how the PI procedure can be implemented in rodents, from training through testing to analysis. We showcase both trial-by-trial and trial-averaged analytical methods as a window into these internal processes. This protocol has the advantages of capturing timing behavior in its full-complexity in a fashion that allows for a theoretical treatment of the data.

Scopolamine and Medial Frontal Stimulus-Processing during Interval Timing

Neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and Alzheimer's disease (AD) involve loss of cholinergic neurons in the basal forebrain. Here, we investigate how cholinergic dysfunction impacts the frontal cortex during interval timing, a process that can be impaired in PD and AD patients. Interval timing requires participants to estimate an interval of several seconds by making a motor response, and depends on the medial frontal cortex (MFC), which is richly innervated by basal forebrain cholinergic projections. Past work has shown that scopolamine, a muscarinic cholinergic receptor antagonist, reliably impairs interval timing. We tested the hypothesis that scopolamine would attenuate time-related ramping, a key form of temporal processing in the MFC. We recorded neuronal ensembles from eight mice during performance of a 12-s fixed-interval timing task, which was impaired by the administration of scopolamine. Consistent with past work, scopolamine impaired timing. To our surprise, we found that time-related ramping was unchanged, but stimulus-related activity was enhanced in the MFC. Principal component analyses revealed no consistent changes in time-related ramping components, but did reveal changes in higher components. Taken together, these data indicate that scopolamine changes stimulus processing rather than temporal processing in the MFC. These data could help understand how cholinergic dysfunction affects cortical circuits in diseases such as PD, DLB, and AD.

Interval timing is disrupted in female 5xFAD mice: An indication of altered memory processes

Temporal information processing in the seconds-to-minutes range is disrupted in patients with Alzheimer's disease (AD). In this study, we investigated the timing behavior of the 5xFAD mouse model of AD in the peak interval (PI) procedure. Nine-month-old female mice were trained with sucrose solution reinforcement for their first response after a fixed-interval (FI) and tested in the inter-mixed non-reinforced PI trials that lasted longer than FI. Timing performance indices were estimated from steady-state timed anticipatory nose-poking responses in the PI trials. We found that the time of maximal reward expectancy (peak time) of the 5xFAD mice was significantly earlier than that of the wild-type (WT) controls with no differences in other indices of timing performance. These behavioral differences corroborate the findings of previous studies on the disruption of temporal associative memory abilities of 5xFAD mice and can be accounted for by the scalar timing theory based on altered long-term memory consolidation of temporal information in the 5xFAD mice. This is the first study to directly show an interval timing phenotype in a genetic mouse model of AD.