Feasibility of applying a noninvasive method for sleep monitoring based on mouse behaviors.

INTRODUCTION: Currently, electroencephalogram (EEG)/electromyogram (EMG) system is widely regarded as the "golden standard" for sleep monitoring. Imperfectly, its invasive monitoring may somehow interfere with the natural state of sleep. Up to now, noninvasive methods for sleep monitoring have developed, which could preserve the undisturbed and naïve sleep state of mice to the greatest extent, but the feasibility of their application under different conditions should be extensive validated. METHODS: Based on existing research, we verified the feasibility of a sleep monitoring system based on mouse behaviors under different conditions. The experimental mice were exposed to various stresses and placed into a combined device comprising noninvasive sleep monitoring equipment and an EEG/EMG system, and the sleep status was recorded under different physiological, pharmacological, and pathophysiological conditions. The consistency of the parameters obtained from the different systems was calculated using the Bland-Altman statistical method. RESULTS: The results demonstrated that the physiological sleep times determined by noninvasive sleep monitoring system were highly consistent with those obtained from the EEG/EMG system, and the coefficients were 94.4% and 95.1% in C57BL/6J and CD-1 mice, respectively. The noninvasive sleep monitoring system exhibited high sensitivity under the sleep-promoting effect of diazepam and caffeine-induced wakefulness, which was indicated by its ability to detect the effect of dosage on sleep times, and accurate determination of the sleep/wakeful status of mice under different pathophysiological conditions. After combining the data obtained from all the mice, the coefficient between the sleep times detected by behavior-based sleep monitoring system and those obtained from the EEG/EMG equipment was determined to .94. CONCLUSION: The results suggested that behavior-based sleep monitoring system could accurately evaluate the sleep/wakeful states of mice under different conditions.

Effects of gestational inflammation on age-related cognitive decline and hippocampal Gdnf-GFRα1 levels in F1 and F2 generations of CD-1 Mice.

BACKGROUND: It has been reported that age-associated cognitive decline (AACD) accelerated by maternal lipopolysaccharide (LPS) insult during late pregnancy can be transmitted to the second generation in a sex-specificity manner. In turn, recent studies indicated that glial cell line-derived neurotrophic factor (GDNF) and its cognate receptor (GFRα1) are critical for normal cognitive function. Based on this evidence, we aimed to explore whether Gdnf-GFRα1 expression contributes to cognitive decline in the F1 and F2 generations of mouse dams exposed to lipopolysaccharide (LPS) during late gestation, and to evaluate also the potential interference effect of pro-inflammatory cytokines. METHODS: During gestational days 15-17, pregnant CD-1 mice (8-10 weeks old) received a daily intraperitoneal injection of LPS (50 µg/kg) or saline (control). In utero LPS-exposed F1 generation mice were selectively mated to produce F2 generation mice. In F1 and F2 mice aged 3 and 15 months, the Morris water maze (MWM) was used to evaluated the spatial learning and memory ability, the western blotting and RT-PCR were used for analyses of hippocampal Gdnf and GFRα1 expression, and ELISA was used to analyse IL-1ß, IL-6 and TNF-α levels in serum. RESULTS: Middle-aged F1 offspring from LPS-treated mothers exhibited longer swimming latency and distance during the learning phase, lower percentage swimming time and distance in targe quadrant during memory phase, and lower hippocampal levels of Gdnf and GFRα1 gene products compared to age-matched controls. Similarly, the middle-aged F2 offspring from the Parents-LPS group had longer swimming latency and distance in the learning phase, and lower percentage swimming time and distance in memory phase than the F2-CON group. Moreover, the 3-month-old Parents-LPS and 15-month-old Parents- and Father-LPS groups had lower GDNF and GFRα1 protein and mRNAs levels compared to the age-matched F2-CON group. Furthermore, hippocampal levels of Gdnf and GFRα1 were correlated with impaired cognitive performance in the Morris water maze after controlling for circulating pro-inflammatory cytokine levels. CONCLUSIONS: Our findings indicate that accelerated AACD by maternal LPS exposure can be transmitted across at least two generations through declined Gdnf and GFRα1 expression, mainly via paternal linage.

Prenatal exposure to inflammation increases anxiety-like behaviors in F1 and F2 generations: possible links to decreased FABP7 in hippocampus.

Anxiety disorder has a high prevalence, and the risk of anxiety increases with age. Prenatal inflammation during key developmental timepoints can result in long-term changes in anxiety phenotype, even over a lifetime and across generations. However, whether maternal inflammation exposure during late gestation has intergenerational transmission effects on age-related anxiety-like behaviors and the possible underlying mechanisms are largely unknown. Fatty acid binding protein 7 (FABP7) is critical in hippocampal neurogenesis and is closely related to neuropsychiatric diseases, including anxiety disorder. The current study investigated the effects of maternal (F0 generation) lipopolysaccharide administration (50 µg/kg, i.p.) during late gestation on anxiety-like behaviors and FABP7 expression in F1 and F2 offspring, as well as the potential sex-specificity of intergenerational effects. Anxiety-like behaviors were evaluated using open field (OF), elevated plus maze, and black-white alley (BWA) tests at 3 and 13 months of age. The protein and messenger RNA levels of FABP7 in the hippocampus were measured using Western blot and real-time quantitative polymerase chain reaction (PCR), respectively. Overall, gestational LPS exposure in the F0 generation increased anxiety levels and decreased FABP7 expression levels in the F1 generation, which carried over to the F2 generation, and the intergenerational effects were mainly transferred via the maternal lineage. Moreover, hippocampal FABP7 expression was significantly correlated with performance in the battery of anxiety tests. The present study suggested that prenatal inflammation could increase age-related anxiety-like behaviors both in F1 and F2 offspring, and these effects possibly link to the FABP7 expression.

Maternal inflammation induces spatial learning and memory impairment in the F1 and F2 generations of mice via sex-specific epigenetic mechanisms.

Mounting evidence indicates that histone modifications are involved in aging-associated cognitive decline (AACD) and can be transmitted to offspring over multiple generations under conditions of stress. Here, we investigated the effects of maternal sub-chronic inflammation caused by lipopolysaccharide (LPS) on AACD and histone modifications in the F1 and F2 generations of experimental mice as well as the potential sex specificity of intergenerational effects. In brief, F0-generation CD-1 dams were exposed to LPS (50 µg/kg) or saline (CON) during late pregnancy. Subsequently, F1 males and females (at 2 months-of-age) from the LPS treatment group were mated with non-littermates from the LPS group or wild-type mice to produce F2 generations of parental- (F2-LPS2), paternal- (F2M-LPS1) and maternal-origin (F2F-LPS1) mice. Then, CON-F1 males and females were mated with wild-type mice to generate F2 generations of paternal- (F2M-CON1) and maternal-origin (F2F-CON1). Next, we evaluated the cognitive ability and levels of hippocampal H4K12ac and H3K9me3 in the F1 and F2 offspring at 3- and 13 months-of-age. Overall, F1 male and female LPS groups presented with elevated corticosterone (P < 0.001, P = 0.036, P = 0.025, 0.012, respectively) and cytokine responses, poorer cognitive performance (all P < 0.05) and H3K9 hypermethylation and H4K12 hypoacetylation in the dorsal hippocampus (all P < 0.05); these issues were carried over to the F2 generation via the parents, predominantly in the paternal lineage. Moreover, the levels of H3K9me3 and H4K12ac were significant correlated with cognitive performance (all P < 0.05), regardless of whether inflammatory insults had been incurred directly or indirectly. These findings indicated that gestational inflammatory insults in the F0 generation accelerated AACD in the F2 generation, along with H3K9 hypermethylation and H4K12 hypoacetylation in the hippocampus, and that these issues were derived from the F1 parents, especially from the F1 fathers.

Long-Term Environmental Enrichment Relieves Dysfunctional Cognition and Synaptic Protein Levels Induced by Prenatal Inflammation in Older CD-1 Mice.

A mounting body of evidence suggests that prenatal inflammation may enhance the rate of age-associated cognitive decline and may involve aberrant amounts of synaptic proteins in the hippocampus, including synaptotagmin-1 (Syt1) and activity-regulated cytoskeleton-associated protein (Arc). However, little is known about the specific impact of adolescent environmental enrichment (EE) on age-associated cognitive decline and the changes in synaptic proteins caused by prenatal inflammation. In this study, CD-1 mice in late pregnancy were given intraperitoneal doses of lipopolysaccharide (LPS, 50 µg/kg) or normal saline. Offspring arising from LPS dams were divided into a LPS group and a LPS plus EE (LPS-E) group. The LPS-E mice were exposed to EE from 2 months of age until the end of the experiment (3 or 15 months old). The Morris water maze (MWM) was used to assess the spatial learning and memory capacities of experimental mice, while western blotting and RNA-scope were used to determine the expression levels of Arc and Syt1 in the hippocampus at the protein and mRNA levels, respectively. Analysis revealed that at 15 months of age, the control mice experienced a reduction in cognitive ability and elevated expression levels of Arc and Syt1 genes when compared to control mice at 3 months of age. The LPS-E group exhibited better cognition and lower protein and mRNA levels of Arc and Syt1 than mice in the LPS group of the same age. However, the enriched environment mitigated but did not counteract, the effects of prenatal inflammation on cognitive and synaptic proteins when tested at either 3 or 15 months of age. Our findings revealed that long-term environmental enrichment improved the expression levels of synaptic proteins in CD-1 mice and that this effect was linked to the dysfunctional cognition caused by prenatal inflammation; this process may also be involved in the reduction of hippocampal Arc and Syt1 gene expression.

Effects of Prenatal Exposure to Inflammation Coupled With Stress Exposure During Adolescence on Cognition and Synaptic Protein Levels in Aged CD-1 Mice.

Age-associated impairment of spatial learning and memory (AISLM) presents substantial challenges to our health and society. Increasing evidence has indicated that embryonic exposure to inflammation accelerates the AISLM, and this can be attributable, at least partly, to changed synaptic plasticity associated with the activities of various proteins. However, it is still uncertain whether social psychological factors affect this AISLM and/or the expression of synaptic protein-associated genes. Synaptotagmin-1 (Syt1) and activity-regulated cytoskeleton-associated protein (Arc) are two synaptic proteins closely related to cognitive functions. In this study, pregnant CD-1 mice received daily intraperitoneal injections of lipopolysaccharide (LPS) (50 µg/kg) or normal saline at days 15-17 of gestation, and half of the offspring of each group were then subjected to stress for 28 days in adolescence. The Morris water maze (MWM) test was used to separately evaluate spatial learning and memory at 3 and 15 months of age, while western blotting and RNAscope assays were used to measure the protein and mRNA levels of Arc and Syt1 in the hippocampus. The results showed that, at 15 months of age, control mice had worse cognitive ability and higher protein and mRNA levels of Arc and Syt1 than their younger counterparts. Embryonic exposure to inflammation or exposure to stress in adolescence aggravated the AISLM, as well as the age-related increase in Arc and Syt1 expression. Moreover, the hippocampal protein and mRNA levels of Arc and Syt1 were significantly correlated with the performance in the learning and memory periods of the MWM test, especially in the mice that had suffered adverse insults in early life. Our findings indicated that prenatal exposure to inflammation or stress exposure in adolescence exacerbated the AISLM and age-related upregulation of Arc and Syt1 expression, and these effects were linked to cognitive impairments in CD-1 mice exposed to adverse factors in early life.

Lipopolysaccharide exposure during late embryogenesis triggers and drives Alzheimer-like behavioral and neuropathological changes in CD-1 mice.

INTRODUCTION: Infections could contribute to Alzheimer's disease (AD) neuropathology in human. However, experimental evidence for a causal relationship between infections during the prenatal phase and the onset of AD is lacking. METHODS: CD-1 mothers were intraperitoneally received lipopolysaccharide (LPS) with two doses (25 and 50 µg/kg) or normal saline every day during gestational days 15-17. A battery of behavioral tasks was used to assess the species-typical behavior, sensorimotor capacity, anxiety, locomotor activity, recognition memory, and spatial learning and memory in 1-, 6-, 12-, 18-, and 22-month-old offspring mice. An immunohistochemical technology was performed to detect neuropathological indicators consisting of amyloid-ß (Aß), phosphorylated tau (p-tau), and glial fibrillary acidic protein (GFAP) in the hippocampus. RESULTS: Compared to the same-aged controls, LPS-treated offspring had similar behavioral abilities and the levels of Aß42, p-tau, and GFAP at 1 and 6 months old. From 12 months onward, LPS-treated offspring gradually showed decreased species-typical behavior, sensorimotor ability, locomotor activity, recognition memory, and spatial learning and memory, and increased anxieties and the levels of Aß42, p-tau, and GFAP relative to the same-aged controls. Moreover, this damage effect (especially cognitive decline) persistently progressed onwards. The changes in these neuropathological indicators significantly correlated with impaired spatial learning and memory. CONCLUSIONS: Prenatal exposure to low doses of LPS caused AD-related features including behavioral and neuropathological changes from midlife to senectitude.

Inflammatory insult during pregnancy accelerates age-related behavioral and neurobiochemical changes in CD-1 mice.

Data shows that inflammation during pregnancy significantly exerts a long-term influence on offspring, such as increasing the risk of adult cognition decline in animals. However, it is unclear whether gestational inflammation affects the neurobehavioral and neurobiochemical outcomes in the mother-self during aging. In this study, pregnant CD-1 mice intraperitoneally received lipopolysaccharide (LPS) in two doses (25 and 50 g/kg, respectively) or normal saline daily during gestational days 15-17. At the age of 15 months, a battery of behavioral tasks was employed to evaluate their species-typical behaviors, sensorimotor ability, anxiety levels, and spatial learning and memory abilities. An immunohistochemical method was utilized preliminarily to detect neurobiochemical indicators consisting of amyloid-ß, phosphorylated tau, presynaptic proteins synaptotagmin-1 and syntaxin-1, glial fibrillary acidic protein (GFAP), and histone-4 acetylation on the K8 site (H4K8ac). The behavioral results showed that LPS exposure during pregnancy exacerbated a decline in 15-month-old CD-1 mice's abilities to nest, their sensorimotor and spatial learning and memory capabilities, and increased their anxiety levels. The neurobiochemical results indicated that gestational LPS exposure also intensified age-related hippocampal changes, including increased amyloid-ß42, phosphorylated tau, synaptotagmin-1 and GFAP, and decreased syntaxin-1 and H4K8ac. Our results suggested that the inflammatory insult during pregnancy could be an important risk factor for the development of Alzheimer's disease, and the H4K8 acetylation might play an important role in the underlying mechanism. This study offers a perspective for improving strategies that support healthy development and successful aging.

Maternal inflammation linearly exacerbates offspring age-related changes of spatial learning and memory, and neurobiology until senectitude.

Maternal inflammation during pregnancy can elevate the risk of neurodegenerative disorders in offspring. However, how it affects age-related impairments of spatial learning and memory and changes in the neurobiological indictors in the offspring in later adulthood is still elusive. In this study, the CD-1 mice with maternal gestational inflammation due to receiving lipopolysaccharide (LPS, i.p. 50 or 25µg/kg) were divided into 3-, 12-, 18-, and 22-month-old groups. The spatial learning and memory were evaluated using a six-radial arm water maze and the levels of presynaptic proteins (synaptotagmin-1 and syntaxin-1) and histone acetylation (H3K9ac and H4K8ac) in the dorsal hippocampus were detected using the immunohistochemical method. The results indicated that there were significant age-related impairments of spatial learning and memory, decreased levels of H4K8ac, H3K9ac, and syntaxin-1, and increased levels of synaptotagmin-1 in the offspring mice from 12 months old to 22 months old compared to the same-age controls. Maternal LPS treatment significantly exacerbated the offspring impairments of spatial learning and memory, the reduction of H3K9ac, H4K8ac, and syntaxin-1, and the increment of synaptotagmin-1 from 12 months old to 22 months old compared to the same-age control groups. The changes in the neurobiological indicators significantly correlated with the impairments of spatial learning and memory. Furthermore, this correlation, besides the age and LPS-treatment effects, also showed a dose-dependent effect. Our results suggest that maternal inflammation during pregnancy could exacerbate age-related impairments of spatial learning and memory, and neurobiochemical indicators in the offspring CD-1 mice from midlife to senectitude.

Hippocampal synaptotagmin-4 is correlated with impaired spatial learning and memory in SAMP8 mice.

The mechanism underlying age-related cognitive impairment remains unclear. To determine whether synaptotagmin (Syt)-1 and Syt-4 are involved in age-related cognitive impairment, we used a radial six-arm water maze (RAWM) to evaluate spatial learning and memory deficits in the senescence accelerated prone mouse 8. The Syt-1 and Syt-4 levels of different subregions of the dorsal hippocampus (DH) were detected through immunohistochemistry. The RAWM results revealed that 13- and 9-month-old mice exhibited longer latencies and more errors in both the learning and memory phases than 5-month-old mice. Similar results were observed in the comparison of 13-month-old mice to 9-month-old mice. Compared with the 9- and/or 5-month-old mice, the 13-month-old mice exhibited higher Syt-1 and Syt-4 levels in the majority of the DH subregions with the exception of Syt-1 in the dentate gyrus-hilus and Syt-4 in the dentate gyrus-hilus and cornu ammonis 1 pyramidal cell layer. With the exception of Syt-1 in the 9-month-old mice, the Syt-1 and Syt-4 levels in several DH subregions overall and in each group were significantly correlated with the performances on the RAWM. Therefore, the altered Syt-1 and Syt-4 levels in the different DH layers may have been involved in the impairments in spatial learning and memory during normal aging.

The reduced serum free triiodothyronine and increased dorsal hippocampal SNAP-25 and Munc18-1 had existed in middle-aged CD-1 mice with mild spatial cognitive impairment.

Changes of synaptic proteins in highlighted brain regions and decreased serum thyroid hormones (THs) have been implied in age-related learning and memory decline. Previously, we showed significant pairwise correlations among markedly impaired spatial learning and memory ability, decreased serum free triiodothyronine (FT3) and increased hippocampal SNAP-25 and Munc18-1 in old Kunming mice. However, whether these changes and the correlations occur in middle-age mice remains unclear. Since this age is one of the best stages to study age-related cognitive decline, we explored the spatial learning and memory ability, serum THs, cerebral SNAP-25 and Munc18-1 levels and their relationships of middle-aged mice in this study. The learning and memory abilities of 35 CD-1 mice (19 mice aged 6 months and 16 mice aged 12 months) were measured with a radial six-arm water maze (RAWM). The SNAP-25 and Munc18-1 levels were semi-quantified by Western blotting and the serum THs were detected by radioimmunoassay. The results showed the middle-aged mice had decreased serum FT3, increased dorsal hippocampal (DH) SNAP-25 and Munc18-1, and many or long number of errors and latency in both learning and memory phases of the RAWM. The Pearson's correlation test showed that the DH SANP-25 and Munc18-1 levels were positively correlated with the number of errors and latency in learning phases of the RAWM. Meanwhile, the DH SANP-25 and Munc18-1 levels negatively correlated with the serum FT3 level. These results suggested that reduced FT3 with increased DH SNAP-25 and Munc18-1 levels might be involved in the spatial learning ability decline in the middle-aged mice.

Correlation of increased hippocampal Sumo3 with spatial learning ability in old C57BL/6 mice.

Age-related impairment of learning and memory is a common phenomenon in humans and animals, yet the underlying mechanism remains unclear. We hypothesize that a small ubiquitin-related modifier (Sumo) might correlate with age-related loss of learning and memory. To test this hypothesis, the present study evaluated age-related spatial learning and memory in C57BL/6 mice (25 aged 7 months and 21 aged 25 months) using a radial six-arm water maze (RAWM). After the behavioral test, the protein expression of Sumo3 was determined in different brain regions using Western blotting. The results showed that the 25-month-old mice had longer latency and a higher number of errors in both learning and memory phases in the RAWM task than the 7-month-old mice. Compared to the latter, the former's level of Sumo3 protein was significantly increased in the dorsal and ventral hippocampus. For the 25-month-old mice, the number of errors and the latency in the learning phase negatively correlated with the Sumo3 level in the dorsal hippocampus. These results suggest that increased Sumo3 in the hippocampus may be correlated with spatial learning ability in old C57BL/6 mice.

Reduced thyroid hormones with increased hippocampal SNAP-25 and Munc18-1 might involve cognitive impairment during aging.

The mechanism underlying the decline of age-related learning and memory remains unclear. Brain-region-specific changes of synaptic proteins and decreased thyroid hormones (THs) have been implied involving this decline. During normal aging, however, the relationships among synaptic proteins, THs and abilities of learning and memory remain to be elucidated. In this study, the age-related spatial learning and memory ability of 41 Kunming mice (KM) (14 mice aged 6 months, 13 mice aged 11 months, 14 mice aged 22 months) was measured with radial six-arm water maze. The levels of SNAP-25 and Munc18-1 in brain regions were semi-quantified by Western blotting and the serum THs were detected by radioimmunoassay. Our results showed the old Kunming mice had marked impairment of spatial learning and memory, with decreased serum free triiodothyronine (FT3) and increased SNAP-25 and Munc18-1 in dorsal hippocampus (DH), ventral hippocampus (VH) and frontal lobe (F). The Pearson's correlation test showed the impairment of spatial learning ability positively correlated with SNAP-25 in DH and Munc18-1 in DH and VH. While, the levels of SNAP-25 (DH, VH and F) and Munc18-1 (DH) negatively correlated with the serum FT3 level, and the spatial memory decline marginal negatively correlate with serum THs. These results suggested that increased hippocampal SNAP-25 and Munc18-1 which seemingly result from decreased serum THs might involve the age-related impairment of spatial learning and memory.

A peptide that binds specifically to the ß-amyloid of Alzheimer's disease: selection and assessment of anti-ß-amyloid neurotoxic effects.

The accumulation of the amyloid-ß peptide (Aß) into amyloid plaques, an essential event in Alzheimer's disease (AD) pathogenesis, has caused researchers to seek compounds that physiologically bind Aß and modulate its aggregation and neurotoxicity. In order to develop new Aß-specific peptides for AD, a randomized 12-mer peptide library with Aß1₋10 as the target was used to identify peptides in the present study. After three rounds of selection, specific phages were screened, and their binding affinities to Aß1₋10 were found to be highly specific. Finally, a special peptide was synthesized according to the sequences of the selected phages. In addition, the effects of the special peptide on Aß aggregation and Aß-mediated neurotoxicity in vitro and in vivo were assessed. The results show that the special peptide not only inhibited the aggregation of Aß into plaques, but it also alleviated Aß-induced PC12 cell viability and apoptosis at appropriate concentrations as assessed by the cell counting kit-8 assay and propidium iodide staining. Moreover, the special peptide exhibited a protective effect against Aß-induced learning and memory deficits in rats, as determined by the Morris water maze task. In conclusion, we selected a peptide that specifically binds Aß1₋10 and can modulate Aß aggregation and Aß-induced neuronal damage. This opens up possibilities for the development of a novel therapeutic approach for the treatment of AD.

Acceleration of age-related learning and memory decline in middle-aged CD-1 mice due to maternal exposure to lipopolysaccharide during late pregnancy.

Previous studies have shown that inflammation process involves pathogenesis of Alzheimer's disease (AD). But, the natural AD model of inflammation has not been obtained yet. In the present study, CD-1 mothers intraperitoneally received a 50 µg/kg lipopolysaccharide (LPS) or normal saline daily during gestational days 15-17. Body weight of the offspring was recorded at ages of 4-33 weeks. A different battery of behavioral tasks was, respectively, completed at ages of 35, 290 and 400 days. The results showed that there was no significant difference in body weight between LPS-treated and control mice during ages of 4-33 weeks. LPS-treated offspring had similar anxiety and locomotor behaviors, and spatial ability of learning and memory at the age of 35 days compared to the controls. At an age of 290 days, the LPS-treated offspring had similar sensorimotor ability, locomotor activity and anxiety, species-typical behaviors, and spatial ability of learning and memory. At an age of 400 days, there were similar sensorimotor ability, locomotor activity and anxiety between the LPS-treated offspring and controls. However, there were impaired species-typical behaviors, and spatial and non-spatial abilities of learning and memory in the LPS-treated offspring. Our results suggested that maternal exposure to LPS in adequate dose in late gestation can deliver term offspring which experience a normal duration of development and maturation, and an accelerated aged-related impairment in memory (spatial and non-spatial) and species-typical behaviors in middle-aged. These meet with the criteria of AD model in behaviors.

Age-related spatial cognitive impairment is correlated with increase of synaptotagmin 1 in dorsal hippocampus in SAMP8 mice.

The age-related decline of learning and memory is a common phenomenon in humans and animals, even though the underlying mechanism is not yet known. In the present study, we propose that synaptotagmin 1 (Syt 1) might be a synaptic protein involved in the loss of learning and memory with aging. To test this hypothesis, the age-related spatial cognitive ability of 36 P8 mice (15 mice aged 4 months, 11 mice aged 8 months and 10 mice aged 13 months) was measured in a Morris water maze. After the behavioral test, both the protein and mRNA levels of Syt 1 were determined in the dorsal hippocampus by means of immunocytochemistry and reverse transcriptase polymerase chain reaction (RT-PCR), respectively. In the Morris water maze, the latency of the 4-month mice to find the submerged platform was significantly shorter than that of the older mice, while there were no significant differences between the 8- and 13-month-old mice in this respect. Compared to the 4-month-old mice, the Syt 1 protein in the 13-month-old mice was significantly increased in almost all layers of each subfield of the hippocampus. The average level of Syt 1 mRNA in the dorsal hippocampus of the P8 mice had not changed with aging. The latency of the 13-month-old P8 mice tested in the Morris water maze was positively correlated with the Syt 1 immunoreactivity in four circuit-specific regions in the dorsal hippocampus. Interestingly, the latency in the Morris water maze was also positively correlated with the level of Syt 1 mRNA in the dorsal hippocampus in individual aged P8 mouse. These results suggest that increased Syt 1 in the dorsal hippocampus in aged mice might be responsible for the age-related impairment of learning and memory.