Acquisition of Spatial Search Strategies and Reversal Learning in the Morris Water Maze Depend on Disparate Brain Functional Connectivity in Mice

Temporal and region-specific tau hyperphosphorylation in the medulla and forebrain coincides with development of functional changes in male obese Zucker rats

Metabolic syndrome (MetS) is associated with development of tauopathies that contribute to cognitive decline. Without functional leptin receptors, male obese Zucker rats (OZRs) develop MetS, and they have increased phosphorylated tau (ptau) with impaired cognitive function. In addition to regulating energy balance, leptin enhances activation of the hippocampus, which is essential for spatial learning and memory. Whether spatial learning and memory are always impaired in OZRs or develop with MetS is unknown. We hypothesized that male OZRs develop MetS traits that promote regional increases in ptau and functional deficits associated with those brain regions. In the medulla and cortex, tau-pSer199,202 and tau-pSer396 were comparable in juvenile (7-8 wk old) lean Zucker rats (LZRs) and OZRs but increased in 18- to 19-wk-old OZRs. Elevated tau-pSer396 was concentrated in the dorsal vagal complex of the medulla, and by this age OZRs had hypertension with increased arterial pressure variability. In the hippocampus, tau-pSer199,202 and tau-pSer396 were still comparable in 18- to 19-wk-old OZRs and LZRs but elevated in 28- to 29-wk-old OZRs, with emergence of deficits in Morris water maze performance. Comparable escape latencies observed during acquisition in 18- to 19-wk-old OZRs and LZRs were increased in 28- to 29-wk-old OZRs, with greater use of nonspatial search strategies. Increased ptau developed with changes in the insulin/phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway in the hippocampus and cortex but not medulla, suggesting different underlying mechanisms. These data demonstrate that leptin is not required for spatial learning and memory in male OZRs. Furthermore, early development of MetS-associated autonomic dysfunction by the medulla may be predictive of later hippocampal dysfunction and cognitive impairment.NEW & NOTEWORTHY Male obese Zucker rats (OZRs) lack functional leptin receptors and develop metabolic syndrome (MetS). At 16-19 wk, OZRs are insulin resistant, with increased ptau in dorsal medulla and impaired autonomic regulation of AP. At 28-29 wk OZRs develop increased ptau in hippocampus with deficits in spatial learning and memory. Juvenile OZRs lack elevated ptau and these deficits, demonstrating that leptin is not essential for normal function. Elevated ptau and deficits emerge before the onset of diabetes in insulin-resistant OZRs.

Investigating the effects of age and prior military service on fluid and crystallized cognitive functions using virtual morris water maze (vMWM) and NIH Toolbox tasks

Much of current knowledge of aging involves war veterans and research about age-related cognitive changes in veterans involves generalized or single function tests or health or neurological disorders. The current study examined military service within the context of comparisons of young and old humans involving generally healthy individuals to address normal age-associated cognitive changes. Adult participants included 11 young females (8 non-veterans; 3 veterans; 21-31 years), 5 young males (non-veterans, 21-24 years), 9 older females (non-veterans, 62-80 years), and 21 older males (11 non-veterans; 10 veterans; 60-86 years). They were tested in virtual Morris water maze (vMWM) tasks, which were designed to test spatial learning, cognitive flexibility and working memory, similar to rodent studies, and were validated by correlations with specific NIH Toolbox (NIH-TB) Cognitive Battery or Wechsler Memory Scale (WMS) Logical Memory I and II tests. Significant age-related deficits were seen on multiple vMWM tasks and NIH-TB fluid cognition tasks. Among older males, vMWM tasks appeared to be more sensitive, based on finding statistical differences, to prior military service than NIH Toolbox tasks. Compared with male non-veterans of comparable age and younger, older male veterans exhibited significant deficits in spatial learning, cognitive flexibility, and working memory on vMWM tasks. Our findings support continued development and characterization of vMWM tasks that are comparable between rodents and humans for translating aging interventions between species, and provide impetus for larger investigations examining the extent to which prior military service can serve as a "hidden" variable in normal biological declines of cognitive functions.

Locating causal hubs of memory consolidation in spontaneous brain network in male mice

Memory consolidation after learning involves spontaneous, brain-wide network reorganization during rest and sleep, but how this is achieved is still poorly understood. Current theory suggests that the hippocampus is pivotal for this reshaping of connectivity. Using fMRI in male mice, we identify that a different set of spontaneous networks and their hubs are instrumental in consolidating memory during post-learning rest. We found that two types of spatial memory training invoke distinct functional connections, but that a network of the sensory cortex and subcortical areas is common for both tasks. Furthermore, learning increased brain-wide network integration, with the prefrontal, striatal and thalamic areas being influential for this network-level reconfiguration. Chemogenetic suppression of each hub identified after learning resulted in retrograde amnesia, confirming the behavioral significance. These results demonstrate the causal and functional roles of resting-state network hubs in memory consolidation and suggest that a distributed network beyond the hippocampus subserves this process.

Chronic Intermittent Ethanol Exposure Alters Behavioral Flexibility in Aged Rats Compared to Adult Rats and Modifies Protein and Protein Pathways Related to Alzheimer's Disease

Repeated excessive alcohol consumption increases the risk of developing cognitive decline and dementia. Hazardous drinking among older adults further increases such vulnerabilities. To investigate whether alcohol induces cognitive deficits in older adults, we performed a chronic intermittent ethanol exposure paradigm (ethanol or water gavage every other day 10 times) in 8-week-old young adult and 70-week-old aged rats. While spatial memory retrieval ascertained by probe trials in the Morris water maze was not significantly different between ethanol-treated and water-treated rats in both age groups after the fifth and tenth gavages, behavioral flexibility was impaired in ethanol-treated rats compared to water-treated rats in the aged group but not in the young adult group. We then examined ethanol-treatment-associated hippocampal proteomic and phosphoproteomic differences distinct in the aged rats. We identified several ethanol-treatment-related proteins, including the upregulations of the Prkcd protein level, several of its phosphosites, and its kinase activity and downregulation in the Camk2a protein level. Our bioinformatic analysis revealed notable changes in pathways involved in neurotransmission regulation, synaptic plasticity, neuronal apoptosis, and insulin receptor signaling. In conclusion, our behavioral and proteomic results identified several candidate proteins and pathways potentially associated with alcohol-induced cognitive decline in aged adults.

Disrupted metabolic and spontaneous neuronal activity of hippocampus in sepsis associated encephalopathy rats: A study combining magnetic resonance spectroscopy and resting-state functional magnetic resonance imaging

BACKGROUND

The diagnosis of sepsis associated encephalopathy (SAE) remains challenging in clinical settings because of a lack of specific biomarkers. Functional magnetic resonance imaging (fMRI) and proton magnetic resonance spectroscopy (1H-MRS) can be used to aid in the diagnosis of cognition related diseases. This study investigated changes in functional activities and brain metabolites in the hippocampus in SAE rats by fMRI and 1H-MRS.

MATERIALS AND METHODS

Sepsis associated encephalopathy rats underwent cecal ligation and perforation (CLP) surgery. The Morris water maze (MWM) test was then used to evaluate cognitive function. Resting state-fMRI and 1H-MRS scanning were performed 7 and 14 days after CLP surgery to reveal spontaneous neuronal activity and metabolite changes in the hippocampus. The amplitude of low-frequency fluctuation (ALFF) was used to evaluate spontaneous neuronal activity in the hippocampus. Creatine (Cr), Myo-inositol (mI), and glutamine/glutamate (Glx) levels were measured with 1H-MRS scanning. Immunofluorescence and levels of interleukin (IL)-1β, interleukin (IL)-6, and C-reactive protein (CRP) in the hippocampus were additionally detected to evaluate microglial mediated inflammatory responses. Statistical analysis was performed to evaluate correlations between hippocampal metabolism and behavioral findings.

RESULTS

Cecal ligation and perforation treated rats exhibited impaired learning and memory function in the MWM test at days 7 and 14. Elevation of IL-1β in the hippocampus, as well as immunofluorescence results, confirmed severe neuro inflammation in the hippocampus in SAE rats. Compared with the sham group, the ALFF of the right CA-1 area of the hippocampus was higher at day 7after CLP surgery. The Glx/Cr and mI/Cr ratios were enhanced at day 7 after CLP surgery and slightly lower at day 14 after CLP surgery. The ALFF value, and Glx/Cr and mI/Cr ratios were negatively correlated with time spent in the target quadrant in the MWM test.

CONCLUSION

Spontaneous neuronal activity and metabolites showed significant alterations in SAE rats. The elevated ALFF value, Glx/Cr ratio, and mI/Cr ratio in the hippocampus were positively associated with cognitive deficits. Changes in ALFF and metabolites in hippocampus may serve as potential neuroimaging biomarkers of cognitive disorders in patients with SAE.

Behavioral tests for evaluating the characteristics of brain diseases in rodent models: Optimal choices for improved outcomes (Review)

Behavioral assessment is the dominant approach for evaluating whether animal models of brain diseases can successfully mimic the clinical characteristics of diseases. At present, most research regarding brain diseases involves the use of rodent models. While studies have reported numerous methods of behavioral assessments in rodent models of brain diseases, each with different principles, procedures, and assessment criteria, only few reviews have focused on characterizing and differentiating these methods based on applications for which they are most appropriate. Therefore, in the present review, the representative behavioral tests in rodent models of brain diseases were compared and differentiated, aiming to provide convenience for researchers in selecting the optimal methods for their studies.

The Anti-Depressive Effects of Ultra-High Static Magnetic Field

BACKGROUND

Ultra-high field magnetic resonance imaging (MRI) has obvious advantages in acquiring high-resolution images. 7 T MRI has been clinically approved and 21.1 T MRI has also been tested on rodents.

PURPOSE

To examine the effects of ultra-high field on mice behavior and neuron activity.

STUDY TYPE

Prospective, animal model.

ANIMAL MODEL

Ninety-eight healthy C57BL/6 mice and 18 depression model mice.

FIELD STRENGTH

11.1-33.0 T SMF (static magnetic field) for 1 hour and 7 T for 8 hours. Gradients were not on and no imaging sequence was used.

ASSESSMENT

Open field test, elevated plus maze, three-chambered social test, Morris water maze, tail suspension test, sucrose preference test, blood routine, biochemistry examinations, enzyme-linked immunosorbent assay, immunofluorescent assay.

STATISTICAL TESTS

The normality of the data was assessed by Shapiro-Wilk test, followed by Student's t test or the Mann-Whitney U test for statistical significance. The statistical cut-off line is P < 0.05.

RESULTS

Compared to the sham group, healthy C57/6 mice spent more time in the center area (35.12 ± 4.034, increased by 47.19%) in open field test and improved novel index (0.6201 ± 0.02522, increased by 16.76%) in three-chambered social test a few weeks after 1 hour 11.1-33.0 T SMF exposure. 7 T SMF exposure for 8 hours alleviated the depression state of depression mice, including less immobile time in tail suspension test (58.32% reduction) and higher sucrose preference (increased by 8.80%). Brain tissue analysis shows that 11.1-33.0 T and 7 T SMFs can increase oxytocin by 164.65% and 36.03%, respectively. Moreover, the c-Fos level in hippocampus region was increased by 14.79%.

DATA CONCLUSION

11.1-33.0 T SMFs exposure for 1 hour or 7 T SMF exposure for 8 hours did not have detrimental effects on healthy or depressed mice. Instead, these ultra-high field SMFs have anti-depressive potentials.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 1.

A multi-dosing regimen to enhance the spatial memory of normal rats with α5-containing GABAA receptor negative allosteric modulator L-655,708

RATIONALE AND OBJECTIVES

The reported inconsistent effects of negative allosteric modulators of α5-containing GABA_A receptors on learning and memory may be attributed to receptor selectivity, effective plasma concentration maintenance, and administration time. This study aimed to compare the effects of L-655,708 administered by single-dosing regimen versus multi-dosing regimen on spatial memory, signaling molecules, and brain functional connectivity.

METHODS

After comparing the maintenance time of the effective plasma concentration of L-655,708 between multi-dosing and single-dosing regimens, we further compared the effects of the administration of the two regimens at different phases (before-learning, during-learning, and before-probe) of the Morris water maze (MWM) test on the performance of learning and memory and the levels of signaling molecules related to learning and memory in hippocampal tissues. Functional connectivity analyses between hippocampal and cortical regions were performed to further clarify the effects of the multi-dosing regimen.

RESULTS

The multi-dosing regimen could maintain the effective plasma concentration of L-655,708 much longer than the single-dosing regimen. Only the multi-dosing regimen for L-655,708 administration during the learning period led to significant improvement in spatial memory in the MWM test and increases in levels of glutamate receptors and phosphorylated signaling molecules (p-PKAα, p-CaMKII, and p-CREB-1). Compared with the vehicle control, the multi-dosing regimen increased the functional connectivity of the left hippocampal CA1 with cingulate and motor cortices.

CONCLUSIONS

A multi-dosing regimen for L-655,708 administered during the learning period is an effective strategy to improve spatial memory, increase signaling molecule levels, and enhance the functional connectivity of the hippocampus.

Protective effects of cerebrolysin against chemotherapy (carmustine) induced cognitive impairment in Albino mice

Chemotherapy-induced cognitive impairment (CICI) comprises different neurological problems, including difficulty in learning new things, concentrating and making decisions that affect daily life activities. Clinical reports indicate that around 70% of cancer patients receiving chemotherapy suffer from cognitive impairment. The purpose of the present study is to examine the effects of widely used anticancer medication (Carmustine) on cognitive function using mice model and investigation of the neuroprotective effects of Cerebrolysin (CBN). Cerebrolysin (CBN) is a mixture of several neurotrophic factors and active peptides with anti-inflammatory, antioxidant, and neuroprotective actions. Our study aimed to establish a mice model of Carmustine (BCNU)-induced cognitive deficits and determine the protective effects of CBN. BCNU (10 mg/kg, i.v.) was administered to mice for 28 days, and behavioral parameters were measured on a weekly basis. CBN (44 and 88 mg/kg, i.p.) was administered daily from day 1 to 28 to BCNU treatment mice. All animals were sacrificed on day 29 and brain hippocampus tissues were used for biochemical, neuroinflammatory, neurotransmitters analysis. BCNU administration animals showed impaired cognition and memory, confirmed from behavioral analysis. Further, BCNU increased oxidative stress, inflammatory cytokines release and altered neurotransmitters concentration as compared to the control group (p < 0.01). However, mice treated with CBN (44 and 88 mg/kg, i.p.) significantly and dose-dependently improved cognitive functions, reduced oxidative stress markers, inflammatory cytokines and restored neurotransmitters concentration as compared to BCNU administered mice (p < 0.05). The finding of current study suggested that CBN could be the promising compound to reverse cognitive impairment associated with use of chemotherapy.

Long-term diet-induced obesity does not lead to learning and memory impairment in adult mice

Obesity arising from excessive dietary fat intake is a risk factor for cognitive decline, dementia and neurodegenerative diseases, including Alzheimer’s disease. Here, we studied the effect of long-term high-fat diet (HFD) (24 weeks) and return to normal diet (ND) on behavioral features, microglia and neurons in adult male C57BL/6J mice. Consequences of HFD-induced obesity and dietary changes on general health (coat appearance, presence of vibrissae), sensory and motor reflexes, learning and memory were assessed by applying a phenotypic assessment protocol, the Y maze and Morris Water Maze test. Neurons and microglia were histologically analyzed within the mediobasal hypothalamus, hippocampus and frontal motor cortex after long-term HFD and change of diet. Long periods of HFD caused general health issues (coat alterations, loss of vibrissae), but did not affect sensory and motor reflexes, emotional state, memory and learning. Long-term HFD increased the microglial response (increased Iba1 fluorescence intensity, percentage of Iba1-stained area and Iba1 gene expression) within the hypothalamus, but not in the cortex and hippocampus. In neither of these regions, neurodegeneration or intracellular lipid droplet accumulation was observed. The former alterations were reversible in mice whose diet was changed from HFD to ND. Taken together, long periods of excessive dietary fat alone do not cause learning deficits or spatial memory impairment, though HFD-induced obesity may have detrimental consequences for cognitive flexibility. Our data confirm the selective responsiveness of hypothalamic microglia to HFD.

Red raspberry (Rubus ideaus) supplementation mitigates the effects of a high-fat diet on brain and behavior in mice

OBJECTIVES

Research has shown that berries may have the ability to reverse, reduce, or slow the progression of behavioral dysfunction associated with aging and neurodegenerative disease. In contrast, high-energy and high-fat diets (HFD) may result in behavioral deficits like those seen in aging animals. This research examined whether red raspberry (Rubus ideaus) mitigates the effects of HFD on mouse brain and behavior.

METHODS

Eight-week-old mice consumed a HFD (60% calories from fat) or a control diet (CD) with and without 4% freeze-dried red raspberry (RB). Behavioral tests and biochemical assays of brain tissue and serum were conducted.

RESULTS

After 12 weeks on the diets, mice fed CD and HFD had impaired novel object recognition, but mice on the RB-supplemented diets did not. After approximately 20 weeks on the diets, mice fed HFD + RB had shorter latencies to find the escape hole in the Barnes maze than the HFD-fed mice. Interleukin (IL)-6 was significantly elevated in the cortex of mice fed HFD; while mice fed the CD, CD + RB, and HFD + RB did not show a similar elevation. There was also evidence of increased brain-derived neurotrophic factor (BDNF) in the brains of mice fed RB diets. This reduction in IL-6 and increase in BDNF may contribute to the preservation of learning and memory in HFD + RB mice.

CONCLUSION

This study demonstrates that RB may protect against the effects HFD has on brain and behavior; however, further research with human subjects is needed to confirm these benefits.

Comparison between touchscreen operant chambers and water maze to detect early prefrontal dysfunction in mice

The relative lack of sensitive and clinically valid tests of rodent behavior might be one of the reasons for the limited success of the clinical translation of preclinical Alzheimer's disease (AD) research findings. There is a general interest in innovative behavioral methodology, and protocols have been proposed for touchscreen operant chambers that might be superior to existing cognitive assessment methods. We assessed and analyzed touchscreen performance in several novel ways to examine the possible occurrence of early signs of prefrontal (PFC) functional decline in the APP/PS1 mouse model of AD. Touchscreen learning performance was compared between APP/PS1-21 mice and wildtype littermates on a C57BL/6J background at 3, 6 and 12 months of age in parallel to the assessment of spatial learning, memory and cognitive flexibility in the Morris water maze (MWM). We found that older mice generally needed more training sessions to complete the touchscreen protocol than younger ones. Older mice also displayed defects in MWM working memory performance, but touchscreen protocols detected functional changes beginning at 3 months of age. Histological changes in PFC of APP/PS1 mice indeed occurred as early as 3 months. Our results suggest that touchscreen operant protocols are more sensitive to PFC dysfunction, which is of relevance to the use of these tasks and devices in preclinical AD research and experimental pharmacology.

Low-Frequency Pulsed Magnetic Field Improves Depression-Like Behaviors and Cognitive Impairments in Depressive Rats Mainly via Modulating Synaptic Function

Transcranial magnetic stimulation (TMS) has shown great promise as a medical treatment of depression. The effectiveness of TMS treatment at high frequency has been well investigated; however, low-frequency TMS in depression treatment has rarely been investigated in depression-induced cognitive deficits. Herein, this study was carried out to assess the possible modulatory role of low-frequency pulsed magnetic field (LFPMF) on reversing cognitive impairment in a model of depression induced by chronic unpredictable stress (CUS). Wistar rats were randomly allocated into four groups as follows: a control group (CON), a control applied with LFPMF (CON + LFPMF), a CUS group, and a CUS treated with LFPMF (CUS + LFPMF) group. During 8 weeks of CUS, compared to those in the CON group, animals not only gained less weight but also exhibited anhedonia, anxiety, and cognitive decline in behavioral tests. After 2-week treatment of LFPMF, a 20 mT, 1 Hz magnetic stimulation, it reversed the impairment of spatial cognition as well as hippocampal synaptic function including long-term potentiation and related protein expression. Thus, LFPMF has shown effectively improvements on depressant behavior and cognitive dysfunction in CUS rats, possibly via regulating synaptic function.