Impaired Long-term Memory Research Articles

β-Lactolin, a Whey-Derived Lacto-Tetrapeptide, Prevents Alzheimer's Disease Pathologies and Cognitive Decline.

The prevention of age-related memory decline and dementia has been becoming a high priority because of the rapid growth in aging populations. Accumulating epidemiological and clinical studies indicate that intake of fermented dairy products rich in β-lactolin improves memory retrieval and executive function and attenuates cognitive decline in the elderly. However, the effects of long-term consumption of β-lactolin on Alzheimer’s disease (AD) pathologies have not been investigated. In the present study, we examined the effects of β-lactolin and whey digestion rich in β-lactolin on AD pathology in 5×FAD transgenic mice and PS19 tauopathy mice. Intake of β-lactolin and whey digestion rich in β-lactolin reduced the levels of inflammatory cytokines, suppressed the infiltration of activated microglia, decreased the levels of amyloid-β, ameliorated impaired long-term object memory, and attenuated decreased synaptophysin, dopamine, brain-derived neurotrophic factor, and insulin-like growth factor 1 levels in the cortex in 5×FAD transgenic mice. In addition, intake of β-lactolin and whey digestion rich in β-lactolin improved behavioral abnormality and reduced the ratio of phosphorylated tau to total tau in the cortex in PS19 tauopathy mice. These findings indicate that consumption with β-lactolin and whey digestion rich in β-lactolin suppresses inflammation and attenuates AD pathology and cognitive impairment.

Effects of embryonic propofol exposure on axonal growth and locomotor activity in zebrafish.

Prenatal propofol exposure induced neurotoxicity in the developing brains and led to persistent learning deficits in the offspring. Our goal was to use zebrafish to explore whether the decline in learning and memory was correlated with inhibition of neuronal growth after propofol exposure. Zebrafish embryos at 6 hours postfertilization (hpf) were exposed to control or 1, 2 or 4 μg/mL propofol until 48 hpf. Spontaneous locomotor activity and swimming behavior in response to dark-to-light photoperiod stimulation were studied in zebrafish larvae at 6 days postfertilization (dpf). The adaptability to repeated stimulation was used to indicate learning and memory function of larvae. Transgenic NBT line zebrafish was used to quantitate the effect of propofol on motor neuronal growth of embryos in vivo. Six dpf transgenic zebrafish larvae went through photoperiod stimulation after their neuronal length had been analyzed during the embryonic period. Our data indicate that embryonic exposure to 1, 2 and 4 μg/mL propofol had no adverse effect on spontaneous movement in zebrafish larvae, but 2 and 4 μg/mL propofol significantly impaired the learning and memory function of larvae. Moreover, propofol significantly inhibited axonal growth of motor neurons during the embryonic stage, which was correlated with learning and memory deficiency in larvae. Our findings demonstrate that the neuronal growth was correlated with learning and memory function, indicating the relevance of zebrafish as a new model to explore the mechanisms through which propofol induces long-term learning and memory impairment.

Persistent Effects on Cardiorespiratory and Nervous Systems Induced by Long-Term Lead Exposure: Results from a Longitudinal Study.

Long-term lead (Pb) exposure alters the normal development of the nervous system and physiology. It affects multiple organ systems, causing hypertension, cardiorespiratory dysfunction, being a well-known neurotoxin, inducing changes in neurogenesis, neurodegeneration, and glial cells. However, studies of the developmental effects of lead and its outcomes throughout life are lacking. Determine morphofunctional, behavioral, and cognitive developmental effects of long-term lead exposure at three different ages. Wistar rats were exposed to a Pb-acetate solution from fetal period until adulthood and compared to a non-exposed control group. General behavior and cognitive skills were evaluated by behavioral tests and physiological data and cardiorespiratory reflexes measured. Neurodegeneration, neuroinflammation, and synaptic activity were assessed by immunohistochemistry. Lead exposure caused long-lasting anxiety-like behavior and strong long-term memory impairment without changes in locomotor and exploratory activity. Hypertension was observed at all time points, concomitant with baroreflex impairment and increased chemoreflex sensitivity. Persistent neuroinflammation, transient synaptic overexcitation without neurodegeneration was observed. Long-term Pb exposure, since fetal period, causes long-lasting anxiety-like behavior, concomitant with hypertension, without general motor skills impairment. Synaptic overexcitation, reactive astrogliosis, and microgliosis could underlie behavioral and long-term memory changes, which might have been caused during developmental phases and consolidated during adulthood. Also, alterations observed in the cardiorespiratory reflexes can explain persistent hypertension. This longitudinal study identifies and characterizes lead toxicity nature and magnitude, important to devise and test potential interventions to attenuate the long-term harmful effects of lead on the nervous and cardiovascular systems.

Edaravone protects from memory impairment induced by chronic L-methionine administration.

Hyperhomocysteinemia is a well-known cause of cognitive impairment and neurodegeneration. Increased oxidative stress in the brain has a major possible role in hyperhomocysteinemia-induced pathogenesis. Edaravone is a potent free radical scavenger that has a neuroprotective effect against memory impairment in several experimental models. The current study investigated the possible protective effect of edaravone in L-methionine-induced vascular dementia in a rat model. L-methionine was given (1.7mg/kg/day) through oral gavage, while edaravone was given (6mg/kg/day) intraperitoneally. The administration of methionine and edaravone started concomitantly and continued for a total of 9weeks. Spatial learning and memory were assessed using the radial arm water maze (RAWM). Changes in the oxidative stress-related biomarkers in the hippocampus were assessed using enzymatic assays. Chronic L-methionine administration resulted in short-term and long-term memory impairment, whereas edaravone prevented such effect. Furthermore, edaravone ameliorated L-methionine induced decrease in the activity of the antioxidant enzymes catalase and glutathione peroxidase as well as the ratio of reduced glutathione to oxidized glutathione (GSH/GSSG ratio). Edaravone also prevented increase in the oxidized glutathione (GSSG) secondary to chronic L-methionine administration. In conclusion, the current study suggests that memory impairment and oxidative stress secondary to chronic L-methionine administration can be prevented by edaravone, probably via enhancing antioxidant mechanisms in the hippocampus.

Chronically skipping breakfast impairs hippocampal memory-related gene expression and memory function accompanied by reduced wakefulness and body temperature in mice

Acute or chronic effects of consuming or skipping breakfast on cognitive performance in humans are controversial. To evaluate the effects of chronically skipping breakfast (SB) on hippocampus-dependent long-term memory formation, we examined hippocampal gene expression and applied the novel object recognition test (NORT) after two weeks of repeated fasting for six hours from lights off to mimic SB in mice. We also examined the effects of SB on circadian rhythms of locomotor activity, food intake, core body temperature (CBT) and sleep-wake cycles. Skipping breakfast slightly but significantly decreased total daily food intake without affecting body weight gain. Locomotor activity and CBT significantly decreased during the fasting period under SB. The degree of fasting-dependent CBT reduction gradually increased and then became stabilized after four days of SB. Electroencephalographic data revealed that repeated SB significantly decreased the duration of wakefulness and increased that of rapid eye movement (REM) and of non-REM (NREM) sleep during the period of SB. Furthermore, total daily amounts of wakefulness and NREM sleep were significantly decreased and increased, respectively, under SB, suggesting that SB disrupts sleep homeostasis. Skipping breakfast significantly suppressed mRNA expression of the memory-related genes, Camk2a, Fkbp5, Gadd45b, Gria1, Sirt1 and Tet1 in the hippocampus. Recognition memory assessed by NORT was impaired by SB in accordance with the gene expression profiles. These findings suggested that chronic SB causes dysregulated CBT, sleep-wake cycles and hippocampal gene expression, which results in impaired long-term memory formation.

Cell-type-specific drug-inducible protein synthesis inhibition demonstrates that memory consolidation requires rapid neuronal translation.

New protein synthesis is known to be required for the consolidation of memories, yet existing methods to block translation lack spatiotemporal precision and cell-type specificity, preventing investigation of cell-specific contributions of protein synthesis. Here, we developed a combined knock-in mouse and chemogenetic approach for cell type-specific and drug-inducible protein synthesis inhibition (ciPSI) that enables rapid and reversible phosphorylation of eIF2α, leading to inhibition of general translation by 50% in vivo. We use ciPSI to show that targeted protein synthesis inhibition pan-neuronally and in excitatory neurons in lateral amygdala (LA) impaired long-term memory. This could be recovered with artificial chemogenetic activation of LA neurons, though at the cost of stimulus generalization. Conversely, genetically reducing phosphorylation of eIF2α in excitatory neurons in LA enhanced memory strength, but reduced memory fidelity and behavioral flexibility. Our findings provide evidence for a cell-specific translation program during consolidation of threat memories.

The intellectual disability PAK3 R67C mutation impacts cognitive functions and adult hippocampal neurogenesis.

The link between mutations associated with intellectual disability (ID) and the mechanisms underlying cognitive dysfunctions remains largely unknown. Here, we focused on PAK3, a serine/threonine kinase whose gene mutations cause X-linked ID. We generated a new mutant mouse model bearing the missense R67C mutation of the Pak3 gene (Pak3-R67C), known to cause moderate to severe ID in humans without other clinical signs and investigated hippocampal-dependent memory and adult hippocampal neurogenesis. Adult male Pak3-R67C mice exhibited selective impairments in long-term spatial memory and pattern separation function, suggestive of altered hippocampal neurogenesis. A delayed non-matching to place paradigm testing memory flexibility and proactive interference, reported here as being adult neurogenesis-dependent, revealed a hypersensitivity to high interference in Pak3-R67C mice. Analyzing adult hippocampal neurogenesis in Pak3-R67C mice reveals no alteration in the first steps of adult neurogenesis, but an accelerated death of a population of adult-born neurons during the critical period of 18-28days after their birth. We then investigated the recruitment of hippocampal adult-born neurons after spatial memory recall. Post-recall activation of mature dentate granule cells in Pak3-R67C mice was unaffected, but a complete failure of activation of young DCX + newborn neurons was found, suggesting they were not recruited during the memory task. Decreased expression of the KCC2b chloride cotransporter and altered dendritic development indicate that young adult-born neurons are not fully functional in Pak3-R67C mice. We suggest that these defects in the dynamics and learning-associated recruitment of newborn hippocampal neurons may contribute to the selective cognitive deficits observed in this mouse model of ID.

Environmental Light Is Required for Maintenance of Long-Term Memory in Drosophila.

Long-term memory (LTM) is stored as functional modifications of relevant neural circuits in the brain. A large body of evidence indicates that the initial establishment of such modifications through the process known as memory consolidation requires learning-dependent transcriptional activation and de novo protein synthesis. However, it remains poorly understood how the consolidated memory is maintained for a long period in the brain, despite constant turnover of molecular substrates. Using the Drosophila courtship conditioning assay of adult males as a memory paradigm, here, we show that in Drosophila, environmental light plays a critical role in LTM maintenance. LTM is impaired when flies are kept in constant darkness (DD) during the memory maintenance phase. Because light activates the brain neurons expressing the neuropeptide pigment-dispersing factor (Pdf), we examined the possible involvement of Pdf neurons in LTM maintenance. Temporal activation of Pdf neurons compensated for the DD-dependent LTM impairment, whereas temporal knockdown of Pdf during the memory maintenance phase impaired LTM in light/dark cycles. Furthermore, we demonstrated that the transcription factor cAMP response element-binding protein (CREB) is required in the memory center, namely, the mushroom bodies (MBs), for LTM maintenance, and Pdf signaling regulates light-dependent transcription via CREB. Our results demonstrate for the first time that universally available environmental light plays a critical role in LTM maintenance by activating the evolutionarily conserved memory modulator CREB in MBs via the Pdf signaling pathway.SIGNIFICANCE STATEMENT Temporary memory can be consolidated into long-term memory (LTM) through de novo protein synthesis and functional modifications of neuronal circuits in the brain. Once established, LTM requires continual maintenance so that it is kept for an extended period against molecular turnover and cellular reorganization that may disrupt memory traces. How is LTM maintained mechanistically? Despite the critical importance of LTM maintenance, its molecular and cellular underpinnings remain elusive. This study using Drosophila is significant because it revealed for the first time in any organism that universally available environmental light plays an essential role in LTM maintenance. Interestingly, light does so by activating the evolutionarily conserved transcription factor cAMP response element-binding protein via peptidergic signaling.

Left-right functional difference of the rat dorsal hippocampus for short-term memory and long-term memory

The existence of left-right hemispheric differences has been suggested not only in humans but also in rodents. In recent studies, left-right anatomical and functional differences of the rodent hippocampus have been revealed. However, there is only one report investigating the left-right difference for short-term memory (STM), and the left-right difference for long-term memory (LTM) is not consistent among previous studies. Therefore, we examined the effects of unilateral hippocampal lesion and stimulation on the formation of STM and LTM in rats. Our results showed that the right, but not the left, hippocampal lesion impaired STM performance, evaluated by the alternation rate in the spontaneous alternation test and the novel-arm choice rate in the novelty preference test. In addition, electrical stimulation of the left, but not the right, hippocampus immediately before the tests impaired STM performance. On the other hand, the left, but not the right, hippocampal lesion impaired the LTM performance, evaluated by the discrimination index in the object recognition test. In addition, the stimulation of the left, but not the right, hippocampus impaired LTM performance. These results suggest that both the left and right hippocampi are involved in STM formation, and the right hippocampus has a facilitating role while the left hippocampus has a suppressing role for STM. On the other hand, LTM may be driven correctly only by the left hippocampus with appropriate level of neural activity. The left and right hippocampi of rodents may work in different mechanisms depending on the demand for STM and LTM.

Deleterious effects of chronic mercury exposure on in vitro LTP, memory process, and oxidative stress.

Heavy metal contamination in aquatic environments plays an important role in the exposure of humans to these toxicants. Among these pollutants, mercury (Hg) is one main concern due to its high neurotoxicity and environmental persistence. Even in low concentrations, Hg bioaccumulation is a major threat to human health, with higher impact on populations whose diet has fish as chief consumption. Mercury compounds have high affinity for neuronal receptors and proteins, which gives Hg its cumulative feature and have the ability to cross cell membranes and blood-brain barrier to show their neurotoxicity. Intoxication with Hg increases levels of reactive oxygen species (ROS), thus depleting faster the resource of antioxidant proteins. To evaluate Hg-induced hippocampal ROS production, synaptic plasticity, anxiety, and memory, a total of 11 male Wistar rats were exposed to HgCl2 (Hg30 group) to produce a residual concentration of 8 ng/mL at the end of 30 days. Behavioral tests (plus-maze discriminative avoidance task), in vitro electrophysiology, and ROS assays were performed. Western blot assay showed decreased levels of antioxidant proteins GPx and SOD in Hg30 group. Increased ROS production was observed in the CA1 and CA3 regions in the Hg-exposed group. Plus-maze task detected long-term memory impairment in Hg30 group, linked to poorer in vitro long-term potentiation as compared to control group. Hg intoxication also promoted higher anxiety-like behavior in the exposed animals. In conclusion, our data suggests that low doses of HgCl2 resulted in impaired long-term memory and unbalance between decreased antioxidant protein expression and increased ROS production in the hippocampus.

Decreased circadian fluctuation in cognitive behaviors and synaptic plasticity in APP/PS1 transgenic mice.

Cognitive decline, memory impairment and circadian rhythm disturbance are iconic manifestations of Alzheimer's disease (AD). APPswe/PS1dE9 (APP/PS1) mice, a model of AD, show deficits in multiple learning and memory abilities, synaptic plasticity, and behavioral circadian rhythm, but whether circadian differences in cognitive performance and synaptic plasticity could be affected in AD remain unclear. Here, the cognitive behaviors of 6-month-old APP/PS1 mice were assessed by multiple behavior tests in the rest phase (light period) or active phase (dark period) of the day. The possible electrophysiological mechanism was subsequently investigated by in vivo hippocampal long-term potentiation (LTP) recording, and the locomotor activity rhythm of the mice was detected using wheel-running activities. Compared to wild-type (WT) mice, APP/PS1 mice exhibited long-term spatial memory impairment and in vivo hippocampal LTP suppression. In addition, in APP/PS1 mice, circadian differences in new object recognition memory and LTP were lost, and the circadian difference in long-term spatial memory was decreased, accompanied by a less robust locomotor activity rhythm. These results indicate that the loss of circadian differences in new object recognition memory and the decrease in the circadian difference in long-term spatial memory in APP/PS1 mice, which are closely associated with the loss of the circadian difference in LTP and less robust locomotor activity, might occur early in the course of AD.

Subjective memory impairment, instrumental activities of daily living and longitudinal effect on mortality among older adults in a population-based cohort study: The HUNT Study

Background: Subjective impairment in memory and instrumental activities in daily living (IADL) are associated with future cognitive decline and poorer mental health in older adults, but their association with mortality is uncertain. Our aim was to examine the associations between subjective memory and IADL impairments and all-cause mortality, as well as the mortality risk for reporting both memory and IADL impairments. Methods: Data from the 70-year-old and older cohort in the third survey of a population-based study, the Nord-Trøndelag Health Study (HUNT3), were linked to the Norwegian Causes of Death Registry. A total of 5802 older adults had complete data from HUNT3 (70.8% of the 70+ cohort). The mean follow-up time was 8.0 years, and 1870 respondents had died. Associations between subjective memory and ADL impairments with mortality were analysed in Cox regression models adjusted for covariates with attained age as the timescale. Analyses were performed separately for two age groups - 70-79 and 80+ years - to fulfil the proportional hazards assumption. Results: Subjective impairments in short-term memory and IADL were significantly associated with mortality both separately and combined. These associations were strongest in the 70- to 79-year-old group, where reporting impairment on one short-term memory item increased the mortality risk by 51% (hazard ratio=1.51; 95% confidence interval 1.20-1.91). Long-term memory impairments were not associated with mortality in the adjusted models. Conclusions: Subjective short-term memory impairments and IADL impairments are associated with increased mortality risk. Neither of these symptoms should be regarded as benign aspects of ageing, and concerns should be properly addressed.

P.763 Factors associated with antipsychotic polypharmacy and high-dose antipsychotics in compulsorily admitted patients

Electronic cigarette (ECIG) use has increased worldwide, including among pregnant and breastfeeding women. In this study, we examined the effect of ECIG aerosol exposure during gestation and lactation on learning and memory of adult male offspring rats.Rats were exposed to either fresh air or ECIG aerosol for one hour daily during gestational period as well as days 4–21 of lactation. Male offspring were followed through 19 weeks and then spatial learning and memory were tested by radial arm water maze (RAWM). The hippocampus was examined for biomarkers of harm, including oxidative stress, superoxide dismutase, catalase, glutathione peroxidase and thiobarbituric acid reactive substances and brain derived neurotrophic factor (BDNF).Relative to exposure to fresh air, exposure to ECIG aerosol during gestation/lactation impaired long-term memory in adult offspring (P < 0.05). This impairment was associated with increased activity of superoxide dismutase in the hippocampus (P < 0.05). BDNF and the other tested oxidative stress biomarkers were not affected by ECIG aerosol exposure (p > 0.05).In conclusion, ECIG aerosol exposure during gestation and lactation impaired long-term memory and increased the activity of superoxide dismutase in the hippocampus of offspring adult rats. These results support the development of strategies to enhance ECIG cessation during pregnancy and breastfeeding.

Long-term memory is maintained by continuous activity of Arp2/3 in lateral amygdala.

Evidence indicates that long-term memory formation involves alterations in synaptic efficacy produced by modifications in neural transmission and morphology. However, it is not clear how such changes induced by learning, that encode memory, are maintained over long period of time to preserve long-term memory. It has been shown that the actin nucleating protein Arp2/3 is essential for supporting neuronal morphology and synaptic transmission. We therefore hypothesized that continuous Arp2/3 activity is needed to maintain long-term memory over time. To test this hypothesis we microinjected into lateral amygdala (LA) of rats CK-666, a specific inhibitor of Arp2/3, two days after fear conditioning and tested the effect on long-term fear memory maintenance a day afterward. We found that injection of CK-666 two days after training abolished fear conditioning memory. Fear conditioning could be formed when a control compound CK-689 was applied two days after training. Microinjection of CK-666 a day before fear conditioning training had no effect on fear conditioning learning and long-term memory formation. We revealed that Arp2/3 is also needed to maintain long-term conditioned taste aversion (CTA) memory in LA. Microinjection of CK-666 two days after CTA training impaired long-term memory tested a day afterwards. We conclude that continuous activity of Arp2/3 in LA is essential for the maintenance of long-term memory.

Impairment of Long-term Memory by a Short-term High-fat Diet via Hippocampal Oxidative Stress and Alterations in Synaptic Plasticity

Excessive dietary fat intake is considered a great risk factor for metabolic disorders as well as cognitive dysfunction. However, the potential mechanisms underlying the effects of a high-fat diet (HFD) on the brain remain rather obscure. The purpose of this study was to address how early exposure to HFD induces biochemical changes in different brain regions and affects short- and long-term memory. Mice were fed HFD or normal chow for 4 or 7 weeks beginning in adulthood. Our results showed that oxidative stress and biochemical alterations first appeared in the hippocampus after 4 weeks of exposure and were aggravated by a longer exposure time. Additionally, the HFD-fed mice displayed long-term memory impairments, but the performance of the mice in both the HF-4W and HF-7W groups on behavioral tests relying on short-term memory was not affected. The effect of HFD on the brain was also assessed by electrophysiology, which detected a gradual decrease in long-term potentiation in the CA1 region of the hippocampus. The abnormal expression of proteins associated with synaptic function, e.g. synaptophysin, CaMKII, CaMKIV, calcineurin A, ERK and c-fos, was observed in the hippocampus in response to HFD. These results indicate that HFD elicits rapid biochemical and neurological abnormalities in the hippocampus that contribute to cognitive defects and are potentially connected to the HFD-induced suppression of brain activity.

Early Effects of Cyclophosphamide, Methotrexate, and 5-Fluorouracil on Neuronal Morphology and Hippocampal-Dependent Behavior in a Murine Model.

Breast cancer (BC) is the most common cancer among women. Fortunately, BC survival rates have increased because the implementation of adjuvant chemotherapy leading to a growing population of survivors. However, chemotherapy-induced cognitive impairments (CICIs) affect up to 75% of BC survivors and may be driven by inflammation and oxidative stress. Chemotherapy-induced cognitive impairments can persist 20 years and hinder survivors' quality of life. To identify early effects of CMF administration in mice, we chose to evaluate adult female mice at 2-week postchemotherapy. Mice received weekly IP administration of CMF (or saline) for 4 weeks, completed behavioral testing, and were sacrificed 2 weeks following their final CMF injection. Behavioral results indicated long-term memory (LTM) impairments postchemotherapy, but did not reveal short-term memory deficits. Dendritic morphology and spine data found increases in overall spine density within CA1 basal and CA3 basal dendrites, but no changes in DG, CA1 apical, or CA3 apical dendrites. Further analysis revealed decreases in arborization across the hippocampus (DG, CA1 apical and basal, CA3 apical and basal). These physiological changes within the hippocampus correlate with our behavioral data indicating LTM impairments following CMF administration in female mice 2-week postchemotherapy. Hippocampal cytokine analysis identified decreases in IL-1α, IL-1β, IL-3, IL-10, and TNF-α levels.

Nestin Null Mice Show Improved Reversal Place Learning

The intermediate filament protein nestin is expressed by neural stem cells, but also by some astrocytes in the neurogenic niche of the hippocampus in the adult rodent brain. We recently reported that nestin-deficient (Nes−/−) mice showed increased adult hippocampal neurogenesis, reduced Notch signaling from Nes−/− astrocytes to the neural stem cells, and impaired long-term memory. Here we assessed learning and memory of Nes−/− mice in a home cage set up using the IntelliCage system, in which the mice learn in which cage corner a nose poke earns access to drinking water. Nes−/− and wildtype mice showed comparable place learning assessed as the incorrect corner visit ratio and the incorrect nose poke ratio. However, during reversal place learning, a more challenging task, Nes−/− mice, compared to wildtype mice, showed improved learning over time demonstrated by the incorrect visit ratio and improved memory extinction over time assessed as nose pokes per visit to the previous drinking corner. In addition, Nes−/− mice showed increased explorative activity as judged by the increased total numbers of corner visits and nose pokes. We conclude that Nes−/− mice exhibit improved reversal place learning and memory extinction, a finding which together with the previous results supports the concept of the dual role of hippocampal neurogenesis in cognitive functions.

P: 55 Decreased Cognitive Performance Is Associated With Reduced Resting State Connectivity and Gray Matter Atrophy in Patients With Minimal Hepatic Encephalopathy

BACKGROUND: Patients with minimal hepatic encephalopathy (MHE) show mild cognitive impairment associated with cognitive alterations and changes in connectivity. We assessed the relationship of abnormalities of resting-state functional connectivity (rs-FC) and gray matter (GM) volume with cognitive alterations and biochemical parameters associated to MHE. We also evaluated the relationship between memory in MHE and structural and functional connectivity (FC) changes in the hippocampal system. METHODS: Twenty-six cirrhotic patients without MHE (NMHE), 13 with MHE, and 24 controls were cognitive assessed with a battery of psychometric tests. Atrophy was determined using Voxel-Based Morphometry and rs-FC was assessed by ICA analysis. Receiver operating characteristic (ROC) curves was performed to assess the diagnostic utility of rs-FC and GM reduction for the discrimination of patients with and without MHE. We also assessed the relationship between alterations in memory and the structural integrity and FC of the hippocampal system. RESULTS: MHE patients showed significant decrease of GM volume and lesser degree of rs-FC in different networks related to attention and executive functions as compared to controls and NMHE. There is a progressive reduction in rs-FC in the default mode network with the progression of cognitive impairment. MHE patients showed GM reduction in right frontal lobe, right insula and right cerebellum compared to NMHE patients. Alterations in GM volume and rs-FC correlated with cognitive tests. MHE patients showed impairments in learning, memory, and recognition, compared to NMHE and controls. Cirrhotic patients showed reduced fimbria volume compared to controls. Larger volumes in hippocampus subfields were related to better memory performance in NMHE patients and controls. MHE patients presented lower FC between the L-presubiculum and L-precuneus than NMHE patients, and a reduced FC between L-presubiculum and subiculum seeds and bilateral precuneus, which correlated with cognitive impairment and memory performance. CONCLUSIONS: Decreased cognitive performance is associated by reduced rs-FC and GM atrophy in MHE patients. These changes could have predictive value for detecting MHE. Alterations in the FC of the hippocampal system could contribute to learning and long-term memory impairments in MHE patients. This study shows the association between alterations in learning and long-term memory and structural and FC disturbances in hippocampal structures in cirrhotic patients. Supported by Ministerio Economía, Industria y Competitividad - Instituto Salud Carlos III (FIS PI15/00035; FIS PI18/00150) to CM; Consellería Educación Generalitat Valenciana (PROMETEOII/2014/033; PROMETEU/2018/051 to VF, CM; ACIF/2018/284 to JJG), co-funded with European Regional Development Funds (ERDF).

Memory impairments and increased GFAP expression in hippocampal astrocytes following hypercaloric diet in rats.

Hypothalamic inflammation and glial fibrillary acidic protein (GFAP) overexpression in astrocytes are well described in obese animals, as are some cognitive and memory deficits. As the hippocampus plays important roles in the consolidation of information, this investigation aimed to observe the memory function and the astrocyte expression of GFAP in the hippocampus of rats that received either a hypercaloric or a normocaloric diet. Adult male Wistar rats received a high-fat (cafeteria) or a standard diet for 60 days. On the 61st day, the rats were submitted to the novel object recognition (NOR) test at three and 24 hours after the first contact with objects, to assess short-term and long-term memory, respectively. Thereafter, the rats were euthanized and their brains were collected for GFAP immunohistochemical investigation in the hippocampus (CA1, CA2, CA3 areas) and hypothalamus (periventricular and arcuate nuclei). Astrocytic reactivity was assessed by morphometry. Different white adipose tissue depots and brown adipose tissue were weighed to calculate the adiposity index. The hypercaloric diet increased body weight gain, adiposity index, white adipose tissue weight (epididymal, subcutaneous and retroperitoneal) and brown adipose tissue weight. Rats fed with the hypercaloric diet showed short-term and long-term memory impairments in the NOR test, as well as increased GFAP expression in astrocytes from all analyzed hypothalamic and hippocampal areas. This astrogliosis suggests that the neuroinflammatory response also occurs in the hippocampus and may be involved in the memory losses observed in obese/overweight animals.

P: 50 Developing a New Animal Model of Episodic Hepatic Encephalopathy

BACKGROUND: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome, a major complication of chronic liver disease (CLD/cirrhosis). The primary cause of hospital admissions for cirrhotic patients is an overt episode of HE. Precipitating factors of HE frequently lead to an increase in blood ammonia. Patients who have experienced multiple episodes of HE are associated with persisting neurological complications post-liver transplantation. Currently, the impact of HE episodes on neurological integrity is unknown. We hypothesize that multiple episodes of HE will accelerate and/or intensify neurological deterioration. To date, an animal model of episodic HE is lacking. Therefore, our goal was to characterize an animal model of episodic HE (precipitated with ammonia) and to evaluate the impact of cumulative episodes on neurological status in cirrhotic rats. METHODS: Animal model of CLD and HE: 6-week bile-duct ligation (BDL) rats, and Sham-operated controls were used. BDL and Sham rats were divided in two groups, episodic and non-episodic. Injection (i.p) of ammonium acetate was used to induce episodes of overt HE (pre-coma; loss of righting reflex) every 4 days starting 3-weeks post-BDL surgery (total 5 episodes). Saline was injected as vehicle for non-episodic groups. Two days following the last HE episode, we assessed motor-coordination (RotaRod), anxiety (elevated plus maze, EPMT), as well as short-term and long-term memory (novel object recognition) in all groups. Upon sacrifice, plasma ammonia was measured. RESULTS: The concentration of ammonia required to induce an episode of overt HE in BDL rats lessened with each subsequent episode, ranging from 7 to 4.5 mmol/kg. Short-term memory (P &lt; 0.05) and motor-coordination (P &lt; 0.05) were impaired in both non-episodic and episodic BDL groups compared to respective Sham-operated controls. Long-term memory impairment (P = 0.06) and increased anxiety (+60.0%, P &lt; 0.05) were exclusively found in episodic BDL rats compared to non-episodic BDL rats. Moreover, there was an increase in blood ammonia (+30.4%, P = 0.06) in episodic compared to non-episodic BDL rats, suggesting that although episodic-BDL rats recover from each HE episode, baseline (pre-episode) ammonia remain higher than non-episodic BDL rats. CONCLUSIONS: Cumulative HE episodes escalate neurological impairments in cirrhotic-BDL rats. Thus, this new episodic HE model represents a good approach to explore the pathological mechanism arising from multiple episodes, as well as further investigate whether higher hyperammonemia and/or increased brain sensitivity to ammonia is responsible for more complex neurological manifestations in episodic-BDL rats. Moreover, this model is an excellent platform to investigate novel therapies to prevent/treat episodic HE.