Emotional and cognitive information processing: Relations to behavioral performance and hippocampal long-term potentiation in vivo during a spatial water maze training in rats

Low-Affinity/High-Selectivity Dopamine Transport Inhibition Sufficient to Rescue Cognitive Functions in the Aging Rat

The worldwide increase in cognitive decline, both in aging and with psychiatric disorders, warrants a search for pharmacological treatment. Although dopaminergic treatment approaches represent a major step forward, current dopamine transporter (DAT) inhibitors are not sufficiently specific as they also target other transporters and receptors, thus showing unwanted side effects. Herein, we describe an enantiomerically pure, highly specific DAT inhibitor, S-CE-123, synthetized in our laboratory. Following binding studies to DAT, NET and SERT, GPCR and kinome screening, pharmacokinetics and a basic neurotoxic screen, S-CE-123 was tested for its potential to enhance and/or rescue cognitive functions in young and in aged rats in the non-invasive reward-motivated paradigm of a hole-board test for spatial learning. In addition, an open field study with young rats was carried out. We demonstrated that S-CE-123 is a low-affinity but highly selective dopamine reuptake inhibitor with good bioavailability. S-CE-123 did not induce hyperlocomotion or anxiogenic or stereotypic behaviour in young rats. Our compound improved the performance of aged but not young rats in a reward-motivated task. The well-described impairment of the dopaminergic system in aging may underlie the age-specific effect. We propose S-CE-123 as a possible candidate for developing a tentative therapeutic strategy for age-related cognitive decline and cognitive dysfunction in psychiatric disorders.

Moderate differences in common feeding diets change lipid composition in the hippocampal dentate gyrus and affect spatial cognitive flexibility in male rats

There is growing evidence that lipids play a fundamental role in neuronal plasticity and learning and memory. Effects of nutrition on brain lipid composition and neuronal functioning are known, but the feeding interventions are often severe and may not reflect nutritional effects below clinical relevance. Therefore, we tested two commercially available rat feeding diets with only moderate differences in the food compositions, a standard diet (gross energy metabolizable 12.8 MJ/kg) and a energy reduced diet (gross energy metabolizable 8.9 MJ/kg) on possible effects upon dentate gyrus lipid composition, spatial learning and memory in a water maze and corticosterone release (blood serum concentrations) in adult male rats. Rats were fed with the standard diet up to an age of 8 weeks. One group was further fed with the standard and another with the energy reduced diet until an age of 5 months. We did not found differences in serum corticosterone levels. We found group differences in a variety of lipids in the hippocampal dentate gyrus.. Most of the lipid levels were lower in energy reduced diets, namely glycerophosphoethanolamines, sphingomyelins and hexosyceramides, whereas some ceramides (Cer18:0 and Cer24:1) and glycerophosphocholines (PC34:3 and PC36:2) were upregulated compared to the standard diet group. The performance in a common reference memory water maze task was not different between groups, however during reversal learning (platform in a different position) after the initial training, the standard diet fed rats learned better and spatial memory was improved compared to the energy reduced diet group. Thus, moderate differences in feeding diets have effects specifically upon spatial cognitive flexibility. Possible relations between differences in lipid composition and cognitive flexibility are discussed.

Effects of chronically high levels of aldosterone on different cognitive dimensions: an investigation in patients with primary aldosteronism

Primary aldosteronism is a natural model for chronic aldosterone excess in humans and associated with symptoms of anxiety and depression. Cognitive deficits are inherent to the symptomatology of depression and anxiety disorders. Mineralocorticoid receptors and aldosterone appear to play a role in memory. Aldosterone was additionally supposed to be a risk factor for cognitive decline in patients with essential hypertension. The objective of this study was to investigate possible effects of chronically high aldosterone concentrations on cognitive function. A range of cognitive dimensions were assessed in 19 patients (9 males, 10 females); mean age 47.1 (12.5) under standardized treatment and several rating scales for anxiety, depression, quality of life and sleep were administered. Cognitive parameters were compared to standard norms from a large, healthy standardization sample. Patients showed increased levels of anxiety and depression without meeting diagnostic criteria for a disorder. Besides a numerically lower attention score, patients did not show any significant differences in the cognitive dimensions. Anxiety and depression were negatively correlated with quantitative performance in males. In females, a negative correlation between sleep disturbances and abstract reasoning and a positive correlation with quantitative performance were found. Our data showed no specific effect of chronic aldosterone in the tested cognitive parameters overall at least in younger patients, but they indicate sexually dimorphic regulation processes.

Huannao Yicong Decoction () extract reduces inflammation and cell apoptosis in Aβ1-42-induced Alzheimer's disease model of rats

OBJECTIVE

Huannao Yicong Decoction (, HYD), an effective herbal formula against Alzheimer's disease (AD), has been proven to have neuroprotective action in amyloid β-protein_1-42 (Aβ_1-42)-induced rat model. This study was designed to characterize mechanisms by which HYD leads to suppression of inflflammation and apoptosis in the brains of Aβ_1-42-induced rat.

METHODS

A total of 72 rats were divided into 6 groups, which were referred to as: sham operation group, model group, donepezil-treated group, HYD low-dose group (HYDL), HYD middle-dose group (HYDM) and HYD high-dose group (HYDH). Rats in HYDL, HYDM and HYDH were injected with Aβ_1-42 at the CA1 region of hippocampus to form AD model and were fed the HYD extract at different dose of 3.78, 7.56 and 18.90 g crude drug/kg. The behavioral changes of rats were evaluated by Morris water maze (MWM) before sacrififice. Pathological changes of the brain tissue were evaluated using hematoxylin eosin (HE) staining. The levels of interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) were measured by radioimmunoassay. The levels of Aβ and proteins that are associated with apoptosis such as B-cell lymphoma-2 protein (Bcl-2), Bcl-2-associated X protein (Bax), cysteine-aspartic protease (caspase)-3, -8, -9 and -12 in serum were measured by immunohistochemistry.

RESULTS

Compared with the sham operation group, the spatial learning and memory abilities of AD rats were signifificantly decreased (P<0.05 or P<0.01; Expressions of IL-1, TNF-α, Aβ and apoptosis-signaling proteins caspase-3, -8, -9, -12 were signifificantly up-regulated (P<0.05 or P<0.01). The ratio of Bcl-2 to Bax were signifificantly decreased in the model group (P<0.01). When treated with HYD extract, the spatial learning and memory abilities of AD-model rats were significantly increased (P<0.05 or P<0.01), IL-1, TNF-α, Aβ, caspase-3, -8, -9 and -12 were down-regulated (P<0.05 or P<0.01), and the ratio of Bcl-2 to Bax were reduced (P<0.05 or P<0.01).

CONCLUSIONS

HYD extract can improve the learning and memory ability defificits, alleviate the inflflammatory response and pathological manifestations induced by Aβ_1-42 injection in the rat model of AD. HYD down-regulates the levels of IL-1, TNF-α and Aβ, and decreases the rate of apoptosis by modulating apoptosis-signaling-related proteins such as caspase-3, -8, -9, and -12.

Expression of c-Fos in the rat retrosplenial cortex during instrumental re-learning of appetitive bar-pressing depends on the number of stages of previous training

Learning is known to be accompanied by induction of c-Fos expression in cortical neurons. However, not all neurons are involved in this process. What the c-Fos expression pattern depends on is still unknown. In the present work we studied whether and to what degree previous animal experience about Task 1 (the first phase of an instrumental learning) influenced neuronal c-Fos expression in the retrosplenial cortex during acquisition of Task 2 (the second phase of an instrumental learning). Animals were progressively shaped across days to bar-press for food at the left side of the experimental chamber (Task 1). This appetitive bar-pressing behavior was shaped by nine stages (“9 stages” group), five stages (“5 stages” group) or one intermediate stage (“1 stage” group). After all animals acquired the first skill and practiced it for five days, the bar and feeder on the left, familiar side of the chamber were inactivated, and the animals were allowed to learn a similar instrumental task at the opposite side of the chamber using another pair of a bar and a feeder (Task 2). The highest number of c-Fos positive neurons was found in the retrosplenial cortex of “1 stage” animals as compared to the other groups. The number of c-Fos positive neurons in “5 stages” group animals was significantly lower than in “1 stage” animals and significantly higher than in “9 stages” animals. The number of c-Fos positive neurons in the cortex of “9 stages” animals was significantly higher than in home caged control animals. At the same time, there were no significant differences between groups in such behavioral variables as the number of entrees into the feeder or bar zones during Task 2 learning. Our results suggest that c-Fos expression in the retrosplenial cortex during Task 2 acquisition was influenced by the previous learning history.

Stress induced hippocampal mineralocorticoid and estrogen receptor β gene expression and long-term potentiation in male adult rats is sensitive to early-life stress experience

Glucocorticoid hormones and their receptors have been identified to be involved in emotional and cognitive disorders in early stressed subjects during adulthood. However, the impact of other steroid hormones and receptors has been considered less. Especially, functional roles of estrogen and estrogen receptors in male subjects are largely unknown. Therefore, we measured hippocampal concentrations of 17β-estradiol, corticosterone and testosterone, as well as the gene expression of estrogen receptor α and β (ERα, β), androgen receptor (AR), glucocorticoid (GR) and mineralocorticoid (MR) receptors after stress in adulthood in maternally separated (MS+; at postnatal days 14-16 for 6h each day) and control (MS-) male rats. In vivo hippocampal long-term potentiation (LTP) serves as a cellular model of learning and memory formation. Population spike- (PSA) and the fEPSP-LTP within the dentate gyrus (DG) were reinforced by elevated-platform-stress (EP-stress) in MS- but not in MS+ rats. MR- and ERβ-mRNA were upregulated 1h after EP-stress in MS- but not in MS+ rats as compared to non-stressed littermates. Infusion of an MR antagonist before LTP induction blocked early- and late-PSA- and -fEPSP-LTP, whereas blockade of ERβ impaired only the late PSA-LTP. Application of a DNA methyltransferase (DNMT) inhibitor partly restored the LTP-reinforcement in MS+ rats, accompanied by a retrieval of ERβ- but not MR-mRNA upregulation. Basal ERβ gene promoter methylation was similar between groups, whereas MS+ and MS- rats showed different methylation patterns across CpG sites after EP-stress. These findings indicate a key role of ERβ in early-stress mediated emotionality and emotion-induced late-LTP in adult male rats via DNA methylation mechanisms.