Brain network function during shifts in learning strategies in portal hypertension animals

Peroxisome proliferator-activated receptor-γ doesn't modify altered electrophysiological properties of the CA1 pyramidal neurons in a rat model of hepatic cirrhosis

Regarding the low quality of life due to the cognitive complications in the patients with hepatic cirrhosis (HC), the goal of this study was to examine the possible neuroprotective effect of pioglitazone (PIO) on the electrophysiological alterations of hippocampus, a major area of cognition, in the experimental model of bile duct ligation (BDL). We used adult male Wistar rats in the present study to perform BDL or sham surgery. Pioglitazone was administered in BDL rats two weeks after the surgery for the next continuous four weeks. The effects of pioglitazone on BDL-induced electrophysiological alterations of the CA1 pyramidal neurons in the hippocampus were evaluated by whole-cell patch clamp recordings. Our findings demonstrated that chronic administration of PIO could not reverse the electrophysiological changes in the CA1 pyramidal neurons of the hippocampus in BDL rats but could improve the hepatic dysfunction.Together, the results of this study suggest that PIO administration cannot counteract altered intrinsic properties of the hippocampal neurons which has been shown recently as an involved mechanism of the cognitive impairments in hepatic encephalopathy (HE).

Prenatal Venlafaxine Exposure-Induced Neurocytoarchitectural and Neuroapoptotic Degeneration in Striatum and Hippocampus of Developing Fetal Brain, Manifesting Long-term Neurocognitive Impairments in Rat Offspring

Depression is a leading cause of disability which at its worst leads to suicide. Its treatment relies on psychotherapy in combination with certain antidepressants (AD_(s)) from various classes such as tricyclics, selective serotonin reuptake inhibitors, or serotonin and norepinephrine reuptake inhibitors (SNRIs). Among SNRIs, venlafaxine (VEN) is one such most commonly prescribed AD which is recently reported to be in the top 50 most prescribed drugs in the USA. Depression during pregnancy is a common condition, where prescribing an AD becomes necessary as untreated depression during pregnancy has its own complications for both mother and the child. This, probably, is why an incredible rise has been reported in prescribing ADs like VEN to pregnant women in the recent past, despite some studies, including the one from our own group, having reported the in-utero VEN-induced apoptotic neurodegeneration in the fetal neocortex and the consequent neurobehavioral anomalies in adulthood. However, there still exists a lack of insight into the effects of intrauterine exposures of VEN on other fetal brain regions like the hippocampus (HPC) and striatum (STR) and the consequent effects on their cognitive and emotional wellbeing in later life. Hence, this study has been conducted where pregnant Charles-Foster (CF) rats were oral gavaged with VEN (25, 40, and 50 mg/kg bw) from gestation day (GD) 05-19. On GD-19, half of the control and treated dams were euthanized to collect their fetuses. Fetal brains were dissected and processed for reactive oxygen species (ROS) estimation neurohistopathology and confocal microscopic studies. The remaining dams were allowed to deliver naturally, and litters were reared for up to 8 weeks then tested for their cognitive abilities by the Morris water maze test and for their emotionality by the Forced swimming test. Our results showed substantial neurocytoarchitectural deficits in both HPC and STR, along with enhanced ROS levels and apoptotic neurodegenerations. Furthermore, VEN-treated young rat offsprings displayed cognitive impairments and depressive behavior as the long-lasting impact of VEN in a dose-dependent manner. So it may be inferred that prenatal VEN-induced oxidative stress causes apoptotic neurodegeneration leading to neuronal loss in HPC and STR which consequently affects the development of the said brain areas resulting in impaired cognitive and emotional abilities of young adult offsprings. Therefore, extrapolating these findings in animal models, caution may be taken before prescribing VEN to pregnant women, especially during the sensitive phase of pregnancy.

The Therapeutic Role of Exercise and Probiotics in Stressful Brain Conditions

Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurological disorders such as Parkinson’s disease, Alzheimer’s dementia, ischemic stroke, and head and spinal cord injury. The increased production of reactive oxygen species (ROS) has been associated with mitochondrial dysfunction, altered metal homeostasis, and compromised brain antioxidant defence. All these changes have been reported to directly affect synaptic activity and neurotransmission in neurons, leading to cognitive dysfunction. In this context two non-invasive strategies could be employed in an attempt to improve the aforementioned stressful brain status. In this regard, it has been shown that exercise could increase the resistance against oxidative stress, thus providing enhanced neuroprotection. Indeed, there is evidence suggesting that regular physical exercise diminishes BBB permeability as it reinforces antioxidative capacity, reduces oxidative stress, and has anti-inflammatory effects. However, the differential effects of different types of exercise (aerobic exhausted exercise, anaerobic exercise, or the combination of both types) and the duration of physical activity will be also addressed in this review as likely determinants of therapeutic efficacy. The second proposed strategy is related to the use of probiotics, which can also reduce some biomarkers of oxidative stress and inflammatory cytokines, although their underlying mechanisms of action remain unclear. Moreover, various probiotics produce neuroactive molecules that directly or indirectly impact signalling in the brain. In this review, we will discuss how physical activity can be incorporated as a component of therapeutic strategies in oxidative stress-based neurological disorders along with the augmentation of probiotics intake.

Akkermansia muciniphila and environmental enrichment reverse cognitive impairment associated with high-fat high-cholesterol consumption in rats

Nonalcoholic steatohepatitis (NASH) is one of the most prevalent diseases globally. A high-fat, high-cholesterol (HFHC) diet leads to an early NASH model. It has been suggested that gut microbiota mediates the effects of diet through the microbiota-gut-brain axis, modifying the host's brain metabolism and disrupting cognition. Here, we target NASH-induced cognitive damage by testing the impact of environmental enrichment (EE) and the administration of either Lacticaseibacillus rhamnosus GG (LGG) or Akkermansia muciniphila CIP107961 (AKK). EE and AKK, but not LGG, reverse the HFHC-induced cognitive dysfunction, including impaired spatial working memory and novel object recognition; however, whereas AKK restores brain metabolism, EE results in an overall decrease. Moreover, AKK and LGG did not induce major rearrangements in the intestinal microbiota, with only slight changes in bacterial composition and diversity, whereas EE led to an increase in Firmicutes and Verrucomicrobia members. Our findings illustrate the interplay between gut microbiota, the host's brain energy metabolism, and cognition. In addition, the findings suggest intervention strategies, such as the administration of AKK, for the management of the cognitive dysfunction related to NASH.

Methylene blue and photobiomodulation recover cognitive impairment in hepatic encephalopathy through different effects on cytochrome c-oxidase

Mitochondrial dysfunction plays a central role in hepatic encephalopathy (HE), due to changes in enzyme cytochrome c-oxidase (CCO), causing a decline in brain metabolism. We used an HE animal model and applied intracranial administration of methylene blue (MB) and transcranial photobiomodulation (PBM), both targeting CCO, to determine their differential effects on recovering cognition. Five groups of rats were used: sham-operated group + saline (SHAM + SAL, n = 6), hepatic encephalopathy + SAL (HE + SAL, n = 7), SHAM + methylene blue (SHAM + MB, n = 7), HE + MB (n = 7), HE + PBM (n = 7). PBM animals were exposed transcranially to 670 +/- 10 nm LED light at a dose of 9 J/cm2 once a day for 7 days, and the MB and SAL groups were injected with 2.2 μg/0.5 μL in the accumbens. Cognitive dysfunction was evaluated on a striatal stimulus-response task using the Morris water maze. Our results showed cognitive improvement in the HE group when treated with MB. This improvement was accompanied by a decrease in CCO activity in the prefrontal cortex, dorsal striatum, and dorsal hippocampus. When comparing MB and PBM, we found that, although both treatments effectively improved the HE-memory deficit, there was a differential effect on CCO. A general decrease in CCO activity was found in the prefrontal and entorhinal cortices, dorsal striatum, and hippocampus when PBM, compared to MB, was applied. Our results suggest that mitochondrial dysfunction and brain metabolic decline in HE might involve CCO alteration and can be improved by administering MB and PBM.

4-Hydroxynonenal Immunoreactivity Is Increased in the Frontal Cortex of 5XFAD Transgenic Mice

Oxidative stress was implicated in the functional impairment of the frontal cortex observed in early Alzheimer’s disease (AD). To elucidate this role in an animal AD model, we assessed cognitive function of 4-month-old five familial AD (5XFAD) transgenic (Tg) mice using a learning strategy-switching task requiring recruitment of the frontal cortex and measuring levels of 4-hydroxy-2-trans-nonenal (4-HNE), a marker of oxidative stress, in their frontal cortex. Mice were sequentially trained in cued/response and place/spatial versions of the water maze task for four days each. 5XFAD and non-Tg mice exhibited equal performance in cued/response training. However, 5XFAD mice used spatial search strategy less than non-Tg mice in the spatial/place training. Immunoblot and immunofluorescence staining showed that 4-HNE levels increased in the frontal cortex, but not in the hippocampus and striatum, of 5XFAD mice compared to those in non-Tg mice. We report early cognitive deficits related to the frontal cortex and the frontal cortex’s oxidative damage in 4-month-old 5XFAD mice. These results suggest that 4-month-old 5XFAD mice be a useful animal model for the early diagnosis and management of AD.

Why are maternally separated females inflexible? Brain activity pattern of COx and c-Fos

Subjects' early life events will affect them later in life. When these events are stressful, such as child abuse in humans or repeated maternal separation in rodents, subjects can show some behavioral and brain alterations. This study used young adult female Wistar rats that were maternally raised (AFR), maternally separated from post-natal day (PND) 1 to PND10 (MS10), or maternally separated from PND1 to PND21 (MS21), in order to assess the effects of maternal separation (MS) on spatial learning and memory, as well as cognitive flexibility, using the Morris Water Maze (MWM). We performed quantitative cytochrome oxidase (COx) histochemistry on selected brain areas in order to identify whether maternal separation affects brain energy metabolism. We also performed c-Fos immunohistochemistry on the medial prefrontal cortex (mPFC), thalamus, and hippocampus to explore whether this immediate early gene activity was altered in stressed subjects. We obtained a similar spatial learning pattern in maternally raised and maternally separated subjects on the reference memory task, but only the controls were flexible enough to solve the reversal learning successfully. Separated groups showed less c-Fos activity in the mPFC and less complex neural networks on COx.

Characterization of the CA1 pyramidal neurons in rat model of hepatic cirrhosis: insights into their electrophysiological properties

Although the key contributors of altering neurological function in hepatic encephalopathy are relatively well known, the electrophysiological mechanism of CA1 damage, a key vulnerable area during hyperammonemia, have not yet been defined. Therefore, here we focus on the electrophysiological mechanisms of cognitive impairments following bile duct ligation (BDL). We performed patch-clamp recordings from the CA1 pyramidal neurons in hippocampus of male Wistar rats, which underwent sham or BDL surgery. A striking electrophysiological change of hippocampal neurons in experimental model of BDL was observed in the present study. Spontaneous firing frequency and rate of action potential (AP) rebound was decreased and afterhyperpolarization amplitude (AHP) was increased significantly in hippocampal cells of BDL animals compared to sham group. Together, the results suggest that altered intrinsic properties of the hippocampal neurons may contribute to the cognitive abnormalities during hepatic encephalopathy (HE), highlighting the electrophysiological mechanisms for providing new treatments against HE.

Differences in the Flexibility of Switching Learning Strategies and CREB Phosphorylation Levels in Prefrontal Cortex, Dorsal Striatum and Hippocampus in Two Inbred Strains of Mice

Flexibility in using different learning strategies was assessed in two different inbred strains of mice, the C57BL/6 and DBA/2 strains. Mice were trained sequentially in two different Morris water maze protocols that tested their ability to switch their learning strategy to complete a new task after first being trained in a different task. Training consisted either of visible platform trials (cued training) followed by subsequent hidden platform trials (place training) or the reverse sequence (place training followed by cued training). Both strains of mice showed equivalent performance in the type of training (cued or place) that they received first. However, C57BL/6 mice showed significantly better performances than DBA/2 mice following the switch in training protocols, irrespective of the order of training. After completion of the switched training session, levels of cAMP response element-binding protein (CREB) and phosphorylated CREB (pCREB) were measured in the hippocampus, striatum and prefrontal cortex of the mice. Prefrontal cortical and hippocampal pCREB levels differed by strain, with higher levels found in C57BL/6 mice than in DBA/2 mice. No strain differences were observed in the medial or lateral region of the dorsal striatum. These findings indicate that the engagement (i.e., CREB signaling) of relevant neural structures may vary by the specific demands of the learning strategy, and this is closely tied to differences in the flexibility of C57BL/6 and DBA/2 mice to switch their learning strategies when given a new task.

The recognition of a novel-object in a novel context leads to hippocampal and parahippocampal c-Fos involvement

Contextual memory implies recognition based on the association between past and present events experienced. It is important for daily functioning and dysfunctional in many neuropsychological disturbances. The network related to this memory is still open for debate, even though it has been associated with medial temporal lobe regions, including the perirhinal, entorhinal and temporal association cortices, as well as the hippocampus and prefrontal cortex. Our work tries to elucidate whether a change in the context, such as differences in the amount of stimuli presented on the walls and floor of an open field during object exploration, affects the recognition of an object that has been experienced before, and whether this context manipulation could be linked to changes in c-Fos expression. For this purpose, we used a one-trial novel-object recognition task. The animals were divided into two different experimental conditions; in the OR-NORMAL group, the sample and probe test were performed in the same context. However, in the OR-CONTEXT group, the probe test was performed in a different context. Our results showed that the OR-NORMAL group presented a greater exploration of objects than the OR-CONTEXT group. However, both groups presented significant exploration of the novel object. To label the brain regions involved in novel-object recognition under these conditions, we marked the expression of c-Fos protein. Results suggest that a neural circuit that includes the hippocampus, entorhinal and temporal association cortices is involved in the recognition of the novel-object in a novel context.