The Molecular Mechanism of Chronic High-Dose Corticosterone-Induced Aggravation of Cognitive Impairment in APP/PS1 Transgenic Mice

Screening for Neuroprotective and Rapid Antidepressant-like Effects of 20 Essential Oils

Depression is a serious psychiatric disorder with high prevalence, and the delayed onset of antidepressant effects remains a limitation in the treatment of depression. This study aimed to screen essential oils that have the potential for rapid-acting antidepressant development. PC12 and BV2 cells were used to identify essential oils with neuroprotective effects at doses of 0.1 and 1 µg/mL. The resulting candidates were treated intranasally (25 mg/kg) to ICR mice, followed by a tail suspension test (TST) and an elevated plus maze (EPM) after 30 min. In each effective essential oil, five main compounds were computationally analyzed, targeting glutamate receptor subunits. As a result, 19 essential oils significantly abolished corticosterone (CORT)-induced cell death and lactate dehydrogenase (LDH) leakage, and 13 reduced lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). From in vivo experiments, six essential oils decreased the immobility time of mice in the TST, in which Chrysanthemum morifolium Ramat. and Myristica fragrans Houtt. also increased time and entries into the open arms of the EPM. Four compounds including atractylon, α-curcumene, α-farnesene, and selina-4(14),7(11)-dien-8-one had an affinity toward GluN1, GluN2B, and Glu2A receptor subunits surpassed that of the reference compound ketamine. Overall, Atractylodes lancea (Thunb.) DC and Chrysanthemum morifolium Ramat essential oils are worthy of further research for fast-acting antidepressants through interactions with glutamate receptors, and their main compounds (atractylon, α-curcumene, α-farnesene, and selina-4(14),7(11)-dien-8-one) are predicted to underlie the fast-acting effect.

Neuroprotective effects of resistance physical exercise on the APP/PS1 mouse model of Alzheimer's disease

Introduction

Physical exercise has beneficial effects by providing neuroprotective and anti-inflammatory responses to AD. Most studies, however, have been conducted with aerobic exercises, and few have investigated the effects of other modalities that also show positive effects on AD, such as resistance exercise (RE). In addition to its benefits in developing muscle strength, balance and muscular endurance favoring improvements in the quality of life of the elderly, RE reduces amyloid load and local inflammation, promotes memory and cognitive improvements, and protects the cortex and hippocampus from the degeneration that occurs in AD. Similar to AD patients, double-transgenic APPswe/PS1dE9 (APP/PS1) mice exhibit Αβ plaques in the cortex and hippocampus, hyperlocomotion, memory deficits, and exacerbated inflammatory response. Therefore, the aim of this study was to investigate the effects of 4 weeks of RE intermittent training on the prevention and recovery from these AD-related neuropathological conditions in APP/PS1 mice.

Methods

For this purpose, 6-7-month-old male APP/PS1 transgenic mice and their littermates, negative for the mutations (CTRL), were distributed into three groups: CTRL, APP/PS1, APP/PS1+RE. RE training lasted four weeks and, at the end of the program, the animals were tested in the open field test for locomotor activity and in the object recognition test for recognition memory evaluation. The brains were collected for immunohistochemical analysis of Aβ plaques and microglia, and blood was collected for plasma corticosterone by ELISA assay.

Results

APP/PS1 transgenic sedentary mice showed increased hippocampal Aβ plaques and higher plasma corticosterone levels, as well as hyperlocomotion and reduced central crossings in the open field test, compared to APP/PS1 exercised and control animals. The intermittent program of RE was able to recover the behavioral, corticosterone and Aβ alterations to the CTRL levels. In addition, the RE protocol increased the number of microglial cells in the hippocampus of APP/PS1 mice. Despite these alterations, no memory impairment was observed in APP/PS1 mice in the novel object recognition test.

Discussion

Altogether, the present results suggest that RE plays a role in alleviating AD symptoms, and highlight the beneficial effects of RE training as a complementary treatment for AD.

Lipopolysaccharide-Induced Model of Neuroinflammation: Mechanisms of Action, Research Application and Future Directions for Its Use

Despite advances in antimicrobial and anti-inflammatory therapies, inflammation and its consequences still remain a significant problem in medicine. Acute inflammatory responses are responsible for directly life-threating conditions such as septic shock; on the other hand, chronic inflammation can cause degeneration of body tissues leading to severe impairment of their function. Neuroinflammation is defined as an inflammatory response in the central nervous system involving microglia, astrocytes, and cytokines including chemokines. It is considered an important cause of neurodegerative diseases, such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Lipopolysaccharide (LPS) is a strong immunogenic particle present in the outer membrane of Gram-negative bacteria. It is a major triggering factor for the inflammatory cascade in response to a Gram-negative bacteria infection. The use of LPS as a strong pro-inflammatory agent is a well-known model of inflammation applied in both in vivo and in vitro studies. This review offers a summary of the pathogenesis associated with LPS exposure, especially in the field of neuroinflammation. Moreover, we analyzed different in vivo LPS models utilized in the area of neuroscience. This paper presents recent knowledge and is focused on new insights in the LPS experimental model.

Serum Corticosterone and Insulin Resistance as Early Biomarkers in the hAPP23 Overexpressing Mouse Model of Alzheimer's Disease

Increasing epidemiological evidence highlights the association between systemic insulin resistance and Alzheimer’s disease (AD). As insulin resistance can be caused by high-stress hormone levels and since hypercortisolism appears to be an important risk factor of AD, we aimed to investigate the systemic insulin functionality and circulating stress hormone levels in a mutant humanized amyloid precursor protein (APP) overexpressing (hAPP23+/−) AD mouse model. Memory and spatial learning of male hAPP23+/− and C57BL/6 (wild type, WT) mice were assessed by a Morris Water Maze (MWM) test at the age of 4 and 12 months. The systemic metabolism was examined by intraperitoneal glucose and insulin tolerance tests (GTT, ITT). Insulin and corticosterone levels were determined in serum. In the hippocampus, parietal and occipital cortex of hAPP23+/− brains, amyloid-beta (Aβ) deposits were present at 12 months of age. MWM demonstrated a cognitive decline in hAPP23+/− mice at 12 but not at 4 months, evidenced by increasing total path lengths and deteriorating probe trials compared to WT mice. hAPP23+/− animals presented increased serum corticosterone levels compared to WT mice at both 4 and 12 months. hAPP23+/− mice exhibited peripheral insulin resistance compared to WT mice at 4 months, which stabilized at 12 months of age. Serum insulin levels were similar between genotypes at 4 months of age but were significantly higher in hAPP23+/− mice at 12 months of age. Peripheral glucose homeostasis remained unchanged. These results indicate that peripheral insulin resistance combined with elevated circulating stress hormone levels could be potential biomarkers of the pre-symptomatic phase of AD.