Decreased excitability of locus coeruleus neurons during hypercapnia is exaggerated in the streptozotocin-model of Alzheimer's disease

Plasma Neurofilament Light Chain: A Potential Biomarker for Neurological Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex disorder characterized by heterogeneous symptoms, which lack specific biomarkers for its diagnosis. This study aimed to investigate plasma neurofilament light chain (NfL) levels as a potential biomarker for ME/CFS and explore associations with cognitive, autonomic, and neuropathic symptoms. Here, 67 ME/CFS patients and 43 healthy controls (HCs) underwent comprehensive assessments, including neuropsychological evaluation, autonomic nervous system (ANS) testing, and plasma NfL level analysis. ME/CFS patients exhibited significantly higher plasma NfL levels compared to HC (F = 4.30, p < 0.05). Correlations were observed between NfL levels and cognitive impairment, particularly in visuospatial perception (r = -0.42; p ≤ 0.001), verbal memory (r = -0.35, p ≤ 0.005), and visual memory (r = -0.26; p < 0.05) in ME/CFS. Additionally, higher NfL levels were associated with worsened autonomic dysfunction in these patients, specifically in parasympathetic function (F = 9.48, p ≤ 0.003). In ME/CFS patients, NfL levels explained up to 17.2% of the results in cognitive tests. Unlike ME/CFS, in HC, NfL levels did not predict cognitive performance. Elevated plasma NfL levels in ME/CFS patients reflect neuroaxonal damage, contributing to cognitive dysfunction and autonomic impairment. These findings support the potential role of NfL as a biomarker for neurological dysfunction in ME/CFS. Further research is warranted to elucidate underlying mechanisms and clinical implications.

Respiratory Dysfunction in Alzheimer's Disease-Consequence or Underlying Cause? Applying Animal Models to the Study of Respiratory Malfunctions

Alzheimer's disease (AD) is a neurodegenerative brain disease that is the most common cause of dementia among the elderly. In addition to dementia, which is the loss of cognitive function, including thinking, remembering, and reasoning, and behavioral abilities, AD patients also experience respiratory disturbances. The most common respiratory problems observed in AD patients are pneumonia, shortness of breath, respiratory muscle weakness, and obstructive sleep apnea (OSA). The latter is considered an outcome of Alzheimer's disease and is suggested to be a causative factor. While this narrative review addresses the bidirectional relationship between obstructive sleep apnea and Alzheimer's disease and reports on existing studies describing the most common respiratory disorders found in patients with Alzheimer's disease, its main purpose is to review all currently available studies using animal models of Alzheimer's disease to study respiratory impairments. These studies on animal models of AD are few in number but are crucial for establishing mechanisms, causation, implementing potential therapies for respiratory disorders, and ultimately applying these findings to clinical practice. This review summarizes what is already known in the context of research on respiratory disorders in animal models, while pointing out directions for future research.

Intermittent theta burst stimulation attenuates oxidative stress and reactive astrogliosis in the streptozotocin-induced model of Alzheimer's disease-like pathology

Introduction

Intracerebroventricularly (icv) injected streptozotocin (STZ) is a widely used model for sporadic Alzheimer's disease (sAD)-like pathology, marked by oxidative stress-mediated pathological progression. Intermittent theta burst stimulation (iTBS) is a noninvasive technique for brain activity stimulation with the ability to induce long-term potentiation-like plasticity and represents a promising treatment for several neurological diseases, including AD. The present study aims to investigate the effect of the iTBS protocol on the animal model of STZ-induced sAD-like pathology in the context of antioxidant, anti-inflammatory, and anti-amyloidogenic effects in the cortex, striatum, hippocampus, and cerebellum.

Methods

Male Wistar rats were divided into four experimental groups: control (icv normal saline solution), STZ (icv STZ-3 mg/kg), STZ + iTBS (STZ rats subjected to iTBS protocol), and STZ + Placebo (STZ animals subjected to placebo iTBS noise artifact). Biochemical assays and immunofluorescence microscopy were used to evaluate functional and structural changes.

Results

The icv STZ administration induces oxidative stress and attenuates antioxidative capacity in all examined brain regions. iTBS treatment significantly reduced oxidative and nitrosative stress parameters. Also, iTBS decreased Aβ-_1-42 and APP levels. The iTBS enhances antioxidative capacity reported as elevated activity of its enzymatic and non-enzymatic components. In addition, iTBS elevated BDNF expression and attenuated STZ-induced astrogliosis confirmed by decreased GFAP⁺/VIM⁺/C3⁺ cell reactivity in the hippocampus.

Discussion

Our results provide experimental evidence for the beneficial effects of the applied iTBS protocol in attenuating oxidative stress, increasing antioxidant capacity and decreasing reactive astrogliosis in STZ-administrated rats.

Synaptic loss and gliosis in the nucleus tractus solitarii with streptozotocin-induced Alzheimer's disease

Obstructive sleep apnea is highly prevalent in Alzheimer's disease (AD). However, brainstem centers controlling respiration have received little attention in AD research, and mechanisms behind respiratory dysfunction in AD are not understood. The nucleus tractus solitarii (nTS) is an important brainstem center for respiratory control and chemoreflex function. Alterations of nTS integrity, like those shown in AD patients, likely affect neuronal processing and adequate control of breathing. We used the streptozotocin-induced rat model of AD (STZ-AD) to analyze cellular changes in the nTS that corroborate previously documented respiratory dysfunction. We used 2 common dosages of STZ (2 and 3 mg/kg STZ) for model induction and evaluated the early impact on cell populations in the nTS. The hippocampus served as control region to identify site-specific effects of STZ. There was significant atrophy in the caudal nTS of the 3 mg/kg STZ-AD group only, an area known to integrate chemoafferent information. Also, the hippocampus had significant atrophy with the highest STZ dosage tested. Both STZ-AD groups showed respiratory dysfunction along with multiple indices for astroglial and microglial activation. These changes were primarily located in the caudal and intermediate nTS. While there was no change of astrocytes in the hippocampus, microglial activation was accompanied by a reduction in synaptic density. Together, our data demonstrate that STZ-AD induces site-specific effects on all major cell types, primarily in the caudal/intermediate nTS. Both STZ dosages used in this study produced a similar outcome and can be used for future studies examining the initial symptoms of STZ-AD.

Inhibition of Pro-Inflammatory Microglia with Minocycline Improves Cognitive and Sleep-Wake Dysfunction Under Respiratory Stress in a Sporadic Model for Alzheimer's Disease

BACKGROUND

Neuroinflammation in Alzheimer's disease (AD) can occur due to excessive activation of microglia in response to the accumulation of amyloid-β peptide (Aβ). Previously, we demonstrated an increased expression of this peptide in the locus coeruleus (LC) in a sporadic model for AD (streptozotocin, STZ; 2 mg/kg, ICV). We hypothesized that the STZ-AD model exhibits neuroinflammation, and treatment with an inhibitor of microglia (minocycline) can reverse the cognitive, respiratory, sleep, and molecular disorders of this model.

OBJECTIVE

To evaluate the effect of minocycline treatment in STZ model disorders.

METHODS

We treated control and STZ-treated rats for five days with minocycline (30 mg/kg, IP) and evaluated cognitive performance, chemoreflex response to hypercapnia and hypoxia, and total sleep time. Additionally, quantification of Aβ, microglia analyses, and relative expression of cytokines in the LC were performed.

RESULTS

Minocycline treatment improved learning and memory, which was concomitant with a decrease in microglial cell density and re-establishment of morphological changes induced by STZ in the LC region. Minocycline did not reverse the STZ-induced increase in CO2 sensitivity during wakefulness. However, it restored the daytime sleep-wake cycle in STZ-treated animals to the same levels as those observed in control animals. In the LC, levels of A and expression of Il10, Il1b, and Mcp1 mRNA remained unaffected by minocycline, but we found a strong trend of minocycline effect on Tnf- α.

CONCLUSION

Our findings suggest that minocycline effectively reduces microglial recruitment and the inflammatory morphological profile in the LC, while it recovers cognitive performance and restores the sleep-wake pattern impaired by STZ.

Resveratrol ameliorates learning and memory impairments induced by bilateral hippocampal injection of streptozotocin in mice

Resveratrol (RES) is a polyphenol with diverse beneficial pharmacological activities, and our previous results have demonstrated its neuroprotective potential. The purpose of this study was to investigate the therapeutic effect of RES in Alzheimer's disease (AD)-like behavioral dysfunction induced by streptozotocin (STZ) and explore it's potential mechanism of action. STZ was microinjected bilaterally into the dorsal hippocampus of C57BL/6J mice at a dose of 3 mg/kg, and RES was administered intragastrically at a dose of 25 mg/kg for 5 weeks. Neurobehavioral performance was observed, and serum concentrations of insulin and Nesfatin-1 were measured. Moreover, the protein expression of amyloid beta 1-42 (Aβ_1-42), Tau, phosphorylated Tau (p-Tau) (Ser396), synaptic ras GTPase activation protein (SynGAP), postsynaptic density protein 95 (PSD95), synapsin-1, synaptogomin-1, and key molecules of the Wnt/β-catenin signaling pathway in the hippocampus and prefrontal cortex (PFC) were assessed. Finally, pathological damage to hippocampal tissue was examined by Nissl and immunofluorescence staining. The results showed that compared with the controls, bilateral hippocampal microinjections of STZ induced task-specific learning and memory impairments, as indicated by the disadvantaged performances in the novel object recognition test (NOR) and Morris water maze (MWM), but not the contextual fear conditioning test (CFC). Treatment with RES could improve these behavioral disadvantages. The serum concentrations of insulin and Nesfatin-1 in the model group were remarkably higher than those of the control group. In addition, protein expression of Aβ_1-42, Tau, and p-Tau (Ser396) was increased but expression of SynGAP, PSD95, brain-derived neurotrophic factor (BDNF), and p-GSK-3β/GSK-3β were decreased in the hippocampus. Although the protein expression of BDNF and SynGAP was also markedly decreased in the PFC of the model mice, there was no significant difference among groups in the protein expression of PSD95, BDNF, synapsin-1, synaptogomin-1, and p-GSK-3β/GSK-3β. RES (25 mg/kg) reversed the enhanced insulin level, the abnormal protein expression of Aβ_1-42, Tau, and p-Tau (Ser396) in the hippocampus and PFC, and the hippocampal protein expression of SynGAP, PSD95 and BDNF. In addition, RES reversed the STZ-induced decrease in the number of Nissl bodies and the increase in fluorescence intensity of IBA1 in the hippocampal CA1 region. These findings indicate that RES could ameliorate STZ-induced AD-like neuropathological injuries, the mechanism of which could be partly related to its regulation of BDNF expression and synaptic plasticity-associated proteins in the hippocampus.

Intermittent theta burst stimulation ameliorates cognitive impairment and hippocampal gliosis in the Streptozotocin-induced model of Alzheimer's disease

Intracerebroventricularly (icv) injected streptozotocin (STZ) model of Alzheimer's disease (AD) is used to explore the effect of intermittent theta burst stimulation (iTBS) on astrocyte and microglia reactivity in selectively vulnerable brain regions and answer the question whether these changes are in the context of cognitive capacity. The iTBS is a non-invasive approach for stimulating neuronal and glial activity with the ability to induce long-term potentiation-like plasticity and represents a promising treatment for different neurological diseases, including AD. Male Wistar rats were assigned to five groups: 1. Control subjected to icv saline solution, 2. STZ subjected to icv-STZ (bilaterally, 3 mg/kg), 3. STZ+iTBS subjected to iTBS therapy after icv-STZ, 4. STZ+iTBS placebo subjected to noise artifact after icv-STZ and 5. Control+iTBS subjected to iTBS therapy after icv- saline solution. The RotaRod result showed that STZ did not alter motor function in rats. Eight arm radial maze test results showed that iTBS significantly improved cognitive impairment induced by STZ intoxication. Reactive gliosis in the hippocampus and periventricular area, manifested through elevated levels of Iba1⁺ and GFAP⁺/VIM⁺ following icv-STZ, was ameliorated after iTBS treatment. Our research identifies iTBS as an effective therapeutic candidate against STZ-induced neurotoxicity and AD-like changes. The beneficial effects of iTBS on cognitive dysfunction might be due to targeting microglia and astrocytes, as they exert a protective role in neurodegenerative and neuroinflammatory diseases. The results could provoke translation into clinical practice as an early/add-on non-invasive therapeutic intervention for cognitive impairment in AD.

Autonomic Dysfunction Impairs Baroreflex Function in an Alzheimer's Disease Animal Model

BACKGROUND

Alzheimer's disease (AD) patients frequently present with orthostatic hypotension. This inability to reflexively increase blood pressure on standing is a serious health concern and increases the risk of stroke and cardiovascular diseases.

OBJECTIVE

Since there are no clear mechanisms for orthostatic hypotension in human AD, the present study assessed the autonomic changes that could explain this comorbidity in an AD animal model.

METHODS

We used the established streptozotocin-induced rat model of AD (STZ-AD), which mimics many hallmark symptoms of sporadic AD in humans. Baroreflex responses were analyzed in anesthetized STZ-AD rats using femoral catheterization for blood pressure and heart rate, and autonomic activity was assessed using specific blockers and splanchnic sympathetic nerve recordings. Expression levels of autonomic receptors at the heart were examined using the western blot technique.

RESULTS

Baroreflex function in STZ-AD showed a blunted heart rate (HR) response to low blood pressure challenges, and the maximal sympathetic nerve activity was reduced. Conversely, HR responses to high blood pressure were similar to control, indicating no change in parasympathetic nerve activity. Under resting conditions, autonomic blockade demonstrated a baseline shift to increased sympathetic tone in STZ-AD. Protein expression levels of beta-1 adrenergic receptor and muscarinic acetylcholine receptor M2 in the heart were unchanged.

CONCLUSION

Our study provides the first data on the pathological influence of AD on baroreflex function, which primarily affected the sympathetic nervous system in STZ-AD. These results represent the first mechanisms that may correlate with the orthostatic hypotension in human AD.