Ameliorative Effects of Different Transcranial Electrical Stimulation Paradigms on the Novel Object Recognition Task in a Rat Model of Alzheimer Disease

Cognitive and Neuropathophysiological Outcomes of Gamma-tACS in Dementia: A Systematic Review

Despite the numerous pharmacological interventions targeting dementia, no disease-modifying therapy is available, and the prognosis remains unfavorable. A promising perspective involves tackling high-frequency gamma-band (> 30 Hz) oscillations involved in hippocampal-mediated memory processes, which are impaired from the early stages of typical Alzheimer's Disease (AD). Particularly, the positive effects of gamma-band entrainment on mouse models of AD have prompted researchers to translate such findings into humans using transcranial alternating current stimulation (tACS), a methodology that allows the entrainment of endogenous cortical oscillations in a frequency-specific manner. This systematic review examines the state-of-the-art on the use of gamma-tACS in Mild Cognitive Impairment (MCI) and dementia patients to shed light on its feasibility, therapeutic impact, and clinical effectiveness. A systematic search from two databases yielded 499 records resulting in 10 included studies and a total of 273 patients. The results were arranged in single-session and multi-session protocols. Most of the studies demonstrated cognitive improvement following gamma-tACS, and some studies showed promising effects of gamma-tACS on neuropathological markers, suggesting the feasibility of gamma-tACS in these patients anyhow far from the strong evidence available for mouse models. Nonetheless, the small number of studies and their wide variability in terms of aims, parameters, and measures, make it difficult to draw firm conclusions. We discuss results and methodological limitations of the studies, proposing possible solutions and future avenues to improve research on the effects of gamma-tACS on dementia.

Vanillin derivatives as antiamnesic agents in scopolamine-induced memory impairment in mice

Amnesia is a major health problem prevalent in almost every part of the world specifically in old age peoples. Vanillin analogues have played an important role in the field medicines. Some of them have been documented to be promising inhibitors of cholinesterases and could therefore, be used as antidepressant, anti-Alzheimer and as neuroprotective drugs. In this connection, the present study was designed to synthesize new vanillin analogues (SB-1 to SB-6) of varied biological potentials. The synthesized compounds were investigated as inhibitors against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes and as scavengers of DPPH and ABTS free radicals followed by behavioural antiamnesic evaluation in mice. The compounds; SB-1, SB-3, SB-4 and SB-6 more potently inhibited AChE with IC50 values of 0.078, 0.157, 0.108, and 0.014 μM respectively. The BChE was more potently inhibited by SB-3 with IC50 of 0.057 μM. Moreover, all of the tested compounds exhibited strong antioxidant potentials with promising results of SB-3 against DPPH with IC50 of 0.305 μM, while SB-5 was most active against ABTS with IC50 of 0.190 μM. The in-vivo studies revealed the improvement in memory deficit caused by scopolamine. Y-Maze and new object recognition test showed a considerable decline in cognitive dysfunctions. In Y-Maze test the spontaneous alteration of 69.44 ± 1% and 84.88 ± 1.35% for SB-1 and 68.92 ± 1% and 80.89 ± 1% for SB-3 at both test doses were recorded while during the novel object recognition test the Discrimination Index percentage of SB-1 was more pronounced as compared to standard drug. All compounds were found to be potent inhibitors of AChE, BChE, DPPH, and ABTS in vitro however, SB-1 and SB-3 were comparatively more potent. SB-1 was also more active in reclamation of memory deficit caused by scopolamine. SB-1 and SB-3 may be considered as excellent drug candidates for treating amnesia subjected to toxicological evaluations in other animal models.

Transcranial pulse stimulation in Alzheimer's disease

BACKGROUND

Transcranial pulse stimulation (TPS) is a novel noninvasive ultrasonic brain stimulation that can increase cortical and corticospinal excitability, induce neuroplasticity, and increase functional connectivity within the brain. Several trials have confirmed its potential in treating Alzheimer's disease (AD).

OBJECTIVE

To investigate the effect and safety of TPS on AD.

DESIGN

A systematic review.

METHODS

PubMed, Embase via Ovid, Web of Science, Cochrane Library, CNKI (China National Knowledge Infrastructure), VIP (China Science and Technology Journal Database), and WanFang were searched from inception to April 1, 2023. Study selection, data extraction, and quality evaluation of the studies were conducted by two reviewers independently, with any controversy resolved by consensus. The Methodological Index for Nonrandomized Studies was used to assess the risk of bias.

RESULTS

Five studies were included in this review, with a total of 99 patients with AD. For cognitive performance, TPS significantly improved the scores of the CERAD (Consortium to Establish a Registry for Alzheimer's Disease) test battery, Alzheimer's Disease Assessment Scale (cognitive), Montreal Cognitive Assessment, and Mini-Mental Status Examination. For depressive symptoms, TPS significantly reduced the scores of the Alzheimer's Disease Assessment Scale (affective), Geriatric Depression Score, and Beck Depression Inventory. By functional magnetic resonance imaging, studies have shown that TPS improved cognitive performance in AD patients by increasing functional connectivity in the hippocampus, parahippocampal cortex, precuneus, and parietal cortex, and activating cortical activity in the bilateral hippocampus. TPS alleviated depressive symptoms in AD patients by decreasing functional connectivity between the ventromedial network (left frontal orbital cortex) and the salience network (right anterior insula). Adverse events in this review, including headache, worsening mood, jaw pain, nausea, and drowsiness, were reversible and lasted no longer than 1 day. No serious adverse events or complications were observed.

CONCLUSIONS

TPS is promising in improving cognitive performance and reducing depressive symptoms in patients with AD. TPS may be a safe adjunct therapy in the treatment of AD. However, these findings lacked a sham control and were limited by the small sample size of the included studies. Further research may be needed to better explore the potential of TPS.

PATIENT AND PUBLIC INVOLVEMENT

Patients and the public were not involved in this study.

The increment of annexin V-positive microvesicles versus annexin V-negative microvesicles in CSF of an animal model of Alzheimer's disease

OBJECTIVE

Extracellular microvesicles (MVs) as a specific signaling molecule have received much attention in nervous system studies. Alterations in the tissue redox status in pathological conditions, such as Alzheimer's disease (AD), facilitate the translocation of cell membrane phosphatidylserine to the outer leaflet and lead to the MVs shedding. Annexin V binds with high affinity to phosphatidylserine. Some arguments exist about whether Annexin V-negative MVs should be considered in pathological conditions.

MATERIAL AND METHOD

We compared the kinetics of two phenotypes of Annexin V-positive and Annexin V-negative MVs in the cerebrospinal fluid (CSF) of amyloid-β (Aβ)-treated male Wistar rats with flow cytometry technique. The Aβ was injected bilaterally into the cerebral ventricles. Thioflavin T staining was used to confirm the presence of hippocampal Aβ fibrils two weeks post-Aβ injection. Levels of hippocampal interleukin-1β were assessed as an inflammatory index. The CSF malondialdehyde (MDA) concentration was determined. The cognitive impairment and anxiety behaviors were assessed by object recognition and elevated plus maze tests, respectively.

RESULTS

Elevation of MDA levels and a significant rise in the scoring of IL-1β staining were found in the Aβ group. The Aβ induced anxiogenic behavior, impaired novel object recognition memory, and increased the CSF levels of the total number of MVs. The number of Annexin V-positive MVs was significantly higher than Annexin V-negative MVs in all groups.

CONCLUSION

Data showed that Annexin V-positive MVs potentially have a significant contribution to the pathophysiology of the Aβ-induced cognitive impairment. To catch a clear image of microvesicle production in pathological conditions, both phenotypes of Annexin V-positive and Annexin V-negative MVs should be analyzed and reported.

The effects of transcranial random noise stimulation on motor function: A comprehensive review of the literature

The present review considers all papers published on the topic up to the end of the year 2022. Transcranial random noise stimulation (tRNS) is a non-invasive neuromodulation technique introduced about 15 years ago whose use is becoming increasingly widespread in neuroscience. It consists of the application over the scalp of a weak, white noise-like current, through electrodes having a surface of several square centimetres, for a duration ranging from seconds to minutes. Despite its relatively low spatial and temporal resolution, tRNS has well defined effects on central motor excitability, which critically depend on stimulation parameters. These effects seem to be chiefly based on an effect on neuronal membrane sodium channels and can last much longer than the stimulation itself. While the effects at the cellular level in the motor cortex are becoming progressively clear, much more studies are needed to understand the effects of tRNS on motor behaviour and performance, where initial research results are nevertheless promising, in both basic and applied research.

Different paradigms of transcranial electrical stimulation improve motor function impairment and striatum tissue injuries in the collagenase-induced intracerebral hemorrhage rat model

Background

In the horizon of therapeutic restrictions in intracerebral hemorrhage (ICH), recently, non-invasive transcranial electrical stimulation (tES) has achieved considerable prosperities. Translational studies have postulated that transcranial direct current stimulation (tDCS) and the other types of tES remain potentially a novel therapeutic option to reverse or stabilize cognitive and motor impairments.

Objective

The aim of this study was to comparatively evaluate the effects of the four main paradigms of tES, including tDCS, transcranial alternating (tACS), pulsed (tPCS), and random noise (tRNS) stimulations on collagenase-induced sensorimotor impairments and striatum tissue damage in male rats.

Methods

To induce ICH, 0.5 μl of collagenase was injected into the right striatum of male Sprague Dawley rats. One day after surgery, tES, was applied to the animals for seven consecutive days. Motor functions were appraised by neurological deficit score, rotarod, and wire hanging tests on the day before surgery and postoperative days 3, 7, and 14. After behavioral tests, brain tissue was prepared appropriately to perform the stereological evaluations.

Results

The results indicated that the application of the four tES paradigms (tDCS, tACS, tRNS, and tPCS) significantly reversed motor disorders in collagenase-induced ICH groups. Further, the motor function improvement of tACS and tRNS receiving rats in wire-hanging and rotarod tests were higher than the other two tES receiving groups. Structural changes and stereological assessments also confirmed the results of behavioral functions.

Conclusion

Our findings suggest that in addition to tDCS application in the treatment of ICH, other tES paradigms, especially tACS and tRNS may be considered as add-on therapeutic strategies in stroke.