Alterations in spontaneous delta and gamma activity might provide clues to detect changes induced by amyloid‐β administration

Abstract

Alzheimer's disease (AD) is the most prevalent form of dementia and has an increasing incidence. The neuropathogenesis of AD is suggested to be a result of the accumulation of amyloid-β (Aβ) peptides in the brain. To date, Aβ-induced cognitive and neurophysiologic impairments have not been illuminated sufficiently. Therefore, we aimed to examine how spontaneous brain activities of rats changed by injection of increasing Aβ doses into the brain hemispheres, and whether these changes could be used as a new biomarker for the early diagnosis of the AD. Rats were randomized into following groups: sham (Sham) and seven Aβ-treated (i.c.v.) groups in increasing concentrations (from Aβ-1 to Aβ-7). After recovery, EEG recordings were obtained from implanted electrodes from eight electrode locations, and then, spectral and statistical analyses were performed. A significant decrement in gamma activity was observed in all Aβ groups compared with the sham group. In delta activity, we observed significant changes from Aβ-4 to Aβ-7 group compared with sham group. Delta coherence values were decreased from Aβ-4 to Aβ-7 and Aβ-5 to Aβ-7 groups for frontal and temporal electrode pairs, respectively. A gradual increment was observed in Aβ level till Aβ-4 group. Positive correlation for global delta power and negative correlation for global gamma power between Aβ peptide levels were detected. Consequently, it is conceivable to suggest gamma oscillation might be used to detect early stages of AD. Moreover, changes in delta activity provide information about the onset of major pathologic changes in the progress of AD.

Auditory evoked potentials might have the potential to serve as early indicators related to amyloid beta peptide toxicity

“…Also, we observed that i.c.v. application of Aβ 1-42 peptide has led to AD-like memory deficits in the rats [26]. In this study, AEPs were recorded from the freely moving rats to examine the effect of Aβ 1-42 peptide on the sensory system and to determine the possible associated biomarkers depending on the accumulation of Aβ 1-42 peptide.…”

“…The details of surgical protocols have been described previously [26]. In briefly, rats were anesthetized with a mixture of ketamine-based anesthetics (ketamine [50 mg/kg] and xylazine [10 mg/kg], intraperitoneally (i.p.))…”

“…The details of electrophysiological recordings have been described previously [26]. In briefly, for the recordings from free-moving rats, chronically implanted electrodes were used.…”

Mild metabolic stress is sufficient to disturb the formation of pyramidal cell ensembles during gamma oscillations

“…Since gamma oscillations are known to be associated with selective attention, memory formation, and sensory perception (Buzsáki and Draguhn, 2004;Colgin, 2016;Colgin and Moser, 2010;Paulsen and Moser, 1998;Uhlhaas and Singer, 2010), it is not surprising that disturbances in gamma oscillations are observed in many brain disorders. This includes AD (Hidisoglu et al, 2018;Hollnagel et al, 2019), schizophrenia (Hamm et al, 2017), ischemia (Barth and Mody, 2011), psychosis (Ahnaou et al, 2017), and depression (Fitzgerald and Watson, 2018). The question remains in these diseases, whether alterations of gamma oscillations are a by-product or are contributing to cognitive impairments.…”

Anodal and cathodal transcranial direct current stimulations of prefrontal cortex in a rodent model of Alzheimer’s disease

“…EEG patterns were abnormal in the brains of AD patients, and atDCS could reverse the patterns and modulate cortical activity ( Marceglia et al, 2016 ; Cespon et al, 2019 ; Gangemi et al, 2020 ). For basic research, the AD animal models also exhibit abnormal EEG activity, such as a prominent EEG slowing ( Dringenberg, 2000 ; Jyoti et al, 2010 ; Platt et al, 2011 ; Schneider et al, 2014 ; Del Percio et al, 2018 ; Hidisoglu et al, 2018 ). However, how tDCS affects the EEG pattern has been rarely reported in the AD animals.…”