Effects of Multisession Anodal Electrical Stimulation of the Auditory Cortex on Temporary Noise-Induced Hearing Loss in the Rat

Abstract

The protective effect of the efferent system against acoustic trauma (AT) has been shown by several experimental approaches, including damage to one ear, sectioning of the olivocochlear bundle (OCB) in the floor of the IV ventricle, and knock-in mice overexpressing outer hair cell (OHC) cholinergic receptors, among others. Such effects have been related to changes in the regulation of the cholinergic efferent system and in cochlear amplification, which ultimately reverse upon protective hearing suppression. In addition to well-known circuits of the brainstem, the descending corticofugal pathway also regulates efferent neurons of the olivary complex. In this study, we applied our recently developed experimental paradigm of multiple sessions of electrical stimulation (ES) to activate the efferent system in combination with noise overstimulation. ABR thresholds increased 1 and 2 days after AT (8–16 kHz bandpass noise at 107 dB for 90 min) recovering at AT + 14 days. However, after multiple sessions of epidural anodal stimulation, no changes in thresholds were observed following AT. Although an inflammatory response was also observed 1 day after AT in both groups, the counts of reactive macrophages in both experimental conditions suggest decreased inflammation in the epidural stimulation group. Quantitative immunocytochemistry for choline acetyltransferase (ChAT) showed a significant decrease in the size and optical density of the efferent terminals 1 day after AT and a rebound at 14 days, suggesting depletion of the terminals followed by a long-term compensatory response. Such a synthesis recovery was significantly higher upon cortical stimulation. No significant correlation was found between ChAT optical density and size of the buttons in sham controls (SC) and ES/AT + 1day animals; however, significant negative correlations were shown in all other experimental conditions. Therefore, our comparative analysis suggests that cochleotopic cholinergic neurotransmission is also better preserved after multisession epidural stimulation.

Comparing the effects of transcranial alternating current and temporal interference (tTIS) electric stimulation through whole-brain mapping of c-Fos immunoreactivity

“…Recordings performed in rats after anodal DC stimulation with trains of pulses delivered to the skin, skull, and dura have demonstrated that voltage declines quickly in the brain towards a low global value of conductivity of 0.57 S/m (Asan et al, 2019 ). Due to physical interactions between electric currents and neural tissues, DC stimulation induces a limited activation of the cortex, which is less than 1 mm deep, as previously shown in rat animal models (Colmenárez-Raga et al, 2019 ; Díaz et al, 2021 ). Alternating current (AC) stimulation, in contrast, does not induce polarizing effects but activates neuronal networks via rhythmic stimulation by synchronizing their endogenous neurophysiological activities (Fröhlich and McCormick, 2010 ; Zaehle et al, 2010 ; Reato et al, 2013 ; Abd Hamid et al, 2015 ; Vossen et al, 2015 ).…”

Efferent Activity Controls Hair Cell Response to Mechanical Overstimulation

“…Intense sounds have been observed to cause temporary threshold shifts in humans and other mammals, as well as to have an effect on cochlear microphonics. The transient nature of this noise-induced hearing loss indicates an underlying protective mechanism against permanent damage ( Clark, 1991 ; Melnick, 1991 ; Patuzzi, 2002 ; Lichtenhan and Chertoff, 2008 ; Díaz et al, 2021 ).…”

“…The efferent system has been linked to the auditory system’s inherent otoprotective capacity ( Handrock and Zeisberg, 1982 ; Reiter and Liberman, 1995 ; Maison and Liberman, 2000 ; Taranda et al, 2009 ; Boero et al, 2018 ; Díaz et al, 2021 ; Ohata et al, 2021 ). A number of studies have detected higher levels of noise-induced damage (hair cell and synaptic deterioration) in subjects with severed efferent innervation ( Zheng et al, 2000 ; Maison et al, 2002 , 2013 ; Kujawa and Liberman, 2009 ; Taranda et al, 2009 ).…”