Neuromodulatory Effects of Transcranial Direct Current Stimulation on Motor Excitability in Rats

Abstract

Transcranial direct current stimulation (tDCS) is a noninvasive technique for modulating neural plasticity and is considered to have therapeutic potential in neurological disorders. For the purpose of translational neuroscience research, a suitable animal model can be ideal for providing a stable condition for identifying mechanisms that can help to explore therapeutic strategies. Here, we developed a tDCS protocol for modulating motor excitability in anesthetized rats. To examine the responses of tDCS-elicited plasticity, the motor evoked potential (MEP) and MEP input-output (IO) curve elicited by epidural motor cortical electrical stimulus were evaluated at baseline and after 30 min of anodal tDCS or cathodal tDCS. Furthermore, a paired-pulse cortical electrical stimulus was applied to assess changes in the inhibitory network by measuring long-interval intracortical inhibition (LICI) before and after tDCS. In the results, analogous to those observed in humans, the present study demonstrates long-term potentiation- (LTP-) and long-term depression- (LTD-) like plasticity can be induced by tDCS protocol in anesthetized rats. We found that the MEPs were significantly enhanced immediately after anodal tDCS at 0.1 mA and 0.8 mA and remained enhanced for 30 min. Similarly, MEPs were suppressed immediately after cathodal tDCS at 0.8 mA and lasted for 30 min. No effect was noted on the MEP magnitude under sham tDCS stimulation. Furthermore, the IO curve slope was elevated following anodal tDCS and presented a trend toward diminished slope after cathodal tDCS. No significant differences in the LICI ratio of pre- to post-tDCS were observed. These results indicated that developed tDCS schemes can produce consistent, rapid, and controllable electrophysiological changes in corticomotor excitability in rats. This newly developed tDCS animal model could be useful to further explore mechanical insights and may serve as a translational platform bridging human and animal studies, establishing new therapeutic strategies for neurological disorders.

Anodal and cathodal tDCS modulate neural activity and selectively affect GABA and glutamate syntheses in the visual cortex of cats

“…These effects are shown to be confined within the local stimulation site (Kunori & Takashima, 2019). Specifically, a-tDCS increases neuronal excitability, whereas c-tDCS inhibits such excitability (Rahman et al 2013;Tremblay et al 2013;Gschwind & Seeck, 2016;Liu et al 2019). We validated this phenomenon in the present study by recording VEPs in A21a of the visual cortex of cats before and after tDCS.…”

“…2013; Gschwind & Seeck, 2016; Liu et al . 2019). We validated this phenomenon in the present study by recording VEPs in A21a of the visual cortex of cats before and after tDCS.…”

“…To account for tDCS-related behavioural effects, a few studies have examined changes in pre-vs. post-tDCS neural activities. It was found that tDCS can modulate the neural excitation/inhibition balance in the stimulated brain region (Krause et al 2013;Barron et al 2016), and the effects depend on tDCS polarity with anodal (a) and cathodal (c)-tDCS, respectively, enhancing and suppressing neuronal excitability (Rahman et al 2013;Tremblay et al 2013;Gschwind & Seeck, 2016;Liu et al 2019). However, the time course of tDCS-induced after-effects is not fully understood (Nitsche & Paulus, 2001;Stagg et al 2011;Bachtiar et al 2015).…”

“…2013; Gschwind & Seeck, 2016; Liu et al . 2019). However, the time course of tDCS‐induced after‐effects is not fully understood (Nitsche & Paulus, 2001; Stagg et al .…”

Effects of Different Types of Electric Fields on Mechanical Properties and Microstructure of Ex Vivo Porcine Brain Tissues

“…As an effective treatment method, electrical stimulation plays a vital role in the clinical treatment of brain diseases, such as stroke, − epilepsy, , Parkinson’s syndrome, , and Alzheimer’s disease. , It has been reported that transcranial direct current stimulation (tDCS) can noninvasively regulate the neural network in the human brain, induce neural plasticity, , and stimulate or inhibit the excitability of neurons. In recent years, transcranial alternating current stimulation (tACS) has also been confirmed to entrain endogenous oscillations by altering gamma activity linked to cognition, thereby enhancing cognitive function or modulating cognitive dysfunction .…”