Enhancing Plasticity Mechanisms in the Mouse Motor Cortex by Anodal Transcranial Direct-Current Stimulation: The Contribution of Nitric Oxide Signaling

Abstract

Consistent body of evidence shows that transcranial direct-current stimulation (tDCS) over the primary motor cortex (M1) facilitates motor learning and promotes recovery after stroke. However, the knowledge of molecular mechanisms behind tDCS effects needs to be deepened for a more rational use of this technique in clinical settings. Here we characterized the effects of anodal tDCS of M1, focusing on its impact on glutamatergic synaptic transmission and plasticity. Mice subjected to tDCS displayed increased long-term potentiation (LTP) and enhanced basal synaptic transmission at layer II/III horizontal connections. They performed better than sham-stimulated mice in the single-pellet reaching task and exhibited increased forelimb strength. Dendritic spine density of layer II/III pyramidal neurons was also increased by tDCS. At molecular level, tDCS enhanced: 1) BDNF expression, 2) phosphorylation of CREB, CaMKII, and GluA1, and 3) S-nitrosylation of GluA1 and HDAC2. Blockade of nitric oxide synthesis by L-NAME prevented the tDCS-induced enhancement of GluA1 phosphorylation at Ser831 and BDNF levels, as well as of miniature excitatory postsynaptic current (mEPSC) frequency, LTP and reaching performance. Collectively, these findings demonstrate that anodal tDCS engages plasticity mechanisms in the M1 and highlight a role for nitric oxide (NO) as a novel mediator of tDCS effects.

Plasma BDNF Levels Following Transcranial Direct Current Stimulation Allow Prediction of Synaptic Plasticity and Memory Deficits in 3×Tg-AD Mice

“…We previously reported that enhanced pCREB Ser133 following tDCS increases BNDF expression in the hippocampus by epigenetic regulation of Bdnf promoter I (Podda et al, 2016), and similar results were observed in auditory and motor cortices exposed to tDCS (Paciello et al, 2018;Barbati et al, 2019). We, therefore, hypothesized that tDCS could differentially impact BNDF expression in WT-3M and 3×Tg-AD-3M mice.…”

“…TDCS over the hippocampus was delivered using a unilateral epicranial electrode arrangement as previously described (Podda et al, 2016;Barbati et al, 2019). The active electrode consisted of a tubular plastic cannula (internal diameter 3.0 mm) filled with saline solution (0.9% NaCl) just prior to stimulation; the counter electrode was a conventional rubber-plate electrode surrounded by a wet sponge (5.2 cm 2 ) positioned over the ventral thorax.…”

“…To test this hypothesis, we performed molecular analyses on hippocampi and blood samples from WT and 3×Tg-AD-3M mice subjected to tDCS or sham stimulation. Our analyses were focused on known upstream mechanisms of tDCS action, such as Ca 2+ -dependent phosphorylation of CREB at Ser133 and of CaMKII at Thr286, and a pivotal downstream effector, i.e., the neurotrophin BDNF (Podda et al, 2016;Kim et al, 2017;Paciello et al, 2018;Stafford et al, 2018;Barbati et al, 2019).…”

Modulation of solute diffusivity in brain tissue as a novel mechanism of transcranial direct current stimulation (tDCS)

“…Expanding on prior mechanisms of action of tDCS such as neuronal polarization 49 – 52 , enhancement in regional blood flow 9 , 27 – 30 , 53 , 54 and in blood nitric oxide (NO) levels 31 , 32 , as well as transient increase in the BBB permeability 23 , our current study uncovered a new target of tDCS: the extracellular space (ECS). By employing non-invasive high resolution (submicron) multiphoton microscopy 44 to image solute spreading around cerebral microvessels in rat brain and fitting the spatio-temporal solute distribution profiles by an unsteady diffusion transport model, we report that tDCS transiently increases the effective solute diffusion coefficients in rat brain tissue D eff to various sized solutes.…”

“…Being a protecting barrier, the BBB consists of endothelial cells (ECs) with tight junctions between adjacent ECs, which are wrapped by the basement membrane (BM), pericytes and astrocyte foot processes 24 – 26 . tDCS modulates brain vascular function 9 , 27 – 30 and nitric oxide (NO) signaling 31 including in patients with Alzheimer’s disease 32 . Cancel et al 22 showed that direct current stimulation can modulate hydraulic conductivity of an in vitro BBB model through tight-junction electro-osmosis.…”