P298 Effects of cerebellar transcranial direct-current stimulation on cerebellar sensory-induced LFPs and Purkinje cell activity in alert mice

Abstract

Introduction During last years the putative effects of cerebellar transcranial direct-current stimulation (tDCS) has attracted the attention of basic and clinical neuroscientist. Nevertheless, the impact of exogenous electric fields on the different components of the cerebellar network is not already elucidated. Objectives The aim of this study was to characterize physiological mechanisms underlying short- and long-term effects associated to cerebellar tDCS in alert behaving mice. In particular, we explored the tDCS impact on the cerebellar response to sensory inputs (whisker stimulation) and the potential modulation of Purkinje Cell (PC) discharge rates. Materials & methods Mice were prepared for chronic recording of local field potentials (LFPs) and PC firing in the CrusI/II region of the cerebellum. Along the experimental sessions spontaneous and stimulus-induced (by electrical whisker pad stimulation) activity of PCs (identified by the presence of simple and complex spikes) were recorded before, during and after anodal and cathodal tDCS applied over the cerebellum. For that, we used ring-electrodes placed over the skull allowing simultaneous tDCS stimulation and glass micropipette insertion for LFPs and extracellular unitary recording. tDCS was performed at different current intensities for 5 s to test the immediate effects on sensory-related LFPs and PC activity, and during 20 min to show after-effects on sensory related LFPs. Results Regarding to the immediate short-term effects (5 s), anodal and cathodal cerebellar tDCS increased and decreased, respectively, the amplitude of N3 component of LFPs induced by simultaneous whisker stimulation. This component has been previously reported to reflect the synaptic activity between parallel fiber and the dendritic tree of PC. Interestingly, longer stimulation sessions (20 min) induced long-term effects that last for more than one hour. Coherently, the firing rate of identified PC was increased or decreased depending of the anodal or cathodal tDCS, respectively. PC response to whisker tactile stimulation was also modulated in the same manner. Conclusions Present results demonstrate tDCS’s capability for short- and long-term modulation of the cerebellar cortex, and specifically PCs firing activities.