title: Evidence that some long-lasting effects of direct current in the rat spinal cord are activity-independent.
abstract: The effects of trans-spinal direct current (DC) stimulation (tsDCS) on specific neuronal populations are difficult to elucidate, as it affects a variety of neuronal networks. However, facilitatory and depressive effects on neurons processing information from the skin and from muscles can be evaluated separately when weak (0.2-0.3 μA) DC is applied within restricted areas of the rat spinal cord. The effects of such local DC application were recently demonstrated to persist for at least 1 h, and to include changes in the excitability of afferent fibres and their synaptic actions. However, whether these effects require activation of afferent fibres in spinal neuronal pathways during DC application, i.e. whether they are activity-dependent or activity-independent, remained an open question. The aim of the present study was to address this question by analysing the effects of local DC application on monosynaptic actions of muscle and skin afferents (extracellular field potentials) and afferent fibre excitability. The results revealed that long-lasting post-polarization changes evoked without concomitant activation of afferent fibres replicate changes evoked by stimuli applied during, before and after polarization. The study leads to the conclusion that the reported effects are activity-independent. As this conclusion applies to the local effects of DC application in at least two spinal pathways and to the effects of both cathodal and anodal polarization, it indicates that some of the more widespread effects of trans-spinal and trans-cranial stimulation (both tsDCS and transcranial DC stimulation) may be activity-independent. The results may therefore contribute to the design of more specific DC applications in clinical practice.
authors.affiliation: Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Medicinaregatan 11, Box 432, SE 405 30, Goteborg, Sweden.
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Jankowska
authors.affiliation: Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Medicinaregatan 11, Box 432, SE 405 30, Goteborg, Sweden.|Department of Neurobiology and Department of Biochemistry, Poznan University of Physical Education, Poznań, Poland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Kaczmarek
authors.affiliation: Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Medicinaregatan 11, Box 432, SE 405 30, Goteborg, Sweden.|Human Physiology Section of the DEPT, Università degli Studi di Milano, Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bolzoni
authors.affiliation: Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Medicinaregatan 11, Box 432, SE 405 30, Goteborg, Sweden.
authors.forename: Ingela
authors.initials: I
authors.lastname: Hammar
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D005260:Female; D008297:Male; D008564:Membrane Potentials; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010543:Peroneal Nerve / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012867:Skin / Q000294:innervation; D012879:Skin Physiological Phenomena; D066148:Spinal Cord Dorsal Horn / Q000502:physiology*; D062187:Spinal Cord Stimulation; D013497:Sural Nerve / Q000502:physiology*
keywords: direct current polarization; excitability; rat; spinal cord; synaptic actions