Abstract
There is evidence that Deep Brain Stimulation (DBS) produces health benefits in patients even before initiating stimulation. Furthermore, DBS electrode insertion in rat infralimbic cortex (ILC) provokes antidepressant-like effects before stimulation, due to local inflammation and astrogliosis. Consequently, a significant effect of implanting electrodes is suspected. External fields, similar in magnitude to the brain’s endogenous fields, induce electric dipoles in conducting materials, in turn influencing neural cell growth through wireless effects. To elucidate if such dipoles influence depressive-like behavior, without external stimulation, the comparative effect of conducting and insulated electrodes along with the glial response is studied in unstressed rats. Naïve and implanted rats with electrically insulated or uninsulated steel electrodes were evaluated in the modified forced swimming test and expression of ILC-glial markers was assessed. An antidepressant-like effect was observed with conducting but not with insulated electrodes. Gliosis was detected in both groups, but astroglial reactivity was larger near uninsulated electrodes. Thus, induced dipoles and antidepressant-like effects were only observed with conducting implants. Such correlation suggests that dipoles induced in electrodes by endogenous fields in turn induce neuron stimulation in a feedback loop between electrodes and neural system. Further research of the effects of unwired conducting implants could open new approaches to regulating neuronal function, and possibly treat neurological disorders.
Highlights
Electrostimulation using implanted electrodes with alternating electric fields of low intensity is known to eliminate symptoms in Parkinson’s disease, dystonia and essential tremor or epilepsy
The observations described above evidence that the simple implantation of a conducting material in the infralimbic cortex (ILC) can produce an antidepressant-like effect in unstressed rats, as reported before [21], and that such effect is blocked when the conducting material is insulated
At some short scale time, the external field effects may be assimilated, as is similar to the possible field effects that endogenous fields from neurons may have on conducting implanted materials, but not for insulating materials
Summary
Electrostimulation using implanted electrodes with alternating electric fields of low intensity is known to eliminate symptoms in Parkinson’s disease, dystonia and essential tremor or epilepsy. In Deep Brain Stimulation (DBS), stimulation electrodes are permanently connected to a neurostimulator with the capability of delivering electrical chronic stimulation of a targeted brain region. The fundamental mechanisms by which external alternating electric fields have such effect are not well known. There is evidence that the presence of continuous fields has intense effects on neurons in vitro including increased differentiation, directional growth of neurites towards the cathode, increased neural branching and filopodial activity [7]. Little focus is given in general to the electrode materials in electrostimulation work. The interaction between the required electrodes and neurons is starting to show that the effects are highly dependent on the electrode material
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