Immediate Cortical and Spinal C-Fos Immunoreactivity After ICMS of the Primary Somatosensory Cortex in Rats

Abstract

Intracortical microstimulation (ICMS) is an invasive stimulation technique through which it is possible to excitate and inhibit the activity of neurons from different cortical regions. The ICMS has been used in the context of neural prostheses targeting the restoration of neurological functions and as possible tactile feedback in brain-machine interfaces. Several protocols of microstimulation have been implemented to stimulate the primary somatosensory cortex (S1). The literature describes the direct effects of ICMS upon the activity of neurons in the stimulated area, though the distribution of the neuronal activity and the indirect effects of that stimulation, that is, those that occur far from the stimulated area, are still not fully described. This study aimed to evaluate the immediate effects of the ICMS on c-Fos cell immunoreactivity upon the stimulated area and the extent of this stimulation in S1, adjacent cortical areas, and also in the spinal cord of rats. It was observed that surrounding the microelectrode implant occurred a lower immunoreactivity extending to $150{-}200\ \upmu$m$^{2}$, however, there was no statistical significance to right and left directions (X$^{2}$(4) = 5.00, p = 0.29; X$^{2}$(4) = 6.33, p = 0.18). It was followed by a higher number of c-Fos immunoreactive cells between $250{-}1000\ \upmu$m from the microelectrode track at the mediolateral directions, being statistically significant to $500\ \upmu$m at the rostroventral direction (F(2, 6) = 6.57, p = 0.031). Despite the qualitative differences in the number of immunoreactive cells, no statistically significant differences were observed to M1, S2, and spinal cord areas. This study corroborates with findings of previous research relative to the extent of neuronal activity and immunoreactivity after ICMS, adding that similar patterns of cortical immunoreactivity are seen in non-anesthetized stimulated animals.