Abstracts

Rationale: Recently we demonstrated the effectiveness of noninvasive transcranial focal electrical stimulation (TFS) via tripolar concentric ring electrodes (TCRE) to control pentylenetetrazole (PTZ) induced seizures in rats. In [1] we showed TFS lessens behavioral seizure activity of recurrent PTZ administrations. In [2] a noninvasive seizure control system based on automatic seizure detection triggering the TFS reduced electrographic seizure activity power in the treated group. In our previous work the TFS current intensity was 50 mA, now we report on the potential effect of 5 mA TFS on PTZ-induced seizure activity which is comparable to the current intensity of transcranial direct current stimulation (tDCS) that can be applied to humans. Methods: Naive male Sprague-Dawley rats were used in this study. The TCREs were placed on the scalp with conductive paste and adhered with dental cement 24 h before the experimental procedure (Fig. 1A). The animals were divided into control (n = 7) and TFS-treated (n = 7) groups based solely on skin-to-electrode impedance. If impedances between the three recording surfaces of TCRE (s) and the isolated ground TCRE (g) were less than 10 KΩ the rat was administered TFS. PTZ (45 mg/kg ip) was given to both groups and TFS (5 mA, 200 µs, 300 Hz, 2 min, biphasic, charge-balanced pulses) was triggered manually in the TFS-treated group only when the first myoclonic jerk (MJ) was observed. To score behavioral seizure activity we adapted the revised Racine's scale from [1] (Table 1). The latency of initial myoclonic activity was defined as the time to the first MJ. The maximal score value and the total number of MJs were counted (first to last) for each animal as well as the duration of myoclonic activity (time elapsed between the first and the last MJs). The non-parametric Mann-Whitney U test was used to make comparisons between the control and TFS-treated groups due to non-normality. Results: The latency of myoclonic activity was significantly different (p = 0.02; Fig. 1B) with medians of 169 s and 74 s for the control and the TFS-treated group, respectively. At the same time there was no significant difference in maximal behavioral seizure activity score (p = 0.41; both medians equal to 3), number of myoclonic jerks (p = 0.28; medians of 12 and 10; Fig. 1C), and duration of myoclonic activity (p = 0.41; medians of 165 s and 100 s; Fig. 1D). Conclusions: The latency of myoclonic activity could not have been affected by TFS in either group since TFS was not turned on until the first MJ was observed. Statistically longer latency in the control group stems from lower initial susceptibility of this group to PTZ. Combined with an absence of any statistically significant differences in the other three metrics affected by TFS this suggests an anticonvulsant effect of TFS at low currents.