TABLE 1.

A brief summary of rodent electrical stimulation studies in the PNS and CNS.

References	CNS/PNS	Stimulation substrate	Parameters	Effects
Al-Majed et al., 2000a	PNS	Electrode wired around injured rat femoral nerve	20 Hz, 0.1 ms, 3 V, continous 1-h	Increased BDNF and trkB expression in motor neurons at 8 h and 2 days after ES.
Al-Majed et al., 2000b	PNS	Electrodes wired around injured rat femoral nerve	20 Hz, 0.1 ms, 3 V, continous 1-h	ES enhanced initiation of motor neuron regeneration after femoral nerve repair.
Al-Majed et al., 2004	PNS	Electrode wired around injured rat femoral nerve	20 Hz, 0.1 ms, 3 V, continous 1-h	Upregulation of GAP43 and Tα1-Tubulin expression in motor neurons at 2days after ES.
English et al., 2007	PNS	Cuff electrode around injured mouse common fibular nerve	20 Hz, 0.1 ms, 0.5 to 5 V (2× motor threshold), continuous 1-h	Enhanced YFP+ axon regeneration through nerve allograft in a NT-4/5 dependent manner. Increased the levels of BDNF and trkB in injured and intact DRGs at 7 and 14 days after ES.
Geremia et al., 2007	PNS	Stainless steel wire electrodes on opposite sides of injured femoral nerve	20 Hz, 0.1 ms, 2× motor threshold 1-h	Increased sensory neuron regeneration after femoral nerve trunk repair, increased BDNF and GAP-43 expression in DRG neurons.
Udina et al., 2008	PNS	Electrode wired around intact rat sciatic nerve	20 Hz, 0.02 ms, ∼3 to 5 V (2× motor threshold), continous 1-h	ES enhanced central axon regeneration was less robust than nerve crush effects after SCI. Increased cAMP levels in DRGs 7 days after ES, comparable to nerve injury.
Chisholm et al., 2018	PNS	Cuff electrodes surrounding intact mouse sciatic nerve	1, 2, 5, and 20 Hz, ES-1: 250 μA, 250 μs. ES-2: 5 mA, 1 ms	Intensity- and frequency-dependent rapid calcium increase in DRG neurons
Goganau et al., 2018	PNS	Cuff electrodes around intact rat sciatic nerve	20 Hz, 0.2 ms, 2× motor threshold, continous 1-h (ES1), 7-h (ES2), or 1-h daily per 7 days (ES3).	ES enhanced central axon regeneration was less robust than nerve crush effects after SCI. 1 h of ES per day for 7 days and 7 hours of ES followed by 7 days of waiting resulted in similar in vitro neurite outgrowth.
Senger et al., 2018	PNS	Electrode wired around intact rat common peroneal nerve	20 Hz, 0.1 ms, continuos 1-h	Upregulation of GAP-43 and BDNF expression in DRG neurons and GFAP in satellite cells at 3 days after ES. Similar to injury-induced changes.
Senger et al., 2019	PNS	Electrode wired around intact rat tibial nerve	20 Hz, 0.1 ms, continuos 1-h	Increased pCREB levels in DRGs at 3 days after ES. 7 day prior electrical conditioning enhanced regeneration and reinnervation.
Brus-Ramer et al., 2007	CNS	Tripolar electrodes on the surface of rats pyramidal tract	333 Hz, 45 ms burst every 2 s, 6 h daily per 10 days.	Chronic ES enhanced intact corticospinal collateral sprouting.
Carmel et al., 2014	CNS	Implanted electrodes into rat forelimb motor cortex	333 Hz, 45 ms burst every 2 s, 6 h daily per 10 days	Chronic ES induced recovery of skilled locomotor function.
Zareen et al., 2017	CNS	Combined bilateral rat epidural (M1) iTBS, and spinal cord (C4-T2) tsDCS stimulation 7 weeks after SCI	iTBS: stimulation intensity 75% of motor threshold. tsDCS: 1.5 mA for 2.5 s and returned to 0 over 2.5 s. Combined stimulation for 30 min daily per 10 day.	Combined ES enhanced injury-dependent corticospinal collateral sprouting below and above the level of injury, and enhanced skilled forelimb functional recovery.
Zareen et al., 2018	CNS	Implanted electrodes into rat forelimb motor cortex	333 Hz, 0.2 ms duration every 2 s, 1.1 to 2 mA, continous 6 h daily per 10 days	Chronic ES induced activation of mTOR and Jak/STAT pathways, inactivation of PTEN, and increased phosphorylation of ribosomal protein s6. Chronic ES induced mTOR-dependent collateral sprouting of intact corticospinal tract.
Jack et al., 2018	CNS	Implanted electrodes into rat forelimb motor cortex	333 Hz, 0.2 ms duration every 500 ms, 30 pulses per train	Single ES to injured CST increased collateral sprouting above injury site, with no further improvement in recovery of function.
Batty et al., 2020	CNS	implanted electrodes into rats forelimb motor cortex	333 Hz, 30 pulses of 0.2 ms width every 0.5 s, for 30 min	Single ES to intact CST enhanced corticospinal collateral sprouting above SCI and improved motor function recovery.