Depolarization and electrical stimulation enhance in vitro and in vivo sensory axon growth after spinal cord injury

Abstract

Activity dependent plasticity is a key mechanism for the central nervous system (CNS) to adapt to its environment. Whether neuronal activity also influences axonal regeneration in the injured CNS, and whether electrical stimulation (ES) can activate regenerative programs in the injured CNS remains incompletely understood. Using KCl-induced depolarization, in vivo ES followed by ex-vivo neurite growth assays and ES after spinal cord lesions and cell grafting, we aimed to identify parameters important for ES-enhanced neurite growth and axonal regeneration. Using cultures of sensory neurons, neurite growth was analyzed after KCl-induced depolarization for 1-72h. Increased neurite growth was detected after short-term stimulation and after longer stimulation if a sufficient delay between stimulation and growth measurements was provided. After in vivo ES (20Hz, 2× motor threshold, 0.2ms, 1h) of the intact sciatic nerve in adult Fischer344 rats, sensory neurons showed a 2-fold increase in in vitro neurite length one week later compared to sham animals, an effect not observed one day after ES. Longer ES (7h) and repeated ES (7days, 1h each) also increased growth by 56-67% one week later, but provided no additional benefit. In vivo growth of dorsal column sensory axons into a graft of bone marrow stromal cells 4weeks after a cervical spinal cord lesion was also enhanced with a single post-injury 1h ES of the intact sciatic nerve and was also observed after repeated ES without inducing pain-like behavior. While ES did not result in sensory functional recovery, our data indicate that ES has time-dependent influences on the regenerative capacity of sensory neurons and might further enhance axonal regeneration in combinatorial approaches after SCI.

Screening of Anxiolytic and Antidepressant of Methanolic Leaves Extract of Syzygium Cumini in Mice

“…Highly significant increase was observed at dose of 500 mg/kg in rearing numbers and its duration; these results were almost similar to the standard treatment group which suggests improved locomotor action [19]. While increase in distance travelled at 500 mg/kg on 15 th day shows improved motor activity and central nervous system stimulation [20]. These results reflect low anxiety potential and high exploratory behavior of S. cumini.…”

Functional Electrical Stimulation and the Modulation of the Axon Regeneration Program

“…In these studies, conditioning by electrical stimulation was found to elicit greater physiological and functional recovery than conditioning by nerve crush. This apparent discrepancy with the effects observed in vitro and in models of subsequent spinal cord injury (Goganau et al, 2018) is likely due to slowing of the regenerating axons upon reaching the disrupted cytoarchitecture, proliferative Schwann cells, and inflammation at the nerve crush site. The efficacy of both pre-and post-injury electrical stimulation in enhancing regeneration of rodent peripheral nerves and accelerating functional outcomes, together with the feasibility of its use in bedside settings makes brief low frequency electrical stimulation a clinically relevant approach to mediate PNS repair.…”

“…In addition to the transcriptional regulation that occurs with electrical stimulation, 1 h of low-frequency stimulation of intact rat sciatic nerves increases intracellular cAMP levels in DRG neurons similar to nerve injury (Udina et al, 2008). Despite the fact that electrical stimulation and axotomy induce similar increases in cAMP, 1 h of low-frequency electrical stimulation is not sufficient to fully recapitulate the regenerative response of peripheral conditioning of sensory neurons to a central spinal cord injury (Udina et al, 2008;Goganau et al, 2018).…”

“…Following a subsequent peripheral injury, previous exposure to low-frequency electrical stimulation enhances the initiation of regeneration, but does not increase the rate of peripheral motor or sensory axon regeneration (Al-Majed et al, 2000b;Brushart et al, 2002). The limited effectiveness of electrical conditioning extends to the CNS as well, as regeneration of the central axon of dorsal column projecting sensory neurons after a spinal cord injury is less robust in rats conditioned 1 week prior with electrical stimulation than those subjected to nerve crush injury (Goganau et al, 2018). Electrical stimulation immediately following a dorsal column spinal cord injury allows for an increased initiation of regeneration; however, these axons fail to elongate through the injury site, in contrast to more robust regenerative effects of nerve crush injury (Udina et al, 2008).…”

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury

“…A limited intrinsic regenerative capacity of adult sensory axons also contributes to the failure of axon regeneration 16,17 . Lesions of DRGs' central axon branches fail to elicit a robust regenerative response 18,19 . Some interventions have been shown to enhance the intrinsic regenerative response of sensory neurons, including a so-called peripheral "conditioning lesion" [20][21][22] , induction of inflammation near the cell body within the ganglia themselves 14,23 , and driving activation of mTOR in DRG neurons 15 .…”