Electrical stimulation and testosterone differentially enhance expression of regeneration-associated genes.

As functional recovery following peripheral nerve injury is dependent upon successful repair and regeneration, treatments that enhance different regenerative events may be advantageous. Using a rat facial nerve crush axotomy model, our lab has previously investigated the effects of a combinatorial treatment strategy, consisting of electrical stimulation (ES) of the proximal nerve stump and testosterone propionate (TP) administration. Results indicated that the two treatments differentially enhance facial nerve regenerative properties, whereby ES reduced the delay before sprout formation, TP accelerated the overall regeneration rate, and the combinatorial treatment had additive effects. To delineate the molecular mechanisms underlying such treatments, the present study investigated the effects of ES and TP on expression of specific regeneration-associated genes. Following a right facial nerve crush at the stylomastoid foramen, gonadectomized adult male rats were administered only ES, only TP, a combination of both, or left untreated. Real time RT-PCR analysis was used to assess fold changes in mRNA levels in the facial motor nucleus at 0 h, 6 h, 1 d, 2 d, 7 d, and 21 d post-axotomy. The candidate genes analyzed included two tubulin isoforms (alpha(1)-tubulin and beta(II)-tubulin), 43-kiloDalton growth-associated protein (GAP-43), brain derived neurotrophic factor (BDNF), pituitary adenylate cyclase-activating peptide (PACAP), and neuritin (candidate plasticity-related gene 15). The two treatments have differential effects on gene expression, with ES leading to early but transient upregulation and TP producing late but steady increases in mRNA levels. In comparison to individual treatments, the combinatorial treatment strategy has the most enhanced effects on the transcriptional program activated following injury.

Effects of electrical stimulation and gonadal steroids on rat facial nerve regenerative properties.

PURPOSE: The neurotherapeutic effects of nerve electrical stimulation and gonadal steroids have independently been demonstrated. The purpose of this study was to investigate the therapeutic potential of a combinatorial treatment strategy of electrical stimulation and gonadal steroids on peripheral nerve regeneration. METHODS: Following a facial nerve crush axotomy in gonadectomized adult male rats, testosterone propionate (TP), dihydrotestosterone (DHT), or estradiol (E(2)) was systemically administered with/without daily electrical stimulation of the proximal nerve stump. Facial nerve outgrowth was assessed at 4 and 7 days post-axotomy using radioactive labeling. RESULTS: Administration of electrical stimulation alone reduced the estimated delay in sprout formation but failed to accelerate the overall regeneration rate. Conversely, TP treatment alone accelerated the regeneration rate by approximately 10% but had no effect on the sprouting delay. Combining TP with electrical stimulation, however, maintained the enhanced rate and reduced the sprouting delay. DHT treatment alone failed to alter the regeneration rate but combining it with electrical stimulation increased the rate by 10%. E(2) treatment alone increased the regeneration rate by approximately 5% but with electrical stimulation, there was no additional effect. CONCLUSIONS: Electrical stimulation and gonadal steroids differentially enhanced regenerative properties. TP, an aromatizable androgen, augmented regeneration most, suggesting a synergism between androgenic and estrogenic effects. Therapeutically, combining electrical stimulation with gonadal steroids may boost regenerative properties more than the use of either treatment alone.

Accelerating functional recovery after rat facial nerve injury: Effects of gonadal steroids and electrical stimulation.

OBJECTIVE: We investigated the combined effects of electrical stimulation and testosterone propionate on overall recovery time in rats with extracranial crush injuries to the facial nerve. STUDY DESIGN: Male rats underwent castration 3 to 5 days prior to right facial nerve crush injury and electrode implantation. Rats were randomly assigned to two groups: crush injury + testosterone or crush injury with electrical stimulation + testosterone. Recovery was assessed by daily subjective examination documenting vibrissae orientation/movement, semi-eye blink, and full eye blink. RESULTS: Milestones of early recovery were noted to be significantly earlier in the groups with electrical stimulation, with/without testosterone. The addition of testosterone to electrical stimulation showed significant earlier return of late recovery parameters and complete overall recovery. CONCLUSION: Electrical stimulation may decrease cell death or promote sprouting to accelerate early recovery. Testosterone may affect the actual rate of axonal regeneration and produce acceleration in functional recovery. By targeting different stages of neural regeneration, the synergy of electrical stimulation and testosterone appears to have promise as a neurotherapeutic strategy for facial nerve injury.

Electrical stimulation facilitates rat facial nerve recovery from a crush injury.

OBJECTIVE: To study the effect of electrical stimulation on accelerating facial nerve functional recovery from a crush injury in the rat model. STUDY DESIGN: Experimental. METHOD: The main trunk of the right facial nerve was crushed just distal to the stylomastoid foramen, causing right-sided facial paralysis in 17 Sprague-Dawley rats. An electrode apparatus was implanted in all rats. Nine rats underwent electrical stimulation and eight were sham stimulated until complete facial nerve recovery. Facial nerve function was assessed daily by grading eyeblink reflex, vibrissae orientation, and vibrissae movement. RESULTS: An electrical stimulation model of the rat facial nerve following axotomy was established. The semi-eyeblink returned significantly earlier (3.71 + 0.97 vs 9.57 + 1.86 days post axotomy) in stimulated rats (P = 0.008). Stimulated rats also recovered all functions earlier, and showed less variability in recovery time. CONCLUSION: Electrical stimulation initiates and accelerates facial nerve recovery in the rat model as it significantly reduces recovery time for the semi-eyeblink reflex, a marker of early recovery. It also hastens recovery of other functions.

alpha-Synuclein budding yeast model: toxicity enhanced by impaired proteasome and oxidative stress.

Parkinson's disease (PD) is a common neurodegenerative disorder that results from the selective loss of midbrain dopaminergic neurons. Misfolding and aggregation of the protein alpha-synuclein, oxidative damage, and proteasomal impairment are all hypotheses for the molecular cause of this selective neurotoxicity. Here, we describe a Saccharomyces cerevisiae model to evaluate the misfolding, aggregation, and toxicity-inducing ability of wild-type alpha-synuclein and three mutants (A30P, A53T, and A30P/A53T), and we compare regulation of these properties by dysfunctional proteasomes and by oxidative stress. We found prominent localization of wild-type and A53T alpha-synuclein near the plasma membrane, supporting known in vitro lipid-binding ability. In contrast, A30P was mostly cytoplasmic, whereas A30P/A53T displayed both types of fluorescence. Surprisingly, alpha-synuclein was not toxic to several yeast strains tested. When yeast mutants for the proteasomal barrel (doa3-1) were evaluated, delayed alpha-synuclein synthesis and membrane association were observed; yeast mutant for the proteasomal cap (sen3-1) exhibited increased accumulation and aggregation of alpha-synuclein. Both sen3-1and doa3-1 mutants exhibited synthetic lethality with alpha-synuclein. When yeasts were challenged with an oxidant (hydrogen peroxide), alpha-synuclein was extremely lethal to cells that lacked manganese superoxide dismutase Mn-SOD (sod2Delta) but not to cells that lacked copper, zinc superoxide dismutase Cu,Zn-SOD (sod1Delta). Despite the toxicity, sod2Delta cells never displayed intracellular aggregates of alpha-synuclein. We suggest that the toxic alpha-synuclein species in yeast are smaller than the visible aggregates, and toxicity might involve alpha-synuclein membrane association. Thus, yeasts have emerged effective organisms for characterizing factors and mechanisms that regulate alpha-synuclein toxicity.