Facial Regeneration Research Articles

Electrical stimulation and testosterone differentially enhance rat facial nerve regeneration following injury

As functional recovery following peripheral nerve injury is dependent upon successful repair and regeneration, treatments that enhance different regeneration events may be advantageous. Our lab has used facial nerve axotomy as a model for studying motor neuron regeneration and has shown that following a facial nerve crush injury in hamsters, administration of gonadal steroids accelerates functional recovery and regeneration rates but fails to shorten the initial delay in sprouting. To target regeneration at earlier time points, our lab has developed an electrical stimulation (ES) model in rat and shown that ES helps initiate functional recovery. Also, the combination of both ES and testosterone shortens recovery time by 22% compared to untreated animals. To further assess the therapeutic potential of ES and testosterone, we now analyze how they affect axonal regeneration. The facial nerve was crushed near its exit from the stylomastoid foramen, and its outgrowth distance was measured at 4‐ and 7‐days post‐injury. We find that testosterone alone increases the regeneration rate, ES alone reduces the initial delay in sprouting, and the use of them together has synergistic effects on axonal regeneration. As ES and testosterone differentially enhance regeneration, together they can serve as an effective treatment for nerve injuries.

Ro5‐4864 promotes neonatal motor neuron survival and nerve regeneration in adult rats

The translocator protein (18 kDa; TSPO), formerly known as the peripheral benzodiazepine receptor, is an outer mitochondrial membrane protein that associates with the mitochondrial permeability transition pore to regulate both steroidogenesis and apoptosis. TSPO expression is induced in adult dorsal root ganglion (DRG) sensory neurons after peripheral nerve injury and a TSPO receptor ligand, Ro5-4864, enhances DRG neurite growth in vitro and axonal regeneration in vivo. We have now found that TSPO is induced in neonatal motor neurons after peripheral nerve injury and have evaluated its involvement in neonatal and adult sensory and motor neuron survival, and in adult motor neuron regeneration. The TSPO ligand Ro5-4864 rescued cultured neonatal DRG neurons from nerve growth factor withdrawal-induced apoptosis and protected neonatal spinal cord motor neurons from death due to sciatic nerve axotomy. However, Ro5-4864 had only a small neuroprotective effect on adult facial motor neurons after axotomy, did not delay onset or prolong survival in SOD1 mutant mice, and failed to protect adult DRG neurons from sciatic nerve injury-induced death. In contrast, Ro5-4864 substantially enhanced adult facial motor neuron nerve regeneration and restoration of function after facial nerve axotomy. These data indicate a selective sensitivity of neonatal sensory and motor neurons to survival in response to Ro5-4864, which highlights that survival in injured immature neurons cannot necessarily predict success in adults. Furthermore, although Ro5-4864 is only a very weak promoter of survival in adult neurons, it significantly enhances regeneration and functional recovery in adults.

Effects of hyperbaric oxygen therapy on facial nerve regeneration

Conclusion. Hyperbaric oxygen treatment (HBOT) promoted an increase of the mean axonal diameter in the group evaluated 2 weeks after lesion induction, which suggests a more advanced regeneration process. However, the number of myelin nerve fibers of the facial nerve of the rabbits was similar when compared to the control and treatment groups, in both evaluation periods. Objective. To evaluate the effect of HBOT on the histological pattern of the facial nerve in rabbits exposed to a nerve crush injury. Materials and methods. Twenty rabbits were exposed to facial nerve crush injury. Ten rabbits received HBOT, 10 rabbits comprised the control group. The rabbits were sacrificed 2 and 4 weeks after the trauma. Qualitative morphological analysis, measurement of the external axonal diameters and myelin fiber count were carried out in an area of 185 000 µm2. Results. There was an increase in the area of the axons and thicker myelin in the 2 weeks treatment group in comparison with the control group. The mean diameter of the axons was of 2.34 µm in the control group and of 2.81 µm in the HBOT group, with statistically significant differences. The 2 week control group had a mean number of myelin fibers of 1865.2±664, and the HBOT group had a mean number of 2026.3±302; this was not statistically significant. The 4 week control group presented a mean of 2495.1±479 fibers and the HBOT group presented a mean of 2359.9±473; this was not statistically significant.

Expression patterns in alternative splicing forms of prosaposin mRNA in the rat facial nerve nucleus after facial nerve transection

Prosaposin acts as a neurotrophic factor, in addition to its role as the precursor protein for saposins A, B, C, and D, which are activators for specific sphingolipid hydrolases in lysosomes. In rats, the prosaposin gene generates two alternative splicing forms of mRNA: Pro + 9 containing a 9-base insertion and Pro + 0 without. The expression of these mRNAs changes after brain injury. We examined the expression patterns of the alternative splicing forms of prosaposin mRNA in the rat facial nerve nucleus for 52 days following facial nerve transection. Pro + 0 mRNA increased within 3 days of transection, peaked after 5–10 days, and remained significantly elevated for 21 days. In contrast, the expression of Pro + 9 mRNA was constant throughout the regenerative period. Prosaposin mRNA expression increased not only in facial motoneurons, but also in microglia during facial nerve regeneration. Our findings indicate that the saposin B domain of prosaposin, which is the domain affected by alternative splicing, plays an important role in both neurons and microglia during neuroregeneration.

Experimentelle Untersuchungen zur Verbesserung der Fazialisregeneration

Using a combination of the following, it is possible to investigate procedures to improve the morphological and functional regeneration of the facial nerve in animal models: 1) retrograde fluorescence tracing to analyse collateral axonal sprouting and the selectivity of reinnervation of the mimic musculature, 2) immunohistochemistry to analyse both the terminal axonal sprouting in the muscles and the axon reaction within the nucleus of the facial nerve, the peripheral nerve, and its environment, and 3) digital motion analysis of the muscles. To obtain good functional facial nerve regeneration, a reduction of terminal sprouting in the mimic musculature seems to be more important than a reduction of collateral sprouting at the lesion site. Promising strategies include acceleration of nerve regeneration, forced induced use of the paralysed face, mechanical stimulation of the face, and transplantation of nerve-growth-promoting olfactory epithelium at the lesion site.

Effect of Platelet Rich Plasma and Fibrin Sealant on Facial Nerve Regeneration in a Rat Model

To investigate the effects of platelet rich plasma (PRP) and fibrin sealant (FS) on facial nerve regeneration. Prospective, randomized, and controlled animal study. Experiments involved the transection and repair of facial nerve of 49 male adult rats. Seven groups were created dependant on the method of repair: suture; PRP (with/without suture); platelet poor plasma (PPP) (with/without suture); and FS (with/without suture) groups. Each method of repair was applied immediately after the nerve transection. The outcomes measured were: 1) observation of gross recovery of vibrissae movements within 8-week period after nerve transection and repair using a 5-point scale and comparing the left (test) side with the right (control) side; 2) comparisons of facial nerve motor action potentials (MAP) recorded before and 8 weeks after nerve transection and repair, including both the transected and control (untreated) nerves; 3) histologic evaluation of axons counts and the area of the axons. Vibrissae movement observation: the inclusion of suturing resulted in overall improved outcomes. This was found for comparisons of the suture group with PRP group; PRP with/without suture groups; and PPP with/without suture groups (P < .05). The PRP without suture group had a significantly greater degree of recovery than the PPP without suture group (P < .05), but it did not have better performance than suture group (P > .05). The movement recovery of the suture group was significantly better than the FS group (P = .014). The recovery of function of the PRP groups was better than that of the FS groups, although this did not reach statistical significance (P = .09). Electrophysiologic testing: there was a significantly better performance of the suture group when compared with the PRP and PPP without suture groups in nerve conduction velocity (P < .05). The PRP with suture group had the best results when compared with the suture as well as the PPP with suture groups in duration and latency-2 of MAP (P < .05). For the FS groups, no results were found demonstrating a biological effect. The PRP with suture group demonstrated the best performance in the latency-2 and the area under the curve of MAP when compared with the suture and FS with suture groups (P < .05). Histomorphometric analysis: PRP with suture demonstrated the greatest increase in axon counts when compared with suture, FS with suture, and PPP with suture groups (P < .05). There was no statistically significant difference seen in axon diameter. The best results for the return of function in our rat facial nerve axotomy models occurred when the nerve ends were sutured together. At the same time, the data demonstrated a measurable neurotrophic effect when PRP was present, with the most favorable results seen with PRP added to suture. There was an improved functional outcome with the use of PRP in comparison with FS or no bioactive agents (PPP). FS showed no benefit over conventional suturing in facial nerve regeneration. Our study provides the potential of a new clinical application for PRP in peripheral nerve regeneration.

Evaluation of the systemic use of riluzole in post-traumatic facial nerve regeneration: experimental study in rabbits

Conclusions. Riluzole promoted increase and/or preservation of axon density in the animals treated with this drug as compared to the control group; it did not increase the mean diameter of facial nerve fibres as compared to the non-treated group; and it did not provide a better functional motor recovery than in the control group. Objective. Traumatic peripheral facial paralysis is a frequent affection. In incomplete nerve injuries, systemic drugs acting on regeneration may decrease the patient's period of morbidity. This study aimed to determine the effect of the drug riluzole on regeneration of the facial nerve of rabbits submitted to post-traumatic facial paralysis. Materials and methods. Eighteen rabbits were submitted to compression of the facial nerve and divided into control (A) and treated (B) groups. The animals were sacrificed 4 weeks after the injury and their nerves were studied regarding density of myelinated axons and measure of external axon diameters. Results. Partial functional recovery was observed within 2 weeks and complete recovery 5 weeks after injury. Mean neural density was 12 679.7 axons/mm2 (SD±237.5) in group A, and 19 073.8 axons/mm2 (SD±3549.9) in group B. Group A presented less than two-thirds the density of group B. There was no statistical difference in axon diameters between the studied groups.

The Effect of Androgen Status on the Structural and Functional Success of Cavernous Nerve Grafting in an Experimental Rat Model

Iatrogenic erectile dysfunction following radical prostatectomy is primarily neurogenic in origin. Attempts to improve postoperative potency aim to preserve or regenerate the autonomic cavernous nerves. Testosterone is integral for erectile function and it has profound positive effects on nerve regeneration. Androgen ablation impairs nerve regeneration. In this animal study we evaluated whether testosterone deprivation effects axonal regeneration in cavernous nerve grafts or the erectile response to cavernous nerve graft stimulation. A total of 45 male Sprague-Dawley rats underwent bilateral cavernous nerve neurotomy, followed by unilateral nerve graft using the genitofemoral nerve. Rats were then randomized to castrate, intact and testosterone treated arms. At 3 months grafts were explored and electrostimulation was performed with intracavernous pressure responses recorded. Grafted nerves were then harvested for immunohistochemical analysis. Univariate analysis demonstrated a significant difference in the maximal intracavernous pressure response between groups. Mean +/- SEM maximal intracavernous pressure was 47 +/- 7.9, 23.7 +/- 4.9 and 59 +/- 7.4 mm Hg in the intact, castrate and testosterone treated groups, respectively (p = 0.003). Total axon counts did not differ between treatment groups with a mean total axon count of 789 +/- 97, 706 +/- 134 and 726 +/- 111, respectively. Castrate animals had lower neuronal nitric oxide synthase axon counts compared to intact animals (p = 0.089). The mean axon count was 480 +/- 78, 285 +/- 53 and 435 +/- 71 in the intact, castrate and testosterone treated groups respectively. Castration resulted in a decreased erectile response to electrostimulation following nerve grafting. This may be due to decreased graft neuronal nitric oxide synthase positive axonal regeneration. This has important implications in patients in whom cavernous nerve grafting could be considered.

Role of extracellular matrix components in facial nerve regeneration: an experimental study

Objective: The aim of this study is to evaluate the role of extracellular matrix components in nerve regeneration. Matrigel, a complex of extracellular matrix components such as laminin (the most abundant) heparan sulphate proteoglycans (HSPG), type IV collagene and fibronectin, was used.Methods: Forty male rabbits, which had undergone section of the right facial nerve, were later treated by reinnervation through an artificial graft of expanded polytetrafluoroethylene (ePTFE). In 20 animals the tubes of ePTFE were filled with Matrigel; in 20 control animals the tubes were filled with saline solution.Results: The Matrigel group showed a better axonal organization and a significantly higher number of regenerated axons in the early phases (at days 15 and 30 respectively) than the control group, whereas the difference of the axons number at day 60 was less significant; besides, the axon diameter and the myelin thickness were not significantly improved by Matrigel.Discussion: Our data suggest that Matrigel is an important factor in promoting and enhancing the early phases of the regeneration after nerve injuries. Tree neurite promoting agents, such as laminin, fibronectin and collagen, allow a more systematic and agonized regeneration. Extracellular matrix components may represent a direction guidance for axonal pathway.

Modelo experimental comportamental e histológico da regeneração do nervo facial em ratos

O estabelecimento de modelos experimentais é o passo inicial para estudos de regeneração neural. OBJETIVO: Estabelecer modelo experimental de regeneração do nervo facial. MATERIAIS E MÉTODOS: Ratos Wistar com secção completa e sutura do tronco do nervo facial extratemporal, com análise comportamental e histológica até 9 semanas. FORMA DE ESTUDO: Estudo prospectivo experimental. RESULTADOS: Progressiva recuperação clínica e histológica dos animais. CONCLUSÃO: Estabelecemos um método aceitável para o estudo de regeneração do nervo facial em ratos.

Behavioral and histologic experimental model of facial nerve regeneration in rats

To setup an experimental model is the first step to study neural regeneration. Setting up an experimental model on facial nerve regeneration. Wistar rats with complete sectioning and suturing of the extratemporal facial nerve trunk; with a behavioral and histological analysis for 9 weeks. Experimental prospective study. Progressive clinical and histological recovery of the animals. Our method is acceptable to study facial nerve regeneration in rats.

Posttraumatic facial nerve regeneration in rabbits.

Posttraumatic facial paralysis is a frequent disease. This work studies posttraumatic regeneration of the facial nerve in rabbits. Functional and histological analysis compared injured and normal nerves on opposite sides. The left facial nerve trunk of twenty rabbits were subjected to compression lesion, and sacrificed after two (subgroup AL), four (BL) and six (CL) weeks. Comparison between groups was made by analysing total and partial densities of myelinated axons. Tukey Method (p<0.05). There was partial functional recovery after two weeks, and complete recovery after five weeks. Qualitative analysis demonstrated a degenerative pattern in the AL group, with an increased tissue inflammatory process. Evident regeneration signs were observed in the BL group, and almost complete regeneration was seen in the CL group. Normal nerves (N) had an average TD of 15705.59 and average PD of 21800.75. The BL group had an average TD of 10818.55 and an average PD of 15340.56. The CL group had an average TD of 13920.36 and an average PD of 16589.15. The BL group had an average TD of N equal to 68.88%, and the CL group had an average TD of N equal to 88,63% (statistically significant). N showed a significant higher PD than injured nerves. However, this was not statistically different between BL and CL subgroups. Nerve DT was a more reliable method than PD in this study.

The role of bone morphogenetic protein-2 in vivo in regeneration of peripheral nerves

We investigated the effects of bone morphogenetic protein-2 (BMP-2) and some other BMPs on regeneration of peripheral motor nerves in vivo. The facial nerves of 24 New Zealand rabbits were crushed to examine a series of retrograde changes in the facial nuclei and axons, in what has been called the “axon reaction”. The facial nerves of the experimental group were treated with epineurial coaptation and BMP-2 after the injury. Nerves not treated with BMP-2 were regarded as controls. The expression of BMP-2 was investigated by in situ hybridisation in the neurons of facial nuclei. The electrophysiology, image analysis and transmission electron microscopy were used to evaluate the level of the recovery of facial nerves. The results showed that the axons in the experimental group were thicker and denser than those in the control group four weeks later. The expression of BMP-2 in the neurons of facial nuclei increased after injury. The electron microscopic observations showed that the axons’ degeneration in the experimental group was less than that in the control group. Despite the morphological difference between the two groups, there was no apparent difference between them in nerve conduction velocity. These findings suggest that BMP-2 might be involved in the regeneration of facial nerves, and might function as a potential neurotrophic factor.

Study on remodeling of astrocytes in facial neuclus after peripheral injury

To observe the glial reactions surrounding facial motor neurons following facial nerve anastomosis. At 1, 7, 21 and 60 d following facial nerve anastomosis, the recovery process of facial movement was observed, the glial fibrillary acidic protein (GFAP) immunoreactivity was analyzed by a combined method of fluorescent retrograde tracing and immunofluorescent histochemical staining, and the ultrastructure of astrocytes were observed under a transmission electron microscope (TEM), respectively. Postoperatively the function of facial muscles could not return to normal, often accompanied with hyperkinetic syndromes such as synkinesis at the late stage. Motor neurons in every facial subnucleus could be retrogradely labeled by fluoro-gold (FG), and displayed an evident somatotopic organization. Normally there was a considerable number of GFAP-positive cells in nonnucleus regions but few inside the facial nucleus region. Postoperatively the GFAP immunoreactivity in the anastomotic side increased significantly, but gradually decreased at the late stage. The ultrastructure of astrocytes in our experiment showed that the sheet-like process of astrocytes invested and protected the injured facial motor neurons. The present study shows that reactive astrocytes undergo some characteristic changes during the process of facial nerve injury and regeneration. The plastic change at the late stage may be involved in the mechanism of synkinesis.

Agmatine treatment and vein graft reconstruction enhance recovery after experimental facial nerve injury

The rate of nerve regeneration is a critical determinant of the degree of functional recovery after injury. Here, we sought to determine whether treatment with the neuroprotective compound, agmatine, with or without nerve reconstruction utilizing a regional autogenous vein graft would accelerate the rate of facial nerve regeneration. Experiments compared the following seven groups of adult male rats: (A) Intact untreated controls. (B) Sham operation with interruption of the nerve blood supply (controls). (C) Transection of the mandibular branch of the facial nerve (generating a gap of 3 mm) followed by saline treatment. (D) Nerve transection with unsutured autogenous vein (external jugular) graft reconstruction plus saline treatment. (E) Nerve transection with sutured vein graft approximation (coaptation of the proximal and distal nerve stumps) plus saline. (F) Nerve transection with sutured vein graft followed by agmatine treatment (four daily intraperitoneal injections of 100 mg/kg agmatine sulfate). (G) Nerve transection with unsutured vein graft followed by agmatine treatment. Functional recovery, as assessed by grading vibrissae movements and by recording nerve conduction velocity and numbers of regenerated axons, indicated that either vein reconstruction or agmatine treatment resulted in accelerated and more complete recovery as compared with controls. But best results were observed in animals that underwent combined treatment, i.e., vein reconstruction plus agmatine injection. We conclude that agmatine treatment can accelerate facial nerve regeneration and that agmatine treatment together with autogenous vein graft offers an advantageous alternative to other facial nerve reconstruction procedures.

INTRODUCTION TO GUEST EDITORS

I want to thank Drs. Eser Yuksel and C. Randall Harrell for serving as guest editors for this edition of Seminars in Plastic Surgery on the topic of “Tissue Repair, Regeneration, and Engineering in Plastic Surgery.” I thank the authors, whose contributions make a difference for patients and academia. Dr. Eser Yuksel is a national of Turkey and 1984 graduate of Hacettepe University Medical School. Dr. Yuksel completed a course of 8 years of training in the most prestigious Turkish training programs in plastic and reconstructive surgery, including advanced cosmetic and maxillofacial surgery. He established a successful practice in Europe as an extraordinarily gifted aesthetic and reconstructive surgeon. Dr. Yuksel came to Baylor College of Medicine to conduct research in emerging tissue growth technology and quickly began to expand his research activities to encompass molecular mechanisms of tissue engineering. In 1997, Dr. Yuksel was recruited and joined the Division of Plastic Surgery, Baylor College of Medicine, as an assistant professor. His research involves in vivo soft tissue engineering and alternative approaches to modulate fibrotic processes in wound healing. Since then he has received 19 grant awards (4 of them as mentor and 15 of them as principal investigator) from professional societies including National Institutes of Health developmental grants (2). He is unique in that he has the combination of skills for performing surgery and the training and fundamentals of basic science to permit him to maintain a level of clinical performance in basic research traits so desirable in an academic institution but frequently so difficult to come by. Dr. C. Randall Harrell, M.D. is a board-certified plastic surgeon trained at the Division of Plastic Surgery, Michael E. DeBakey Department of Surgery at Baylor College of Medicine, Houston, Texas. Dr. Harrell is an internationally recognized authority on the investigation of new innovative medical devices with the Food and Drug Administration clinical studies that enhance facial regeneration. He holds worldwide patents for human collagen–based biomaterials used in tissue engineering and regeneration. He is the Chairman and Medical Director of Albiorex International, a biotechnology company specializing in tissue regeneration. He is a member of the American Society of Plastic Surgery, the American Society for Aesthetic Plastic Surgery, the American Society of Laser Medicine and Surgery, and the Endocrine Society. Dr. Harrell has been a lecturer and published author of numerous journal articles on plastic surgery. Dr. Harrell was nominated for the Nobel Peace Prize in 2002 for his contribution to “Mission for Mercy” in El Salvador. Again, my thanks to Drs. Yuksel and Harrell for serving as guest editors and to all the authors who contributed to this issue.

Botulinum Toxin for Aberrant Facial Nerve Regeneration: Double-Blind, Placebo-Controlled Trial Using Subjective Endpoints

Aberrant facial nerve regeneration syndrome is systematically studied by constructing a subjective questionnaire organized into pertinent domains (impairment of quality of life, social interactions, perception of self-appearance, visual function, and perception of problem severity) and by physical assessment of degree of involuntary palpebral fissure closure during routine facial movements using videotaping and a physicians' grading scale. The videotape measurements of corneal light reflex to upper lid margin distance and vertical palpebral distance were made during adynamic and active facial expression. Thirty-six patients were studied (six in an open-label pilot study design and 30 in a multicenter, double-blind, placebo-controlled trial). Botulinum toxin type A injections consistently suppressed the degree of involuntary eyelid movement associated with smiling, chewing, and puckering by each measurement and in both study designs. In all subjective morbidity domains, improvement was demonstrated in the double-blind study design (quality of life, p < 0.05; social interaction, p < 0.001; personal appearance, p < 0.001; peripheral visual impairment, p < 0.01; and perception of severity, p < 0.05). Correlation between degrees of physical impairment was significant but low comparing degree of subjective impairment to direct videotaped measurements. Correlation was more significant comparing subjective scores to the physicians' grading scale assessment of degree of physical impairment. Impairment in quality of life, social interactions, and self-assessment of appearance closely reflected the nature of the morbidity associated with palpebral fissure asymmetry associated with aberrant facial nerve regeneration. The physicians' grading scale best reflected subjective morbidity over direct videotaped measurements.

Changes in expression of prosaposin in the rat facial nerve nucleus after facial nerve transection

Prosaposin is the precursor of saposins A, B, C and D, which are activators of sphingolipid hydrolases. In addition, unprocessed prosaposin functions as a neurotrophic factor in the central and peripheral nervous systems by acting to prevent neuronal apoptosis, to elongate neurites and to facilitate myelination. In this study, the expression pattern of prosaposin in the facial nerve nucleus after facial nerve transection was examined by immunohistochemistry and in situ hybridization. Prosaposin immunoreactivity in the neurons on the operated side facial nerve nucleus showed a biphasic pattern: it was significantly increased on day 3 after transection, decreased dramatically on day 7, started to increase gradually on day 14 and reached another peak on day 21 after transection. Significant increases in the levels of prosaposin mRNA were identified in the neurons on the operated side, suggesting that prosaposin was synthesized vigorously by the neurons themselves in the case of facial nerve transection. The diverse changes in prosaposin immunoreactivity during the process of facial nerve regeneration may reflect the diverse neurotrophic activities of prosaposin in facial motoneurons.

A comparison of thyroxine- and polyamine-mediated enhancement of rat facial nerve regeneration

Thyroid hormones and spermidine, a motor neuron trophic polyamine (PA), have been shown to enhance peripheral motor nerve regeneration; however, the mechanism by which these treatment modalities exert their effect is unknown. Similarities in treatment outcome suggest that these molecules may be working via a common mechanism. Such an explanation is plausible since thyroid hormone is a potent inducer of ornithine decarboxylase (ODC), which is the rate-limiting enzyme involved in polyamine synthesis. This study was designed to morphologically evaluate the effects of exogenous thyroxine and spermidine on the regeneration of the rat facial nerve. Myelinated fiber density, axonal size, and degree of myelination were assayed by light and electron microscopy 21 days following facial nerve crush. Strikingly, the two treatment modalities had identical effects on all parameters tested. Each significantly enhanced the density of myelinated axons in regenerating nerves relative to the vehicle control. In addition, relative to the control treatment, both thyroxine and spermidine significantly increased the cross-sectional area of regenerating axons ( P < 0.05). Interestingly, neither of the drug treatments had any effect on remyelination at the position where this parameter was analyzed. The concurrent administration of both thyroxine and spermidine did not synergistically enhance motor neuron regeneration. These data support the hypothesis that thyroxine and spermidine enhance neural regeneration by a common mechanism.

Neurotherapeutic action of testosterone on hamster facial nerve regeneration: temporal window of effects

Neurotherapeutic or neuroprotective effects of gonadal steroids on the injured nervous system have been demonstrated in our laboratory and others. We have previously demonstrated that testosterone propionate (TP) administered systemically at supraphysiological levels accelerates both recovery from facial paralysis and regeneration rates following facial nerve injury in the hamster. Initial temporal studies of steroidal enhancement of functional recovery from facial paralysis established that steroid exposure is necessary during the first postoperative week. Furthermore, accumulated evidence suggests that TP manifests its effects on neuronal regeneration in the immediate postoperative or preregenerative phase by altering the cellular stress response. The purpose of this study was to identify the effective temporal window of TP exposure sufficient to enhance regenerative properties of injured facial motoneurons and functional recovery from facial paralysis induced by facial nerve injury. Adult castrated male hamsters received a right facial nerve crush axotomy at the stylomastoid foramen and were divided into (1) short term, (2) delayed, (3) continuous, and (4) no TP treatment groups. Short term and continuous groups were implanted with 1 subcutaneous (sc) TP capsule each immediately after axotomy, with the capsule removed at 30 min, 2, 4, or 6 h in short-term groups and allowed to remain for the duration of the experiment in the continuous group. In the delayed TP group, 1 sc TP capsule was implanted 6 h after axotomy and allowed to remain for the duration of the experiment. For regeneration rate studies, postoperative times ranged from 4 to 7 days. For the behavioral studies, observations were made for 26 days postaxotomy. The results point to a critical 6-h interval immediately after injury when TP enhances nerve outgrowth distances and augments behavioral recovery.