Facial nerve regeneration via body-brain crosstalk: The role of stem cells and biomaterials.

The human body is a complex, integral whole, and disruptions in one organ can lead to dysfunctions in other parts of the organ network. The facial nerve, as the seventh cranial nerve, arises from the brainstem, controls facial expression muscles and plays a crucial role in brain-body communication. This vulnerable nerve can be damaged by trauma, inflammation, tumors, and congenital diseases, often impairing facial expression. Stem cells have gained significant attention for repairing peripheral nerve injuries due to their multidirectional differentiation potential. Additionally, various biomaterials have been used in tissue engineering for regeneration and repair. However, the therapeutic potential of stem cells and biomaterials in treating facial nerve injuries requires further exploration. In this review, we summarize the roles of stem cells and biomaterials in the regeneration and repair of damaged facial nerves, providing a theoretical basis for the recovery and reconstruction of body-brain crosstalk between the brain and facial expression muscles.

Predictive value of facial motor-evoked potential and electromyography for facial motor function in vestibular schwannoma surgery.

PURPOSE: Intraoperative neuromonitoring (IONM) aims to preserve facial nerve (FN) function during vestibular schwannoma (VS) surgery. However, current techniques such as facial nerve motor evoked potentials (FNMEP) or electromyography (fEMG) alone are limited in predicting postoperative facial palsy (FP). The objective of this study was to analyze a compound fEMG/FNMEP approach. METHODS: Intraoperative FNMEP amplitude and the occurrence of fEMG-based A-trains were prospectively determined for the orbicularis oris (ORI) and oculi (OCU) muscle in 322 VS patients. Sensitivity and specificity of techniques to predict postoperative FN function were calculated. Confounding factors as tumor size, volume of intracranial air, or IONM duration were analyzed. RESULTS: A relevant immediate postoperative FP was captured in 105/322 patients with a significant higher risk in large VS. While fEMG demonstrated a high sensitivity (77% and 86% immediately and 15 month postoperative, respectively) for identifying relevant FP, specificity was low. In contrast, FNMEP have a significantly higher specificity of 80.8% for predicting postoperative FP, whereas the sensitivity is low. A retrospective combination of techniques demonstrated still an incorrect prediction of FP in ~ 1/3 of patients. CONCLUSIONS: FNMEP and fEMG differ in sensitivity and specificity to predict postoperative FP. Although a combination of IONM techniques during VS surgery may improve prediction of FN function, current techniques are still inaccurate. Further development is necessary to improve IONM approaches for FP prediction.

[Intraoperative Neuromonitoring in Vestibular Schwannoma Surgery].

Vestibular schwannoma surgery necessitates intraoperative neuromonitoring to secure long-term tumor control by sufficient tumor removal and preservation of neural function. Therein, facial nerve function can be assessed in real-time and quantitatively by intraoperative continuous facial nerve monitoring with repetitive direct stimulation. The ABR and, further, CNAP, are closely monitored for the continuous assessment of the hearing function. In addition, the evoked masseter and extraocular electromyograms, SEP, MEP, and neuromonitoring of the lower cranial nerves are implemented as needed. In this article, we introduce our neuromonitoring techniques during vestibular schwannoma surgery with an illustrative video.

Photobiomodulation enhances facial nerve regeneration via activation of PI3K/Akt signaling pathway-mediated antioxidant response.

Facial nerve dysfunction is a common clinical condition that leads to disfigurement and emotional distress in the affected individuals. This study aimed to evaluate whether photobiomodulation can enhance regeneration of crushed facial nerves and attempt to investigate the possible underlying mechanism of neuroprotective function and therapeutic target. Various parameters of photobiomodulation were assigned to the facial nerves and Schwann cells (SCs) separately during crushed injury in rats. Axonal regeneration, functional outcomes, and SC apoptosis, proliferation, and underlying mechanisms of action were evaluated by morphological, histopathological, and functional assessments, flow cytometry, western blotting, real-time PCR, and IncuCyte. The results showed that photobiomodulation improved axonal regeneration and functional recovery, and also promoted proliferation, and inhibited apoptosis of SCs, both of these were considered as the most effective parameters in 250mW group. In addition, the neuroprotective effects of photobiomodulation (500mW) were likely associated with oxidative stress-induced SC apoptosis via activation of the PI3K/Akt signaling pathway. Our results revealed that photobiomodulation significantly promoted axonal regeneration, functional recovery, and regeneration of the facial nucleus, and its mechanism was related to the up-regulation of the PI3K/Akt signaling pathway. These findings provide clear experimental evidence of photobiomodulation as an alternative therapeutic strategy for peripheral nerve damage.

Effect of Pre-Induced Mesenchymal Stem Cell-Coated Cellulose/Collagen Nanofibrous Nerve Conduit on Regeneration of Transected Facial Nerve.

(1) Objective: In order to evaluate the effect of a pre-induced mesenchymal stem cell (MSC)-coated cellulose/collagen nanofibrous nerve conduit on facial nerve regeneration in a rat model both in vitro and in vivo. (2) Methods: After fabrication of the cellulose/collagen nanofibrous conduit, its lumen was coated with either MSCs or pre-induced MSCs. The nerve conduit was then applied to the defective main trunk of the facial nerve. Rats were randomly divided into three treatment groups (n = 10 in each): cellulose/collagen nanofiber (control group), cellulose/collagen nanofiber/MSCs (group I), and cellulose/collagen nanofiber/pre-induced MSCs (group II). (3) Results Fibrillation of the vibrissae of each group was observed, and action potential threshold was compared 8 weeks post-surgery. Histopathological changes were also observed. Groups I and II showed better recovery of vibrissa fibrillation than the control group. (4) Conclusions: Group II, treated with the pre-induced MSC-coated cellulose/collagen nanofibrous nerve conduit, showed the highest degree of recovery based on functional and histological evaluations.

COVID-19 can cause blink reflex abnormalities.

Background and purpose: Neurological symptoms and complications associated with coronavirus 2019 (COVID-19) are well known. It was aimed to evaluate the brainstem and trigeminal/facial nerves and the pathways between these structures in COVID-19 using the blink reflex test. Methods: Thirty patients with post COVID-19 (16 males, 14 females) and 30 healthy individuals (17 males, 13 females) were included in this prospective study. Individuals who previously had a positive nose swap polymerase chain reaction test for severe acute respiratory syndrome coronavirus 2 and whose previously clinical features were compatible with COVID-19 were included in the post COVID-19 patient group. Neurological examination of the participants should be normal. Blink reflex test was performed on all participants. R1, ipsilateral R2 (IR2), and contralateral R2 (CR2) waves obtained from the test were analyzed. Results: The mean ages of healthy individuals and post COVID-19 patients were 34.0±6.4 and 38.4±10.6 years, respectively. Both age and gender were matched between the groups. R1, IR2, and CR2 latencies/amplitudes were not different between the two groups. The side-to-side R1 latency difference was 0.5±0.3 and 1.0±0.8 ms in healthy individuals and post COVID-19 patients, respectively (p=0.011). One healthy individual and 12 patients with post COVID-19 had at least one abnormal blink reflex parameter (p=0.001). Conclusion: This study showed that COVID-19 may cause subclinical abnormalities in the blink reflex, which includes the trigeminal nerve, the seventh nerve, the brainstem, and pathways between these structures.

Is Decorin a Promising New Agent for Facial Nerve Regeneration? An Experimental Study.

OBJECTIVE: The aim of this study was to investigate the effects of systemic administration of decorin (DC) on facial nerve (FN) regeneration. METHODS: A total of 32 female albino Wistar rats were divided into 4 groups: control (C) group: no bilateral FN neurorrhaphy (B-FNN), no DC application, sham-operated group: B-FNN without DC application, DC group: DC application without B-FNN, and B-FNN + DC group: B-FNN and DC application. Nerve conduction studies were performed before and after skin incisions at 1st, 3rd, 5th, and 7th weeks in all groups. The amplitude and latency of compound muscle action potentials were recorded. FN samples were obtained and were investigated under light microscopy and immunohistochemical staining. The nerve and axon diameter, number of axons, H score, Schwann cell proliferation, and myelin and axonal degeneration were recorded quantitatively. RESULTS: In the sham group, the 3rd and 5th postoperative week, amplitude values were significantly lower than those of the B-FNN + DC group (p < 0.05). Nerve diameters were found to be significantly larger in the sham, DC, and B-FNN + DC groups than in the C group (p < 0.05). The number of axons, the axon diameter, and the H scores were found to be significantly higher in the B-FNN + DC group than in the sham group (p < 0.05). The Schwann cell proliferation, myelin degeneration, and axonal degeneration scores were significantly lower in the B-FNN + DC group than in the sham group (p < 0.05). CONCLUSION: Electrophysiological and histopathological evaluation revealed the potential benefits provided by DC. This agent may increase FN regeneration.

Flexible endoscopic assistance in the surgical management of vestibular schwannomas.

Endoscopic-assisted techniques have extensively been applied to vestibular schwannoma (VS) surgery allowing to increase the extent of resection, minimize complications, and preserve facial nerve and auditory functions. In this paper, we retrospectively analyze the effectiveness of flexible endoscope in the endoscopic-assisted retrosigmoid approach for the surgical management of VS of various sizes. The authors conducted a retrospective analysis on 32 patients who underwent combined microscopic and flexible endoscopic resection of VS of various sizes over a period of 16 months. Flexible endoscopic-assisted retrosigmoid approach was performed in all cases, and in 6 cases, flexible and rigid endoscopic control were used in combination to evaluate the differences between the two surgical instruments. The surgical results were additionally compared with a previous case series of 141 patients operated for VS of various sizes without endoscopic assistance. Gross-total resection was achieved in 84% of the cases and near-total resection was accomplished in the rest of them. Excellent or good facial nerve function was observed in all except one case with a preoperative severe facial palsy. Hearing preservation surgery (HPS) was attempted in 11 cases and accomplished in 9 (81.8%). A tumor remnant was endoscopically identified in the fundus of the IAC in all cases (100%). Endoscopic assistance increased the rate of total removal and no intrameatal residual tumor was seen at radiological follow-up. Comparative analysis with a surgical cohort of patients operated with the sole microsurgical technique showed a significative association between endoscopic assistance and intracanalicular extent of resection. Combined microsurgical and flexible endoscopic assistance provides remarkable advantages in the pursuit of maximal safe resection of VS and preservation of facial nerve and auditory functions, minimizing the risk of post-operative complications.

TcMEP threshold change is superior to A-train detection when predicting facial nerve outcome in CPA tumour surgery.

OBJECT: Surgery of tumours in the cerebellopontine angle (CPA) can lead to loss of facial nerve function. Different methods of intra-operative nerve monitoring (IOM) (including free-running EMG, direct nerve stimulation and transcranial motor evoked potentials (TcMEP)) have been used to predict facial nerve outcome during surgery. Recent research has shown TcMEP threshold increase and the occurrence of A-trains on the EMG to have great potential in doing so. This study compares these two methods and correlates them to House-Brackmann (HB) scores post-op in patients with tumours in the cerebellopontine angle. METHOD: Forty-three patients (one was operated twice) with large CPA tumours treated surgically in the Radboud University Medical Center between 2015 and 2019 were included in this study. During surgery, TcMEP threshold increases and A-train activity were measured. Because our treatment paradigm aims at facial nerve preservation (accepting residual tumour), TcMEP threshold increase of over 20 mA or occurrence of A-trains were considered as warning signs and used as a guide for terminating surgery. HB scores were measured post-op, at 6 weeks, 6 months and 1 year after surgery. Spearman's correlation was calculated between the IOM-values and the HB scores for a homogeneous subgroup of 30 patients with vestibular schwannoma (VS) without neurofibromatosis type II (NF-II) and all patients collectively. RESULTS: TcMEP threshold was successfully measured in 39 (90.7%) procedures. In the homogeneous VS non-NFII group, we found a statistically significant moderate-to-strong correlation between TcMEP threshold increase and House Brackmann score immediately post-op, at 6 weeks, 6 months and 1 year after surgery (Spearman's rho of 0.79 (p < 0.001), 0.74 (p < 0.001), 0.64 (p < 0.001) and 0.58 (p = 0.002), respectively). For A-trains, no correlation was found. Similar results were found when including all patients with CPA tumours. A threshold increase of < 20 mA was a predictor of good facial nerve outcome. CONCLUSION: These results show that TcMEP threshold increases are strongly correlated to post-operative HB scores, while A-trains are not. This suggests TcMEP threshold increases can be a valuable predictor for facial nerve outcome in patients with large tumours when facial nerve preservation is prioritized over total resection. In this study, we found no use for A-trains to prevent facial nerve deficits.

Validation of the Turkish version of the Sunnybrook facial grading system

Background/aim: To adapt the Sunnybrook facial grading system (SFGS) into Turkish and perform validation and reliability studies on the Turkish version. Materials and Methods: The original English version of the SFGS was translated into Turkish by performing a linguistic validity study based on international standards. The evaluators comprised 6 physicians. Evaluations were performed twice independently using the video recordings of 65 facial palsy patients. Synchronously, the House-Brackman facial grading system (HBFGS) was filled out to display concurrent validity. The intraclass correlation coefficient (ICC) and Cronbach's alpha was used for the examination of the inter- and intra-rater reliability. As another indication of reliability, the generalizability (G) was also examined. Results: The ICC for the inter-rater reliability for resting symmetry, symmetry of voluntary movement, synkinesis, and the composite score, which are 4 components of the SFGS, were determined, respectively, as 0.822, 0.956, 0.606, and 0.957 for the first evaluation, and 0.805, 0.965, 0.584, and 0.965 for the second evaluation. For the intra-rater reliability, the ICC were determined as 0.842, 0.956, 0.794, and 0.937, while the Cronbach's alpha coefficients were determined as 0.809, 0.956, 0.792, and 0.948, respectively. The G coefficient was determined as G = 0.772. For the concurrent validity, a strong correlation was found between the SFGS and HBFGS scores. Conclusion: The present study adapted the SFGS into Turkish, and demonstrated that the adapted scale was valid and reliable. The Turkish version can be used for the evaluation of facial palsy, the follow-up of treatment efficiency, and standardization in reporting outcomes with the international literature.

Optical analysis of functional development of the facial motor nucleus in the embryonic rat brainstem.

Facial motor neurons of the rat embryo are first generated in rhombomere 4 and then migrate in the caudo-ventral direction. This migration forms a unique axonal trajectory called the genu, a loop of facial motor axons around the abducens nucleus. It is still unclear when and how this unique structure is functionally established during ontogenesis. Using voltage-sensitive dye (VSD) recording and the DiI staining method, we identified neural responses evoked by facial nerve (N.VII) stimulation and examined developmental processes of the facial motor nucleus in E12-E17 rat brainstems. We identified two types of fast spike-like signals; a long-duration signal, which corresponded to the action potential in the N.VII soma, and a short-duration signal, which reflected the action potential in the N.VII axons. The long-duration signal was detected as early as E13, suggesting that the N.VII motor neuron is already excitable at the beginning of cell migration. The response area of the long-duration signal extended caudally at E13-E14, and shifted in a ventral direction at E15. At E16-E17, the long-duration signal was concentrated in the caudo-ventral area, which was comparable to the location of the facial motor nucleus in the adult rat brainstem. These results demonstrate that developmental processes of cell migration and nuclear organization can be visualized and identified functionally with the VSD recording. We discuss the results by comparing functiogenesis and morphogenesis of the N.VII pathway.

Impact of peripheral immune status on central molecular responses to facial nerve axotomy.

When facial nerve axotomy (FNA) is performed on immunodeficient recombinase activating gene-2 knockout (RAG-2-/-) mice, there is greater facial motoneuron (FMN) death relative to wild type (WT) mice. Reconstituting RAG-2-/- mice with whole splenocytes rescues FMN survival after FNA, and CD4+ T cells specifically drive immune-mediated neuroprotection. Evidence suggests that immunodysregulation may contribute to motoneuron death in amyotrophic lateral sclerosis (ALS). Immunoreconstitution of RAG-2-/- mice with lymphocytes from the mutant superoxide dismutase (mSOD1) mouse model of ALS revealed that the mSOD1 whole splenocyte environment suppresses mSOD1 CD4+ T cell-mediated neuroprotection after FNA. The objective of the current study was to characterize the effect of CD4+ T cells on the central molecular response to FNA and then identify if mSOD1 whole splenocytes blocked these regulatory pathways. Gene expression profiles of the axotomized facial motor nucleus were assessed from RAG-2-/- mice immunoreconstituted with either CD4+ T cells or whole splenocytes from WT or mSOD1 donors. The findings indicate that immunodeficient mice have suppressed glial activation after axotomy, and cell transfer of WT CD4+ T cells rescues microenvironment responses. Additionally, mSOD1 whole splenocyte recipients exhibit an increased astrocyte activation response to FNA. In RAG-2-/- + mSOD1 whole splenocyte mice, an elevation of motoneuron-specific Fas cell death pathways is also observed. Altogether, these findings suggest that mSOD1 whole splenocytes do not suppress mSOD1 CD4+ T cell regulation of the microenvironment, and instead, mSOD1 whole splenocytes may promote motoneuron death by either promoting a neurotoxic astrocyte phenotype or inducing Fas-mediated cell death pathways. This study demonstrates that peripheral immune status significantly affects central responses to nerve injury. Future studies will elucidate the mechanisms by which mSOD1 whole splenocytes promote cell death and if inhibiting this mechanism can preserve motoneuron survival in injury and disease.

Dedifferentiated Fat (DFAT) cells: A cell source for oral and maxillofacial tissue engineering.

Tissue engineering is a promising method for the regeneration of oral and maxillofacial tissues. Proper selection of a cell source is important for the desired application. This review describes the discovery and usefulness of dedifferentiated fat (DFAT) cells as a cell source for tissue engineering. Dedifferentiated Fat cells are a highly homogeneous cell population (high purity), highly proliferative, and possess a multilineage potential for differentiation into various cell types under proper in vitro inducing conditions and in vivo. Moreover, DFAT cells have a higher differentiation capability of becoming osteoblasts, chondrocytes, and adipocytes than do bone marrow-derived mesenchymal stem cells and/or adipose tissue-derived stem cells. The usefulness of DFAT cells in vivo for periodontal tissue, bone, peripheral nerve, muscle, cartilage, and fat tissue regeneration was reported. Dedifferentiated Fat cells obtained from the human buccal fat pad (BFP) are a minimally invasive procedure with limited esthetic complications for patients. The BFP is a convenient and accessible anatomical site to harvest DFAT cells for dentists and oral surgeons, and thus is a promising cell source for oral and maxillofacial tissue engineering.

Intraoperative monitoring of Z-L response (ZLR) and abnormal muscle response (AMR) during microvascular decompression for hemifacial spasm. Interpreting the role of ZLR.

BACKGROUND: Z-L response (ZLR) has been suggested to a new electromyographic (EMG) potential recorded from the facial muscle of patient with hemifacial spasm (HFS) during microvascular decompression (MVD). Although ZLR has been suggested to be useful, experience of ZLR monitoring is limited and its significance during MVD is still unclear. METHODS: To investigate the significance of ZLR, both ZLR and abnormal muscle response (AMR) were simultaneously recorded before and after decompression of root exit zone (REZ) in 20 consecutive patients with HFS. RESULTS: All 19 AMRs elicited before REZ decompression disappeared immediately after decompression of REZ. ZLRs were also observed before decompression of REZ in 19 (95%) of 20 patients. Despite negative conversion of AMR after decompression in 19 patients, ZLR disappeared in only 13 (68.4%) of 19 patients. Among six sustained ZLRs, three showed reduction in the intensity of ZLRs while the other three remained unchanged. There were nine cases featuring attachment of the distal, non-offending portion of offending vessels to the distal course of the facial nerve in addition to attachment to REZ. Negative ZLR conversion and presence of peripheral contact of offending vessels to distal facial nerves showed significant correlations (p < 0.05). ZLR could be elicited by electrical stimulation at non-REZ-offending portion of the offending arterial wall, attached to the distal course of the facial nerve. HFS disappeared immediately in all 20 patients. CONCLUSIONS: Although ZLR might be helpful in cases with multiple offenders, interpretation of ZLR needs caution for non-specific transmission of electric current through vessel wall to facial nerve.

[Vestibular Schwannoma Surgery with Continuous Intraoperative Monitoring of Evoked Facial Nerve Electromyograms].

Preservation of facial nerve function is crucial during vestibular schwannoma surgery. Here, we report the utility of continuous intraoperative monitoring of evoked facial nerve electromyograms(EMGs)for preservation of facial nerve function during vestibular schwannoma surgery. A 64-year-old man presented with left ear hearing disturbance. CT and MRI revealed a tumor mass(4cm)with cyst formation in the left cerebellopontine angle. Microsurgical removal was performed with continuous intraoperative monitoring of evoked facial nerve EMGs. An electrode with Ag wire and absorbable gelatin sponge, which we developed, was used for continuous monitoring. It could be placed and fixed more easily on the root exit zone of the facial nerve than the previously reported electrodes and provide reliable information during surgery. The tumor mass could be removed safely without inducing facial nerve palsy. Continuous intraoperative monitoring of evoked facial nerve EMGs with this newly developed electrode could facilitate successful schwannoma surgery.

The Nature of the Sensory Input to the Neonatal Rat Barrel Cortex.

UNLABELLED: Sensory input plays critical roles in the development of the somatosensory cortex during the neonatal period. This early sensory input may involve: (1) stimulation arising from passive interactions with the mother and littermates and (2) sensory feedback arising from spontaneous infant movements. The relative contributions of these mechanisms under natural conditions remain largely unknown, however. Here, we show that, in the whisker-related barrel cortex of neonatal rats, spontaneous whisker movements and passive stimulation by the littermates cooperate, with comparable efficiency, in driving cortical activity. Both tactile signals arising from the littermate's movements under conditions simulating the littermates' position in the litter, and spontaneous whisker movements efficiently triggered bursts of activity in barrel cortex. Yet, whisker movements with touch were more efficient than free movements. Comparison of the various experimental conditions mimicking the natural environment showed that tactile signals arising from the whisker movements with touch and stimulation by the littermates, support: (1) a twofold higher level of cortical activity than in the isolated animal, and (2) a threefold higher level of activity than in the deafferented animal after the infraorbital nerve cut. Together, these results indicate that endogenous (self-generated movements) and exogenous (stimulation by the littermates) mechanisms cooperate in driving cortical activity in newborn rats and point to the importance of the environment in shaping cortical activity during the neonatal period. SIGNIFICANCE STATEMENT: Sensory input plays critical roles in the development of the somatosensory cortex during the neonatal period. However, the origins of sensory input to the neonatal somatosensory cortex in the natural environment remain largely unknown. Here, we show that in the whisker-related barrel cortex of neonatal rats, spontaneous whisker movements and passive stimulation by the littermates cooperate, with comparable efficiency, in driving cortical activity during the critical developmental period.

Preserving normal facial nerve function and improving hearing outcome in large vestibular schwannomas with a combined approach: planned subtotal resection followed by gamma knife radiosurgery.

OBJECTIVE: To perform planned subtotal resection followed by gamma knife surgery (GKRS) in a series of patients with large vestibular schwannoma (VS), aiming at an optimal functional outcome for facial and cochlear nerves. METHODS: Patient characteristics, surgical and dosimetric features, and outcome were collected prospectively at the time of treatment and during the follow-up. RESULTS: A consecutive series of 32 patients was treated between July 2010 and June 2016. Mean follow-up after surgery was 29 months (median 24, range 4-78). Mean presurgical tumor volume was 12.5 cm3 (range 1.47-34.9). Postoperative status showed normal facial nerve function (House-Brackmann I) in all patients. In a subgroup of 17 patients with serviceable hearing before surgery and in which cochlear nerve preservation was attempted at surgery, 16 (94.1%) retained serviceable hearing. Among them, 13 had normal hearing (Gardner-Robertson class 1) before surgery, and 10 (76.9%) retained normal hearing after surgery. Mean duration between surgery and GKRS was 6.3 months (range 3.8-13.9). Mean tumor volume at GKRS was 3.5 cm3 (range 0.5-12.8), corresponding to mean residual volume of 29.4% (range 6-46.7) of the preoperative volume. Mean marginal dose was 12 Gy (range 11-12). Mean follow-up after GKRS was 24 months (range 3-60). Following GKRS, there were no new neurological deficits, with facial and hearing functions remaining identical to those after surgery in all patients. Three patients presented with continuous growth after GKRS, were considered failures, and benefited from the same combined approach a second time. CONCLUSION: Our data suggest that large VS management, with planned subtotal resection followed by GKRS, might yield an excellent clinical outcome, allowing the normal facial nerve and a high level of cochlear nerve functions to be retained. Our functional results with this approach in large VS are comparable with those obtained with GKRS alone in small- and medium-sized VS. Longer term follow-up is necessary to fully evaluate this approach, especially regarding tumor control.

Fine motor control of the jaw following alteration of orofacial afferent inputs.

OBJECTIVE: The study was designed to investigate if alteration of different orofacial afferent inputs would have different effects on oral fine motor control and to test the hypothesis that reduced afferent inputs will increase the variability of bite force values and jaw muscle activity, and repeated training with splitting of food morsel in conditions with reduced afferent inputs would decrease the variability and lead to optimization of bite force values and jaw muscle activity. MATERIAL METHODS: Forty-five healthy volunteers participated in a single experimental session and were equally divided into incisal, mucosal, and block anesthesia groups. The participants performed six series (with ten trials) of a standardized hold and split task after the intervention with local anesthesia was made in the respective groups. The hold and split forces along with the corresponding jaw muscle activity were recorded and compared to a reference group. RESULTS: The hold force and the electromyographic (EMG) activity of the masseter muscles during the hold phase were significantly higher in the incisal and block anesthesia group, as compared to the reference group (P < 0.001). However, there was no significant effect of groups on the split force (P = 0.975) but a significant decrease in the EMG activity of right masseter in mucosal anesthesia group as compared to the reference group (P = 0.006). The results also revealed that there was no significant effect of local anesthesia on the variability of the hold and split force (P < 0.677). However, there was a significant decrease in the variability of EMG activity of the jaw closing muscles in the block anesthesia group as compared to the reference group (P < 0.041), during the hold phase and a significant increase in the variability of EMG activity of right masseter in the mucosal anesthesia group (P = 0.021) along with a significant increase in the EMG activity of anterior temporalis muscle in the incisal anesthesia group, compared to the reference group (P = 0.018), during the split phase. CONCLUSIONS: The results of the present study indicated that altering different orofacial afferent inputs may have different effects on some aspects of oral fine motor control. Further, inhibition of afferent inputs from the orofacial or periodontal mechanoreceptors did not increase the variability of bite force values and jaw muscle activity; indicating that the relative precision of the oral fine motor task was not compromised inspite of the anesthesia. The results also suggest the propensity of optimization of bite force values and jaw muscle activity due to repeated splitting of the food morsels, inspite of alteration of sensory inputs. CLINICAL RELEVANCE: Skill acquisition following a change in oral sensory environment is crucial for understanding how humans learn and re-learn oral motor behaviors and the kind of adaptation that takes place after successful oral rehabilitation procedures.

The Relationship of the Temporal Branch of the Facial Nerve to the Fascial Planes of Temporal Region in Human Fetuses.

The aim of this study was to obtain information by assessing the relationship between temporal region fascial structures, fat pads, and temporal branches of facial nerve in human fetuses to use the knowledge on treatment of early childhood period surgeries. This anatomic dissection study was conducted on 40 hemifaces with no visible external abnormalities on their faces. Fascial layers and related fat pads of temporal region were dissected layer by layer beginning from superficial to deep. The relations of temporal branches of facial nerve and temporoparietal fascia and the structures of these fascial layers were evaluated. Temporoparietal fascia showed continuity below zygomatic arc with superficial musculoaponeurotic system. Temporal branches of facial nerve showed a multiple branching. Parotid-masseteric fascia became very thin on the superficial of zygomatic arch and ran with superficial layer of temporal fascia above without attaching to periosteum. Temporal branches of facial nerve entered between multilayered layers of temporoparietal fascia. Temporoparietal fascia became thicker on anterior and middle parts because of the localization of superficial temporal fat pad. Temporal fascia was a 2-layered thick and fibrous tissue enveloping intermediate fat pad. Deep layer connected to periosteum of zygomatic arch and superficial layer continued passing superficial of zygomatic arch and connected to the parotid-masseteric fascia. Deep temporal fat pad was found on the deep to deep layer of temporal fascia and surface of temporal muscle. The findings of this study may contribute to the knowledge of the topographical localization of temporal branches of facial nerve with temporal region fascial structures and fat pads in fetuses.

Activation of medullary dorsal horn γ isoform of protein kinase C interneurons is essential to the development of both static and dynamic facial mechanical allodynia.

The γ isoform of protein kinase C (PKCγ), which is concentrated in a specific class of interneurons within inner lamina II (IIi ) of the spinal dorsal horn and medullary dorsal horn (MDH), is known to be involved in the development of mechanical allodynia, a widespread and intractable symptom of inflammatory or neuropathic pain. However, although genetic and pharmacological impairment of PKCγ were shown to prevent mechanical allodynia in animal models of pain, after nerve injury or reduced inhibition, the functional consequences of PKCγ activation alone on mechanical sensitivity are still unknown. Using behavioural and anatomical approaches in the rat MDH, we tested whether PKCγ activation in naive animals is sufficient for the establishment of mechanical allodynia. Intracisternal injection of the phorbol ester, 12,13-dibutyrate concomitantly induced static as well as dynamic facial mechanical allodynia. Monitoring neuronal activity within the MDH with phospho-extracellular signal-regulated kinases 1 and 2 immunoreactivity revealed that activation of both lamina I-outer lamina II and IIi -outer lamina III neurons, including lamina IIi PKCγ-expressing interneurons, was associated with the manifestation of mechanical allodynia. Phorbol ester, 12,13-dibutyrate-induced mechanical allodynia and associated neuronal activations were all prevented by inhibiting selectively segmental PKCγ with KIG31-1. Our findings suggest that PKCγ activation, without any other experimental manipulation, is sufficient for the development of static and dynamic mechanical allodynia. Lamina IIi PKCγ interneurons have been shown to be directly activated by low-threshold mechanical inputs carried by myelinated afferents. Thus, the level of PKCγ activation within PKCγ interneurons might gate the transmission of innocuous mechanical inputs to lamina I, nociceptive output neurons, thus turning touch into pain.