Motor neuronal and glial apoptosis in the adult facial nucleus after intracranial nerve transection

Delivery of neurotrophin-3 by RVG-Lamp2b-modified mesenchymal stem cell-derived exosomes alleviates facial nerve injury

We aim to investigate the effect of RVG-Lamp2b-modified exosomes (exos) loaded with neurotrophin-3 (NT-3) on facial nerve injury. Exos were collected from control cells (Ctrl Exo) or bone marrow mesenchymal stem cells co-transfected with RVG-Lamp2b and NT-3 plasmids (RVG-NT-3 Exo) by gradient centrifugation and identified by western blotting, transmission electron microscopy, and nanoparticle tracking analysis. Effect of RVG-NT-3 Exo on oxidative stress damage was determined by analysis of the morphology, viability, and ROS production of neurons. Effect of RVG-NT-3 Exo on facial nerve axotomy (FNA) was determined by detecting ROS production, neuroinflammatory reaction, microglia activation, facial motor neuron (FMN) death, and myelin sheath repair. Loading NT-3 and modifying with RVG-Lamp2b did not alter the properties of the exos. Moreover, RVG-NT-3 Exo could effectively target neurons to deliver NT-3. Treatment with RVG-NT-3 Exo lowered H2O2-induced oxidative stress damage in primary neurons and Nsc-34 cells. RVG-NT-3 Exo treatment significantly decreased ROS production, neuroinflammatory response, FMN death, and elevated microglia activation and myelin sheath repair in FNA rat models. Our findings suggested that RVG-NT-3 Exo-mediated delivery of NT-3 is effective for the treatment of facial nerve injury.

Differential Vulnerability of Oculomotor Versus Hypoglossal Nucleus During ALS: Involvement of PACAP

Amyotrophic lateral sclerosis (ALS) is a progressive multifactorial disease characterized by the loss of motor neurons (MNs). Not all MNs undergo degeneration: neurons of the oculomotor nucleus, which regulate eye movements, are less vulnerable compared to hypoglossal nucleus MNs. Several molecular studies have been performed to understand the different vulnerability of these MNs. By analyzing postmortem samples from ALS patients to other unrelated decedents, the differential genomic pattern between the two nuclei has been profiled. Among identified genes, adenylate cyclase activating polypeptide 1 (ADCYAP1) gene, encoding for pituitary adenylate cyclase-activating polypeptide (PACAP), was found significantly up-regulated in the oculomotor versus hypoglossal nucleus suggesting that it could play a trophic effect on MNs in ALS. In the present review, some aspects regarding the different vulnerability of oculomotor and hypoglossal nucleus to degeneration will be summarized. The distribution and potential role of PACAP on these MNs as studied largely in an animal model of ALS compared to controls, will be discussed.

ENTÉRATE DE CÓMO CAMBIA EL CEREBRO CUANDO SE LESIONA UN NERVIO

<p>Desde hace algunos años el grupo de investigación de Neurofisiología Comportamental de la Universidad Nacional de Colombia ha venido evaluando los cambios que ocurren en el sistema nervioso central luego de la lesión de un nervio periférico. Específicamente trabajamos con el modelo de lesión del nervio facial en roedores para evaluar las modificaciones funcionales y estructurales que ocurren en la corteza sensoriomotora primaria luego de la lesión. Al lesionarse el nervio facial, el cerebro entra en un programa de reorganización que incluye cambios electrofisiológicos en las neuronas de la corteza motora que comandan los movimientos faciales (M1). En este sentido, las células de la corteza motora cerebral se vuelven más excitables y modifican su respuesta ante estímulos sensoriales. La reorganización tras la lesión también incluye cambios morfológicos en M1: las células piramidales de la corteza motora retraen su árbol dendrítico y disminuye la densidad de sus espinas dendríticas. En asociación con estos cambios, las células de M1 disminuyen transitoriamente su inmunorreactividad para NeuN (marcador específico de núcleos neuronales) y aumentan la expresión de GAP43 (proteína de crecimiento axonal). Esto indica, posiblemente, un cambio metabólico celular en asociación con la búsqueda de nuevas dianas sinápticas. Finalmente, hallamos que la glía circundante en M1 (tanto astrocitos como microglía) se activa de manera muy temprana luego de lesiones del nervio facial. Esto podría indicar que el remodelamiento estructural y funcional hallado en las neuronas corticales es el resultado de la interacción entre la activación de la glía circundante y las células piramidales de M1 (aunque se necesitan muchos experimentos adicionales que así lo demuestren).</p><p> </p><p>Abstract</p><p>Our research group (Neurofisiología Comportamental, Universidad Nacional de Colombia) has evaluated changes in the central nervous system induced by peripheral nerve injuries. We have characterized facial nerve lesion-induced structural and functional changes in primary motor cortex pyramidal neurons (M1) in rodents. Following the lesion, M1 neurons modified their spontaneous basal firing frequency: they become more excitable. Moreover, we found changes in evoked-activity with somatosensory stimulation after facial nerve lesion. Morphologically, it was found that facial nerve lesion induced long-lasting changes in the dendritic morphology of M1 pyramidal neurons. Dendritic branching of the pyramidal cells underwent overall shrinkage and dendrites suffered transient spine pruning. Additionally, we evaluated the reorganization processes in the central nervous system by using both neuronal and glial markers. Decreased NeuN (neuronal nuclei antigen) immunoreactivity and increased GAP-43 (growth-associated protein 43) immunoreactivity were found M1 after facial nerve lesion. In addition, we also observed astrogliosis and microglial activation sourrounding M1 early after facial nerve injury. Taken together these findings suggest that facial nerve lesions induce widespread reorganization in M1 including neuronal shrinkage, axon sprouting as well as astrocytic and microglia activation. These results suggest that facial nerve injuries elicit active remodeling due to pyramidal neuron and glia interaction (although additional experiments that demonstrate it are needed)</p>

Chronic stress induced remodeling of the prefrontal cortex: structural re-organization of microglia and the inhibitory effect of minocycline

Recently, it has been discovered that the working memory deficits induced by exposure to chronic stress can be prevented by treating stressed animals with minocycline, a putative inhibitor of microglial activity. One of the pressing issues that now requires clarification is exactly how exposure to chronic stress modifies microglial morphology, this being a significant issue as microglial morphology is tightly coupled with their function. To examine how chronic stress alters microglial morphology, we digitally reconstructed microglia within the rat medial prefrontal cortex. Our analysis revealed that stress increased the internal complexity of microglia, enhancing ramification (i.e. branching) without altering the overall area occupied by the cell and that this effect was more pronounced in larger cells. We subsequently determined that minocycline treatment largely abolished the pro-ramifying effects of stress. With respect to mechanisms, we could not find any evidence of increased inflammation or neurodegeneration (interleukin-1β, MHC-II, CD68, terminal deoxynucleotidyl transferase dUTP nick end labeling, and activated caspase-3). We did, however, find that chronic stress markedly increased the expression of β1-integrin (CD29), a protein previously implicated in microglial ramification. Together, these findings highlight that increased ramification of microglia may represent an important neurobiological mechanism through which microglia mediate the behavioral effects of chronic psychological stress.

Abnormal motor reflexes and dormant facial motor neurons in rats with facial-facial anastomosis

After facial nerve injury, some post-paralysis sequelae, such as synkinesis, hemispasm and 'crocodile tears' syndrome appear. The psychosocial impact of these sequelae is unavoidable. Despite recent advances and the growing popularity of this field, the pathophysiological mechanisms of facial nerve injury and regeneration are still not well understood. In this report, an abnormal motor reflex coincident with synkinetic facial movement was examined in a rat model using the blink reflex technique. Some dormant facial motor neurons were found which could not innervate through the suture site but remained alive. These results suggest that such dormant neurons might exert roles distinct from those of re-innervated neurons during facial nerve injury and regeneration. Further study is required to elucidate the biomolecular structure and electrophysiological features of such neurons.

Changes in the expression of P2X1 and P2X2 purinergic receptors in facial motoneurons after nerve lesions in rodents and correlation with motoneuron degeneration

Involvement of P2X1 and P2X2 purinergic receptors in motoneuron response to injury was investigated with Western blotting and immunohistochemistry and correlated with motoneuron loss, Bcl-2 expression, nitric oxide synthase induction and glial activation. P2X1 was highly induced in rat facial motoneurons after nerve resection, which causes slowly occurring neurodegeneration. P2X1 induction was lower and less persistent after nerve crush, permissive for fiber regeneration. P2X2 expression was found in nuclei of rat facial motoneurons, with nuclear export in the cytoplasm after nerve resection. P2X1 induction in axotomized facial motoneurons was impaired in superoxide dismutase (SOD)1-G93A-mutant mice, a model of motoneuron disease. The data in rats point to a correlation of P2X1 induction with motoneuron degeneration, which also involves P2X2 intracellular changes, rather than with axon regeneration effort. The data in mice show that the SOD1 mutation interferes with injury-elicited P2X1 induction, suggesting alterations of ATP release from mutant motoneurons after damage.