Origins of Neural Progenitor Cell-Derived Axons Projecting Caudally after Spinal Cord Injury.

Neural progenitor cells (NPCs) transplanted into sites of spinal cord injury (SCI) extend large numbers of axons into the caudal host spinal cord. We determined the precise locations of neurons in the graft that extend axons into the caudal host spinal cord using AAV9-Cre-initiated retrograde tracing into floxed-TdTomato-expressing NPC grafts. 7,640 ± 630 grafted neurons extended axons to a single caudal host spinal cord site located 2 mm beyond the lesion, 5 weeks post injury. While caudally projecting axons arose from neurons located in all regions of the graft, the majority of caudally projecting graft neurons (53%) were located within the caudal one-third of the graft. Numerous host corticospinal axons formed monosynaptic projections onto caudally projecting graft neurons; however, we find that the majority of host axonal neuronal projections formed by neural progenitor cell interneuronal "relays" across sites of SCI are likely polysynaptic in nature

Pain Modulation by Nitric Oxide in the Spinal Cord

Nitric oxide (NO) is a versatile messenger molecule first associated with endothelial relaxing effects. In the central nervous system (CNS), NO synthesis is primarily triggered by activation of N-methyl-D-aspartate (NMDA) receptors and has a Janus face, with both beneficial and harmful properties. There are three isoforms of the NO synthesizing enzyme nitric oxide synthase (NOS): neuronal (nNOS), endothelial (eNOS), and inducible nitric oxide synthase (iNOS), each one involved with specific events in the brain. In the CNS, nNOS is involved with modulation of synaptic transmission through long-term potentiation in several regions, including nociceptive circuits in the spinal cord. Here, we review the role played by NO on central pain sensitization

Copaiba Oil-Resin Treatment Is Neuroprotective and Reduces Neutrophil Recruitment and Microglia Activation after Motor Cortex Excitotoxic Injury

The oil-resin of Copaifera reticulata Ducke is used in the Brazilian folk medicine as an anti-inflammatory and healing agent. However, there are no investigations on the possible anti-inflammatory and neuroprotective roles of copaiba oil-resin (COR) after neural disorders. We have investigated the anti-inflammatory and neuroprotective effects of COR following an acute damage to the motor cortex of adult rats. Animals were injected with the neurotoxin N-Methyl-D-Aspartate (NMDA) (n = 10) and treated with a single dose of COR (400 mg/kg, i.p.) soon after surgery (Group 1) or with two daily doses (200 mg/kg, i.p.) during 3 days (Group 2) alter injury. Control animals were treated with vehicle only. COR treatment induced tissue preservation and decreased the recruitment of neutrophils and microglial activation in the injury site compared to vehicle animals. The results suggest that COR treatment induces neuroprotection by modulating inflammatory response following an acute damage to the central nervous system

Microglial Plasticity Contributes to Recovery of Bone Marrow Mononuclear Cells during Experimental Stroke

Brain stroke is an acute neural disorder characterized by obstruction (ischemic) or rupture (hemorrhagic) of blood vessels causing neural damage and subsequent functional impairment. Its pathophysiology is complex and involves a multitude of pathological events including energetic collapse, excitotoxicity, oxidative stress, metabolic acidosis, cell death and neuroinflammation. Despite its clinical importance, there is no effective pharmacological therapies available to diminish secondary damage avowing functional deficits. Considering the failure of pharmacological approaches for stroke, cell therapy came as promising alternative. Different cell types have been investigated in different experimental models with promising results. An important issue regarding the transplantation of stem cells into the damaged CNS tissue is how the pathological environment influences the transplanted cells. It has been established that an exacerbated inflammation in the pathological environment is detrimental to the survival of the transplanted stem cells. This prompted us to develop an experimental strategy to improve the therapeutic actions of bone marrow mononuclear cells (BMMCs) transplanted into the acute phase of brain stroke by modulating microglial activation with minocycline. In this chapter, we first review the basic pathophysiology of ischemic stroke with emphasis on the role of microglia to the pathological outcome. We then review the experimental approach of modulating microglia activation in order to enhance therapeutic actions of BMMCS for experimental stroke. We suggest that such an approach may be applied as an adjuvant therapy to control excessive neuroinflammation in the pathological environment allowing acute transplants and improving therapeutic actions of different kind of stem cells

Histochemical Characterization, Distribution and Morphometric Analysis of NADPH Diaphorase Neurons in the Spinal Cord of the Agouti

We evaluated the neuropil distribution of the enzymes NADPH diaphorase (NADPH-d) and cytochrome oxidase (CO) in the spinal cord of the agouti, a medium-sized diurnal rodent, together with the distribution pattern and morphometrical characteristics of NADPH-d reactive neurons across different spinal segments. Neuropil labeling pattern was remarkably similar for both enzymes in coronal sections: reactivity was higher in regions involved with pain processing. We found two distinct types of NADPH-d reactive neurons in the agouti's spinal cord: type I neurons had large, heavily stained cell bodies while type II neurons displayed relatively small and poorly stained somata. We concentrated our analysis on type I neurons. These were found mainly in the dorsal horn and around the central canal of every spinal segment, with a few scattered neurons located in the ventral horn of both cervical and lumbar regions. Overall, type I neurons were more numerous in the cervical region. Type I neurons were also found in the white matter, particularly in the ventral funiculum. Morphometrical analysis revealed that type I neurons located in the cervical region have dendritic trees that are more complex than those located in both lumbar and thoracic regions. In addition, NADPH-d cells located in the ventral horn had a larger cell body, especially in lumbar segments. The resulting pattern of cell body and neuropil distribution is in accordance with proposed schemes of segregation of function in the mammalian spinal cord

Chronic Alcohol Intoxication and Cortical Ischemia: Study of Their Comorbidity and the Protective Effects of Minocycline

Chronic alcohol intoxication (CAI) increases both morbidity and mortality of stroke patients. Despite the high prevalence of CAI and ischemic stroke, studies addressing their comorbidity and/or protective alternatives remain scarce. Thus, the influence of CAI on both stroke outcome and minocycline treatment (recognized for its neuroprotective effect) was investigated. Female Wistar rats (35 days old) were treated with water or ethanol (6.5 g/kg/day, 22.5% w/v) for 55 days. Then, focal ischemia was induced by endothelin-1 in the motor cortex. Two hours later, four doses of 50 mg/kg of minocycline every 12 hours followed by five doses of 25 mg/kg every 24 hours were administered. Behavioral performance (open field and rotarod tests) and immunohistochemical (cellular density, neuronal death, and astrocytic activation) and biochemical (lipid peroxidation and nitrite levels) analyses were performed. CAI increased motor disruption, nitrite and lipid peroxidation levels, and neuronal loss caused by ischemia, whereas it reduced the astrogliosis. Minocycline was effective in preventing the motor and tissue damage caused by stroke. However, these effects were attenuated when CAI preceded stroke. Our data suggest that CAI beginning in adolescence contributes to a worse outcome in ischemic stroke survivors and reduces the benefits of minocycline, possibly requiring adjustments in therapy

Neurodegeneration and Glial Response after Acute Striatal Stroke: Histological Basis for Neuroprotective Studies

Stroke is a leading cause of death and neurological disability worldwide and striatal ischemic stroke is frequent in humans due to obstruction of middle cerebral artery. Several pathological events underlie damage progression and a comprehensive description of the pathological features following experimental stroke in both acute and chronic survival times is a necessary step for further functional studies. Here, we explored the patterns of microglial activation, astrocytosis, oligodendrocyte damage, myelin impairment, and Nogo-A immunoreactivity between 3 and 30 postlesion days (PLDs) after experimental striatal stroke in adult rats induced by microinjections of endothelin-1 (ET-1). The focal ischemia induced tissue loss concomitant with intense microglia activation between 3 and 14 PLDs (maximum at 7 PLDs), decreasing afterward. Astrocytosis was maximum around 7 PLDs. Oligodendrocyte damage and Nogo-A upregulation were higher at 3 PLDs. Myelin impairment was maximum between 7 and 14 PLDs. Nogo-A expression was higher in the first week in comparison to control. The results add important histopathological features of ET-1 induced stroke in subacute and chronic survival times. In addition, the establishment of the temporal evolution of these neuropathological events is an important step for future studies seeking suitable neuroprotective drugs targeting neuroinflammation and white matter damage

Why microglia kill neurons after neural disorders? The friendly fire hypothesis

Neuroinflammation plays a fundamental role on the pathophysiology of acute and chronic neural disorders. Microglia activation is a major event following central nervous system inflammation displaying different phenotypes with beneficial and detrimental actions (a Janus face). The reason for this apparent duality is unknown. We have previously shown that following experimental middle cerebral artery occlusion in the rat brain, microglia seem to support and impair adult neurogenesis in the same ischemic striatum. Based on these results, we raised the hypothesis that in the same pathologic environment, gradients of different ligands distributed over different anatomical niches might contribute to both detrimental and beneficial microglial phenotypes. These ligands (“danger signals”) are released by dying cells and bind to microglial receptors in their membranes. Activation of different microglial receptors induces downstream biochemical pathways culminating in a spectrum of microglial phenotypes like M1 and M2 and others. In this paper, we first review the immune functions of microglia and the role of toll-like receptors on the fight against infections. We then briefly revise the dual role of microglia after neural disorders. We then propose a novel hypothesis to explain the Janus face of microglia during the pathophysiology of central nervous system diseases: the “friendly fire hypothesis”. According to this idea “danger signals” or danger associated molecular patterns released by stressed, damaged and/or dying cells during stroke, trauma and other diseases might activate microglial pattern-recognition receptors (i.e., toll like receptors) or other unidentified receptors normally activated by pathogens. This could activate the same genetic and biochemical machinery used by microglia to fight against pathogens even in the absence of infection. According to this notion, microglia may cause bystander neuronal damage with a kind of blind “friendly fire”, fighting against a non-existing infection during non-infectious disorders, like stroke and trauma. The “friendly fire hypothesis” is a novel proposal to explain why microglia may be detrimental and beneficial after acute and chronic neural disorders and may direct future investigations for developing of neuroprotective agents