Morphometric analysis of NADPH diaphorase reactive neurons in a rat model of focal excitotoxic striatal injury

Astrocytosis, Inflammation, Axonal Damage and Myelin Impairment in the Internal Capsule following Striatal Ischemic Injury

Secondary degeneration is defined as a set of destructive events that damage cells and structures that were initially spared or only peripherally affected by the primary insult, constituting a key factor for functional impairment after traumatic brain injury or stroke. In the present study, we evaluated the patterns of astrocytosis, inflammatory response, axonal damage and oligodendrocytes/myelin impairment in the internal capsule following a focal injection of endothelin-1 (ET-1) into the dorsal striatum. Animals were perfused at 1, 3 and 7 post-lesion days (PLD), and tissue was processed to immunohistochemistry for neutrophils (MBS1), macrophages/microglia (ED1), astrocytes (GFAP), axonal lesion (βAPP), oligodendrocytes (Tau) and myelin (MBP). A significant number of neutrophils was observed at 1PLD, followed by intense recruitment/activation of macrophages/microglia at 3PLD and astrocytic reaction with a peak at 7PLD. Oligodendrocyte damage was pronounced at 3PLD, remaining at 7PLD. Progressive myelin impairment was observed, with reduction of immunoreactivity at 7PLD. Axonal lesion was also identified, mainly at 7PLD. Our results indicate that acute inflammatory response elicited by the ischemic insult in the striatum can be associated with the axonal impairment and damage of both oligodendrocytes and myelin sheath identified in the internal capsule, which may be related to loss of tissue functionality observed in secondary degeneration.

Microelectrode implants, inflammatory response and long-lasting effects on NADPH diaphorase neurons in the rat frontal cortex

At present, one of the main therapeutic challenges comprises the development of technologies to improve the life quality of people suffering from different types of body paralysis, through the reestablishment of sensory and motor functions. In this regard, brain-machine interfaces (BMI) offer hope to effectively mitigate body paralysis through the control of paralyzed body parts by brain activity. Invasive BMI use chronic multielectrode implants to record neural activity directly from the brain tissue. While such invasive devices provide the highest amount of usable neural activity for BMI control, they also involve direct damage to the nervous tissue. In the cerebral cortex, high levels of the enzyme NADPH diaphorase (NADPH-d) characterize a particular class of interneurons that regulates neuronal excitability and blood supply. To gain insight into the biocompatibility of invasive BMI, we assessed the impact of chronic implanted tungsten multielectrode bundles on the distribution and morphology of NADPH-d-reactive neurons in the rat frontal cortex. NADPH-d neuronal labeling was correlated with glial response markers and with indices of healthy neuronal activity measured by electrophysiological recordings performed up to 3 months after multielectrode implantation. Chronic electrode arrays caused a small and quite localized structural disturbance on the implanted site, with neuronal loss and glial activation circumscribed to the site of implant. Electrodes remained viable during the entire period of implantation. Moreover, neither the distribution nor the morphology of NADPH-d neurons was altered. Overall, our findings provide additional evidence that tungsten multielectrodes can be employed as a viable element for long-lasting therapeutic BMI applications.

Effect of senescence on the tyrosine hydroxylase and S100B immunoreactivity in the nigrostriatal pathway of the rat

Senescence is a natural and progressive physiological event that leads to a series of morphophysiological alterations in the organism. The brain is the most vulnerable organ to both structural and functional changes during this process. Dopamine is a key neurotransmitter for the proper functioning of the brain, directly involved in circuitries related with emotions, learning, motivation and reward. One of the main dopamine- producing nuclei is the substantia nigra pars compacta (SNpc), which establish connections with the striatum forming the so-called nigrostriatal pathway. S100B is a calcium binding protein mainly expressed by astrocytes, involved in both intracellular and extracellular processes, and whose expression is increased following injury in the nervous tissue, being a useful marker in altered status of central nervous system. The present study aimed to analyze the impact of senescence on the cells immunoreactive for tyrosine hydroxylase (TH) and S100B along the nigrostriatal pathway of the rat. Our results show an decreased expression of S100B⁺ cells in SNpc. In addition, there was a significant decrease in TH immunoreactivity in both projection fibers and TH⁺ cell bodies. In the striatum, a decrease in TH immunoreactivity was also observed, as well as an enlargement of the white matter bundles. Our findings point out that senescence is related to the anatomical and neurochemical changes observed throughout the nigrostriatal pathway.

Inflammatory Response and Secondary White Matter Damage to the Corpus Callosum after Focal Striatal Stroke in Rats

Stroke is one of the leading causes of death and long-term disabilities worldwide, resulting in a debilitating condition occasioned by disturbances in the cerebral vasculature. Primary damage due to metabolic collapse is a quick outcome following stroke, but a multitude of secondary events, including excitotoxicity, inflammatory response, and oxidative stress cause further cell death and functional impairment. In the present work, we investigated whether a primary ischemic damage into the dorsal striatum may cause secondary damage in the circumjacent corpus callosum (CC). Animals were injected with endothelin-1 and perfused at 3, 7, 14, and 30 post-lesion days (PLD). Sections were stained with Cresyl violet for basic histopathology and immunolabeled by antibodies against astrocytes (anti-GFAP), macrophages/microglia (anti-IBA1/anti MHC-II), oligodendrocytes (anti-TAU) and myelin (anti-MBP), and Anti-Nogo. There were conspicuous microgliosis and astrocytosis in the CC, followed by later oligodendrocyte death and myelin impairment. Our results suggest that secondary white matter damage in the CC follows a primary focal striatal ischemia in adult rats.

FBXW7alpha Promotes the Recovery of Traumatic Spinal Cord

BACKGROUND

White matter damage and neuronal cell death are incurred by spinal cord injury (SCI). FBXW7α, an important mediator of cell division and growth was investigated to explore its role in repairing the traumatic spinal cord in rats. Underlying mechanisms such as oxidative stress and inflammasomes signaling were also studied.

METHODS

Spinal cord injury in rats was established by longitudinal surgical incision from the lower to mid-thoracic vertebrae on the backside, followed by 20-g weight placed on the exposed Th12 surface for 30 min. AAV-delivered FBXW7α and -sh-FBXW7α were intrathecally injected into the rat spinal cord. Indices of oxidation, neurotrophic factors, and pyroptosis were measured by Western blot, Elisa, and RT-PCR.

RESULTS

We found the overexpression of FBXW7α in spinal cord rescue neuronal death triggered by the injury. Specifically, the nutritional condition, oxidative stress, and pyroptosis were improved. A synchronization of BNDF and GDNF expression patterns in various groups indicated the secretion of neurotrophic factors affect the outcome of SCI. The SOD1, CAT, and GSH-px were suppressed after trauma but all restored in response to FBXW7α overexpression. Inflammasomes-activated pyroptosis was incurred after the injury, and relevant biomarkers such as GSDMD, caspase-1, caspase- 11, IL-1β, and IL-18 were down-regulated after the introduction of FBXW7α into the injured cord. Additionally, up-regulating FBXW7α also repaired the mitochondria dysfunction.

CONCLUSION

Our data indicate FBXW7α probably serves as an important molecular target for the therapy of spinal cord injury.

Effects of methylmercury on the pattern of NADPH diaphorase expression and astrocytic activation in the rat

Mercury (Hg) is an environmental contaminant that poses great risk to human health. However, it is still widely used in artisanal gold-mining enterprises around the world, especially in developing countries. Methylmercury (MeHg) is produced environmentally by biomethylation of inorganic Hg present in water sediments, leading to its subsequent accumulation in the aquatic food chain. Due to its high metabolic rate, the Central Nervous System (CNS) is one of the main targets of MeHg. In the present study, we investigate the impact of chronic MeHg intoxication on NADPH diaphorase (NADPH-d) activity and astrocyte mobilization in the visual cortex of the rat. After 60 days of MeHg administration by oral gavage (0.04 mg/kg/day), tissue samples containing the visual cortex were submitted to measurements of Hg levels, NADPH-d activity, and GFAP immunohistochemistry for identification of astrocytes. MeHg intoxication was associated with increased Hg deposits and with reduced NADPH-d neuropil reactivity in the visual cortex. A morphometric analysis suggested that NADPH-d-positive neurons were mostly spared from MeHg harmful action and intoxicated animals had astrocytic activation similar to the control group. The decrease in NADPH-d neuropil reactivity may be due to the negative effect of chronic MeHg poisoning on both the synthesis and transport of this enzyme in afferent pathways to the visual cortex. The relative resistance of NADPH-d-reactive neurons to chronic MeHg intoxication may be associated with peculiarities in cell metabolism or to a protective role of nitric oxide, safeguarding those neurons from Hg deleterious effects.

Methylmercury intoxication and cortical ischemia: Pre-clinical study of their comorbidity

Stroke is one of the main causes of human disability worldwide. Ischemic stroke is mostly characterized by metabolic collapse and fast tissue damage, followed by secondary damage in adjacent regions not previously affected. Heavy metals intoxication can be associated with stroke incidence, because of their damaging action in the vascular system. Mercury, in particular, possesses a high tropism by metabolically active regions, such as the brain. In the present study we sought to evaluate whether methylmercury (MeHg) intoxication can aggravate the tissue damage caused by an ischemic stroke induced by microinjections of endothelin-1 (ET-1) into the motor cortex of adult rats. Following MeHg intoxication by gavage (0.04 mg/kg/day) during 60 days, the animals were injected with ET-1 (1 μl, 40 pmol/μl) or vehicle (1 μl). After 7 days, all animals were submitted to behavioral tests and then their brains were processed to biochemical and immunohistochemical analyses. We observed that long-term MeHg intoxication promoted a significant Hg deposits in the motor cortex, with concomitant increase of microglial response, followed by reduction of the neuronal population following ischemia and MeHg intoxication, as well as disturbance in the antioxidant defense mechanisms by misbalance of oxidative biochemistry with increase of both lipid peroxidation and nitrite levels, associated to behavioral deficits. MeHg exposure and cortical ischemia demonstrated that both injuries are able of causing significant neurobehavioural impairments in motor coordination and learning accompanied of an exacerbated microglial activation, oxidative stress and neuronal loss in the motor cortex, indicating that MeHg as a source of metabolic disturbance can act as an important increasing factor of ischemic events in the brain.

Dibutyryl Cyclic Adenosine Monophosphate Rescues the Neurons From Degeneration in Stab Wound and Excitotoxic Injury Models

Dibutyryl cyclic adenosine monophosphate (dBcAMP), a cell-permeable synthetic analog of cAMP, has been shown to induce astrogliosis in culture. However, the exact mechanism underlying how dBcAMP exerts its function in situ is not clear. The objective of this study was to examine the effects of dBcAMP on astrogliosis and survival of neurons in stab wound and kainic acid models of brain injury. Stab wound was done in cerebral cortex of BALB/c male mice. Kainic acid lesion was induced in hippocampus by injecting 1μl kainic acid into the lateral ventricle. Animals in both models of injury were divided into L+dBcAMP and L+PBS groups and treated with dBcAMP or PBS for 3, 5, and 7 days respectively. The brain sections were stained for Cresyl violet and Fluro jade-B to assess the degenerating neurons. Immunostaining for GFAP and Iba-1 was done for assessing the astrogliosis and microglial response respectively. Expression of GFAP and BDNF levels in the tissue were estimated by Western blotting and ELISA respectively. The results showed a gradual increase in the number of both astrocytes and microglia in both injuries with a significant increase in dBcAMP-treated groups. The number of degenerating neurons significantly decreased in dBcAMP treated groups. In addition, it was found that dBcAMP stimulated the expression of GFAP and BDNF in both stab wound and kainic acid injuries. Treatment with BDNF receptor inhibitor AZ-23, showed an increase in the degenerating neurons suggesting the role of BDNF in neuroprotection. This study indicates that dBcAMP protects neurons from degeneration by enhancing the production of BDNF and may be considered for use as therapeutic agent for treatment of brain injuries.

Characterization of NADPH Diaphorase- and Doublecortin-Positive Neurons in the Lizard Hippocampal Formation

The lizard cortex has remarkable similarities with the mammalian hippocampus. Both regions process memories, have similar cytoarchitectural properties, and are important neurogenic foci in adults. Lizards show striking levels of widespread neurogenesis in adulthood and can regenerate entire cortical areas after injury. Nitric oxide (NO) is an important regulatory factor of mammalian neurogenesis and hippocampal function. However, little is known about its role in nonmammalian neurogenesis. Here, we analyzed the distribution, morphology, and dendritic complexity (Neurolucida reconstructions) of NO-producing neurons through NADPH diaphorase (NADPHd) activity, and how they compare with the distribution of doublecortin-positive (DCX+) neurons in the hippocampal formation of the neotropical lizard Tropidurus hispidus. NADPHd-positive (NADPHd+) neurons in the dorsomedial cortex (DMC; putatively homologous to mammalian CA3) were more numerous and complex than the ones in the medial cortex (MC; putatively homologous to the dentate gyrus). We found that NADPHd+ DMC neurons send long projections into the MC. Interestingly, in the MC, NADPHd+ neurons existed in 2 patterns: small somata with low intensity of staining in the outer layer and large somata with high intensity of staining in the deep layer, a pattern similar to the mammalian cortex. Additionally, NADPHd+ neurons were absent in the granular cell layer of the MC. In contrast, DCX+ neurons were scarce in the DMC but highly numerous in the MC, particularly in the granular cell layer. We hypothesize that NO-producing neurons in the DMC provide important input to proliferating/migrating neurons in the highly neurogenic MC.