Red neurons - Acute neuronal injury

Red neurons - Acute neuronal injury

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“Red neurons” are evident by about 12 to 24 hours after an irreversible hypoxic/ ischemic insult. The morphologic features consist of shrinkage of the cell body, pyknosis of the nucleus, disappearance of the nucleolus, and loss of Nissl substance, with intense eosinophilia of the cytoplasm. -Robbins textbook of pathology

Taken from Robbins pathologic basis of disease, 9e, pg.no1265, fig: 28-13B

Why in case of neurons there is shrinkage instead of swelling as in other cells?

There is not some simple dichotomy of "neurons shrink and other cells swell" in response to hypoxia/ischemia.

Neuronal death can be necrotic or apoptotic or both, and at different stages different morphology is observed: generally swelling earlier, shrinkage later, though both are observed together early as well. Eosinophilia/"red neurons" tends to occur later as mentioned in this passage (after 6 hours, consistent with 12-24 hours) so that's probably why the author is referring mostly to shrinkage. Cells can also have swelling of some organelles, like mitochondria, despite shrinking overall.

Without further context of the passage you provided it's hard to say much more.

Garcia, J. H., Yoshida, Y., Chen, H., Li, Y., Zhang, Z. G., Lian, J. I. N. Y. I. N. G.,… & Chopp, M. (1993). Progression from ischemic injury to infarct following middle cerebral artery occlusion in the rat. The American journal of pathology, 142(2), 623.

Jenkins, L. W., Povlishock, J. T., Lewelt, W., Miller, J. D., & Becker, D. P. (1981). The role of postischemic recirculation in the development of ischemic neuronal injury following complete cerebral ischemia. Acta neuropathologica, 55(3), 205-220.

Portera‐Cailliau, C., Price, D. L., & Martin, L. J. (1997). Excitotoxic neuronal death in the immature brain is an apoptosis‐necrosis morphological continuum. Journal of Comparative Neurology, 378(1), 10-87.

Search for Exicitotoxic programed cell death. Acute Neuronal injury occur by this pathway. This is like Necroptosis. Cell shrinkage is seen due to Glutamate. I have added some screenshots of my search,, rest you can search yourself. Read more at


In excitotoxicity, nerve cells suffer damage or death when the levels of otherwise necessary and safe neurotransmitters such as glutamate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or N-methyl-D-aspartic acid (NMDA) become pathologically high resulting in excessive stimulation of receptors. For example, when glutamate receptors such as the NMDA receptor or AMPA receptor encounter excessive levels of the excitatory neurotransmitter glutamate significant neuronal damage might ensue. Excess glutamate allows high levels of calcium ions (Ca 2+ ) to enter the cell. Ca 2+ influx into cells activates a number of enzymes, including phospholipases, endonucleases, and proteases such as calpain. These enzymes go on to damage cell structures such as components of the cytoskeleton, membrane, and DNA. [1] [2] In evolved, complex adaptive systems such as biologic life it must be understood that mechanisms are rarely, if ever, simplistically direct. For example, NMDA in subtoxic amounts induces neuronal survival to otherwise toxic levels of glutamate. [3] [4]

Excitotoxicity may be involved in cancers, spinal cord injury, stroke, traumatic brain injury, hearing loss (through noise overexposure or ototoxicity), and in neurodegenerative diseases of the central nervous system such as multiple sclerosis, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, alcoholism, alcohol withdrawal or hyperammonemia and especially over-rapid benzodiazepine withdrawal, and also Huntington's disease. [5] [6] Other common conditions that cause excessive glutamate concentrations around neurons are hypoglycemia. Blood sugars are the primary glutamate removal method from inter-synaptic spaces at the NMDA and AMPA receptor site. Persons in excitotoxic shock must never fall into hypoglycemia. Patients should be given 5% glucose (dextrose) IV drip during excitotoxic shock to avoid a dangerous build up of glutamate around NMDA and AMPA neurons. [ citation needed ] When 5% glucose (dextrose) IV drip is not available high levels of fructose are given orally. Treatment is administered during the acute stages of excitotoxic shock along with glutamate antagonists. Dehydration should be avoided as this also contributes to the concentrations of glutamate in the inter-synaptic cleft [7] and "status epilepticus can also be triggered by a build up of glutamate around inter-synaptic neurons." [8]


Rogelio Garcia-Cavazos , Robin Brey , in Systemic Lupus Erythematosus (Fourth Edition) , 2004

Autoantibodies and NPSLE

Autoantibody production has been implicated in vasculopathic and autoantibody-mediated neuronal injury mechanisms . Anti-ribosomal P antibodies (anti-P) have been linked to diffuse CNS involvement in NPSLE [ 18, 19 ].

Anti-phospholipid antibodies (aPL) are a family of antibodies directed against plasma proteins bound to negatively-charged phospholipids that lead to hypercoaguability through effects on the protein C/protein S system, platelets, endothelial cells, and complement activation [ 59, 60 ]. APLs, defined as the lupus anticoagulant (LA), anticardiolipin (aCL), and anti-β2 glycoprotein 1 (anti-β2GP1), are strongly associated with localized NPSLE, including TIA (transient ischemic attack), stroke, seizure, and cerebral vein thrombosis [ 61 ].

Multiple studies have also shown an association of aPLs with cognitive dysfunction in SLE [ 62–65 ]. Denburg et al. [ 63 ] found, in a cross-sectional study, that LA-positive patients were two to three times more likely than LA-negative patients to be cognitively impaired, primarily on tasks of verbal memory, cognitive flexibility, and psychomotor speed. In a 5-year prospective study, Hanly et al. found that patients who had persistent IgG aCL positivity had a reduction in psychomotor speed, and patients who had persistent IgA positivity had a reduction in conceptual reasoning and executive ability [ 62 ]. In a study of 45 SLE patients assessed twice, persistently elevated aCL levels were associated with poorer cognitive function, particularly speed of attention and concentration [ 64 ]. High titers of CSF IgG aCL have been detected in SLE patients (vs controls) with lupus headache, acute psychosis, cognitive dysfunction, higher cortical dysfunction, and altered consciousness [ 65 ]. Lupus anticoagulant, but not IgG aCL, was associated with reduced regional cerebral blood flow in a SPECT study [ 66 ]. However, one comparative study of positron emission tomography (PET), HMPAO-SPECT, and magnetic resonance imaging (MRI) scans did not find any correlation with aCL [ 67 ]. Anti-phospholipid (aPL) autoantibodies are also implicated in both microvascular thrombo/embolic episodes and endothelial damage.

Neuroplasticity and Repair

In contrast to other organs that can replace even large numbers of cells lost to injury or disease (such as the skin and liver), brain tissue’s capacity to regenerate is extremely limited. However, nervous tissue has a remarkable ability to adapt its function rather than to regenerate its structure in response to a changing environment this ability constitutes the basis for learning. In neurobiological terms, this ability to adapt to and learn from experiences is called neural plasticity. At the structural level, neural plasticity could be defined by the number and complexity of dendrites and axons, the density of synapses (connections between neurons, through which information is transmitted from one neuron to another), and in some brain regions also by the number of neurons. Brain injury leads to increased neural plasticity in the spared regions. This allows the neurons in these regions to take over the sensory or motor functions that had been performed by the damaged areas. This remapping of function (indeed similar to drawing a new map) is critical in the recovery of function.

Astrocytes are important regulators, controlling the number of neurotransmitter molecules present in the space between neuronal and astroglial cells. A large change in the size of this space leads to the development of brain swelling. Recent findings show that the capacity of astrocytes to take up the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is reduced in the zone surrounding brain cells killed by stroke. 13 The inhibition of neurons by excessive amounts of GABA counteracts neural plasticity and impairs functional recovery. Importantly, a drug that blocks the binding of GABA to some of its receptors can reduce this GABA-mediated inhibition. Such a treatment, if provided at the right time after stroke, results in a faster recovery of function in mouse models. 13 However, when administered too early, the drug can increase the amount of brain tissue damaged by stroke. These findings, together with many other reports, demonstrate that the response of brain tissue to injury is complex, that many cellular and biochemical events take place in an orchestrated cascade, and that each phase of the healing process has a specific purpose. Therefore, the timing of any therapeutic intervention is critically important to the outcome.

Neural plasticity peaks within one to three months after injury this creates a unique window of opportunity. During this window, neurorehabilitation—physical therapy, for example—is most effective. However, significant improvements can occur even at later stages, especially when rehabilitation combines task-specific training with therapies that activate neural plasticity. 14

Parvalbumin Interneurons Shape Neuronal Vulnerability in Blunt TBI

Excessive excitation has been hypothesized to subsume a significant part of the acute damage occurring after traumatic brain injury (TBI). However, reduced neuronal excitability, loss of neuronal firing, and a disturbed excitation/inhibition balance have been detected. Parvalbumin (PV) interneurons are major regulators of perisomatic inhibition, principal neurons firing, and overall cortical excitability. However, their role in acute TBI pathogenic cascades is unclear. We exploited the chemogenetic Pharmacologically Selective Activation Module and Pharmacologically Selective Effector Module control of PV-Cre+ neurons and the Designer Receptors Exclusively Activated by Designer Drug (DREADD) control of principal neurons in a blunt model of TBI to explore the role of inhibition in shaping neuronal vulnerability to TBI. We demonstrated that inactivation of PV interneurons at the instance or soon after trauma enhances survival of principal neurons and reduces gliosis at 7 dpi whereas, activation of PV interneurons decreased neuronal survival. The protective effect of PV inactivation was suppressed by expressing the nuclear calcium buffer PV-nuclear localisation sequence in principal neurons, implying an activity-dependent neuroprotective signal. In fact, protective effects were obtained by increasing the excitability of principal neurons directly using DREADDs. Thus, we show that sustaining neuronal excitation in the early phases of TBI may reduce neuronal vulnerability by increasing activity-dependent survival, while excess activation of perisomatic inhibition is detrimental to neuronal integrity.

Keywords: chemogenetics nuclear calcium parvalbumin interneurons traumatic brain injury.

Brain, Neuron - Necrosis

This panel of brain necrosis images is intended to familiarize pathologists with the morphologic variations of neuronal cell death ranging from the morphology of acute necrosis to that of late stages of necrosis in which mineralization sometimes is prominent. Figure 1 depicts the most commonly recognized evidence of early neuronal necrosis. Features include neuronal cytoplasmic shrinkage and intense eosinophilia accompanied by shrinkage and basophilia of the nucleus (black arrow). Neuronal necrosis is commonly the result of ischemia, or any influence that impairs neuronal energy metabolism. In this case, the change has been referred to as acute eosinophilic necrosis, “acute metabolic arrest,” “acute ischemic change,” or, more colloquially, “red dead” neurons. Neuronal necrosis should be carefully differentiated from dark neuron artifact (see Brain - Introduction) by screening for various stages of necrosis and/or the presence of inflammatory cells or other lesions in the vicinity of the truly necrotic neurons. In this case, the appearance of these necrotic neurons can be contrasted with the more normal morphology of an adjacent Purkinje cell (red arrow). Further, important substantiating evidence of brain tissue injury is represented by the edematous vacuolar change of the subjacent neuropil and the presence of necrotic condensed (pyknotic) nuclei of glial cells (arrowhead) within that region.

Figure 2 depicts an ultraviolet microscopy image showing the positive green fluorescent, empiric staining by Fluoro-Jade B of necrotic hippocampal pyramidal cells (blue arrow). Use of the Fluoro-Jade family of empiric neurodegenerative stains is extremely valuable in quickly identifying even small numbers of degenerative neurons, even at low magnification. Although given much investigation, the actual mechanism whereby the stain has this affinity for necrotic neurons is still poorly understood. Fluorescence of affected cells highlights the injured neurons, but the use of hematoxylin and eosin is also important to identify associated neural changes corroborating the fluorescent findings and defining the chronology of the lesions. Fluoro-Jade C is the most recent of the Fluoro-Jade stains and has been found to stain all degenerating neurons, regardless of specific insult or mechanism of cell death. Fluoro-Jade C exhibits the greatest signal-to-background ratio, as well as the highest resolution, therefore giving maximal contrast and affinity for degenerating neurons. The stain also identifies degenerated distal dendrites, axons, and terminals. The dye is resistant to fading and is compatible with most histologic methods. Activated astrocytes, degenerating neurons, and cell nuclei can be labeled together using glial fibrillary acidic protein immunofluorescence, Fluoro-Jade C, and 4',6-diamidino-2-phenylindole (DAPI), respectively. Some care needs to be taken in interpretation, since Fluoro-Jade also lightly stains artifactual basophilic neurons (PB Little, personal observations). Note that normal red blood cells ( Figure 2 , white arrow) also stain positive in the blood vessels.

In Figure 3 , necrotic neurons (arrows) are evident adjacent to more normal neurons in the piriform cortex. Note that some are particularly faded and almost invisible. This image depicts neuronal necrosis at a later stage, evolving from that seen with acute eosinophilic neuronal necrosis (see Figure 1 ). With chronologic progressive degenerative change, there is noticeable fading of the eosinophilia of the cytoplasm and basophilia of the nucleus. The fading is followed by vague outlines of the former neurons, referred to as “ghost forms,” followed by the loss of any observable degenerate structure. The presence of more normal neurons in adjacent areas assists with the recognition of these forms of degenerate cells differentiating the changes from that of autolysis. Depending on the time of observation after neurotoxic effects, a chronologic continuum of degenerative neuronal morphologic changes may be apparent. Some, such as acute eosinophilic necrosis, are readily apparent however, the pathologist must be aware of the more subtle, often overlooked, changes shown in Figure 3 consisting of faded “ghost” profiles of neurons.

In Figure 4 , basophilic necrotic neurons have escaped the more rapid process of dissolution shown in Figure 3 . Note the subtle punctate ferrugination (dystrophic mineralization) of neuronal membrane (arrows). The degenerate neurons remain in situ and have early accumulation of mineral (ferrugination) at their surfaces. The image depicts multiple small punctate aggregations of mineral, some of which may represent mineralization of dendritic terminal boutons.

Figure 5 depicts neuronal necrosis of hippocampal pyramidal cells in the CA2 region. Note that there is more prominent, advanced ferrugination (dystrophic mineralization) of neurons (arrows) than shown in Figure 4 . Some aspects of neuronal morphology are still apparent, but the perikaryon is more completely infused with mineral as the dystrophic mineralization process proceeds.

Necrosis of small neurons, such as the granule cells of the olfactory bulb and dentate gyrus and the internal granule cell layer of the cerebellum, is characterized by basophilic nuclear pyknosis with hematoxylin and eosin staining. In Figure 6 , granule cells of the cerebellar internal granule cell layer have this pyknotic basophilic appearance typical of acute necrosis for this type of neuron (arrow). Many Purkinje cells retain a normal appearance in spite of the regional granule cell necrosis. For comparison, Figure 7 is a higher magnification of the cerebellar granule necrosis. Note the pyknotic nuclei (arrows) and adjacent normal nuclei (arrowheads). It is important to differentiate granule cell necrosis shown in Figure 6 and Figure 7 from the morphologic change seen in autolysis. In autolysis, while granule cell nuclei shrink, there are other indicators of autolysis in the tissue, such as widespread tissue fading and neuropil vacuolation. The marked contrast between adjacent normal and necrotic cells is helpful in differentiation of autolysis from genuine lesions of nervous tissue.

Mineralization of necrotic tissue, including brain cells, occurs over time. Where mineral deposits encrust a recognizable cell or its dendritic terminal boutons, it is important for the pathologist to recognize this chronologic feature of degenerated cells in brain and to differentiate it from yeast or mycotic hyphae with which it may be confused.


Despite the small patient sample size, our findings provide further evidence that suggests ongoing neuronal injury in patients with temporal lobe epilepsy, even in subjects with long disease durations. This pilot study lays the groundwork for future work that expands the frequency of sample collection as well as the patient cohort size, with the intention of establishing NSE as a relevant biomarker [46]. Because our study explicitly involved patients with intractable epilepsy, the measurement of seizure-associated NSE spikes in serum raises the question of whether neuron loss in these individuals is the cause of their intractable disease state. In other words, does the ongoing and accumulative low level injury of hippocampal neurons in these patients propagate neural circuit disruptions that render the system refractory to current drug strategies? If so, then initiation of neuroprotective therapy may effectively short-circuit a pathogenic feedback loop and convert even patients with long-standing intractable disease to a state that is amenable to standard treatment. Coupled with the obvious benefits for preventing cognitive decline, the potential to reverse intractability suggests that neuroprotective strategies must be more aggressively pursued in patients with temporal lobe epilepsy.


Department of Neurosciences, University of California San Diego, La Jolla, CA, USA

Gunnar H. D. Poplawski, Erna Van Niekerk, Paul Lu, Neil Mehta, Philip Canete, Richard Lie, Jessica M. Meves, Binhai Zheng & Mark H. Tuszynski

Department of Psychiatry, University of California Los Angeles, Los Angeles, CA, USA

Riki Kawaguchi & Giovanni Coppola

Department of Neurology, University of California Los Angeles, Los Angeles, CA, USA

Riki Kawaguchi & Giovanni Coppola

Veterans Administration Medical Center, San Diego, CA, USA

Paul Lu, Binhai Zheng & Mark H. Tuszynski

Department of Physiology, University of Tennessee, Memphis, TN, USA

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G.H.D.P. and M.H.T. conceptualized the study G.H.D.P., R.K., G.C. and M.H.T. performed analysis of transcriptomic data G.H.D.P., P.C. and R.L. performed data validation G.H.D.P., R.L., N.M. and P.C. performed formal analysis G.H.D.P., R.L., N.M., P.C., E.V.N. and J.M.M. performed investigation G.H.D.P., N.M., P.C. and R.L. performed experiments and analysis for Fig.1 G.H.D.P., R.K. and G.C. performed experiments and data analysis and validation for Fig. 2, Extended Data Figs. 2, 6, 7 E.V.N. and J.M.M. performed experiments and analysis for Fig. 3 P.L. performed experiments for Extended Data Fig. 1 G.H.D.P. performed analysis for Extended Data Fig. 3 G.H.D.P. performed experiments and analysis for Extended Data Fig. 5 G.H.D.P. performed experiment and analysis for Extended Data Fig. 7 I.D., B.Z., G.C. and M.H.T. provided materials used for experiments G.H.D.P., R.K. and G.C. performed data curation G.H.D.P. and M.H.T. wrote the original draft G.H.D.P., M.H.T., R.K. and G.C. reviewed and edited the manuscript.

Corresponding authors

How brain tissue recovers after injury

Figure: diagram of the research findings (Taken from article's Table of Contents Image) bFGF is produced in the injured zone of the cerebral cortex. Ror2 expression is induced in some population of the astrocytes that receive the bFGF signal, restarting their proliferation by accelerating the progression of their cell cycle. Credit: Kobe University

A research team led by Associate Professor Mitsuharu ENDO and Professor Yasuhiro MINAMI (both from the Department of Physiology and Cell Biology, Graduate School of Medicine, Kobe University) has pinpointed the mechanism underlying astrocyte-mediated restoration of brain tissue after an injury. This could lead to new treatments that encourage regeneration by limiting damage to neurons incurred by reduced blood supply or trauma. The findings were published on October 11 in the online version of Glia ahead of print release in January 2017.

When the brain is damaged by trauma or ischemia (restriction in blood supply), immune cells such as macrophages and lymphocytes dispose of the damaged neurons with an inflammatory response. However, an excessive inflammatory response can also harm healthy neurons.

Astrocytes are a type of glial cell, and the most numerous cell within the human cerebral cortex. In addition to their supportive role in providing nutrients to neurons, studies have shown that they have various other functions, including the direct or active regulation of neuronal activities.

It has recently become clear that astrocytes also have an important function in the restoration of injured brain tissue. While astrocytes do not normally proliferate in healthy brains, they start to proliferate and increase their numbers around injured areas and minimize inflammation by surrounding the damaged neurons, other astrocytes, and inflammatory cells that have entered the damaged zone. Until now the mechanism that prompts astrocytes to proliferate in response to injury was unclear.

The research team focused on the fact that the astrocytes which proliferate around injured areas acquire characteristics similar to neural stem cells. The receptor tyrosine kinase Ror2, a cell surface protein, is highly expressed in neural stem cells in the developing brain. Normally the Ror2 gene is "switched off" within adult brains, but these findings showed that when the brain was injured, Ror2 was expressed in a certain population of the astrocytes around the injured area.

Ror2 is an important cell-surface protein that regulates the proliferation of neural stem cells, so the researchers proposed that Ror2 was regulating the proliferation of astrocytes around the injured areas. They tested this using model mice for which the Ror2 gene did not express in astrocytes. In these mice, the number of proliferating astrocytes after injury showed a remarkable decrease, and the density of astrocytes around the injury site was reduced. Using cultured astrocytes, the team analyzed the mechanism for activating the Ror2 gene, and ascertained that basic fibroblast growth factor (bFGF) can "switch on" Ror2 in some astrocytes.

This research showed that in injured brains, the astrocytes that show (high) expression of Ror2 induced by bFGF signal are primarily responsible for starting proliferation. bFGF is produced by different cell types, including neurons and astrocytes in the injury zone that have escaped damage. Among the astrocytes that received these bFGF signals around the injury zone, some express Ror2 and some do not. The fact that proliferating astrocytes after brain injury are reduced during aging raises the possibility that the population of astrocytes that can express Ror2 might decrease during aging, which could cause an increase in senile dementia. Researchers are aiming to clarify the mechanism that creates these different cell populations of astrocytes.

By artificially controlling the proliferation of astrocytes, in the future we can potentially minimize damage caused to neurons by brain injuries and establish a new treatment that encourages regeneration of damaged brain areas.

This manuscript has been released as a pre-print at bioRxiv (Puls et al., 2019).

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Keywords: spinal cord, NeuroD1, astrocyte, neuronal conversion, in vivo reprogramming

Citation: Puls B, Ding Y, Zhang F, Pan M, Lei Z, Pei Z, Jiang M, Bai Y, Forsyth C, Metzger M, Rana T, Zhang L, Ding X, Keefe M, Cai A, Redilla A, Lai M, He K, Li H and Chen G (2020) Regeneration of Functional Neurons After Spinal Cord Injury via in situ NeuroD1-Mediated Astrocyte-to-Neuron Conversion. Front. Cell Dev. Biol. 8:591883. doi: 10.3389/fcell.2020.591883

Received: 05 August 2020 Accepted: 25 November 2020
Published: 16 December 2020.

Friederike Klempin, Max Delbr࿌k Center for Molecular Medicine, Germany

Philip John Horner, Houston Methodist Research Institute, United States
Paul Lu, University of California, San Diego, United States

Copyright © 2020 Puls, Ding, Zhang, Pan, Lei, Pei, Jiang, Bai, Forsyth, Metzger, Rana, Zhang, Ding, Keefe, Cai, Redilla, Lai, He, Li and Chen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

† These authors share first authorship

‡ These authors share senior authorship

§ Present address: Hedong Li, Department of Neuroscience & Regenerative Medicine, Medical College of Georgia at Augusta University, Augusta, GA, United States


Department of Biochemistry and Molecular Biology, Monash University, Building 13D, Clayton Campus, Clayton, VIC, 3800, Australia

Gavin C. Higgins, Rodney J. Devenish & Phillip Nagley

Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, Monash University, Clayton Campus, Clayton, VIC, 3800, Australia

Rodney J. Devenish & Phillip Nagley

Florey Neuroscience Institutes, University of Melbourne, Parkville, VIC, 3010, Australia

Department of Pharmacology, University of Melbourne, Parkville, VIC, 3010, Australia

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