Brain inflammation

Neuroinflammation — inflammatory activation within the brain that clouds cognition and depresses mood.

Barrier integrity reduces it.

This comprehensive review shows that an intact blood-brain barrier excludes plasma proteins, peripheral immune cells and neurotoxins from brain parenchyma, and that when barrier integrity is lost those components enter and trigger glial activation and neuroinflammatory injury. doi 10.1152/physrev.00050.2017 · PMID 30280653

Calms inflammation increases it.

Anilkumar & Wright-Jin 2024, Cells 13:485 — microglial NF-κB upregulates proinflammatory genes, driving neuroinflammation. PMID 38534329. Mechanism: microglia, the primary immune responders of the CNS, upregulate NF-kappa-B on activation in pathological conditions; NF-kappa-B activation drives proinflammatory functional change and release of cytokines and chemokines that act on other CNS cells, and microglial crosstalk can then induce cell death, exacerbating pathology. Loss-of-function, stated plainly by the authors: microglia-specific NF-kappa-B inhibition is typically associated with positive downstream results. Independently, microglia-specific deletion of NIK (noncanonical NF-kappa-B) had NO effect on EAE disease onset but attenuated disease progression (Cell Mol Immunol 2025, doi 10.1038/s41423-025-01310-w) — the pathway matters for progression, not initiation. The authors close by noting that the diverse effect of NF-kappa-B across CNS cell types requires further investigation before this pathway can be manipulated therapeutically. 'Lowering NF-kappa-B' remains an incoherent whole-body instruction; the compartment decides. doi 10.1038/s41423-025-01310-w · PMID 38534329

Inflammatory alarm increases it.

Microglial NLRP3 study 2018 — NLRP3 inflammasome activates caspase-1 → IL-1β, driving neuroinflammation and neuronal loss. PMID 29786072

Clears worn-out cells increases it.

Coppé 2008, PLoS Biol 6:e301 — senescent cells secrete an inflammatory secretome (SASP: IL-6/IL-8) that drives neuroinflammation. PMID 19053174

Lowers cortisol increases it.

Glucocorticoids are the archetypal anti-inflammatory drug in the body. In the brain they do the opposite: a paper is titled glucocorticoids mediate stress-induced priming of microglial pro-inflammatory responses, and another finds glucocorticoids exacerbate lipopolysaccharide-induced signaling in the frontal cortex and hippocampus. Dose-dependent and molecularly specified: chronic corticosterone raised gene expression of NLRP3, Iba-1, MHCII and NF-kappa-B-I-alpha in a concentration-dependent manner; glucocorticoids induce NLRP3 at mRNA and protein level, priming inflammasome formation for a subsequent stimulus and potentiating the cytokine response. HPA hyperactivity drives overproduction of brain pro-inflammatory cytokines through microglial activation. The mechanism is disinhibition, not activation: stress DISINHIBITS microglia via down-regulation of CD200R — a brake is removed rather than an accelerator pressed. And the primed state outlasts the stressor by weeks: it is maintained as long as 24 days after the last stress, with primed microglia showing an exaggerated response to any subsequent immune challenge. That is why a past stressor changes how the next infection feels. doi 10.1212/NXI.0000000000200023

Gut barrier reduces it.

10.1038/nn.4030 — ,germ-free mice display global defects in microglia and show immature microglia with reduced pro-inflammatory cytokine production. The requirement is continuous, not developmental: even during adulthood, continuous input from complex microbiota is necessary for maintenance of normal microglia — and if the input is lost, for example after antibiotics, microglia return to an immature status. A course of antibiotics de-matures the brain's immune cells. So the arrow is not read as gut causes brain inflammation. It is: the gut keeps microglia mature and responsive. Absence gives immature, hypo-responsive cells — which is why germ-free animals show reduced amyloid pathology, a benefit, in the same literature. doi 10.1038/nn.4030

Gut-brain signal reduces it.

The vagus nerve plays a role in modulating inflammation and immune responses through the cholinergic anti-inflammatory pathway, and treatments that target the vagus nerve increase the vagal tone and inhibit cytokine production. It is described as A NEUROIMMUNE feedback loop rather than a one-way output, which matters because neuroinflammation is also on the inbound list for this pathway — cytokine load reduces vagal tone. Clinical arm: vagus nerve stimulation is a promising ADD-ON treatment for treatment-refractory depression, posttraumatic stress disorder and inflammatory bowel disease. The reviewers call that evidence preliminary and the word is theirs. doi 10.1016/j.bbi.2024.11.009 · PMC5859128

Cellular aging increases it.

the Neuroinflammation → Cellular Aging link carried the caveat: emerging evidence suggests a bidirectional and cyclical relationship between chronic inflammation and the development of age-related conditions. With both arms the pair registers reinforcing, which matches the NAD+/sirtuin loop recorded on the same sources: inflammaging can induce a positive feedback loop through altered SIRT function to drive ROS production, mitochondrial dysfunction, and more inflammation. doi 10.1016/j.molmet.2023.101755

Tryptophan balance increases it.

Quinolinic acid, a downstream metabolite, is an NMDA agonist. Carried by the intermediary-metabolism and clinical reviews. doi 10.1016/j.molmet.2023.101755 · PMC9967593

Cortical spreading wave increases it.

CSD opens neuronal pannexin-1 channels and activates caspase-1, releasing pro-inflammatory mediators that drive parenchymal and meningeal inflammation. doi 10.1152/physrev.00027.2020 · PMC7786797

Neuronal overexcitation increases it.

Excitotoxic injury recruits inflammatory activation, which in turn lowers the threshold for further injury. doi 10.1186/s40035-021-00278-7 · PMC8788129

Eases ER stress increases it.

ER stress and unfolded protein response activation initiate and worsen chronic neuroinflammation alongside oxidative and nitrosative stress. doi 10.1016/j.jhep.2018.06.008 · PMC4100367

The Long Tenant reduces it.

Taenia solium cysticerci in the central nervous system provoke inflammation around degenerating larvae. doi 10.1155/2017/8494572

It reduces Memory & focus.

Depression neuroinflammation review 2025 — microglial cytokines impair hippocampal neurogenesis and synaptic function, producing cognitive deficits. PMID 40305200. The claim is supported, by a different paper: Int J Mol Sci 2025;26(15):7212 (doi 10.3390/ijms26157212, PMID 40806341) -- persistent microglial activation leads to chronic neuroinflammation which alters neuronal signaling pathways, resulting in accelerated cognitive decline, with PI3K identified as the driver connecting inflammation to neurodegeneration. Verified at source against the correct paper. doi 10.3390/ijms26157212 · PMID 40305200

It reduces Mood.

Depression neuroinflammation review 2025 — cytokines drive the kynurenine pathway, depleting serotonin and dysregulating the HPA axis, lowering mood. PMID 40305200. cytokine-to-symptom correlations are moderate, not strong -- IL-6 and IL-1beta showed moderate correlation with HAM-D scores. The review states depression is increasingly linked to neuroinflammation, which is an association claim, not proof of causation. PMID 40305200

It increases Headache peptide.

CGRP previously had NO upstream edge at all, leaving migraine with a single unrooted driver. Verified at source: in acidic inflammatory environments, protons activate TRPV1 on sensory neurons; calcium entry activates calcium-calmodulin-dependent kinase, which phosphorylates CREB at Ser133; phospho-CREB binds cAMP response elements in the CGRP promoter and raises transcription (Mol Biol Cell doi 10.1091/mbc.e10-01-0049; Int J Mol Sci 2026 doi 10.3390/ijms27114973). TRPV1-deficient DRG showed reduced CGRP induction by acid, and a selective TRPV1 antagonist decreased it — loss-of-function both ways. Inflammatory mediators act in parallel: PGE2 raises CGRP and RAMP1 expression via EP4 and EP1/EP2 receptors, and COX-2 expression correlates positively with CGRP mRNA in human synovium (PMC5067902, n=43). This is a positive feedback loop, stated as such by the authors: CGRP further sensitizes nociceptors to subsequent noxious stimuli, raising CGRP again. Species: rat DRG and human synovial tissue. doi 10.1091/mbc.e10-01-0049 · PMC5067902

It increases Calm under stress.

Observationally the association is large and dose-dependent: in up to 144,890 UK Biobank participants, CRP concentration was associated with depressive and anxiety symptom scores and with probable diagnoses of depression and generalized anxiety disorder in a dose-response fashion — stronger for depression than anxiety, and stronger in women. In joint UKB+NESDA analysis (147,478 + 2,905) higher CRP tracked the anxiety symptoms of irritability (OR 1.06) and worrying control (OR 1.03). But Mendelian randomization reverses the sign for CRP: genetically-predicted higher CRP concentration was associated with decreased risks of depressive and anxiety symptoms, while genetically-predicted higher IL-6 activity was associated with increased depressive symptom risk. The authors' own conclusion attributes the causal candidate to the IL-6/IL-6R pathway, not to CRP — CRP is a marker that rises with inflammation, not the agent. And they state the gap directly: MR studies of inflammation and anxiety ARE lacking, and the field now requires experimental studies of IL-6 modulation in humans to examine causality. Anything that lowers CRP has not thereby been shown to lower anxiety. doi 10.1038/s41380-021-01188-w · PMC8413248

It increases Quiets overexcitation.

activated microglia secrete glutamate through system xC-, the cystine/glutamate antiporter, in a 1:1 exchange of extracellular cystine for intracellular glutamate. And the cell is not attacking — it is feeding itself: inside the cell that cystine is reduced to cysteine, the limiting reagent for glutathione biosynthesis. The in-vivo caveat is the most important part and the authors state it themselves: the view that microglia cause excitotoxicity has evolved mostly from in-vitro studies. In vivo, low-dose LPS microinjected into spinal gray matter activated CNS macrophages without causing overt NEUROPATHOLOGY — neurotoxic inflammation occurred only when LPS and cystine were co-injected. Activation alone is not sufficient; it takes activation plus substrate. Two hits, not one. And the relationship is a loop: activated microglia secrete glutamate but ARE also activated by exogenous glutamate, expressing both metabotropic and ionotropic glutamate receptors, so released glutamate can act in an AUTOCRINE fashion on neighboring microglia. Human: activated human monocytes release glutamate through xc- with xCT upregulated on activation, and xCT expression is raised in multiple sclerosis in both CNS and peripheral blood cells. doi 10.1186/s12974-023-02972-x · PMC3268895

It reduces Sleep.

10.1186/1742-2094-9-91 — give it: administration of exogenous IL-1-beta OR TNF-alpha induces increased NREM sleep and enhances EEG delta power. Block it: inhibition of IL-1 OR TNF — by soluble receptors or IL-1 receptor antagonist — suppresses spontaneous sleep. Not just induced sleep; the ordinary kind. And it runs on a daily rhythm, which separates a regulator from a side effect: there is a diurnal rhythm of TNF-alpha and IL-1-beta mRNA in brain with highest levels occurring during peak sleep periods. The authors call TNF an endogenous SOMNOGEN. Two reversals in the conditional. Stage: these cytokines raise NREM and reduce REM — the stereotyped sleep of illness is described as an evolutionarily conserved NEUROIMMUNE adaptation, not an incidental consequence. Dose: low doses of IL-1 increase NREM at night while high doses suppress NREM during the day. More is not more. REFUTED ON A SECOND READING. This link was shown by linked steps until a source was opened that does not support it: “TNFα or IL1β injection enhances non-rapid eye movement sleep.” — Involvement of cytokines in slow wave sleep. Progress in Brain Research, 2011, 193, 39-47. doi:10.1016/b978-0-444-53839-0.00003-x | PMID 21854954 |. doi 10.1186/1742-2094-9-91 · PMID 21854954 · PMC3645329

It increases Daily energy.

Inflammation seems to have a key role in fatigue before, during and after cancer treatment; in newly diagnosed acute myelogenous leukemia or myelodysplastic syndrome, IL-6, IL-1 receptor antagonist and TNF-α correlated with fatigue ratings (Bower, Nat Rev Clin Oncol 2014;11:597). Guided by research on neuro-immune interactions, a review examines the hypothesis that cancer-related fatigue is driven by activation of the pro-inflammatory cytokine network. doi 10.1016/j.bbi.2012.06.011

It reduces Brain adaptability.

IL-1 receptor antagonist had no effect on LTP at 21-24 degrees C, but displayed a concentration-dependent inhibition of LTP at 34-36 degrees C. doi 10.1007/s11064-018-2517-8 · PMID 14597099

It reduces Sympathetic drive.

The claim is specific: TNF-alpha drives negative INOTROPY through beta-adrenergic receptors. Sympathetic hormones mediate cardiac contractility through betaARs, and diminution in betaAR signaling to catecholamines occurs through betaAR desensitization, contributing to the pathogenesis of heart failure. The desensitization is enzymatically specified: phosphorylation of the receptor by G-protein-coupled receptor kinases (GRK2, 3, 5 and 6), protein kinase C and protein kinase A. And it pairs with a second link on the same receptor population from the opposite direction: the thyroid-to-sympathetic link rests on beta-receptor number — T3 more than doubles the binding sites by synthesising new receptor protein. This edge is about how well those receptors work once they exist. One population, two independent controls: how many there are, and whether they are phosphorylated into silence. Neither literature cites the other. A direction note: this edge is drawn inhibitory because the cytokine reduces effective adrenergic signaling. The same simplification applies to the serotonin-to-vagus link, where one pathway stands for two anatomically separate pools. The desensitization mechanism is well characterized in heart failure; the specific claim that TNF engages the GRK pathway is described as an area of intense study rather than settled (PMC6311126; doi 10.1152/ajpregu.1998.274.3.R577). REFUTED ON A SECOND READING. This link was shown by linked steps until a source was opened that does not support it: “elevated TNF-α within the PVN has been shown to increase sympathetic activity” — Obesity- and High-Fat-Diet-Induced Neuroinflammation: Implications for Autonomic Nervous System Dysfunction and Endothelial Disorders. International Journal of Molecular Sciences, 2025, 26(9), 4047. doi 10.1152/ajpregu.1998.274.3.R577 · PMC6311126

It increases Cellular aging.

The hallmark list itself was revised to include this: recently, the hallmarks of aging were updated to include dysbiosis, disabled macroautophagy, and chronic inflammation. Inflammaging is no longer a consequence of aging in this framing - it is one. Emerging evidence suggests a bidirectional and cyclical relationship between chronic inflammation and age-related conditions, so the single arrow drawn here compresses a loop. doi 10.1016/j.molmet.2023.101755 · PMC11233824

It increases Nerve protection.

C. acnes promotes inflammation via TLR2 and TLR4; TLR signals induce NF-kB-dependent expression of NLRP3, pro-IL-18 and pro-IL-1beta. Androgens raise sebum secretion, triggering acne. doi 10.21037/atm-22-1362 · PMC2904443

It increases Neurovascular calm.

C. acnes promotes inflammation via TLR2 and TLR4; TLR signals induce NF-kB-dependent expression of NLRP3, pro-IL-18 and pro-IL-1beta. Androgens raise sebum secretion, triggering acne. doi 10.21037/atm-22-1362 · PMC2904443

It increases Calm pain signaling.

C. acnes promotes inflammation via TLR2 and TLR4; TLR signals induce NF-kB-dependent expression of NLRP3, pro-IL-18 and pro-IL-1beta. Androgens raise sebum secretion, triggering acne. doi 10.21037/atm-22-1362 · PMC2904443

It reduces Fear extinction.

Named in the extinction-circuit reviews as a modulator of fear-extinction learning and its consolidation. doi 10.1111/j.1601-183X.2012.00801.x · PMC8598288

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