Neurogenic Inflammation

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Introduction[edit | edit source]

Inflammation is known to be the driving factor in many diseases, including atherosclerosis, cancer, autoimmunity and chronic infections and a major contributor in age-related conditions. The classical definition of inflammation includes rubor (redness), calor (warmth), dolor (pain), and tumor (swelling), as stated by Celsus (30BC-38AD), and functio laesa (loss of function), as added by Galen (129AD-210AD). Inflammation plays a protective response by invading pathogens or endogenous substances such as damaged cells, and eliminates the initial cause of injury, clears the necrotic cells, and aids in tissue repair.[1]

The complexity of the molecular, immunological and physiological processes involved in the inflammatory reaction leads to the inflammatory process in various tissues and diseases, like complex regional pain syndrome, migraine, and irritable bowel, arthritis, bladder inflammation, asthma and bladder syndromes.

Neurogenic inflammation (NI) is a physiological process in which mediators are released directly from the cutaneous nerves to initiate an inflammatory reaction in response to tissue damage or a painful stimuli. In the setting of wound healing, neurogenic inflammation helps maintain tissue integrity and facilitate tissue repair.[1]

Mechanism of Injury[edit | edit source]

Neurogenic inflammation is initiated by activation of peripheral nervous system C-fibre neurons causing a release of neuropeptides, such as substance P and calcitonin gene-related peptide (CGRP), which triggers inflammation at the site that is different from the original stimuli. Many different chemicals, including formaldehyde, ether, and cigarette smoke, can exert an irritant effect by stimulating these c-fibers in humans[1].

Post Stroke Depression[edit | edit source]

Post Stroke Depression (PSD) is one of the most common mood disorders with depressive consequences in stroke patients[2]. PSD affects approximately one-third of stroke patients[3] and is a significant factor in poor recovery[4]. PSD negatively affects the quality of life, functional ability and prognostic outcomes[4]. Studies suggests that it is also linked to an increased likelihood of stroke recurrence and death[5][6]. PSD may reduce life expectancy through multiple factors such as: cognitive decline, increased risk of falls, high suicidal rate, functional impairment, stagnated recovery process and poor response to rehabilitation [7][8].

Contrarily, a reduction of depressive symptoms has been associated with better functional recovery; also, patients treated for depression show a better functional prognosis compared to untreated, depressed patients[7].

Mechanisms of inflammation

Several mechanisms correlate PSD to neurologic dysfunction[4]. Inflammation is closely linked with depression. There is evidence of the central role of neuroinfammation in development of post stroke depression[9]. Various studies show increase in secretion of of proinflammatory cytokines interleukin (IL)‑1β, IL-6, IL-8, and tumor necrosis factor α (TNFα).[4] During an ischemic injury, a series of complex neurochemical events occur in time and space that are characterised by focal cerebral hypoperfusion, bioenergetic failure, excitotoxicity, acidotoxicity, oxidative stress, microvascular injury, post-ischemic inflammation, blood brain barrier disruption and finally death of neurons, endothelial cells, and neuroglia[4]

  • Inflammation: Inflammation resulting from stroke and depression impacts neuroplasticity, as seen by the decreased availability of brain-derived neurotrophic factor (BDNF) in synapses.
  • Increased stress: A disproportionate increase in stress also causes physiological changes predisposing patients to hypertension and cardiac dysrhythmias
  • Immune and inflammatory pathways: individual’s emotional and social experiences triggers the activation of various components of the immune and inflammatory pathways .
  • Cytokines: act a mediator in chronic inflammatory processes linked to stroke-related complications

Factors

Various factors influence the severity and duration of PSD. [9]

  • Genetic factors: Research shows that the serotonin-transporter-linked polymorphic region 5-HTTLPR and STin2VNTR polymorphisms of the serotonin transporter gene (SERT) and hypermethylation of the 5-HTTLPR s/s genes have been associated with PSD in stroke survivors.[9][10]
  • Location of the lesion: Various observations are noticed concerning the site of lesion and PSD with some studies indicating lesions proximal to or in the frontal pole, or the limbic area to be frequently associated with PSD, whereas other studies not supporting these topological correlations. While several studies linked PSD with lesions of the medial prefrontal cortex, thalamus, amygdala, or pallidum by defining the disruption of frontal cortico‑limbic neuronal circuits, dorsolateral prefrontal and left cerebellar hemispheric localization.[9]
  • Physical disability: In some patients, physical disability may be a causation factor.[9] There is a link between severity of impairments/disability and PSD.[10]
  • Cognitive impairments: According to various studies, there exists a link between PSD and cognitive deficits. [10]
  • Social Support: Lack of social support is associated with PSD
  • Medical and psychiatric history: Personal history of depression and/or anxiety, diabetes was considered as risk factors for PSD.


Diagnosis

According to DSM-5, poststroke mood disorders are mood disorders due to stroke with depressive features, major depressive-like episode, or mixed-mood features. Patients must have depressed mood or loss of interest or pleasure along with at least two but less than five symptoms of major depression lasting 2 weeks or longer.[10]

Multiple Sclerosis[edit | edit source]

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by chronic inflammation, demyelination, gliosis, and neuronal loss. Inflammation is a major driver of the pathology. In addition, oxidative stress contributes to tissue injury and promotes existing inflammatory response. [11]

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References[edit | edit source]

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  1. ↑ 1.0 1.1 1.2 Chiu IM, von Hehn CA, Woolf CJ. Neurogenic inflammation – the peripheral nervous system’s role in host defense and immunopathology. Nat Neurosci. 2012;15:1063-1067.
  2. ↑ (Robinson RG and Jorge RE: Post-stroke depression: A review. Am J Psychiatry. 173:221–231. 2016.PubMed/NCBI View Article : Google Scholar).
  3. ↑ Hackett, M.L.; Pickles, K. Part I: Frequency of depression after stroke: An updated systematic review and meta-analysis of observational studies. Int. J. Stroke 2014, 9, 1017–1025
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Wijeratne T, Sales C. Understanding why post-stroke depression may be the norm rather than the exception: The anatomical and neuroinflammatory correlates of post-stroke depression. Journal of Clinical Medicine. 2021 Apr 14;10(8):1674.
  5. ↑ Wu QE, Zhou AM, Han YP, Liu YM, Yang Y, Wang XM, Shi X. Poststroke depression and risk of recurrent stroke: A meta-analysis of prospective studies. Medicine. 2019 Oct;98(42).
  6. ↑ Sibolt G, Curtze S, Melkas S, Pohjasvaara T, Kaste M, Karhunen PJ, Oksala NK, Vataja R, Erkinjuntti T. Post-stroke depression and depression-executive dysfunction syndrome are associated with recurrence of ischaemic stroke. Cerebrovascular Diseases. 2013 Dec 1;36(5-6):336-43.
  7. ↑ 7.0 7.1 Paolucci S, Iosa M, Coiro P, Venturiero V, Savo A, De Angelis D and Morone G: Post-stroke depression increases disability more than 15% in ischemic stroke survivors: A case-control study. Front Neurol. 10(926)2019.PubMed/NCBI View Article : Google Scholar
  8. ↑ Robinson RG and Jorge RE: Post-stroke depression: A review. Am J Psychiatry. 173:221–231. 2016.PubMed/NCBI View Article : Google Schola
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Nagy EE, Frigy A, Szász JA, Horváth E. Neuroinflammation and microglia/macrophage phenotype modulate the molecular background of post-stroke depression: A literature review. Experimental and Therapeutic Medicine. 2020 Sep 1;20(3):2510-23.
  10. ↑ 10.0 10.1 10.2 10.3 Medeiros GC, Roy D, Kontos N, Beach SR. Post-stroke depression: a 2020 updated review. General hospital psychiatry. 2020 Sep 1;66:70-80.
  11. ↑ Pegoretti V, Swanson KA, Bethea JR, Probert L, Eisel UL, Fischer R. Inflammation and oxidative stress in multiple sclerosis: consequences for therapy development. Oxidative medicine and cellular longevity. 2020 Oct;2020.

 

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