Temporal analysis of histopathology and cytokine expression in the rat cerebral cortex after insulin‐induced hypoglycemia

Abstract

Hypoglycemic coma causes neuronal death in the cerebral neocortex; however, its unclear pathogenesis prevents the establishment of preventive measures. Inflammation plays a pivotal role in neuronal damage in the hypoglycemic state; however, the dynamics of glial cell activation or cytokine expression remain unknown. Here, we aimed to elucidate the spatiotemporal morphological changes of microglia and time‐course cytokine expression profiles in the rat cerebral cortex after hypoglycemic coma. We performed histopathological and immunohistochemical (Iba1, neuronal nuclei, glial fibrillary acidic protein) analyses in the cingulate cortex and four areas of the neocortex: hindlimb area (HL), parietal cortex area 1 (Par1), parietal cortex area 2 (Par2), and perirhinal cortex (PRh). We measured tumor necrosis factor alpha (TNFα) and interleukin‐6 messenger RNA (mRNA) expression by real‐time reverse transcriptase‐polymerase chain reaction. Necrotic neurons appeared in the neocortex as early as 3 h after hypoglycemic coma, while they were absent in the cingulate cortex. Neuronal nuclei‐immunopositive neurons in the HL, Par2, and PRh were significantly less abundant than in the control at day 1. In Iba1 immunostaining, large rod‐shaped cells were detected at 3–6 h after hypoglycemia, and commonly observed in the HL, Par2, and PRh. After 6 h, rod‐shaped cells were rarely observed; instead, there was a prominent infiltration of hypertrophic and ameboid‐shaped cells until day 7. The mRNA expression of TNFα was significantly higher than the control at 3–6 h after hypoglycemia in the neocortex, while it was significantly higher only at 3 h in the cingulate cortex. Our results indicate that early and transient appearance of rod‐shaped microglia and persisting high TNFα expression levels characterize inflammatory responses to hypoglycemic neuronal damage in the cerebral neocortex, which might contribute to neuronal necrosis in response to transient hypoglycemic coma.

Variable histopathology features of neuronal dyslamination in the cerebral neocortex adjacent to epilepsy‐associated vascular malformations suggest complex pathogenesis of focal cortical dysplasia ILAE type IIIc

“…Accordingly, we report for the first time that shallower CPLS of varying thickness, the lesion pattern similar to TLS, frequently occurs in the cerebral cortex adjacent to LMA‐SWS. Although unraveling the pathogenesis of CPLS as well as TLS is a scope of future investigation, the fact that the shallower zone of the cerebral cortex is vulnerable to hypoglycemia in both humans [ 17 ] and animal models [ 18 ] may suggest a possible role of localized relative glucose deficiency caused by a supply‐demand gap during repetitive hyperexcitation the pathogenesis of CPLS, which needs to be further studied and pathophysiologically confirmed.…”

Effects of diabetes on microglial physiology: a systematic review of in vitro, preclinical and clinical studies

“…In the neocortex, rod-shaped microglia are transiently observed within an early period (3-6 h) after hypoglycemia, indicating microglial response to glucose deprivation. These cells are then replaced by hypertrophic amoeboid microglia (1-14 days post-hypoglycemia), which might be involved in phagocytosing irreversibly damaged neurons [233]. In the hippocampus, oxidative stress appears as early as 3 h after glucose deprivation with increased superoxide production [234,235], resulting in decreased antioxidant glutathione and exacerbated oxidative injury at 7 days after the insult [236], time by which a severe pattern of neuronal death is evident [234][235][236][237].…”