Increased Excitability and Heightened Magnitude of Long-Term Potentiation at Hippocampal CA3-CA1 Synapses in a Mouse Model of Neonatal Hyperoxia Exposure

From diabetic hyperglycemia to cerebrovascular Damage: A narrative review

Diabetes mellitus is a globally significant disease that can lead to systemic complications, particularly vascular damage, including cardiovascular and cerebrovascular diseases of relevance. The physiological changes resulting from the imbalance in blood glucose levels play a crucial role in initiating vascular endothelial damage. Elevated glucose levels can also penetrate the central nervous system, triggering diabetic encephalopathy characterized by oxidative damage to brain components and activation of alternative and neurotoxic pathways. This brain damage increases the risk of ischemic stroke, a leading cause of mortality worldwide and a major cause of disability among surviving patients. The aim of this review is to highlight important pathways related to hyperglycemic damage that extend to the brain and result in vascular dysfunction, ultimately leading to the occurrence of a stroke. Understanding how diabetes mellitus contributes to the development of ischemic stroke and its impact on patient outcomes is crucial for implementing therapeutic strategies that reduce the incidence of diabetes mellitus and its complications, ultimately decreasing morbidity and mortality associated with the disease.

Pierre M, Rastogi N, Nugent M, Duck SA, Kirkwood A, Chavez-Valdez R. Dysregulation of ErbB4 Signaling Pathway in the Dorsal Hippocampus after Neonatal Hypoxia-Ischemia and Late Deficits in PV+ Interneurons, Synaptic Plasticity and Working Memory

Neonatal hypoxic-ischemic (HI) injury leads to deficits in hippocampal parvalbumin (PV)⁺ interneurons (INs) and working memory. Therapeutic hypothermia (TH) does not prevent these deficits. ErbB4 supports maturation and maintenance of PV⁺ IN. Thus, we hypothesized that neonatal HI leads to persistent deficits in PV⁺ INs, working memory and synaptic plasticity associated with ErbB4 dysregulation despite TH. P10 HI-injured mice were randomized to normothermia (NT, 36 °C) or TH (31 °C) for 4 h and compared to sham. Hippocampi were studied for α-fodrin, glial fibrillary acidic protein (GFAP), and neuroregulin (Nrg) 1 levels; erb-b2 receptor tyrosine kinase 4 (ErbB4)/ Ak strain transforming (Akt) activation; and PV, synaptotagmin (Syt) 2, vesicular-glutamate transporter (VGlut) 2, Nrg1, and ErbB4 expression in coronal sections. Extracellular field potentials and behavioral testing were performed. At P40, deficits in PV⁺ INs correlated with impaired memory and coincided with blunted long-term depression (LTD), heightened long-term potentiation (LTP) and increased Vglut2/Syt2 ratio, supporting excitatory-inhibitory (E/I) imbalance. Hippocampal Nrg1 levels were increased in the hippocampus 24 h after neonatal HI, delaying the decline documented in shams. Paradoxically ErbB4 activation decreased 24 h and again 30 days after HI. Neonatal HI leads to persistent deficits in hippocampal PV⁺ INs, memory, and synaptic plasticity. While acute decreased ErbB4 activation supports impaired maturation and survival after HI, late deficit reemergence may impair PV⁺ INs maintenance after HI.

Hyperoxia by short-term promotes oxidative damage and mitochondrial dysfunction in rat brain

Oxygen (O₂) therapy is used as a therapeutic protocol to prevent or treat hypoxia. However, a high inspired fraction of O₂ (FIO₂) promotes hyperoxia, a harmful condition for the central nervous system (CNS). The present study evaluated parameters of oxidative stress and mitochondrial dysfunction in the brain of rats exposed to different FIO₂. Male Wistar rats were exposed to hyperoxia (FIO₂ 40 % and 60 %) compared to the control group (FIO₂ 21 %) for 2 h. Oxidative stress, neutrophilic infiltration, and mitochondrial respiratory chain enzymes were determined in the hippocampus, striatum, cerebellum, cortex, and prefrontal cortex after O₂ exposure. The animals exposed to hyperoxia showed increased lipid peroxidation, formation of carbonyl proteins, N/N concentration, and neutrophilic infiltration in some brain regions, like hippocampus, striatum, and cerebellum being the most affected. Furthermore, CAT activity and activity of mitochondrial enzyme complexes were also altered after exposure to hyperoxia. Rats exposed to hyperoxia showed increase in oxidative stress parameters and mitochondrial dysfunction in brain structures.