Long-Lasting Actions of Progesterone Protect the Neonatal Brain Following Hypoxia-Ischemia

Lactate administration causes long-term neuroprotective effects following neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) is one of the main causes of mortality and long-term disabilities in newborns, and the only clinical approach to treat this condition is therapeutic hypothermia, which shows some limitations. Thus, putative neuroprotective agents have been tested in animal models of HI. Lactate is a preferential metabolic substrate of the neonatal brain and has already been shown to produce beneficial neuroprotective outcomes in neonatal animals exposed to HI. Here, we administered lactate as a treatment in neonatal rats previously exposed to HI and evaluated the impact of this treatment in adulthood. Seven-day-old (P7) male and female Wistar rats underwent permanent common right carotid occlusion combined with an exposition to a hypoxic atmosphere (8% oxygen) for 60 min. Animals were assigned to one of four experimental groups: HI, HI+LAC, SHAM, SHAM+LAC. Lactate was administered intraperitoneally 30 min and 2 h after hypoxia in HI+LAC and SHAM+LAC groups, whereas HI and SHAM groups received vehicle. Animals were tested in the behavioral tasks of negative geotaxis and righting reflex (P8), cylinder test (P24), and the modified neurological severity score was calculated (P25). Open field (OF), and novel object recognition (NOR) were evaluated in adulthood. Animals were killed at P60, and the brains were harvested and processed to evaluate the volume of brain injury. Our results showed that lactate administration reduced the volume of brain lesion and improved sensorimotor and cognitive behaviors in neonatal, juvenile, and adult life in HI animals from both sexes. Thus, lactate administration might be considered as a potential neuroprotective strategy for the treatment of neonatal HI, which is a prevalent disorder affecting newborns.

Bumetanide Attenuates Cognitive Deficits and Brain Damage in Rats Subjected to Hypoxia-Ischemia at Two Time Points of the Early Postnatal Period

Neonatal hypoxia-ischemia (HI) is one of the main causes of tissue damage, cell death, and imbalance between neuronal excitation and inhibition and synaptic loss in newborns. GABA, the major inhibitory neurotransmitter of the central nervous system (CNS) in adults, is excitatory at the onset of neurodevelopment and its action depends on the chloride (Cl-) cotransporters NKCC1 (imports Cl-) and KCC2 (exports Cl-) expression. Under basal conditions, the NKCC1/KCC2 ratio decreases over neurodevelopment. Thus, changes in this ratio caused by HI may be related to neurological disorders. The present study evaluated the effects of bumetanide (NKCC cotransporters inhibitor) on HI impairments in two neurodevelopmental periods. Male Wistar rat pups, 3 (PND3) and 11 (PND11) days old, were submitted to the Rice-Vannucci model. Animals were divided into 3 groups: SHAM, HI-SAL, and HI-BUM, considering each age. Bumetanide was administered intraperitoneally at 1, 24, 48, and 72 h after HI. NKCC1, KCC2, PSD-95, and synaptophysin proteins were analyzed after the last injection by western blot. Negative geotaxis, righting reflex, open field, object recognition test, and Morris water maze task were performed to assess neurological reflexes, locomotion, and memory function. Tissue atrophy and cell death were evaluated by histology. Bumetanide prevented neurodevelopmental delay, hyperactivity, and declarative and spatial memory deficits. Furthermore, bumetanide reversed HI-induced brain tissue damage, reduced neuronal death and controlled GABAergic tone, maintained the NKCC1/KCC2 ratio, and synaptogenesis close to normality. Thereby, bumetanide appears to play an important therapeutic role in the CNS, protecting the animals against HI damage and improving functional performance.

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.

Therapeutic hypothermia for the treatment of neonatal hypoxia-ischemia: sex-dependent modulation of reactive astrogliosis

Therapeutic hypothermia (TH) is the standard treatment for neonatal hypoxia-ischemia (HI) with a time window limited up to 6 h post injury. However, influence of sexual dimorphism in the therapeutic window for TH has not yet been elucidated in animal models of HI. Therefore, the aim of this study was to investigate the most effective time window to start TH in male and female rats submitted to neonatal HI. Wistar rats (P7) were divided into the following groups: NAÏVE and SHAM (control groups), HI (submitted to HI) and TH (submitted to HI and TH; 32ºC for 5 h). TH was started at 2 h (TH-2 h group), 4 h (TH-4 h group), or 6 h (TH-6 h group) after HI. At P14, animals were subjected to behavioural tests, volume of lesion and reactive astrogliosis assessments. Male and female rats from the TH-2 h group showed reduction in the latency of behavioral tests, and decrease in volume of lesion and intensity of GFAP immunofluorescence. TH-2 h females also showed reduction of degenerative cells and morphological changes in astrocytes. Interestingly, females from the TH-6 h group showed an increase in volume of lesion and in number of degenerative hippocampal cells, associated with worse behavioral performance. Together, these results indicate that TH neuroprotection is time- and sex-dependent. Moreover, TH started later (6 h) can worsen volume of brain lesion in females. These data indicate the need to develop specific therapeutic protocols for each sex and reinforce the importance of early onset of the hypothermic treatment.

Inhibition of progesterone receptor membrane component-1 exacerbates neonatal hypoxic-ischemic cerebral damage in male mice

This study investigated the expression of progesterone receptor membrane component 1 (pgrmc1) in the brains of male and female mice, and the effect of inhibiting pgrmc1 on neonatal hypoxic-ischemic (HI) cerebral injury in male mice. A mouse model of neonatal HI brain injury was established, and AG205, a specific antagonist of pgrmc1, was injected into the left lateral cerebral ventricle 1 h before HI. Histological staining, behavior testing, Western blots, and quantitative PCR (qPCR) were employed to evaluate pgrmc1 expression, brain damage, neurological function, and molecular mechanisms. Results demonstrated that the mRNA and protein levels of pgrmc1 increased significantly in the cortex and hippocampus 72 h after HI without sex differences. The inhibition of pgrmc1 exacerbated the neonatal brain damage in the acute stage of HI in male mice as seen in the increase in brain water content, infarction area, and neuronal death. Inhibition of pgrmc1 also aggravated the neurological dysfunction and anxiety induced by HI brain injury. In addition, inhibition of pgrmc1 activated the NF-kB signaling and NF-κB-mediated cytokines, and inhibited BDNF/PI3K/AKT pathway in the brains of the newborn HI mice. The results indicated that pgrmc1 inhibition exacerbated the brain damage in newborn male mice subjected to HI by activating IκBα/NFκB signaling and inhibiting BDNF/PI3K/Akt pathway.

Lactate Administration Reduces Brain Injury and Ameliorates Behavioral Outcomes Following Neonatal Hypoxia-Ischemia

Neonatal hypoxic-ischemic encephalopathy is a major cause of mortality and disability in newborns and the only standard approach for treating this condition is therapeutic hypothermia, which shows some limitations. Thus, putative neuroprotective agents have been tested in animal models. The present study evaluated the administration of lactate, a potential energy substrate of the central nervous system (CNS) in an animal model of hypoxia-ischemia (HI), that mimics in neonatal rats the brain damage observed in human newborns. Seven-day-old (P7) male and female Wistar rats underwent permanent common right carotid occlusion combined with an exposition to a hypoxic atmosphere (8% oxygen) for 60 min. Animals were assigned to four experimental groups: HI, HI + LAC, SHAM, SHAM + LAC. Lactate was administered intraperitoneally 30 min and 2 h after hypoxia in HI + LAC and SHAM + LAC groups. HI and SHAM groups received vehicle at the same time points. The volume of brain lesion was evaluated in P9. Animals underwent behavioral assessments: negative geotaxis, righting reflex (P8 and P14), and cylinder test (P20). Lactate administration reduced the volume of brain lesion and improved behavioral parameters after HI in both sexes. Thus, lactate administration could be a neuroprotective strategy for the treatment of neonatal HI, a disorder still affecting a significant percentage of human newborns.