Objective Birth asphyxia (BA) is often associated with seizures that may exacerbate the ensuing hypoxic–ischemic encephalopathy. In rodent models of BA, exposure to hypoxia is used to evoke seizures, that commence already during the insult. This is in stark contrast to clinical BA, in which seizures are typically seen upon recovery. Here, we introduce a term‐equivalent rat model of BA, in which seizures are triggered after exposure to asphyxia. Methods Postnatal day 11–12 male rat pups were exposed to steady asphyxia (15 min; air containing 5% O2 + 20% CO2) or to intermittent asphyxia (30 min; three 5 + 5‐min cycles of 9% and 5% O2 at 20% CO2). Cortical activity and electrographic seizures were recorded in freely behaving animals. Simultaneous electrode measurements of intracortical pH, Po2, and local field potentials (LFPs) were made under urethane anesthesia. Results Both protocols decreased blood pH to <7.0 and brain pH from 7.3 to 6.7 and led to a fall in base excess by 20 mmol·L–1. Electrographic seizures with convulsions spanning the entire Racine scale were triggered after intermittent but not steady asphyxia. In the presence of 20% CO2, brain Po2 was only transiently affected by 9% ambient O2 but fell below detection level during the steps to 5% O2, and LFP activity was nearly abolished. Post‐asphyxia seizures were strongly suppressed when brain pH recovery was slowed down by 5% CO2. Significance The rate of brain pH recovery has a strong influence on post‐asphyxia seizure propensity. The recurring hypoxic episodes during intermittent asphyxia promote neuronal excitability, which leads to seizures only after the suppressing effect of the hypercapnic acidosis is relieved. The present rodent model of BA is to our best knowledge the first one in which, consistent with clinical BA, behavioral and electrographic seizures are triggered after and not during the BA‐mimicking insult.

Aim To study brain‐sparing physiological responses in a rodent model of birth asphyxia which reproduces the asphyxia‐defining systemic hypoxia and hypercapnia. Methods Steady or intermittent asphyxia was induced for 15‐45 minutes in anaesthetized 6‐ and 11‐days old rats and neonatal guinea pigs using gases containing 5% or 9% O2 plus 20% CO2 (in N2). Hypoxia and hypercapnia were induced with low O2 and high CO2 respectively. Oxygen partial pressure (PO2) and pH were measured with microsensors within the brain and subcutaneous (“body”) tissue. Blood lactate was measured after asphyxia. Results Brain and body PO2 fell to apparent zero with little recovery during 5% O2 asphyxia and 5% or 9% O2 hypoxia, and increased more than twofold during 20% CO2 hypercapnia. Unlike body PO2, brain PO2 recovered rapidly to control after a transient fall (rat), or was slightly higher than control (guinea pig) during 9% O2 asphyxia. Asphyxia (5% O2) induced a respiratory acidosis paralleled by a progressive metabolic (lact)acidosis that was much smaller within than outside the brain. Hypoxia (5% O2) produced a brain‐confined alkalosis. Hypercapnia outlasting asphyxia suppressed pH recovery and prolonged the post‐asphyxia PO2 overshoot. All pH changes were accompanied by consistent shifts in the blood‐brain barrier potential. Conclusion Regardless of brain maturation stage, hypercapnia can restore brain PO2 and protect the brain against metabolic acidosis despite compromised oxygen availability during asphyxia. This effect extends to the recovery phase if normocapnia is restored slowly, and it is absent during hypoxia, demonstrating that exposure to hypoxia does not mimic asphyxia.

Birth asphyxia (BA) is a pathologic condition that arises from severe perinatal hypoxia and hypercapnia.Recovery following BA is often associated with seizures which may exacerbate the ensuing hypoxicischemic encephalopathy (HIE). Drugs used to treat post-BA seizures are often ineffective and there are concerns over their safety. Therefore, novel seizure-suppressing therapies are urgently needed. Most rodent models of BA-induced seizures are based on exposing neonatal rats or mice to hypoxia (or hypoxiaischemia), and overlook the fact that the hypercapnic acidosis linked to asphyxia has brain-sparing effects by suppressing neuronal excitability and enhancing cerebral blood flow. Thus, the aim of the present study was to investigate the dependence of asphyxia-induced seizures on brain pH and oxygen (Po 2 ) levels in a rodent model of term BA based on postnatal day 11-12 rat pups. Cortical activity and electrographic seizures were recorded in freely-behaving animals using epidural electrodes. Simultaneous measurements of cortical local field potentials as well as intracortical pH and Po 2 were made using microelectrodes and microsensors in urethane-anesthesized animals. The pups were exposed either to steady asphyxia (duration 15 min; with ambient air containing 5 % O 2 plus 20 % CO 2 ) or to intermittent asphyxia (30 min; with repetitive 5 min steps from 9 % to 5 % O 2 at constant 20 % CO 2 ). Both protocols led to acidemia (blood pH <7.0) coupled to a fall in base excess by 20 mmol/l, and to a large increase in plasma copeptin (from 0.2 nM to about 5 nM), a biomarker of BA. Brain pH decreased from 7.3 to 6.7 by the end of intermittent asphyxia.Brain Po 2 was only transiently affected by 9% ambient O 2 , but it fell below the level of detection with steps to 5 % O 2 , during which neuronal activity was near-abolished. The Po 2 steps to 9% were associated with a moderate increase in pH (0.12 units) and a slight recovery (~10 % of baseline) in ongoing neuronal activity.Behavioral seizures spanning the entire Racine scale were triggered after intermittent but not steady asphyxia, and they were tightly associated with neocortical electrographic seizures. The seizures were strongly suppressed when the post-asphyxia brain pH recovery was slowed down by a low level (5 %) of ambient CO 2 . The post-asphyxia overshoot in brain Po 2 (from 30 to 85 mmHg) had no discernible effect on neuronal activity. Our data suggest that the recurring hypoxic episodes during intermittent asphyxia promote neuronal excitability, which becomes established as hyperexcitability and seizures once the suppressing effect of the hypercapnic acidosis is relieved. The present rodent model of BA is to our best knowledge the first one where, consistent with the clinical picture of BA, robust behavioral and electrographic seizures are triggered after and not during the asphyxic insult. HIGHLIGHTS Experimental asphyxia induced severe acidemia and abolished most cortical activity. Cortical activity during asphyxia was closely linked with changes in brai...

Snake genome sequencing is in its infancy—very much behind the progress made in sequencing the genomes of humans, model organisms and pathogens relevant to biomedical research, and agricultural species. We provide here an overview of some of the snake genome projects in progress, and discuss the biological findings, with special emphasis on toxinology, from the small number of draft snake genomes already published. We discuss the future of snake genomics, pointing out that new sequencing technologies will help overcome the problem of repetitive sequences in assembling snake genomes. Genome sequences are also likely to be valuable in examining the clustering of toxin genes on the chromosomes, in designing recombinant antivenoms and in studying the epigenetic regulation of toxin gene expression.

Objective Seizures are common in neonates recovering from birth asphyxia but there is general consensus that current pharmacotherapy is suboptimal and that novel antiseizure drugs are needed. We recently showed in a rat model of birth asphyxia that seizures are triggered by the post‐asphyxia recovery of brain pH. Here our aim was to investigate whether carbonic anhydrase inhibitors (CAIs), which induce systemic acidosis, block the post‐asphyxia seizures. Methods The CAIs acetazolamide (AZA), benzolamide (BZA), and ethoxzolamide (EZA) were administered intraperitoneally or intravenously to 11‐day‐old rats exposed to intermittent asphyxia (30 min; three 7+3 min cycles of 9% and 5% O2 at 20% CO2). Electrode measurements of intracortical pH, Po2, and local field potentials (LFPs) were made under urethane anesthesia. Convulsive seizures and blood acid‐base parameters were examined in freely behaving animals. Results The three CAIs decreased brain pH by 0.14–0.17 pH units and suppressed electrographic post‐asphyxia seizures. AZA, BZA, and EZA differ greatly in their lipid solubility (EZA > AZA > BZA) and pharmacokinetics. However, there were only minor differences in the delay (range 0.8–3.7 min) from intraperitoneal application to their action on brain pH. The CAIs induced a modest post‐asphyxia elevation of brain Po2 that had no effect on LFP activity. AZA was tested in freely behaving rats, in which it induced a respiratory acidosis and decreased the incidence of convulsive seizures from 9 of 20 to 2 of 17 animals. Significance AZA, BZA, and EZA effectively block post‐asphyxia seizures. Despite the differences in their pharmacokinetics, they had similar effects on brain pH, which indicates that their antiseizure mode of action was based on respiratory (hypercapnic) acidosis resulting from inhibition of blood‐borne and extracellular vascular carbonic anhydrases. AZA has been used for several indications in neonates, suggesting that it can be safely repurposed for the treatment of neonatal seizures as an add‐on to the current treatment regimen.