Repeated hyperbaric oxygen exposure increases seizure susceptibility despite GABAergic modulation and is associated...

GABAergic inhibition delays oxygen-induced seizures, but whether this protection is maintained during repeated hyperbaric oxygen (HBO₂) exposure is unclear. We hypothesized that tiagabine (TGB) prevents increased seizure susceptibility during repeated HBO₂ by preserving presynaptic nerve-terminal function and tested whether single and repeated HBO₂ alter mitochondrial bioenergetics, mitophagy/autophagy, and region-specific transcriptional responses. Mice were exposed to 4.5 ATA O₂ for 60 min and re-exposed after 48 h, 72 h, or 7 d intervals. Measurements included seizure latency, synaptosomal neurotransmitters and oxygen consumption, mitophagy (mito-QC reporter)/autophagy (p62 and LC3-II/LC3-I), and spatial transcriptomics with gene ontology enrichment to define region-specific responses. Repeated HBO₂ shortened seizure latency and reduced the antiseizure efficacy of TGB. Synaptosomal neurotransmitters were altered by HBO₂ but not modified by TGB. Mitophagy/autophagy showed region-specific changes, with increased LC3-II/LC3-I at 48 h and region- and time-dependent changes in p62 expression, accompanied by reduced mitolysosomal signal at 7 d in hippocampal CA3 and cerebellar granular layer, while TGB increased signal in the cerebellar molecular layer. Synaptosomal mitochondrial respiration showed time-dependent changes, with early increases in oxygen consumption followed by reduced maximal respiration and spare respiratory capacity after repeated exposure. Spatial transcriptomics revealed region-specific responses, shifting from broad activation after a single exposure to more restricted intracellular and metabolic programs after repeated exposure. These findings indicate that TGB does not preserve presynaptic neurotransmitter content or prevent increased seizure susceptibility during repeated HBO₂ exposure. Repeated HBO₂ induces mitochondrial and transcriptional adaptations associated with reduced bioenergetic reserve, with susceptibility to oxygen toxicity influenced by recovery interval.