POST-SEIZURE ACTIVATION PATTERNS OF GASOTRANSMITTER SYSTEMS IN RELATION TO ELECTROPHYSIOLOGICAL AND BEHAVIOURAL MEASURES

Epileptic seizures are commonly attributed to an imbalance between excitatory glutamatergic and inhibitory GABAergic neurotransmission. However, this framework may underestimate the contribution of non-classical signalling pathways. Gasotransmitters, nitric oxide (NO) and carbon monoxide (CO), are neuromodulators that could shape seizure-related dynamics, yet their involvement in seizure responses and epileptogenesis remains poorly defined. Here, we characterised spatiotemporal activation patterns of NO- and CO-related systems following induced seizures in relation to electrophysiological and behavioural measures. Seizures were induced in adult male Wistar rats by intraperitoneal pilocarpine (250 mg/kg b.w.) and behaviourally scored with simultaneous EEG recording. Animals were sacrificed at 6, 12, 24 hours or 2, 4, 8 days post-seizure induction (p.s.i.). Hippocampal sections were immunohistochemically stained for neuronal nitric oxide synthase (nNOS) and haem oxygenase-1 (HO-1). Immunoreactivity was quantified in FIJI. EEG was analysed using custom MATLAB-based tools. Seizure induction produced robust, time-dependent changes in the gasotransmitter-synthesising enzymes’ expression. The number of nNOS+ neurones was persistently reduced from early post-seizure timepoints. HO-1 exhibited a delayed response, peaking at 24 h p.s.i. and gradually returning toward baseline between 4-8 days p.s.i. These changes varied across hippocampal subregions (CA1, CA2/3, dentate gyrus) and were partially associated with behavioural seizure severity. No significant correlations were observed between immunohistochemical and electrophysiological parameters. Together, these results suggest that gasotransmitting systems participate in brain's seizure response. Future studies should examine pharmacological and non-pharmacological modulation of these pathways to determine whether altering them influences seizure-associated reactive changes. Our research was funded by the National Science Centre, Poland (2021/43/O/NZ4/02208).