ID 40 – Successive synaptic and membrane failure depend on depth and duration of hypoxia in an vitro model of the ischemic penumbra

Abstract

Objective There is limited understanding of the nature of dynamic neuronal processes leading to either secondary irreversible damage or recovery in the ischemic penumbra. We use cultured neuronal networks to study neuronal dynamics during partial hypoxia, focusing on changes of synaptic transmission and membrane integrity. Methods Twenty-two cultured networks of rat cortical neurons grown over multi electrode arrays were exposed to hypoxia of various depth and duration (pO 2 of 160 mmHg lowered to 90 or 30 mmHg, during 6–48 h). Synaptic functioning was assessed before, during, and after hypoxia by the amount of spontaneous network activity and network responses to electrical stimulation. Action potential shapes and direct (non-synaptic) stimulus responses were used as measures of neuronal integrity. Results During pO 2 =30 mmHg, synaptic transmission failed within an hour. Isolated synaptic failure was reversible after 6–12 h of hypoxia, but partly irreversible after 24 h. Irreversible membrane failure occurred between 24 and 48 h, but later with pO 2 = 90 mmHg. Conclusion The cascade of neuronal pathophysiological events in the ischemic penumbra includes reversible synaptic failure, irreversible synaptic failure, and membrane failure, respectively. The timescale of this cascade depends on remaining perfusion levels.