Effects of stobadine, melatonin, and other antioxidants on hypoxia/reoxygenation-induced synaptic transmission failure in rat hippocampal slices

Abstract

In vitro reversible ischemia was simulated with rat hippocampal slices in order to test the neuroprotective activity of selected antioxidants with emphasis on the pyridoindole stobadine. Slices were exposed to hypoxia (HYP) combined with lowered d-glucose concentration to induce synaptic transmission (ST) failure, which turned out to be irreversible in approximately 80%–100% of slices during reoxygenation (ROX). The amplitude of population spikes (PoS) evoked transsynaptically by electrical stimulation of Schäffer collaterals and recorded in CA1 neurons was the parameter of ST. Pretreatment of slices with stobadine dissolved in slice superfusion media (1 to 100 μM) improved ST recovery after 20-min tissue ROX. Stobadine decreased the number of irreversibly damaged slices and increased the average amplitude of PoS during tissue ROX. The concentration–response relationship of protective activity was bell-shaped, with maximum at 3–30 μM. Moreover, the half-time of PoS decay ( t 1/2) during HYP was significantly delayed in stobadine treated groups (10 to 100 μM). The neurohormone melatonin (30 to 100 μM) and 21-aminosteroid U-74389G (10 μM) revealed similar protective activity on ST recovery and on t 1/2 during HYP. Trolox (200 μM) improved the PoS recovery, yet it had no effect on t 1/2. The iron chelator deferoxamine (250 and 500 μM) had no protective effects at all. α-Tocopherol administered to animals orally (200 mg/kg for 10 days) only marginally improved the PoS recovery. Comparing the protective effect of compounds tested on PoS recovery, we assume the following rank order of potency: U-74389G>stobadine>melatonin≫trolox. Our findings suggest that stobadine as well as trolox, U-74389G and melatonin, antioxidants with remarkably different chemical structures, exerted neuroprotective activity, probably determined by antioxidative properties of these compounds. Moreover, stobadine, U-74389G, and melatonin were able to delay the early ST decay during HYP, which might indicate improved energetic state of neurons in the treated tissue. The study supports the notion about the neuroprotective activity of certain antioxidants.