Mechanisms underlying the neurotoxicity induced by glyphosate-based herbicide in immature rat hippocampus: Involvement of glutamate excitotoxicity

Graphical abstract: - Highlights: • Roundup^® induces Ca²⁺ influx through L-VDCC and NMDA receptor activation. • The mechanisms underlying Roundup^® neurotoxicity involve glutamatergic excitotoxicity. • Kinase pathways participate in Roundup^®-induced neural toxicity. • Roundup^® alters glutamate uptake, release and metabolism in hippocampal cells. - Abstract: Previous studies demonstrate that glyphosate exposure is associated with oxidative damage and neurotoxicity. Therefore, the mechanism of glyphosate-induced neurotoxic effects needs to be determined. The aim of this study was to investigate whether Roundup^® (a glyphosate-based herbicide) leads to neurotoxicity in hippocampus of immature rats following acute (30 min) and chronic (pregnancy and lactation) pesticide exposure. Maternal exposure to pesticide was undertaken by treating dams orally with 1% Roundup^® (0.38% glyphosate) during pregnancy and lactation (till 15-day-old). Hippocampal slices from 15 day old rats were acutely exposed to Roundup^® (0.00005–0.1%) during 30 min and experiments were carried out to determine whether glyphosate affects ⁴⁵Ca²⁺ influx and cell viability. Moreover, we investigated the pesticide effects on oxidative stress parameters, ¹⁴C-α-methyl-amino-isobutyric acid (¹⁴C-MeAIB) accumulation, as well as glutamate uptake, release and metabolism. Results showed that acute exposure to Roundup^® (30 min) increases ⁴⁵Ca²⁺ influx by activating NMDA receptors and voltage-dependent Ca²⁺ channels, leading to oxidative stress and neural cell death. The mechanisms underlying Roundup^®-induced neurotoxicity also involve the activation of CaMKII and ERK. Moreover, acute exposure to Roundup^® increased ³H-glutamate released into the synaptic cleft, decreased GSH content and increased the lipoperoxidation, characterizing excitotoxicity and oxidative damage. We also observed that both acute and chronic exposure to Roundup^® decreased ³H-glutamate uptake and metabolism, while induced ⁴⁵Ca²⁺ uptake and ¹⁴C-MeAIB accumulation in immature rat hippocampus. Taken together, these results demonstrated that Roundup^® might lead to excessive extracellular glutamate levels and consequently to glutamate excitotoxicity and oxidative stress in rat hippocampus