Inhibitory avoidance acquisition in adult rats exposed to a combination of ethanol and methylmercury during central nervous system development

Abstract

Previous studies have shown that combined exposure to ethanol (EtOH) and methylmercury (MeHg) in rats during central nervous system development produces several behavioural impairments. This present study was done to investigate inhibitory avoidance acquisition and panic-like disorders in rats in an elevated T-maze (ETM) model of anxiety. Pregnant rats received tap water or EtOH at 22.5% (w/v) (6.5 g/kg per day, by gavage) during pregnancy and lactation. On the 15th day of pregnancy, half of each group received MeHg (8 mg/kg, by gavage). Adult offspring intoxicated by both EtOH + MeHg showed an increase in the ETM re-exposure time. Upon analysis of the enclosed arms latency in baseline and avoidance 1 session it was observed that the rats spent less time inside the arm, suggesting impairment in their short-term memory. The escape latency decreased for EtOH + MeHg and also for EtOH and MeHg groups, suggesting panic-like behaviour. After 24-h and 7-day trials (tests and retests), MeHg and EtOH + MeHg groups had their latency in the enclosed arm reduced with the exception of the EtOH group, revealing memory impairment. Upon analysis of the risk assessment, animals treated with EtOH + MeHg were the only ones to show a decrease in all evaluation stages. This study demonstrates that the exposure to both EtOH and MeHg has an impact on memory and panic-related behaviours, leading to the assertion that this association of toxicants should be studied more in detail to clarify the precise mechanisms of these pharmacological effects.