| The amino acid L-glutamate is a major excitatory neurotransmitter which is involved in many CNS functions including learning, memory, and synaptic plasticity. Acute exposure to ethanol (50-200 mM) has been shown to inhibit NMDA mediated responses, whereas chronic ethanol exposure leads to adaptive supersensitivity and is thought to be involved in ethanol dependence and tolerance. Previous studies found supersensitivity of NMDA mediated excitotoxicity following 4 days of ethanol exposure to neuronal cultures. This supersensitivity could be due to either an increase in receptor number, increased sensitivity, or other downstream elements. As a result of early studies which reported an increase in NMDA receptor binding in mice which were made tolerant and dependent to ethanol, and followed with studies of our own. Four different ethanol treatment protocols were investigated. None of the chronic ethanol treatments results in pronounced or consistent effects upon NMDA receptor binding. These in vivo studies suggested that mechanisms other than receptor upregulation are involved in the development of supersensitivity to NMDA following chronic ethanol exposure. This supersensitivity could be due to changes in receptor response or downstream elements such as increased sensitivity to oxidative stress. Therefore, we have investigated the relationship of NMDA and reactive oxygen species (ROS) formation in vitro. These studies suggest that transient FeSO{dollar}sb4{dollar} induced, ROS formation results in a delayed cell death, which is dose dependent, and is consistent with the results seen following NMDA exposure in vitro. However, combination experiments (100 {dollar}mu{dollar}M NMDA + 40 {dollar}mu{dollar}M FeSO{dollar}sb4){dollar} showed no synergistic effects on cell death. Further, NMDA by itself did not show increased oxidative stress in our system. Thus, oxidative stress can cause neuronal death, but the interaction between NMDA induced delayed neuronal death and oxidation is not clear. In addition, neurons treated chronically with ethanol displayed decreased amounts of both FeSO{dollar}sb4{dollar} and NMDA induced oxidation, but no protective effects upon cell death were seen. This suggests that oxidative stress is not involved in the development of ethanol tolerance and dependance. |
