Acamprosate is neuroprotective against glutamate-induced excitotoxicity when enhanced by ethanol withdrawal in neocortical cultures of fetal rat brain

Background: Acamprosate reduces relapse, and the drug may interact with glutamate transmission and with glutamate/NMDA receptors. Because these systems are implicated in excess calcium entry leading to alcohol withdrawal-induced neurotoxicity, we evaluated the effects of acamprosate on these parameters in neuronal cultures. Methods: Primary cultures of neocortical neurons from fetal Sprague-Dawley rats were maintained either in normal medium or in medium containing 100 mM ethanol for 4 days. After this time, cultures were challenged with glutamate for 10 rain and then returned to medium (all in the absence of ethanol). ⁴⁵Ca²⁺ uptake was measured during the challenge, and glutamate-induced toxicity was assessed after 20 hr. The effects of acamprosate present during the glutamate challenge were measured on both parameters. Results: In controls, acamprosate did not significantly affect glutamate-induced neurotoxicity but produced a significant inhibition of calcium entry. The NMDA receptor antagonists dizocilpine and D-amino-phosphonovalerate (D-APV) inhibited both glutamate neurotoxicity and calcium entry. In cultures previously exposed to ethanol, glutamate-induced neurotoxicity and calcium entry were both significantly enhanced. Dizocilpine reduced both these parameters to unstimulated control values, and D-APV reduced both calcium entry and neurotoxicity with the same relation that we obtained in control cultures. In the ethanol-withdrawn cultures, acamprosate reduced both the enhanced glutamate-induced calcium entry and the enhanced neurotoxicity in a concentration-dependent manner. Acamprosate also significantly reduced calcium entry caused by 80 mM K⁺ in control and ethanol-exposed cultures. Conclusions: Acamprosate had protective effects against glutamate-induced neurotoxicity only in ethanol-withdrawn cultures. The neuroprotective effects of the drug did not correlate with its effects on calcium entry, making it unlikely that acamprosate directly affects NMDA receptors via the glutamate binding site or the receptor-operated calcium channel. The results are, however, compatible with other inhibitory effects on NMDA receptor function.