The effect of the NMDA receptor blocker, dextromethorphan, on cribbing in horses

Stereotypic cribbing in horses is thought to involve excess dopaminergic ac tivity within the striatum. Various models of stress-induced stereotypies i ncluding cribbing in horses postulate that stress stimulates the release of endorphins. triggering the release of striatal dopamine. Dopamine in turn activates basal ganglia motor programs, reinforcing behavior via a reward m echanism. Furthermore, the release of dopamine by endorphins has been shown to depend on activation of NMDA receptors. In the present study, horses id entified as cribbers and volunteered by their owners were treated with the NMDA receptor antagonist dextromethorphan (DM). When DM was administered vi a jugular injection (1 mg/kg), eight of nine horses responded with reductio ns in cribbing rate (CR) compared to baseline, and cribbing was suppressed completely for a period of time in almost half of the horses tested. (C) 20 01 Elsevier Science Inc. All rights reserved.