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

The research investigates the impact of the drug dextromethorphan (DM) on the behavior of cribbing in horses, a known stereotypic condition often linked to excess dopamine activity within the horse’s striatum. The study finds that when administered, the drug reduces the rate of cribbing overall and in some cases suppresses the behavior completely for a period of time.

Understanding Stereotypic Cribbing in Horses

• Stereotypic cribbing in horses is a cognitive condition where horses bite on fences, gates or any other object within reach and then gulp air repetitively.
• This behavior is often thought to be linked to an excess of dopaminergic activity in the region of the horse’s brain called the striatum.
• Theories concerning stress-induced stereotypies like cribbing suggest that stress triggers the release of endorphins, a type of hormones which then stimulate the release of dopamine, a neurotransmitter associated with reward and pleasure mechanisms in the brain.
• The dopamine activates motor programs within the part of the brain known as the basal ganglia, which in turn rewards and reinforces the behavior.
• Previous research suggests that dopamine’s release in response to endorphins relies on the activation of NMDA receptors, a type of receptor in the brain that allows for electrical signals to pass between neurons in the brain.

Examining the Effect of Dextromethorphan

• The study uses dextromethorphan (DM), a known NMDA receptor blocker or ‘antagonist’ which can prevent the receptor’s normal function.
• Horses identified as cribbers were treated with DM, administered through injection into the jugular vein.
• The drug dose was calibrated to 1mg/kg of the horse’s body weight.

Results and Conclusions

• The investigation found that eight out of the nine horses that were administered with DM showed a reduction in the rate of cribbing in contrast to their behavior prior to the treatment.
• Additionally, almost fifty percent of the tested horses showed a complete suppression of the cribbing behavior for a certain period after treatment.
• This suggests that DM, an NMDA receptor blocker, can have a significant impact on the rate of cribbing behavior in horses, presenting a potential pharmaceutical intervention for managing such stereotypic behavior.