Electrically elicited blink reflex in horses with trigeminal and facial nerve blocks.

The research article presents an evaluation of electrically induced blink reflexes in horses, providing reference values for the components and discussing the applicability of the blink reflex as a diagnostic tool for assessing peripheral nervous system dysfunctions involving the trigeminal and facial nerves.

Research Methodology

• A total of 10 healthy adult horses, comprising of 8 males and 2 females with no reported neurologic abnormalities, were utilized in this study.
• The blink reflex tests were conducted by electrically stimulating the supraorbital (trigeminal) nerve and facial (auriculopalpebral) nerve.
• Changes in these reflexes and direct muscle-evoked potentials were examined in the orbicularis oculi muscles, which control the eyelid movement. These changes were recorded using needle electrodes inserted into these muscles.
• Local anesthetic blocks using lidocaine hydrochloride injections were performed to the supraorbital and auriculopalpebral nerves.

Research Findings

• The supraorbital nerve stimulation resulted in 2 or 3 ipsilateral (same side) and 1 contralateral (opposite side) reflex muscle potentials in the orbicularis oculi muscles.
• The auriculopalpebral nerve stimulation generated a direct and reflex muscle potential in the ipsilateral orbicularis oculi muscle.
• Post supraorbital nerve block, no muscle responses could be recorded on either side upon stimulating the blocked nerve. However, bilateral responses were observed upon stimulation of the non-blocked supraorbital nerve.
• A successful block of the right auriculopalpebral nerve resulted in absence of responses from the right orbicularis oculi muscle upon stimulation of either of the supraorbital nerves.

Conclusions

• The study concluded by highlighting that the reference values established for the components of the blink reflex and the facial motor nerve conduction velocity could be valuable for diagnosing equine neurologic disorders involving the trigeminal and facial nerves, the brainstem, and the cranial end of the spinal cord.
• The researchers advocate for the use of blink reflex tests in horses to diagnose peripheral nerve dysfunctions specifically of the trigeminal and facial nerves.