Is substance P necessary for corneal nociception?

Area of Science:

• Ophthalmology
• Neuroscience
• Neuropeptide Research

Background:

• Substance P (SP) is a neuropeptide involved in sensory neurotransmission.
• Rabbit corneas have few SP-containing nerve fibers but abundant acetylcholinesterase-positive fibers.

Purpose of the Study:

• To investigate the role of SP in corneal sensitivity and the blood-aqueous barrier disruption following ocular injury.
• To differentiate the functions of SP in nociception versus trauma response.

Main Methods:

• Capsaicin treatment to deplete SP in corneal nerves.
• Testing corneal sensitivity to tactile and chemical stimuli.
• Assessing blood-aqueous barrier disruption after iris irradiation.
• Administering SP antagonist, oxibuprocaine, or tetrodotoxin.

Main Results:

• Capsaicin depleted SP without affecting other nerve fibers.
• All tested treatments reduced blood-aqueous barrier disruption.
• Only oxibuprocaine and tetrodotoxin abolished corneal sensitivity.
• SP appears involved in trauma response but not corneal nociception.

Conclusions:

• SP nerve fibers are a minor component of corneal sensory supply.
• Neurogenic mechanisms for ocular injury differ from corneal nociception.
• Uveal SP plays a role in ocular trauma, while corneal SP is likely not essential for nociception.