Pupillary function test in rat: Establishment of imaging setup and pharmacological validation within modified Irwin...

Area of Science:

• Pharmacology
• Ophthalmology
• Neuroscience

Background:

• Pupillary function is a key indicator of drug effects in humans.
• Rodent pupillary responses to drugs are not well understood, hindering preclinical research.
• Improved methods are needed to quantify pupillary responses in conscious rodents.

Purpose of the Study:

• To develop and validate a novel camera-based method for assessing pupillary function in conscious rats.
• To investigate the effects of known human-acting reference compounds on rat pupil and iris diameter and light reflex.
• To compare pupillary responses between albino and pigmented rats.

Main Methods:

• A camera-based pupillary imaging system was developed for conscious rats under red-light conditions.
• Reference compounds (pilocarpine, tropicamide, phenylephrine, clonidine, cocaine, morphine) were administered topically and/or systemically.
• Pupil diameter and light reflex were measured to assess drug effects.

Main Results:

• The method successfully detected drug-induced changes in pupil diameter and light reflex in both albino and pigmented rats.
• Albino rats primarily showed mydriasis, while pigmented rats exhibited both mydriasis and miosis.
• Strain-specific pharmacological responses were observed, with pigmented rats showing more human-like responses.

Conclusions:

• The developed pupillary imaging system is a valuable tool for assessing drug effects on pupillary function in rodents.
• Rat pupillary responses to drugs are strain-dependent and cannot be directly extrapolated to humans.
• Quantifying pupillary changes in rats can serve as a functional endpoint in early drug development and safety pharmacology.