Opposite pupillary size effects in the cat and dog after microinjections of morphine, normorphine and clonidine in the Edinger-Westphal nucleus

The Edinger-Westphal complex (EW) was explored as a possible site of action for the effects of morphine and clonidine to produce mydriasis in the cat and miosis in the dog. Morphine, normorphine and clonidine, dissolved in 0.5 μl 0.9% NaCl, were injected via chronic indwelling cannulae into or near the EW of the restrained cat and dog. In the cat, all 3 drugs produced a dose-dependent mydriasis. Clonidine (3–30 nmol) was 1.7 times more potent than normorphine (3–30 nmol) and 9.6 times more potent than morphine (10–60 nmol). Normorphine was 5.5 times more potent than morphine. Significant miosis resulted from single doses of morphine (17.5 nmol), normorphine (15.5 nmol) and clonidine (19 nmol) injected in the EW of the dog. Injections sites closest to the EW yielded the greatest changes in pupillary diameter. Naloxone antagonized the pupillary effects of normorphine in the cat and dog but had no effect on clonidine mydriasis in one cat. It was concluded that the EW region is an important site of action for the effects of morphine and clonidine on pupil diameter in both species. However, the neurocircuitry and neurochemistry of the EW probably differ between the cat and dog.