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 microliter
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.