Abstract
ABSTRACT
Clonidine (3-300 μg/kg, i-p.) produced dose-dependent pupillary dilation in unanesthetized rats. At low levels of illumination (30 lux), this effect was similar to that seen in anesthetized animals but was diminished under higher ambient lighting conditions. αMethyldopa (60 mg/kg, i.p.) produced mydriasis that took several hours to develop and was prevented by pretreatment with a dopamine β-hydroxylase inhibitor (FLA-63). Yohimbine antagonized pupillary dilation induced by both clonidine and methyldopa. These results demonstrate that mydriasis in the conscious rat can be an effective index of CNS α2-adrenoceptor activation, particularly when measured under low lighting levels.
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