The Mu opioid receptor is responsible for the following effects except (DNB Dec 2012)
a. Morphine and most mu and kappa agonists cause constriction of the pupil by an excitatory action on the parasympathetic nerve innervating the pupil.
b. Morphine like opioids depress respiration, at least in part by virtue of a direct effect on the brainstem respiratory centers. The primary mechanism of respiratory depression by opioid involves a reduction in the responsiveness of the brainstem respiratory centers to carbon dioxide.
Opioids also depress the pontine and medullary centers involved in regulating respiratory rhythmicity and the responsiveness of the medullary respiratory centers to electrical stimulation