Edinger-Westphal nucleus, opioids

Opioids elicit pupiiiary narrowing (miosis) by stimulating the parasympathetic portion (Edinger-Westphal nucleus) of the oculomotor nucleus. 

Miosis, or the pinpoint pupillary response to the opioids, is diagnostic of the use and abuse of the opioids. No tolerance to such an effect is observed. Miosis is due to disinhibition of the Edinger-Westphal nucleus in the cortex resulting in increased pupillary constrictor tone. 

Central nervous system depression is the usual effect of morphine, and sedation and drowsiness are frequently observed with therapeutic doses. When given in the absence of pain morphine may sometimes produce dysphora—an unpleasant sensation of fear and anxiety. The most important stimulatory effects of morphine in man are emesis and miosis. Miosis, due to stimulation of the Edinger-Westphal nucleus of the third nerve, occurs with all opioids. The combination of pinpoint pupils, coma, and respiratory depression are classical signs of morphine overdosage. Stimulation of the solitary nuclei may also be responsible for depression of the cough reflex (antitussive effect). Pharmacokinetics and metabolism... 

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See also in sourсe #XX -- [ ]

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