Modifications in the distribution of met-enkephalin in the pons of the cat, following the intravenous administration of clonidine: An immunocytochemical experimental study

Abstract

The distribution of rnet-enkephalin in the cat and its rnodifications following the stirnulation by intravenous clonidine, was studied with indirect irnrnunocytochernical techniques. We observed a decrease in the irnrnunoreactivity of rnet-enkephalin following the adrninistration of clonidine, relative to the controls, in the following structures: locus coeruleus, nucleus cuneforrnis, forrnatio reticularis, nucleus gigantocellularis, nucleus reticularis lateralis, nucleus reticularis, nucleus reticularis parvocellularis, nucleus sensorius superior n. trigernini, nucleus raphes, substantia grisea periventricularis, nucleus erninentiae teretis, colliculus inferior, nucleus rnotorius n. trigemini, nucleus tracto spinalis n. trigernini, tractus spinalis n. trigernini and nucleus tracto rnesencephalici n. trigernini. These experimental observations link the irnrnunoreactivity changes to the structures that are associated with the direct action of clonidine and conclude that the pars rnetencephalinergicus of the efferent pontine pathway of pain is in rnorpho-functional relationship with the analgesia produced by clonidine; an analgesic of an endogenous opiate character.