CHANGES IN STRIATAL MU-OPIOID AND DELTA-OPIOID RECEPTORS AFTER TRANSIENT FOREBRAIN ISCHEMIA - A QUANTITATIVE AUTORADIOGRAPHIC STUDY

Transient forebrain ischemia induces specific changes in several neurochemical markers in the dorsolateral striatum. In the present paper, the density and distribution of mu and sigma-opioid receptors were analyzed in rat striatum 7 days after 30 min forebrain ischemia using the 4-vessel occlusion model. A marked (about 70%) decrease in the density of both opioid receptor subtypes was found in the dorsolateral striatum overlapping the areas of histological damage and of D1 dopamine receptor disappearance. Moreover, the density of sigma-opioid receptors and of the diffuse mu-opioid receptors was also affected (30% decrease) in the ventromedial striatum, an area which is substantially spared by the ischemic lesion. In contrast, the striatal patches of mu-opioid receptors were not affected in the ventromedial striatum and were preserved to a large extent in the area of lesion, although their area and receptor density resulted markedly reduced. The impairment of both opioid receptor subtypes suggests that opiate systems, like dopaminergic systems, are involved in the neurochemical changes observed in the striatum after transient forebrain ischemia.