Opioid mu and delta and dopamine receptor number changes in rat striatum during stress

The question whether acute and repeated immobilization stress is accompanied by changes in the number of opioid mu- and delta- -receptor and that of dopamine receptor in the rat corpus striatum was studied. The number of opioid mu- and delta-receptors as well as that of dopamine receptors was estimated in corpus striatum of rats subjected either to a single (acute) immobilization stress (IMO) for 150 min or to identical repeated stress exposure for 7 or 40 consecutive days. The number of mu-receptors was estimated by the use of 3H-dihydromorphine binding (an agonist) or 3H-naloxone binding (an antagonist). Increased number of mu-receptors was found after acute IMO as estimated from the binding of both mu-specific ligands. However, the binding of 3H-dihydromorphine showed no changes after 7x and elevated mu-receptor number after 40x repeated IMO, although the binding of 3H-naloxone after 7x and 40x IMO was decreased. This paradoxical pattern might be explained by different affinity of both ligands to mu-receptor subpopulations (i.e. mu1- and mu2-receptors). In addition, the number of delta-receptors (assayed by 3H-D-Ala2,D-Leu5-enkephalin binding) was increased after acute as well as repeated (7x and 40x) IMO. The changes of dopamine receptor number (as measured from 3H-spiroperidol saturation analysis) correlated well with delta-receptor changes after 1x and 7x repeated IMO, but not after 40x IMO, since in the latter group the number of dopamine receptors decreased.(ABSTRACT TRUNCATED AT 250 WORDS)