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)