DELTA-OPIATE AND KAPPA-OPIATE RECEPTORS IN PRIMARY ASTROGLIAL CULTURES .2. RECEPTOR SETS IN CULTURES FROM VARIOUS BRAIN-REGIONS AND INTERACTIONS WITH BETA-RECEPTOR ACTIVATED CYCLIC-AMP

In a previous paper, delta and kappa-opiate receptors were shown to be co-localized on the same cell in enriched primary cultures of astroglia from neonatal rat cerebral cortex. Activation of the receptors inhibited adenylate cyclase. In this work, the presence of opiate receptors was investigated in astroglial primary cultures from neonatal rat striatum and brain stem. Cyclic adenosine 3',5'-monophosphate accumulation was quantified in the presence of different opioid receptor ligands after stimulation of the cyclic adenosine 3',5'-monophosphate system with forskolin. Morphine was used as a mu-receptor agonist. [D-Ala2, D-Leu5]-enkephalin or [D-Pen2, D-Pen5]-enkephalin were used as delta-receptor agonists and dynorphin 1-13 or U-50,488H were used as kappa-receptor agonists. Specific antagonists for the respective receptors were used. After striatum or brain stem cultures had been incubated in 10(-9) - 10(-5)M of each [D-Ala2, D-Leu5]-enkephalin, [D-Pen2, D-Pen5]-enkephalin and Dynorphin 1-13 or U-50,488H, dose related inhibitions of the 10(-5)M forskolin stimulated cyclic adenosine 3',5'-monophosphate accumulation were observed. The changes were reversed to the forskolin-induced control level in the presence of the respective antagonists. 10(-9) - 10(-5)M morphine did not significantly change the forskolin-induced accumulation of cyclic adenosine 3',5'-monophosphate in the cultures studied. Furthermore, cultures from cerebral cortex, striatum or brain stem were incubated with isoproterenol alone or together with morphine or [D-Ala2, D-Leu5]-enkephalin. Isoproterenol stimulated cyclic adenosine 3',5'-monophosphate accumulation more prominently in the cerebral cortex and striatum cultures than in the brain stem cultures. Morphine did not influence isoproterenol-induced cyclic adenosine 3',5'-monophosphate accumulation, while [D-Ala2, D-Leu5]-enkephalin inhibited the accumulation. The results indicate that astroglial cells in primary cultures from striatum, brain stem and cerebral cortex express-delta and kappa-opioid receptors linked to the adenylate cyclase/cyclic adenosine 3',5'-monophosphate system. No mu-receptors were detected, however, in the present model. Aspects of the relation between the expression of opioid peptides and opioid receptors are discussed, while speculations are also made on the functional aspects of opioid receptors on astroglia.