Opioids Regulate Cgmp Formationin Cloned Neuroblastoma Cells
Proc. NatL. Acad. Sci. USA Vol. 79, pp. 690-694, January 1982 Neurobiology Opioids regulate cGMP formation in cloned neuroblastoma cells (cyclic nucleotides/opiate receptor/desensitization) GERMAINE J. GWYNN AND ERMINIO COSTA* Laboratory of Preclinical Pharmacology, National Institute of Mental Health, Saint Elizabeths Hospital, Washington, D.C. 20032 Communicated by Floyd E. Bloom, October 8, 1981 ABSTRACT Opioid agonists caused a rapid dose-related el- cumulation in rat striatal slices with characteristics that fulfill evation of the cGMP content of N4TG1 murine neuroblastoma the criteria for a specific narcotic action (6). In contrast, the cells. An excellent correlation was found between the rank order decrements in the cGMP content ofcerebellar tissue observed of potency of agonists in stimulating cGMP accumulation and in after morphine administration are probably indirect effects of displacing [3H]etorphine ([H]ETP) bound to intact cells. The nar- opioid receptor stimulation mediated by the modulation of y- cotic antagonists naloxone and diprenorphine failed to increase aminobutyric acid or acetylcholine collateral neuronal loops (7, cGMP content; moreover, in the presence of 5 ,IM naloxone, the 8). A functional role for cGMP in opioid action is further sug- EC50 of ETP increased from w9 nM to >1 ,uM. N4TG1 cells that had been incubated for 20 min with 0.32 ItM ETP and thoroughly gested by the pivotal role that calcium ions play both in regu- washed displayed a marked loss in sensitivity to subsequent ETP lating cGMP formation (for review, see refs. 9, 10) and in me- challenge. This desensitization was characterized by a 40-50% diating the acute and chronic effects ofopioids (for review, see decrease in maximal response and an increase in the apparent Ka refs.
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