Increase of ryanodine receptors by dopamine D1 receptors is negatively regulated by γ-aminobutyric acid type B receptors in primary cultures of mouse cerebral cortical neurons

摘要

Although upregulation of ryanodine receptor (RyR)-1 and -2 is mediated through the activation of dopamine D1 receptors (D1DRs) in the development of psychostimulant-induced place preference, little is known about how such increased expressions of RyRs are negatively regulated. This study investigated negative regulatory mechanisms of increase of RyR-1 and -2 expression by D1DR stimulation with its full agonist, SKF82958 or A 68930, using cultures of mouse cerebral cortical neurons. Sustained exposure to SKF82958 or A 68930 of the neurons increased RyR-1 and -2 proteins in a dose- and time-dependentmanner. The SKF82958-induced increases of RyR-1 and -2 proteins were significantly suppressed by SCH23390 (a selective D1DR antagonist). In addition, the SKF82958- or A 68930-induced increases of RyR-1 and -2 proteins were completely abolished by baclofen (a selective γ-aminobutyric acid type B [GABA B] receptor agonist), whereas muscimol (an agonist specific to GABA A receptors) had no effect. SKF82958 or A 68930 significantly increased intracellular cAMP level, which was completely suppressed by baclofen. Furthermore, sustained exposure to phorbol 12,13-dibutyrate, a protein kinase C activator, did not change the expression of RyR-1 or -2 proteins. Immunohistochemical study showed colocalizaton of immunoreactivities for three types of proteins, D1DRs and GABA B receptor R1 and R2 subunits in the same neuronal bodies, suggesting that the neurochemical changes induced by the activation of D1DRs and GABA B receptors occur in the same neurons. These results indicate that RyR-1 and -2 expression facilitated by D1DR stimulation are negatively regulated by GABA B receptor via suppression of cAMP production.