In Vivo Evidence that Nonneuronal β‐Adrenoceptors as Well as Dopamine Receptors Contribute to Cyclic AMP Efflux in Rat Striatum

Abstract

We applied in vivo microdialysis to assess the effects of dopaminergic and beta-adrenergic receptor stimulation on cyclic AMP efflux in rat striatum under chloral hydrate anesthesia. Dopamine (up to 1 mM) infused for 20 min through the probe did not increase cyclic AMP, whereas both the selective dopamine D1 agonist SKF 38393 and D2 antagonist sulpiride produced modest increases. It is interesting that the beta-adrenoceptor agonist isoproterenol produced a marked increase (204.7% of basal level at 1 mM) which was antagonized by the beta-adrenoceptor antagonist propranolol. Pretreatment with a glial selective metabolic inhibitor, fluorocitrate (1 mM), by a 5-h infusion through the probe attenuated basal cyclic AMP efflux by 30.3% and significantly blocked the response to isoproterenol. By contrast, striatal injection of a neurotoxin, kainic acid (2.5 micrograms), 2 days before the dialysis experiment did not affect basal cyclic AMP or the response to isoproterenol, but blocked the response to SKF 38393. These data demonstrate the beta-adrenoceptors as well as dopamine receptors contribute to cyclic AMP efflux in rat striatum in vivo. They also suggest that basal and beta-adrenoceptor-stimulated cyclic AMP efflux are substantially dependent on intact glial cells.