Opposing effects of dopaminergic to cholinergic compounds on a cerebral dopamine-activated adenylate cyclase.

Abstract

We have studied these possibilities in the hope of advancing the treatments of Parkinson's disease and of psychosis. To this end we used adenylate cyclase from mouse caudate to screen agents that can affect the symptoms of Parkinson's disease. These included drugs that stimulate the dopaminergic system in man or animals and inactive metabolites and precursors thereof and compounds that activate or inhibit the cholinergic system, which counterbalances the dopaminergic one in the brain (7,8).MATERIALS AND METHODS Animals. These were 5-to 6-week-old male Swiss albino mice, weighing 23-27 g, maintained on Purina Chow and water ad lib., and kept in an air-conditioned room on a 12-hr lightto-darkness cycle. The experiments were started in midday by decapitating the animals in a cold room. The brains were removed within 30 sec and placed on a cold watch glass. The lateral ventricles were entered by removing their roofs. The exposed heads of the caudates were scooped out with forceps.Determination of Dopamine-Stimulated Adenylate Cyclase Activity. The methods are essentially those developed in Greengard's laboratory (9). All fragments of both caudates (about 30 mg) were placed in Krebs-Ringer bicarbonate solution, pH 7.4, which had been gassed for 2 min with 5% CO2/ 95% 02. They were homogenized in 0.5 ml of 50 mM Trismaleate buffer, pH 7.4, containing 12.5 mM theophylline, 0.25 mM ethylene glycol-bis(Q-aminoethyl ether)-NN'-tetraacetic acid, and 2.5 mM MgSO4. Aliquots (0.4 ml) of the homogenates were placed in 5-ml Pyrex tubes that had previously been equilibrated to 30°in an orbital water bath. The control tubes received 50 gl of H20. The experimental tubes received different additives in different series of experiments, the concentrations of which are given below. In one series, 50 ,ul containing either dopamine or a dopaminergic substance was added. In another series, the tubesi received 25 ,ul containing one of the above substances plus 25 jul containing-an inhibitor, a metabolite, or a precursor thereof. In another series, the precursors and metabolites were tested in various concentrations for activation of the cyclase. In still another series, the metabolites were screened for inhibition of the dopamine-dependent activation. Finally, some cholinergic and anticholinergic agents were screened for activation or inhibition of the cyclase.The reaction was started by adding 50 jul of a 0.5 mM solution of ATP with mixing and then incubating in a 30°orbital water bath. After 2.5 min, the reaction was terminated by immersion of the tubes into a boiling water bath for 2 min. The homogenates were centrifuged at 1500 X g for 5 min. The supernatant solutions were quick-frozen until analyzed for adenosine 3': 5'-cyclic monophosphate (cyclic AMP) according to Gilman (10).The results of the cyclic AMP determinations were used as follows. We first computed the mean ±SEM of both nonstimulated and stimulated samples. From these we calculated the net dopamine-stimulated cyclic AMP produced by subtracting the mean nonstimulated acti...

Muscarinic Receptors Modulate Dopamine‐Activated Adenylate Cyclase of Rat Striatum

“…Moreover, the inhibitory effect was a property of cholinergic agonists that was not shared by cholinergic antagonists. The pharmacological profile of the muscarinic attenuation of adenylate cyclase in rat striatum is therefore different from that described by Tang and Cotzias (1977) in mouse striatum, in which both cholinergic agonists and antagonists competitively inhibited the DA-activated adenylate cyclase. Further, ACh had no effect on the activation of adenylate cyclase by PIA, an adenosine A2 receptor agonist, indicating that the inhibition of the DA-activated enzyme was not the re-…”