Topographical distribution of dopaminergic innervation and of dopaminergic receptors in the rat striatum. II. Distribution and characteristics of dopamine adenylate cyclase--interaction of d-LSD with dopaminergic receptors.

The characteristics of dopamine adenylate cyclase in the rat striatum were first studied on homogenates of fresh tissues. In the assay conditions used, dopamine (10(-4) M) stimulated the enzyme activity by 250%. This effect was completely blocked by fluphenazine (10(-5) M; Ki=9X10(-9) M) and by phentolamine (10(-5) M; Ki=3 X 10(-7) M). D-LSD stimulated the adenylate cyclase activity (Km=1.4 X 10(-7) M) by interacting with dopamine receptors; indeed the dopamine effect on the enzyme activity was competitively reduced in presence of D-LSD. L-Isoproterenol (Km=10(-6) M) activated an adenylate cyclase through a receptor distinct form the dopaminergic receptor; this stimulation was not affected by fluphenazine or phentolamine but suppressed by DL-propranolol (10(-4) M). The topographical distribution of the dopamine, D-LSD and L-isoproterenol adenylate cyclase activities were examined in homogenates prepared from discs punched out on serial frozed (--7C) slices of the striatum. Under this condition, tge dioanube naxunak stunykatuib was if 150%. A 4.8-fold progressive decrease in the amount of cyclic AMP produced in presence of dopamine (10(-4) M) was observed in the rostrocaudal plane of the structure; the decline of the basal activity was 3.6-fold. The topographical curves of maximal activation of adenylate cyclase by dopamine and D-LSD were superimposable confirming that D-LSD acts on dopaminergic receptors. This topographical distribution of dopamine sensitive adenylate cyclase is comparable on one hand to that of endogenous dopamine and on the other hand to that of the dopamine high affinity uptake activity measured in simultaneous experiments. In contrast to that observed with dopamine or D-LSD, the topographical distribution of the adenylate cyclase sensitive to L-isoproterenol was homogenous within the striatum.