Interactions between lysergic acid diethylamide and dopamine-sensitive adenylate cyclase systems in rat brain

Abstract

Investigations were carried out on the interactions of the hallucinogenic drug, d-lysergic acid diethylamide ( d-LSD), and other serotonin antagonists with catecholamine-sensitive adenylate cyclase systems in cell-free preparations from different regions of rat brain. In equimolar concentration, d-LSD, 2-bromo- d-lysergic acid diethylamide (BOL), or methysergide (UML) strongly blocked maximal stimulation of adenylate cyclase activity by either norepinephrine or dopamine in particulate preparations from cerebral cortices of young adult rats. d-LSD also eliminated the stimulation of adenylate cyclase activity by equimolar concentrations of norepinephrine or dopamine in particulate preparations from rat hippocampus. The effects of this hallucinogenic agent on adenylate cyclase activity were most striking in particulate preparations from corpus striatum. Thus, in 10 μM concentration, d-LSD not only completely eradicated the response to 10 μM dopamine in these preparations but also consistently stimulated adenylate cyclase activity. l-LSD (80 μM) was without effect. Significant activation of striatal adenylate cyclase was produced by 0.1 μM d-LSD. Activation of striatal adenylate cyclase by either d-LSD or dopamine was strongly blocked by the dopamine-blocking agents trifluoperazine, thioridazine, chlorpromazine, and haloperidol. The stimulatory effects of d-LSD and dopamine were also inhibited by the serotonin-blocking agents, BOL, 1-methyl- d-lysergic acid diethylamide (MLD), and cyproheptadine, but not by the β-adrenergic-blocking agent, propranolol. However, these serotonin antagonists by themselves were incapable of stimulating adenylate cyclase activity in the striatal preparations. Several other hallucinogens, which were structurally related to serotonin, were also inactive in this regard, e.g., mescaline, N,N-dimethyltryptamine, psilocin and bufotenine. Serotonin itself produced a small stimulation of adenylate cyclase activity in striatal preparations and, in relatively high concentration (100 μM), partially blocked the activation by 10 μM dopamine, but was without effect on the stimulation by 10 μM d-LSD. The present results indicate that serotonin antagonists, in general, are potent inhibitors of catecholamine-induced stimulation of adenylate cyclase systems in brain cell-free preparations. In addition, these results, coupled with earlier findings on the capacity of d-LSD to interact with serotonin-sensitive adenylate cyclase systems from rat brain 23,24 and other neural systems 16, strongly suggest that this hallucinogenic agent is capable of acting as an agonist at central dopamine and serotonin receptors, as well as functioning as an antagonist at dopamine, norepinephrine, and serotonin receptors in the brain.