The ergot alkaloids studied do exert selective effects on monoamine receptor 
systems. Lisuride acts as a very potent stimulator of adenylate cyclase in 
cortical brain regions, and may function as a mixed agonist-antagonist at high 
concentrations. It is most likely that in cortex, lisuride effects both dopamine 
and serotonin receptors, but predominantly serotonin receptors coupled to 
adenylate cyclase. The antagonist molindone exhibits selectivity for cortical 
serotonin-stimulated cyclase versus dopamine-stimulated cyclase and may prove 
useful for further elucidating the sites of lisuride action. LSD interacts with 
serotonin-stimulated cortical adenylate cyclase at higher concentrations than 
are needed for lisuride stimulation but, nevertheless, at lower concentrations 
than for serotonin itself (2-4). Bromocriptine, lergotrile and ergonovine may 
also act as agonists in stimulating adenylate cyclase, but with considerably 
less potency, and with differences in regional specificity for this stimulation, 
from lisuride and LSD. Each of these ergots may act as a mixed 
agonist-antagonist at high concentrations. With respect to the regions studied, 
antagonist effects on cyclase appear to be more prominent in striatum than in 
the cortical regions. The greater specificity of lisuride for serotonergic 
cortical receptors should make this compound useful in further studies of this 
system.