Monoaminergic neuronal systems have been implicated in the mechanisms of action of most ergot derivatives (including those that are clinically useful and those that are "hallucinogenic"). Among the various assays that have been useful in determining the extent of such involvement is drug discrimination. In this procedure, animals are trained to respond in one way (e.g., press the right lever) following saline and to respond differently (e.g., press the left lever) after either a particular ergot or a neurotransmitter agonist, and are subsequently tested with other ergots, transmitter agonists or antagonists (alone or in combination with the training drug). The results to date indicate that: 1) There are similarities in the discriminable effects of lergotrile, lisuride and bromocriptine, which probably involve catecholaminergic neuronal systems (DA or NE). 2) These effects are clearly separable from those of ergonovine and LSD, which may be relatively more serotonergic. More precise delineation of the mechanisms underlying these cues (e.g., D1, D2-selective agonism, antagonism, etc.) awaits further testing with highly specific pharmacological interventions.
The degree of suppression of on-going, food-motivated behavior induced by punishing electric shock was exponentially related to the intensity of the aversive stimulus. No evidence for recovery from these effects during punishment sessions was observed.
