Neurochemical mechanisms of consolidation of associative aversive learning to food in the common snail.

Studies of the effects of the protein synthesis inhibitor cycloheximide and serotonin and NMDA glutamate receptor antagonists on the processes of consolidation of the associative skill of rejecting particular foodstuffs were performed in the common snail. The skill was not acquired when animals were trained on the background of cycloheximide. Repeated training of "amnestic" snails to reject the same foodstuff in the absence of the inhibitor also failed to produce learning. Training of snails on the background of the nonselective serotonin receptor antagonist methiothepin or the NMDA glutamate receptor antagonist MK-801 (dizocilpine maleate) did not result in the acquisition of the conditioned reflex to food. However, repeated training led to the rapid formation of the skill. These experiments provide the first evidence that interventions influencing different molecular mechanisms during a single type of training produce either reversible or irreversible impairment of the mechanisms of consolidation of long-term memory. It is suggested that the reversible effect is associated with suppression of reproduction processes, while irreversible impairment was associated with impairments to engram storage.