[The neurotransmitter basis of mollusk behavior: the control of the choice between exploratory and defensive responses to the presentation of an unknown object].

: The role of serotonin and opioid peptides in decision making was studied in the pond snail Lymnaea stagnalis. It was shown that 5-HTP increased the number of searching responses to a sudden presentation of a novel object. Opiate antagonist naloxone decreased the number of searching responses and increased the number of defensive and escape reactions. The effect of 5-HTP and naloxone on decision making appear to be coordinated with their effects on their behavioural state.