Facilitation of defense reactions during the consumption of food in snails: The participation of glucose and gastrin/cholecystokinin-like peptide

The molecular-cellular mechanisms of the interrelationships between the alimentary and defense behavior of snails were investigated. The clarity of manifestation of defense reactions at various stages of the satisfaction of alimentary need was studied. It was found that the defense reactions were attenuated in starved molluscs, whereas after a 20-minute feeding session the facilitation of generalized defense reactions takes place, the clarity of manifestation of which depends on the duration of food deprivation. It was demonstrated that an increase in the level of glucose in the hemolymph of the starved molluscs to the level present in the hemolymph during a meal (1.6-2.0 mM), as well as the administration of 20-30 ng of analogs of gastrointestinal peptides (pentagastrin or cholecystokinin octapeptide, CCK-8) elicits the facilitation of generalized defense reactions similar to that found during the feeding of the snails. The directionality of the changes in the activity of the L-RPl 1 neurons during the application of carrot juice to the lip of semi-intact preparations of starved snails depended on the presence of glucose in the solution bathing the central nervous system. Similar glucose-dependant changes were found after the application of CCK-8 to the CNS of starved snails, but not of FMRFamide, whereas the isolated application of glucose did not exhibit such an effect. It was found that the L-RPl1 neurons were the most sensitive to the change in the concentration of glucose and CCK-8 in the perfusate. The adaptive significance of the dependance of the clarity of manifestation of defense reactions on the level of alimentary need of the snails and the participation of glucose and gastrin or cholecystokinin-like peptide in these processes are discussed.