Behavioral and Electrophysiological Studies on Chemoreception inAplysia

Using the typical mouth opening response (MOR) as the index of chemore-ception, several amino acid constituents of natural food for Aplysia were effective in eliciting MOR in concentrations as low is 10−6 10−7m (glutamic acid) and 10−5 10−6m (aspartic acid). It was suggested that these substances may serve as food attractants for this animal. Combined results of behavioral and electrophysiological experiments indicated that the most sensitive food receptors of Aplysia are predominantly located in the anterior tentacular groove area of the oral veil. These receptors appeared to strongly project to the caudal dark cell clusters of the cerebral ganglion. Extracellular recording of single afferent units following oral veil stimulation with various chemicals showed that the chemoreceptors in the anterior tentacular groove area were 100 to 1000 times more sensitive to food substances than other stimuli tested. It was suggested that these receptors are relatively “specific” to food attractants. There was a correlation between behavioral and electrophysiological threshold data for the individual compounds. The electrophysiological thresholds however were 5–15 times higher than the behavioral thresholds.