Amino acid-induced reflexes and their neural pathways in an opisthobranch mollusc Pleurobranchaea japonica

Abstract

Certain behavioral acts of Pleurobranchaea japonica may be elicited in response to chemical stimulants applied to the rhinophores, tentacles or oral veil. These include feeding and escape. Upon treatment with chemical stimulants, the organs respond directly by extending or withdrawing. Beyond this, aversive responses involved withdrawal of the rhinophores, tentacles and oral veil plus contraction of the whole body. Feeding behavior was elicited by glycine, phenylalanine, proline, aspartic acid, alanine, asparagine, tryptophan and glutamine. An aversive response was induced by glutamate. Neural pathways responsible for these chemoreceptive reflexes have been identified. In addition to known nerves, a newly identified pair of nerves, the second pedal nerves arise from the pedal ganglion and send branches to the three organs. The nerves contain afferent pathways for chemoreception of the organs and efferent motor pathways for the movements of the organs. The rhinophore ganglion is responsible for the glutamate-induced contraction of the rhinophore. This withdrawal reflex of the rhinophore is under inhibitory control, exerted by the cerebral ganglion through the rhinophore nerve, and under an excitatory influence, emanating from the pedal ganglion through the second pedal nerve.