Neuropeptide Gene Expression and Behavior in Aplysia

Abstract

The relatively simple nervous system of the marine mollusk Aplysia califomica is especially suitable for examining the molecular and cellular basis of fundamental neural processes common to both invertebrates and vertebrates. The Aplysia nervous system is amenable to this kind of study because it is composed of only some 20, 000 central neurons organized into four easily accessible pairs of symmetrical ganglia and a single asymmetric abdominal ganglion. Extensive physiological studies by previous investigators have helped elucidate how individual neurons interact to achieve the level of sophistication required to coordinate the physiological, behavioral, and learning processes of this organism (reviewed by Kandel, 1979). One common theme emerging from studies of invertebrate nervous systems is the wide diversity of neurons and the precise interconnections they make to provide the neural circuitry necessary to control even relatively simple behavioral components. This diversity is thought to be due to a large extent to differential expression of the structural genes of the nervous system. Indeed, an important question is how only an estimated 10, 000 genes, in the case of Aplysia, can provide the necessary genetic information to give rise to some 20, 000 neurons as well as to the numerous cells composing the other tissues of the organism. In recent years, advances in the field of molecular biology have allowed neurobiologists to approach questions such as this by examining the genetic foundation of neural systems.