Physiological properties of vertebrate nerve cells in tissue culture.

Vertebrate neurons in tissue culture are providing us with a new model system for studying the complex events which occur during neuronal differentiation, synaptogenesis, and neural network formation. It is already apparent that dissociated embryo neurons are capable of differentiating both morphologically and physiologically along predetermined lines in the absence of external influences. These neurons can form new connections with one another but retain some specificity in their selections. Both simple and complex neural networks can be seen. At the present time, the development of the invitro model system is just being explored. The potential value of a system of this kind at a variety of investigative levels should be appreciated. Questions of a fundamental nature in neurobiology, such as how synapses form, what rules govern such interaction, how cells recognize one another, and the nature of the basic two-, three-, or four-cell circuits that comprise the more complex neurons tissue can be approached with this system. Studies of the neurons and synapses themselves can lead to a more basic understanding of vertebrate nervous system functioning. The development of certain pathophysiological processes and the effects of neuroactive drugs on vertebrate neurons may be studied at the cellular level. Finally, the basic mechanism of some genetic abnormalities which produce abnormal nervous structure and function may be more easily determined in a simplified in vitro model than in the intact central nervous system. The value of any model is not inherent in the elegance of the model itseld, but only in its ability to suggest answers to fundamental questions about the system being modeled. Many fundamental questions about brain mechanisms in mental retardation remain unanswered. Perhaps some day the model of nerve cells in tissue culture will bring us closer to the answers to these questions.