Pathfinding by Arthropod Sensory Nerves
In the cellular sociology of Metazoa, no cells discriminate in their associations more than neurons. It is true that positional individuality may be highly developed in other epithelia such as insect epidermis or in embryonic primordia, but neurons are unique in expressing specificity in contacts often much removed from near neighbors. Just how specific and how flexible neuronal relations must be and how they are achieved have long been focal questions in neurobiology. And yet, despite contributions of well-known experimental studies exploring development and regeneration in the lower vertebrate visual system by Sperry, Gaze, Jacobson, and others (Hunt and Jacobson, 1974), there is much contention about the significance of such things as chemical specificity, the nature of gradients in space and time, and trial and error and functional validation as causal mechanisms. One reason why so many elegant experiments should lead to such an impasse is the level of resolution that can be achieved in measuring specificity. Most studies are concerned with populations rather than individual neurons. Other approaches to neural development include experimental modification of the developmental milieu of such well-known cell types as are found in the cerebellum (Sidman, 1974). But with the exception of the Mauthner neuron (Hibbard, 1965), single-cell interactions have been beyond the resolution of vertebrate studies.
KeywordsImaginal Disk Thoracic Ganglion Sensory Axon Mauthner Neuron Giant Fiber
Unable to display preview. Download preview PDF.