A properly functioning brain requires development of the most highly precise connectivity known among cells. Assembly of such specific neural circuits during development depends on two very different kinds of mechanisms. First, individual neurons (nerve cells) carry molecular labels that determine the outlines of the circuit to be assembled; the mechanism called chemoaffinity allows the growing processes of a cell to "recognize" the molecular label on the proper target cells. Second, there are ways in which this assembly from chemoaffinity can be modified. Nervous systems are dynamic structures, and the wiring diagrams may be affected by competition between cells for available contact sites, by internal irregularities and by different environmental circumstances acting on the animal. This project is a high resolution examination of the dynamic aspects of circuit assembly. A model system, the cricket, has been chosen because it contains large identifiable single neurons that have been well defined for their detailed structure, specific connections, and physiological properties. In crickets, the growth stages are well defined, and regeneration of processes allows examination of connection formation at a variety of stages. Some of the defined circuits in the cricket are relatively simple structures that are very accessible for physiology and anatomy. The synapses, which are the functional sites of communication between nerve cells, will be examined to see whether the physiological transmission of signals changes during maturation, whether there are changes at the ultrastructural in these synapses during reorganization, whether the incoming process controls the strength of the synapse, and whether the strength of different terminals depends on competition of some sort. Results will have an impact on both developmental biology as well as neuroscience; the need for fine tuning of connections is a hallmark of all nervous systems.
