The nervous system contains a stereotyped complement of neurons with different properties. Neurons have different shapes, respond to and release different biochemical messengers, and exert their effects on unique subsets of target neurons. The processes underlying the development of this neuronal specificity will be investigated in the simple nervous system of the grasshopper. The investigator has previously characterized a group of 100 midline neurons that arise from a single identified precursor stem cell. This group of neurons contains three basic cell types that function in different sets of behaviors. It will be determined how the final complement of neurons in the group arises temporally during development, over what time course neurons are added to the population and when and to what extent cell death reduces the population to its final size. In addition, the birthdays of identified neurons, i.e. the timing of a neuron's final cell division, will be correlated with cell lineage to test the hypothesis that birth order and cell type are related, with sequential switches occurring during development to produce efferent neurons, local interneurons, and then intersegmental interneurons. Differential staining of cell types and birthdating of individual neurons by labeling DNA during cell divisions will be applied. The system is unique in the high degree of resolution for identifying individual neurons of a population and the potential for spanning several levels of inquiry in studying the relationships between developmental events and the functioning of mature neuronal circuits. The study of neurogenesis in this simple nervous system that is easily accessible to experimental manipulation promises to increase our general knowledge of processes involved in the formation of different kinds on neurons.
