This project is part of a long-term study to determine the sequence and pattern of development of spinal neurons from the neuroblast stage to the adult. The objective of the research is to determine the relationship between a neuron's time of origin and its ultimate functional properties. The specific aim is to determine the birth dates (time of final cell division) of various types of neurons in the upper lumbar spinal cord defined by their 1) axon projection, and 2) neurotransmitter. To accomplish this aim, two sets of experiments have been devised which combine tritiated thymidine autoradiography (for birth date determination) on the same tissue sections with tract tracing and immunohistochemical techniques. The first experiment will employ tract tracing techniques using Fluoro-Gold, Rhodamine microspheres and/or HRP in conjunction with tritiated thymidine autoradiography to determine the relationship between a neuron's projection (i.e., ascending tract, long propriospinal , short propriospinal, etc.) and its time of origin. The second experiment will employ tritiated thymidine autoradiography and immunohistochemistry to determine the relationship of a neuron's time of origin with its neurotransmitter substance. From the data produced, distribution maps of the spinal gray matter will be made which show the location, relative number, and distribution of neurons characterized according to their time of origin, size, shape, axon projection, and neurotransmitter. This study is unique in that it is the first comprehensive examination of neurogenesis in a single CNS center which will demonstrate the proliferative period of specific types of neurons defined by functional parameters. This research is clinically significant because it will provide a more complete understanding of the neuronal organization of an area directly involved in the transmission of sensory information including pain, and it is important because it will examine local neuronal interactions. Determining the chronological order of developing neurons is a first step in approaching the problem of how neurons interact during development. The results of this research will be important when choosing appropriate embryonic stages for intraspinal transplants in spinal cord regeneration experiments and will be of value when studying the interruptive effects that various teratogens have on the proliferation and maturation of specific types of neurons.
