Previous studies of the dendritic structure of neurons have predominantly relied on the century-old Golgi methods and the technique of injecting biological markers into single neurons in vivo. For technical reasons, however, it has been difficult to effectively combine these methods with other neuroanatomical labeling techniques. The recently introduced method of intracellularly injecting a fluorescent dye, Lucifer yellow, in fixed tissue slices is capable of providing a complete picture of neuronal geometry and has the potential for use in conjunction with other neuroanatomical techniques. This project involves intracellular injection of Lucifer yellow in combination with retrograde labeling techniques and immunohistochemistry, and its objective is to extend the analysis of neuronal connectivity and transmitter specificities to a finer level than previously possible. Initially two questions will be addressed: (1) is there a point-to- point reciprosity between thalamocortical axon collaterals that innervate the thalamic reticular nucleus and the neurons in the nucleus which project back to the thalamus; and (2) where on the dendrites of retricular nucleus neurons do thalamocrotical axon collaterals terminate?