In the next 12-month period it is planned to concentrate on the source of axo-axonic synapses on P.A. endings and of the components of glomeruli, employing a modification of the methodology originally described in Protocol 1, items B and D. Electrolytic lesions will be made in the reticular substance of the medulla (N. gigantocellularis) and in the other experiments in the hilus of the N. proprius as described in item C. Primary afferents will be labeled with radioactive amino acids injected into the appropriate dorsal root ganglia; in this manner the relatively small numbers of descending fibers will all be identifiable and the vagaries of radioautographic labelling will be limited to the much better known dorsal root system. In addition, a study of convergence on dorsal horn interneurons in C1 and C2 from the segmental level and from the trigeminal root system using the above described double labeling technique will be carried out. The latter is of particular interest from the standpoint of mechanisms of referred pain in clinical situations.