The objective of this study is to provide some fundamental data regarding degenerative and possible regenerative changes in the mammalian central nervous system. The first part involves a study of axonal sprouting of dorsal roots in the spinal cord and medulla after chronic primary deafferentation and utilizes the Nauta-Gygax and Fink-Heimer silver methods in conjunction with the autoradiographic method for tracing neuroanatomical connections. This part of the investigation is being undertaken because of controversy regarding the contradictory evidence for sprouting as seen in light microscopic studies in the adult animals. The second part involves a study of the descending connections from the brainstem to the spinal cord, with particular emphasis on central autonomic pathways using the anterograde axonal transport of various marker material as well as immunohistochemical techniques. The third part involves a study of autonomic pathways in the spontaneously hypertensive rat and the potential effects of 6-hydroxydopamine on these pathways that might be related to blood pressure control.