EVOLUTION OF MORPHOLOGICAL AND HISTOCHEMICAL-CHANGES IN THE ADULT CATCUNEATE NUCLEUS FOLLOWING FORELIMB DENERVATION

Morphological and histochemical changes were studied in the ipsilatera l cuneate nucleus between one and 52 weeks after forelimb denervation in adult cats. The deafferented nucleus and neighboring fasciculus wer e noticeably reduced in size within four weeks and decreased further b y 13 weeks. The intensity of acetylcholinesterase staining decreased w ithin one week and was further reduced one month after nerve transecti ons. This reduction in acetylcholinesterase staining was transient, ap proaching control levels within one year. Parvalbumin immunostaining w as also altered by the nerve transections; on the deafferented side, t he neuropil staining in the cuneate nucleus and fasciculus decreased, but the number of parvalbumin-positive cells was consistently greater than in the contralateral side. These cell counts returned to normal l evels within one year. One month after the injury, cytochrome oxidase activity was reduced. This reduction persisted and was even more appar ent after one year. In parallel, the cell clusters of the nucleus beca me progressively less distinct. These observations in an adult mammal indicate that peripheral nerve injury imposes molecular and morphologi cal changes on second-order sensory neurons which evolve differentiall y with time. Although some changes developed rapidly after deafferenta tion, the onset of others was slower; and whereas some seemed irrevers ible, others eventually regressed. Taken together with the functional studies of others, these findings suggest that early molecular changes observed in cuneate neurons reflect adaptive reactions to lesion-indu ced alterations in afferent activity. Permanent deprivation of the nor mal input, however, would eventually lead to chronic, and perhaps irre versible, degenerative changes. (C) 1996 Wiley-Liss, Inc.