Dorsal column nuclei afferents in the lateral funiculus of the cat: distribution pattern and absence of sprouting after chronic deafferentation.

In adult cats the successive degeneration technique has been used to demonstrate the existence and distribution pattern of lateral funicular fibers to the dorsal column nuclei (DCN) originating from the brachial and thoracic cord. In a first operation, interruption of the dorsal columns at appropriate cervical levels and of the lateral funiculus at low thoractic levels was performed. Thirteen months later, a lesion was made in the lateral funiculus at upper brachial or uppermost thoracic levels. Fiber degeneration in the DCN consequent to this second operation is not contaminated by damage to dorsal roots or by interruption of lateral funicular afferents from lumbo-sacro-coccygeal segments. All animals were sacrificed 7 days after the second operation. Serial sections through the medulla oblongata, impregnated with the Fink-Heimer technique, show that fibers ascending from brachial levels in the dorsal part of the lateral funiculus reach the cuneate nucleus either by a dorsomedial route through the tegmentum or by cuneate nucleus either by a dorsomedial route through the tegmentum or by ascending in the restiform body. Degenerated fibers distribute selectively to the rostral part, and to a lesser extent to the base of the cuneate nucleus. Only very few fibers ascending from thoracic levels in the lateral funiculus distribute to the DCN. In another group of animals, not previously deafferented, a lesion of the lateral funiculus was made at upper brachial levels. This group served as a control to assess whether sprouting had occurred in the chronic preparations as a consequence of the long-term deafferentation. Comparison of the results in the cuneate nucleus of the two groups of animals shows no difference in the pattern of distribution or in the amount of degenerated fibers in this nucleus. These observations are discussed in relation to the question of collateral sprouting in the adult mammalian central nervous system.