Abstract
The thesis that the operation of the central nervous system can be satisfactorily explained in terms of fixed neurone arrangements, rests largely on the interpretation of the structural organization of the central gray, as it presents itself in the normal animal. If the central nervous system really owes its fundamental functional manifestations to the minute details of its neurone architecture, any major disorganization of the latter should thoroughly derange the former. Accordingly, a study of the functional capacities of a central nervous system whose anatomical connections have been thrown into confusion promises information of crucial interest. Such a condition can be produced by transplantation.
Fragments of spinal cord, including several segments, excised from larval salamanders (Amblystoma punctatum) were grafted into the gelatinous connective tissue of the dorsal fin fold. Hosts and donors were of identical age (ca 2 cm in length) and had been in full functional activity for many weeks. In 7 of the 14 animals thus operated a limb was grafted at some distance anteriorly or posteriorly to the cord graft. All grafts became quickly vascu-larized and well incorporated.
Histological study revealed 3 main changes in the grafted cord fragments: (1) varying degrees of reduction of the gray matter; (2) considerable deformation and disorganization of the surviving portion; (3) outgrowth of bundles of nerve fibers into the surroundings.
The outgrowing nerve fibers form connections with skin, trunk muscles, and in the presence of a grafted limb, also with the latter. The cables connecting cord and limb grafts are always much stronger than other bundles. This fact, highly significant for the interpretation of normal nerve development, suggests that the first pioneering fibers to become attached to the limb thereby acquire some faculty—a kind of “stickiness”, as it were—converting them into a preferential contact pathway for later fibers.
Get full access to this article
View all access options for this article.