Heterogeneous regeneration of motor fibers following union of the ventral and the dorsal roots in frogs.
In frogs, the dorsal and ventral roots of one of the large lumbar segments (8th or 9th) of the spinal cord were severed and the central stumps were united in order to let motor fibers of the ventral root regenerate into the spinal cord via the dorsal root. After a survival period of 7 to 30 weeks, regeneration was tested in stimulation experiments and in histological investigations. Stimulation experiments involved recordings of field potentials and ventral root potentials evoked by stimulation of the regenerated dorsal root. Appreciable responses could be recorded only from a fraction of the animals investigated. Histological investigation following cobalt labelling of the united dorsal root revealed the presence of a significant amount of regenerated fibers. The arborization pattern of some regenerated fibers resembled the muscle end-plate formation. The results indicate that cholinergic motor fibers are able to replace, to a limited extent, dorsal root fibers. This suggests that there is not a strict receptor-nerve specificity in the sense that a synaptic site can be exclusively stimulated by the appropriate mediator, but rather a preferential selection for the appropriate connection. This preference is higher when both the morphology and the chemistry of the presynaptic structure match with the postsynaptic medium.
D000818:Animals; D004558:Electric Stimulation; D005071:Evoked Potentials; D005727:Ganglia, Spinal / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009412:Nerve Fibers / Q000502:physiology*; D009416:Nerve Regeneration; D011893:Rana esculenta; D013126:Spinal Nerve Roots / Q000502:physiology*; D013569:Synapses / Q000502:physiology