Transient synapses in the embryonic primate spinal cord.

Electron microscopic and tritiated thymidine autoradiographic analysis of the embryonic spinal cord in the rhesus monkey reveals considerable rearrangement of cellular and synaptic relationships in the posterior (sensory) quadrant during early developmental stages. This remodeling involves the death of an entire population of neurons that received synapses from sensory afferent axons and the possible relocation of these afferents upon subsequently generated viable substantia gelatinosa neurons.