Chronic peripheral nerve section results in a rearrangement of the central axonal arborizations of axotomized A beta primary afferent neurons in the rat spinal cord.

In order to investigate the reorganization of the neuropil of the dorsal horn following peripheral nerve injury, the central terminal arborizations of 35 A beta primary afferent neurons, chronically injured by a cut and ligation of the sural nerve 6-12 weeks previously, were studied by the intra-axonal injection of horseradish peroxidase. Their morphology was compared to 13 intact sural nerve hair follicle afferents. Following axotomy, three kinds of morphological abnormalities were observed in the collateral arbors of the 26 afferents that were hair follicle-like. Atrophy with thin stem axons and reduced terminal branch patterns with few boutons was seen in 5 afferents. Sprouting of bouton-containing terminals into lamina I and IIo was found in 8 afferents. Finally, abnormal arborization patterns in the deeper laminae were observed in 29% of the collateral arbors. Changes included the loss in some arbors of a flame-shaped appearance, which is characteristic of hair follicle afferents, atypical branching patterns and ventrally directed axons producing wider and deeper arbors, compared to normal. Axotomy also caused a disruption of the normal somatotopic organization of sural nerve A beta afferents. This disruption manifested as a variability in the normally mediolaterally restricted terminal sheet, with a consequent loss of the strict somatotopic register in the rostrocaudal direction. Damage to the peripheral axon of A beta primary afferents induces a structural reorganization of their central terminals in the dorsal horn of the spinal cord, which may modify sensory input to the central nervous system.