Journal of Neuroscience, Vol 3, 1135-1144, Copyright © 1983 by Society for Neuroscience
Axonal regeneration in lamprey spinal cord
HS Yin and ME Selzer
Spinal cords of sea lamprey larvae were transected at one of two levels:
(a) rostral, at the last gill, or (b) caudal, at the cloaca. Following
various recovery times, regeneration of the posteriorly projecting giant
reticulospinal axons (RAs) was demonstrated by intra- axonal injection of
horseradish peroxidase (HRP). Regeneration of axons of anteriorly
projecting dorsal cells (DCs) and giant interneurons (GIs) was demonstrated
by intrasomatic HRP injection into cells located just below the transection
scar. After 40 days of recovery, 55% of proximally transected RAs (rostral
cut) regenerated at least as far as the center of the scar, whereas only
15% of distally transected RAs (caudal cut) did so. Maximum distance of
regeneration was 5.3 mm beyond the scar for proximally transected RAs but
only 38 u for distally transected RAs. Proximally transected RAs also
branched more profusely than distally transected ones. These data (when
combined with others in the literature) suggest that the regenerative
capacity of RAs may decrease with distance of axotomy from the cell body.
Distance of regeneration and degree of branching of proximally transected
RAs peaked between 40 and 100 days. Thereafter, there appeared to be a
tendency toward neurite retraction. Of axotomized GIs, 76% regenerated
anteriorly at least as far as the center of a caudal transection scar (GIs
are located only in the caudal part of the cord). The maximum distance of
regeneration was 1.3 mm beyond the scar. Of DC axons, 56% regenerated
anteriorly at least as far as the transection site. The maximum distance
was 1.1 mm beyond the scar. DCs located just below a caudal transection
regenerated at least as well as those located below a rostral transection.
Axonal regeneration was also demonstrated for a few lateral cells, edge
cells, and crossed caudally projecting interneurons.
