In the present study rat sciatic nerves (n = 60) were transected: in h
alf of the animals the nerve was allowed to regenerate freely, in the
other half the regeneration was prevented by suturing beside the point
of transection. Macrophages were stained with ED-1 antibody and count
ed (number/mm(2)) in both the epi- and endoneurium 3, 7, 14, 48 and 56
days post transection. Macrophages were observed first in the epineur
ium; the local density of macrophages was considerably higher in the e
pineurium than in the endoneurium during the first few days. The numbe
r of macrophages in the epineurium was maximal at 3 days (1000-2000/mm
(2)), and thereafter it declined sharply. In the endoneurium macrophag
es were most abundant after 2 weeks (1000/mm(2)), after which their nu
mber declined steadily. A migration of epineurial macrophages appeared
to take place through the perineurium from epineurial areas containin
g a high concentration of macrophages. Initially an endoneurial accumu
lation of macrophages was noted in the subperineurial area. These find
ings suggest an alternative route for macrophages into the endoneurial
space. No statistical difference was observed between the regeneratin
g and non-regenerating experimental groups. The present study indicate
s that regenerating axons do not have an effect on the number of macro
phages in either the epineurium or the endoneurium.