Astrogliosis in different zones of the spinal cord gray
matter after sciatic nerve axotomy in the newborn rat:
A morphometric and immunohistochemical study
Astrocytic response following unilateral
sciatic nerve axotomy was examined in the spinal gray
matter of newborn rats. Using an antiserum to glial
fibrillary acidic protein (GFAP), immunoreactive
astrocytes were studied in the ventral, dorsal and
transitional region between the dorsal and ventral gray
matters (TDVG) at intervals of one day, one week, two
weeks and one month postaxotomy. The axotomized side
showed an obvious increase in the number of
immunoreactive astrocytes at one week, two weeks and
one month after surgery. The numerical density per area
of the glial cells (N(a)) was determined in all groups on
both the intact and axotomized sides, and it increased in
all groups at the axotomized sides. The percentage of
glial cell increase (Pgi) was also determined. At the
ventral horn Pgi increased at day one and continued to
increase in all groups, while the increase in TDVG and
the dorsal horn occurred at later time points.
The total motoneuron count in the ventral horn at the
axotomized and intact sides was done at all time points,
and the percentage of motoneuron reduction (Pmr) was
calculated, the highest Pmr being noticed at one month
(41%). A nonlinear regression for Pmr and Pgi showed
that the rate of Pgi was approximately double that of
Pmr.
The rate of glial cell increase at each time point (one
day, one week, two weeks and one month groups) was
calculated, and the highest rate of glial cell increase in
the ventral horn occurred one week after axotomy, while
the highest rate in the dorsal horn and TDVG occurred at
the second week. The conclusion of the study is that
there may be an initial post-axotomic proliferative phase
of the glial cells, which was followed by a differentiation
phase. Also a gradient of an increase in the rate glial cell
proliferation was noticed from the ventral horn toward
the dorsal horn, maybe due to stimulation by a paracrine
factor