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.