Predominant neuronal B-cell loss in L5 DRG of p75 receptor-deficient mice.

The significance of the p75 low-affinity neurotrophin receptor, for the maintenance and survival of DRG cells, was studied in p75-deficient mice. Perikarya of the L5 DRG of 12-week-old p75 receptor-deficient mice and healthy Balb C mice were compared using stereological techniques. Following systematic sampling, the optical fractionator and the planar vertical rotator were used to estimate the number and mean volume of the cell bodies of the two neuronal subpopulations. The loss of B-cells was 57% (P < 0.00001), numbers being 7300 (CV = 0.12) in controls and 3100 in p75 receptor-deficient mice (CV = 0.18). Also, A-cells showed a significant loss of 39% (P < 0.0001), numbers being 2600 (CV = 0.12) in control mice and 1500 (CV = 0.16) in p75 receptor-deficient mice. The volume of A-cells was reduced by 30% (P<0.01), from 24.700 microm3 (CV=0.17) perikarya in p75 knock-out mice to 15.100 microm3 (CV=0.17) in controls. B-cell volume did not change significantly. It is concluded that the p75 receptor plays a major role in the survival of DRG cells. The predominant loss of small B-cells indicates that the effect of neurotrophins is dependent upon the presence of the p75 low-affinity receptor.