Non-neuronal cells are not the limiting factor for the low axonal regeneration in C57BL/6J mice

Peripheral axonal regeneration was investigated in adult male mice of the C 57BL/6J (C), BALB/cJ (B) and A/J (A) strains and in their Fl descendants us ing a predegenerated nerve transplantation model. Four types of transplants were performed: 1) isotransplants between animals of the C, B and A strain s; 2) donors of the C strain and recipients of the C x B and C x A breeding ; 3) donors of the B strain and recipients of the C x B breeding, and 4) do nors of the A strain and recipients of the C x A breeding. Donors had the l eft sciatic nerve transected and two weeks later a segment of the distal st ump was transplanted into the recipient. Four weeks after transplantation t he regenerated nerves were used to determine the total number of regenerate d myelinated fibers (TMF), diameter of myelinated fibers (FD) and myelin th ickness (MT). The highest TMF values were obtained in the groups where C57B L/6J mice were the donors (C to Fl (C x B) = 4658 +/- 304; C to Fl (C x A) = 3899 +/- 198). Also, A/J grafts led to a significantly higher TMF (A to F l (C x A) = 3933 +/- 565). Additionally, isotransplant experiments showed t hat when the nerve is previously degenerated, C57BL/6J mice display the lar gest number of myelinated fibers (C to C = 3136 +/- 287; B to B = 2759 +/- 170, and A to A = 2835 +/- 239). We also observed that when C57BL/6J was th e graft donor, FD was the highest and MT did not differ significantly when compared with the other groups. These morphometric results reinforce the id ea that Schwann cells and the nerve environment of C57BL/6J provide enough support to the regenerative process. In this respect, the present results s upport the hypothesis that the non-neuronal cells, mainly Schwann cells, pr esent in the sciatic nerve of C57BL/6J mice are not the main limiting facto r responsible for low axonal regeneration.