Nimodipine accelerates axonal sprouting after surgical repair of rat facial nerve

Facial-facial anastomosis (FFA), i.e., suture of transected facial nerve, was performed in adult Wistar rats. For 10-112 d post-operation (DPO), half of the animals received standard food (placebo) and half received food pellets containing 1000 ppm nimodipine, a Ca2+ channel blocker. The time course of mimetic reinnervation between these two groups was compared by counting all retrogradely labeled motoneurons after injection of horseradish peroxidase (HRP) into the whiskerpad. In unoperated animals, injection of HRP labeled 1280 +/- 113 motoneurons. After FFA, this number dropped to zero, and the first HRP-labeled facial motoneurons reappeared in both placebo- and nimodipine-treated animals at 14 DPO. The treatment with nimodipine yielded two beneficial effects. (1) It accelerated axonal sprouting until 28 DPO. Whereas the number of HRP-labeled cells in the placebo group was 171 +/- 9 (mean +/- SD) at 16 DPO, 372 +/- 43 at 21 DPO, and 636 +/- 187 at 28 DPO, the number of sprouted motoneurons in nimodipine-treated rats was twice as high: 386 +/- 34 at 16 DPO, 620 +/- 28 at 21 DPO, and 756 +/- 257 at 28 DPO. (2) Nimodipine reduced the polyneuronal innervation of the target muscles. Whereas the number of HRP-labeled cells in the placebo group increased to 1430 +/- 36 at 56 DPO and 1600 +/- 31 at 112 DPO, the number of labeled motoneurons in nimodipine-treated rats remained almost within the normal range: 1315 +/- 31 at 56 DPO and 1354 +/- 33 at 112 DPO.