Muscle denervation is common in various
neuromuscular diseases and after
trauma. It induces skeletal muscle
atrophy. Only muscle reinnervation leads to functional recovery. In previous studies, denervated adult rat muscles were rescued by
transplantation of embryonic day 14-15 (E14-15) ventral spinal cord cells into a nearby peripheral nerve. In the present study, changes were made in the environment into which the cells were placed to test whether reinnervation was improved by: 1) prior
nerve degeneration, induced by sciatic nerve transection 1 week before
cell transplantation; 2)
transplantation of 1 million versus 5 million cells; 3) addition of
nerve growth factor (
NGF) to the transplant. Ten weeks after
cell transplantation, axons had grown from all of the transplants. The numbers of myelinated axons that regenerated into the tibial, medial (MG), and lateral gastrocnemius-soleus (LGS) nerves were similar across treatments. The mean diameters of large LGS axons (>6 microm) were significantly larger with
nerve degeneration before
transplantation. The mean diameters of MG and LGS axons were significantly larger with
transplantation of 1 million versus 5 million cells.
Silver-stained experimental and control lateral gastronemius (LG) muscles showed axons that terminated at motor end plates. Nodal and terminal sprouts were more common in reinnervated muscles (45-63% of all end plates) than in control muscles (10%). Electrical stimulation of the transplants induced weak contractions in 39 of 47 MG muscles (83%) and 33 of 46 LG muscles (72%) but at higher voltages than needed to excite control muscles. The threshold for MG contraction was lower with
transplantation of 1 million cells, while LG thresholds were lower without
NGF. The cross-sectional area of whole LG muscles was significantly larger with
cell transplantation (immediate or delayed) than with media alone, but all of these muscle areas were reduced significantly compared with control muscle areas. These data suggest that delayed
transplantation of fewer cells without
NGF assists regeneration of larger diameter axons and prevents some
muscle atrophy.