Affiliations: Department of Physiology, School of Medicine, Sapporo
Medical University, South 1, West 17, Chuo-ku, Sapporo 060, Japan
Note: [] Corresponding author: Ikuhide Kohama, Yale University School of
Medicine, Neuroscience and Regeneration Research Center, 127A, VA Medical
Center Building 34, 950 Campbell Ave., West Haven, CT 06516, USA. Tel.: +1 203
937 3802; Fax: +1 203 937 3801
Abstract: The present aimed to identify the origin of medullary and upper
cervical respiratory neurons regenerating their axons into the peripheral nerve
grafts in adult rats. We employed an antidromic activation technique and a
retrograde horseradish peroxidase (HRP) tracing method for determining the
origins of the regenerating axons. Autologous segments of the common peroneal
nerve were successfully implanted ventrolaterally into the proximal cut end of
the C2 spinal cord hemisection (n = 24). Two to 5 months after implantation,
spontaneous multi-unit discharges were recorded in all grafts;
respiratory-related discharges in 21 (87.5%) grafts; and non-respiratory
discharges in 3 (12.5%) grafts. The respiratory discharge patterns were similar
to those for normal respiratory efferent neurons in rats. After the recordings
were completed, 5 of 182 respiratory units explored in the medullary ventral
respiratory cell group (VRG) neurons were antidromically activated by
electrical stimulation of the grafts (n = 15). The estimated axonal conduction
velocities ranged from 5.6 to 7.4 (mean 6.7) m/s. Retrograde horseradish
peroxidase (HRP) labelings applied to the distal cut end of the grafts (n = 13)
revealed that HRP-labeled cells were located, predominantly ipsilaterally, in
the brainstem up to 5-10 mm distant from the implanted site. Some HRP-labeled
cells were observed in the region of the nucleus ambiguus where many
respiratory neurons exist. These results demonstrate that peripheral nerve
grafts implanted in the C2 segment can induce axonal regeneration of medullary
VRG neurons conveying funcional efferent signals.
