Glial cell line-derived neurotrophic factor added to a sciatic
nerve fragment grafted in a spinal cord gap ameliorates motor impairments in
rats and increases local axonal growth
Affiliations: Neuroregeneration Center, Department of Neurology,
University of São Paulo School of Medicine, University of São Paulo,
São Paulo, Brazil
Note: [] Corresponding author: Gerson Chadi. M.D., Ph.D., Full Professor,
Department of Neurology, University of São Paulo, Av. Dr. Arnaldo, 455 2nd
floor, room 2115, 01246-903, São Paulo, Brazil. Tel.: +55 11 3061 7460;
E-mail: gerchadi@usp.br
Abstract: Purpose: The aversive nature of regenerative milieu is the main
problem related to the failure of neuronal restoration in the injured spinal
cord which however might be addressed with an adequate repair intervention. We
evaluated whether glial cell line-derived neurotrophic factor (GDNF) may
increase the ability of sciatic nerve graft, placed in a gap promoted by
complete transections of the spinal cord, to enhance motor recovery and local
fiber growth. Methods: Rats received a 4 mm-long gap at low thoracic level
and were repaired with a fragment of the sciatic nerve. GDNF was added
(NERVE±GDNF) or not to the grafts (NERVE--GDNF). Motor behavior score (BBB)
and sensorimotor tests-linked to the combined behavior score (CBS), which
indicate the degree of the motor improvement and the percentage of functional
deficit, respectively, and also the spontaneous motor behavior in an open field
by means of an infrared motion sensor activity monitor were analyzed. At the
end of the third month post surgery, the tissue composed by the graft and the
adjacent regions of the spinal cord was removed and submitted to the
immunohistochemistry of the neurofilament-200 (NF-200), growth associated
protein-43 (GAP-43), microtubule associated protein-2 (MAP-2),
5-hidroxytryptamine (serotonin, 5-HT) and calcitonin gene related peptide
(CGRP). The immunoreactive fibers were quantified at the epicenter of the graft
by means of stereological procedures. Results: Higher BBB and lower CBS levels (p < 0.001) were
found in NERVE±GDNF rats. GDNF added to the graft increased the levels of
individual sensorimotor tests mainly at the third month. Analysis of the
spontaneous motor behavior showed decreases in the time and number of small
movement events by the third month without changes in time and number of large
movement events in the NERVE$+$GDNF rats. Immunoreactive fibers were
encountered inside the grafts and higher amounts of NF-200, GAP-43 and MAP-2
fibers were found in the epicenter of the graft when GDNF was added. A small
amount of descending 5-HT fibers was seen reentering in the adjacent caudal
levels of the spinal cords which were grafted in the presence of GDNF, event
that has not occurred without the neurotrophic factor. GDNF in the graft also
led to a large amount of MAP-2 perikarya and fibers in the caudal levels of the
cord gray matter, as determined by the microdensitometric image analysis. Conclusions: GDNF added to the nerve graft favored the motor
recovery, local neuronal fiber growth and neuroplasticity in the adjacent
spinal cord.
