Biology Reference
In-Depth Information
damage (
Herbison, Jaweed, Ditunno, & Scott, 1973
), especially if applied
too early after PNS injury (
Herbison et al., 1974
). The impact of physical
exercise in the function of reinnervated muscles is not straightforward. Free
access to running wheels by mice following tibial nerve transection and
repair caused delayed reinnervation of soleus muscle but strengthened syn-
aptic transmission at the level of the neuromuscular junction, at least during
the initial weeks following the nerve injury (
Badke, Irintchev, & Wernig,
1989
). This is in accordance with findings demonstrating inhibition of nerve
sprouting in muscle partially denervated by L4 or L5 ventral root avulsion
due to running exercise (
Tam, Archibald, Jassar, Tyreman, & Gordon,
2001
). The conflicting results regarding the effect of physical exercise on
nerve regeneration and functional recovery probably reflect differences in
the type, duration, and intensity of the exercise regimens. In fact, treadmill
running following sciatic nerve crush in the rat impaired recovery of motor
function, but not of sensitive function (
van Meeteren et al., 1998
), whereas
swimming or rising on the rear limbs for water reaching globally improved
functional recovery (
van Meeteren et al., 1997
).
2.2. Physical exercise action on neurobiological mechanisms
of nerve regeneration
Although physical exercise may aid recovery after PNS damage or act in the
opposite way, the view that physical exercise stimulates key neurobiological
processes underlying nerve regeneration is getting wide acceptance.
Table 6.1
summarizes evidence regarding the effect of exercise stimulation
on a number of molecular mechanisms of nerve regeneration. Retrograde
labeling of motoneurons (
English, Cucoranu, Mulligan, & Sabatier,
2009
), direct visualization of fluorescent growing axons (
Sabatier,
Redmon, Schwartz, & English, 2008
), and counting of nerve fibers in semit-
hin transverse nerve sections (
Asensio-Pinilla, Udina, Jaramillo, & Navarro,
2009; Ilha et al., 2008
), combined with neurophysiological and behav-
ioral outcome measures, support the view that physical exercise promotes
nerve regeneration and functional recovery in models of traumatic nerve
injury (
Udina, Cobianchi, et al., 2011
; reviewed in
English, Wilhelm,
et al., 2011
).
2.2.1 Physical exercise, neuronal cell survival, and neuroprotection
Critical for successful nerve regeneration is ensuring survival of axotomized
neurons, together with increasing the number of growing neurons. Several
studies demonstrate that treadmill exercise augments the number of axons
