Biology Reference
In-Depth Information
to structural changes in nerves and diminish their ability to sustain
physiologic strain. Accordingly, motor end plate degeneration and
polyinnervation (
Pachter & Eberstein, 1984
), delayed soleus reinnervation
(
Marciniak, 1985
), and deepest loss of contractile force during muscle
reinnervation (
Herbison et al., 1984
) accompany limb immobilization.
There is growing acceptance that mechanical strain plays a role in
growth, guidance, and function of neurons (reviewed in
Suter & Miller,
2011
). Axons display a remarkable ability to elongate in response to
externally applied forces. Cultured neurons can grow their axons at an
extraordinary rate of 8 mm/day (
Pfister, Iwata, Meaney, & Smith, 2004
).
Of course, such high axonal elongation rate cannot be directly translated
to
in vivo
conditions. However, it has been shown that extreme
leg-lengthening causes minute axon damage in the rat's sciatic nerve (
Abe
et al., 2004
). Although current understanding of the mechanisms of rapid
growth of stretched axons is still incomplete, it is nevertheless certain that
it relies on intracellular signaling set in motion by mechanotransduction
(
Pfister et al., 2004
). That passive exercise may potentially trigger these
signaling pathways is an attractive hypothesis.
3. EFFECT OF EXERCISE ON NEUROPATHIC PAIN
Neuropathic pain is a frequent and adverse consequence of traumatic
PNS injury and is a major cause of disability and poor quality of life in these
conditions (
Ciaramitaro et al., 2010
). Treadmill exercise has been shown to
reduce allodynia and hyperalgesia due to chronic constriction injury (CCI)
(
Cobianchi, Marinelli, Florenzano, Pavone, & Luvisetto, 2010
) or sciatic
nerve crush (
Bobinski et al., 2011
). The impact of treadmill exercise on
the development of allodynia is dependent on the timing and duration
of the exercise protocol. Accordingly, treadmill running for 1 h/day from
day 3 to day 7 following CCI diminishes signs of allodynia throughout the
entire survival time and improves functional recovery, while keeping the
exercise protocol for a longer period of time produces the opposite effect
(
Cobianchi et al., 2010
). The antinociceptive effect of short-term tread-
mill running is in relationship with blunted microglia and astrocytes
activation in the dorsal and ventral horns of the spinal cord ipsilateral to
the constricted sciatic nerve (
Cobianchi et al., 2010
). Mechanisms relating
treadmill running and diminished neuropathic pain probably involve chan-
ged cytokines and that of proinflammatory mediators release, within the
