Biology Reference
In-Depth Information
unloading via exposure to simulated microgravity (
Benavides Damm et al.,
2013
). Also, ramp and cyclic stretching determines alternative splicing and
production of IGF-1 isoforms in myoblasts, which might help myogenesis
(
Cheema et al., 2005
; reviewed in
Goldspink, 1999
).
BDNF- and trkB-deficient mice also are unable of recovering whisking
function and improving the pattern of muscle end plate innervation follow-
ing facial nerve injury and in response to manual stimulation (
Sohnchen
et al., 2010
). Although these results are in accordance with the key role
played by BDNF and trkB in nerve regeneration (
Gordon, 2009;
Grothe & Unsicker, 1987; Morcuende et al., 2011
), they also suggest that
passive exercise might induce BDNF and trkB upregulation following
axotomy.
Passive limb mobilization also seems to encourage axonal regeneration
and target reinnervation following sciatic nerve transection and repair
(
Udina, Cobianchi, et al., 2011
). Rhythmical motion of the hindlimb, such
as that produced by passive bicycling, during the initial weeks of recovery
from sciatic nerve injury, increases the number of regenerated nerve fibers
in the distal nerve and enhances reinnervation of the hindpaw muscles. In
addition, passive exercise counteracts hyperreflexia that develops as a result
of peripheral nerve injury (
Navarro, Viv´ , Valero-Cabr´, 2007; Udina,
Cobianchi, et al., 2011
).
2.3.1 Passive exercise and mechanical strain
An alternative hypothesis is that passive exercise might stimulate axo-
nal growth by direct mechanical strain. Regeneration of peripheral
nerves is drastically impaired by tension (
Sunderland et al., 2004
), most likely
as a result of severe reduction in blood flow (
Clark, Trumble,
Swiontkowski, & Tencer, 1992
). However,
in situ
peripheral nerves are
under some degree of tensile load (
Rydevik et al., 1990
) and undergo sig-
nificant length changes during joint movements. Therefore, a certain degree
of nerve compliance is necessary for normal function (
Dilley, Lynn,
Greening, & DeLeon, 2003
). The amount of nerve excursion is higher
when combining movements of several limb joints and strain is not uniform
along the length of the nerves, usually being higher near the moving joints
(
Coppieters & Alshami, 2007; Dilley et al., 2003; Wright, Glowczewskie,
Cowin, & Wheeler, 2001; Wright, Glowczewskie, Wheeler, Miller, &
Cowin, 1996
; reviewed in
Topp & Boyd, 2006
). On the other hand, con-
fining nerve excursion, for instance through limb immobilization, can lead
