Biology Reference
In-Depth Information
of new hippocampal neurons in mice (
Rhodes et al., 2003
) and protecting the
cells against ischemicdamage in thehippocampus (
Stummer,Weber,Tranmer,
Baethmann, & Kempski, 1994
) and neurotoxic damage in the neostriatum
(
Smith & Zigmond, 2003
).
It is now understood that the action of exercise is to modulate the func-
tion of the BDNF system of intracellular signaling systems, for example, the
calcium-calmodulin kinase II and mitogen-activated protein kinase, with
endpoint effects on the production and function of CREB. Enhanced learn-
ing after chronic activity-wheel running has also been accompanied by de-
creases in extracellular amyloid plaques and proteolytic fragments of amyloid
precursor proteins in a transgenic mouse model of Alzheimer's disease
(
Adlard, Perreau, Pop, & Cotman, 2005
).
IGF-1 is also related to exercise. It has been reported that this 70 amino
acid protein plays a prominent role in the growth factor cascade in response
to exercise in the brain (
Llorens-Mart´n, Torres-Alem´n, & Trejo, 2008
).
These actions are especially relevant in the hippocampus, where IGF1 in-
fluences neural plasticity, adult neurogenesis (
Trejo, Carro, & Torres-
Aleman, 2001
), and cognition (Trejo, Llorens-Mart´n, & Torres-Alem´n,
2007). These findings are consistent with the extensive evidence indicating
that blood-borne IGF-1, mostly synthesized and secreted by the liver, is re-
sponsible for mediating other effects of physical and cognitive activity within
the brain (
Torres Aleman, 2005
).
5.2.2 Environmental light stimulation
It is well documented that both spontaneous synaptic activity before eye
opening and light-evoked retinal activity after eye opening are critical for
the normal development of synaptic circuitry in higher centers of the visual
system. Conventional environment lighting (12 h light-12 h dark) or addi-
tional flashing lights are essential for the survival and axonal regeneration of
axotomized RGCs (
Watanabe, Inukai, & Fukuda, 1999
). Light stimulation
also has neuroprotective properties that enhance photoreceptor survival by
elevating bFGF and CNTF in animal models of RP (
Liu, Peng, Laties, &
Wen, 1998; Nir, Liu, &
Wen, 1999).
Another candidate for the neuroprotective effects of light stimulation is
dopamine. Dopamine is known to enhance the survival of RGCs in culture
by elevating the intracellular level of cAMP (
Kashii et al., 1994
). The level of
dopamine has been shown to increase in the goldfish retina under constant
light (
Vaquero, Pignatelli, Partida, & Ishida, 2001
). High intracellular concen-
tration of cAMP facilitates both survival and axonal regeneration of RGCs.
