Intravitreal injections of neurotrophic factors and forskolin enhance
survival and axonal regeneration of axotomized beta ganglion cells in cat
retina.
Watanabe M, Tokita Y, Kato M, Fukuda Y.
Department of Physiology, Institute for Developmental Research, Kasugai, Aichi,
Japan. mwatan@inst-hsc.pref.aichi.jp
Some retinal ganglion cells in adult cats survive axotomy for two months and
regenerate their axons when a peripheral nerve is transplanted to the transected
optic nerve. However, regenerated retinal ganglion cells were fewer than 4% of
the total retinal ganglion cell population in the intact retina. The present
study examined the effects of intravitreal injections of neurotrophic factors
(brain-derived neurotrophic factor, ciliary neurotrophic factor, basic
fibroblast growth factor, glial cell-derived neurotrophic factor, neurotrophin
4), first on the survival of axotomized cat retinal ganglion cells within 2
weeks, and then on axonal regeneration of the retinal ganglion cells for 2
months after peripheral nerve transplantation. We tested first enhancement of
the survival by one of the factors, and then one or two of them supplemented
with forskolin, which increases intracellular cAMP. Single injections of 0.5
microg or 1 microg brain-derived neurotrophic factor, 1 microg ciliary
neurotrophic factor, or 1 microg glial cell-derived neurotrophic factor
significantly increased total numbers of surviving retinal ganglion cells;
1.6-1.8 times those in control retinas. Identification of retinal ganglion cell
types with Lucifer Yellow injections revealed that the increase of surviving
beta cells was most conspicuous: 2.5-fold (brain-derived neurotrophic factor) to
3.6-fold (ciliary neurotrophic factor). A combined injection of 1 microg
brain-derived neurotrophic factor, 1 microg ciliary neurotrophic factor, and 0.1
mg forskolin resulted in a 4.7-fold increase of surviving beta cells, i.e. 50%
survival on day 14. On the axonal regeneration by peripheral nerve
transplantation, a combined injection of brain-derived neurotrophic factor,
ciliary neurotrophic factor, and forskolin resulted in a 3.4-fold increase of
beta cells with regenerated axons. The increase of regenerated beta cells was
mainly due to the enhancing effect of neurotrophic factors on their survival,
and possibly to a change of retinal ganglion cell properties by cAMP to
facilitate their axonal regeneration.