Analysis of Brain-Derived Neurotrophic Factor Expression in Normal Dog Eyes by Immunofluorescence and Real Time Reverse Transcriptase--Polymerase Chain Reaction Techniques
Biomedical Research Institute, UNAM, Mexico; Division of Biotechnology & Molecular Medicine, Louisiana State University, USA
Brain-Derived Neurotrophic Factor (BDNF) is the neurotrophin responsible for neuron development, maintenance and survival. In retina BDNF also helps in ganglion cells repair after a severe damage.
Frozen retinal sections from 6 normal dogs' eyes were stained with fluorescence secondary antibody to evaluate BDNF expression. BDNF expression was estimated by quantitative reverse transcriptase-PCR (RT-PCR) with Taqman fluorescence methodology, using a total of 10 normal dogs' eyes.
In normal eyes BDNF immunofluorescence was detected in retinal ganglion cell layer, nerve fiber layer, photoreceptor layer, outer nuclear layer, outer plexiform layer, lamina cribosa cells, optic nerve head astrocytes and optic nerve head tissue. However it was not seen in retinal pigment epithelium. BDNF mRNA expression was quantified in dorsal retina, ventral retina and vitreous; nevertheless no expression was detected in ciliary body. An increased BDNF mRNA expression was noticeable in retina compared to ciliary body and vitreous; as well as an obviously increased expression in dorsal retina compared to ventral retina in both (right and left) eye.
This is the first evidence of BDNF expression in dog retina and optic nerve head; this expression was previously reported in rats, bovines, porcine and humans. BDNF mRNA expression was found in retina such as it was expected, once ganglion cells are localized in this part of the eye. The same expression was not observed in ciliary body probably due to low yield of total RNA in this section of the eye. The presence of BDNF mRNA in vitreous suggests that it could be acting as a carrier in the paracrine/autocrine mechanism of the neurotrophins to the retina ganglion cells. The increased expression of BDNF mRNA observed in the retina compared to the others segments is due to it constitutes the neural part of the eye. As well as the difference found in BDNF mRNA expression in dorsal compared to ventral retina is probably because of the anatomic distribution of the retinal ganglion cells among the tapetal and non-tapetal area.
1. Liu ZZ, et al. 1997, J Neurosci, 17: 8749-8755.
2. Seki M, et al. 2003, Invest Ophthalmol Vis Sci, 44: 3211-3218.
3. Hackett SF, et al. 1998, Brain Res, 789: 201-212.