December 1, 1997;
Expression of brain-derived neurotrophic factor and its receptor mRNA in the vestibuloauditory system of the bullfrog.
-derived neurotrophic factor (BDNF
) is a neurotrophin which has been suggested to play a crucial role in the development and maintenance of the inner ear
. In the present study, we investigated the expression of mRNAs of BDNF
and its high-affinity receptor trkB
in the vestibuloauditory system of the adult bullfrog. In situ hybridization was performed using riboprobes transcribed from Xenopus BDNF
cDNA clones. BDNF
mRNA was expressed in the sensory epithelia of the ampullary cristae, utricular and saccular maculae, lagena
, and amphibian and basilar papillae. Strong hybridization for BDNF
mRNA was also found in neuron
somata of the vestibuloauditory nuclear complex. trkB
mRNA was detected in the sensory epithelia of all vestibular and auditory endorgans. High levels of both BDNF
mRNAs were found in vestibuloauditory ganglion
cells. These results support the hypothesis that BDNF
participates in the maintenance of vestibuloauditory neurons and may be important for the trophic regulation of vestibular and auditory sensory epithelia in this animal model.
[+] show captions
Fig. I. Expression of BDNF mRNA in the vestibular and auditory endorgans. Sections a--e were hybridized with the BDNF antisense riboprobe.
Section f was prepared with the BDNF sense riboprobe, a,c,d: Darkfield photomicrographs show strong BDNF hybridization in the (a)
macular sacculi, (c) amphibian papilla, and (d) amputlary cristae. Scale bar= 35 gm. b,e: Brightfield photomicrographs demonstrate high levels
of BDNF transcripts in the (b) macular sacculi and (e) ampullary cristae. Scale bar = 17 ~tm. f: Darkfield photomicrograph demonstrates sense
riboprobe control in section adjacent to c. Note the lack of specific hybridization. Scale bar = 35 gm.
Fig. 2. Cellular localization of BDNF and trkB mRNA in the vestibuloauditory ganglion cells. Sections a,b were treated with BDNF or trkB
sense riboprobes. Sections c-f were hybridized with BDNF or trkB antisense riboprobes, a,b: Darkfield photomicrographs depict sense riboprobe
controls for (a) BDNF and (b) trkB. Note the lack of specific hybridization. Scale bar= 50 ~m. c: Darkfield photomicrograph displays
BDNF mRNA in the vestibuloauditory ganglion. Scale bar= 50 l-tm. d: Darkfield photomicrograph illustrates similar expression levels of trkB
mRNA in the vestibuloauditory ganglion. Scale bar = 50 ~tm. e: Brightfield photomicrograph at higher magnification demonstrates BDNF transcripts
concentrated over neuron somata (arrowheads). Scale bar= 12 ~tm. f: Brighfield photomicrograph at higher magnification shows neuronal
cell bodies (arrowheads) containing trkB transcripts. Scale bar = 12 gm.
Fig. 3. Expression trkB mRNA in the auditory and vestibular endorgans. Sections were hybridized with the trkB antisense riboprobe, a,c:
Darkfield (a) and brightfield (c) photomicrographs illustrate trkB mRNA in the sensory epithelia of the macular sacculi. Scale bar= 35 blm.
b,d: Darkfield photomicrographs of trkB hybridization in the (b) ampullary cristae and (d) amphibian papilla. Scale bar= 17 btm.
Fig. 4. BDNF and trkB mRNA localization in the brainstem. Sections were hybridized with BDNF or trkB antisense riboprobes, a: Darkfield
photomicrograph of the brainstem demonstrates BDNF mRNA in the vestibuloauditory nuclei at the level of entry of the eighth nerve• DO,
dorsal (auditory) nucleus; LVN, lateral vestibular nucleus: MVN, medial vestibular nucleus: DVN, descending veslibular nucleus. Scale
bar = 140 lam. b: Darkfield photomicrograph of the brainstem at the level of the eighth nerve root displays trkB hybridization in cells (arrows)
of the lateral vestibular nuclei. Scale bar= 140 I-tm.