Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
Xenopus laevis is one of the most widely used model organism in neurobiology. It is therefore surprising, that no detailed and complete description of the cranial nerves exists for this species. Using classical histological sectioning in combination with fluorescent whole mount antibody staining and micro-computed tomography we prepared a detailed innervation map and a freely-rotatable three-dimensional (3D) model of the cranial nerves and anterior-most spinal nerves of early X. laevis tadpoles. Our results confirm earlier descriptions of the pre-otic cranial nerves and present the first detailed description of the post-otic cranial nerves. Tracing the innervation, we found two previously undescribed head muscles (the processo-articularis and diaphragmatico-branchialis muscles) in X. laevis. Data on the cranial nerve morphology of tadpoles are scarce, and only one other species (Discoglossus pictus) has been described in great detail. A comparison of Xenopus and Discoglossus reveals a relatively conserved pattern of the post-otic and a more variable morphology of the pre-otic cranial nerves. Furthermore, the innervation map and the 3D models presented here can serve as an easily accessible basis to identify alterations of the innervation produced by experimental studies such as genetic gain- and loss of function experiments.
FIGURE 1 Volume rendering of a mCT-scan of a PTA-stained Xenopus laevis tadpole at NF stage 47/48. The neuromasts are visible as
white dots in the gray skin of the specimen. (a) lateral view. The four neuromasts of the angular lateral line are not visible in the scan but
their positions are indicated by black asterisks. (b) frontolateral view. (c) ventral view. (d) dorsal view
FIGURE 2 3D reconstruction of a dorso-ventral scan of a whole mount antibody staining against acetylated-alpha tubulin of a Xenopus laevis
larva at NF stage 47/48. The nerves have been reconstructed only on the left side. Cranial nerves are color-coded according to a rainbow
color map. The brain is shown in light yellow, the eye in white, and the cartilaginous head skeleton in transparent blue. A smaller
overview of the whole 3D model is shown in the lower left corner. (b) lateral view. (c) ventral view. A smaller overview of the whole 3D
model is shown in the upper left corner [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 3 The lateral line nerves. (a–f) 3D depth coding views of a whole mount antibody staining (acetylated alpha-tubulin) of a NF stage
47/48 X. laevis tadpole. (a) dorsal view of the region of the otic capsule. (b) lateral view of the region of the otic capsule. (c) lateral view of
the eye region. (d) lateral view of the region ventral to the eye. (e) lateral view of the brachial region. (f) dorsal view of the posterior head
region. The dotted line outlines the course of the ventralposteriorlateral line nerve lying under the lateral auricular nerve. (g and h)
transverse sections of a X. laevis tadpole at NF stage 46. (g) section through the region posterior to the eye to show the ganglia of the
anteriorlateral line nerve, the profundal and trigeminal nerves and the facial nerve. (h) section through the region posterior to the otic
capsule to show the ganglia of the posteriorlateral line nerve and the glossopharyngeal and vagal nerves. (i–k) schematic diagrams
illustrating the rami and ramuli of the lateral line nerves. Components of the lateral line nerves are colored in gray, while components of the
associated cranial nerves are colored in black. (i) anteriorlateral line nerve. (j) middle lateral line nerve. (k) posteriorlateral line nerve. White
scale bar is 200 mm. Black scale bar is 100 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 4 The olfactory and optic nerves. (a and b) 3D depth coding views of a whole mount antibody staining (acetylated alpha-tubulin)
of a NF stage 47/48 X. laevis tadpole. (a) dorsal view of the anteriorhead region. (a1) maximum intensity projection of the same digital
stack. Dorsal view of the olfactory nerve (I). (b) dorsal view of the anteriorhead region around the eye. (b1) maximum intensity projection
of the same digital stack. Dorsal view of the optic nerve (II). (b2) 3D projection of the same digital stack. Lateral view of the eye to show
the convergence of the optic fibers toward the optic papilla. (b3) histological section through the diencephalic region of a X. laevis tadpole
at NF stage 46. The Chiasma opticum is closely associated with the ventral region of the diencephalon. Black and white scale bars are
200 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 5 The nerves innervating the extra-ocular muscles. Whole mount antibody staining of the nerves (anti-acetylated alpha-tubulin)
and muscles (anti-desmin) of a NF stage 47/48 X. laevis tadpole. (a and b) 3D depth coding views of the anteriorhead region. (a) dorsal
view. The route of the oculomotor nerve (III) is indicated by the white arrows. (a1) dorsal view of the anteriorhead region around the eye.
Nerves are shown in green and muscles are shown in red. The white arrows indicate the route of the III. The white asterisks indicate its
innervation sites. (a2) 3D reconstruction of the extra-ocular muscles and nerves of the same specimen in dorsal view. The oculomotor nerve
is shown in red. (b) dorsal view. The route of the trochlear nerve (IV) is indicated by the white arrows. (b1) dorsal view of the anteriorhead
region around the eye. Nerves are shown in green and muscles are shown in red. The white arrows indicate the route of the IV. The white
asterisks indicate its innervation site. (b2) 3D reconstruction of the extra-ocular muscles and nerves of the same specimen in dorsal view.
The trochlear nerve is shown in red. (c) dorsal view of the border region between the metencephalon and myelencephalon. Nerves are
shown in green. The white arrows indicate the routes of the abducensnerve (VI). (c1) dorsal view of the anteriorhead region around the
eye. Nerves are shown in green and muscles are shown in red. The white arrows indicate the route of the VI. (c2) 3D reconstruction of the
extra-ocular muscles and nerves of the same specimen in dorsal view. The abducensnerve is shown in red. The white scale bar is 200 mm
[Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 6 The profundal and trigeminal nerves. Whole mount antibody staining of the nerves (anti-acetylated alpha-tubulin) and muscles
(anti-desmin) of a NF stage 47/48 X. laevis tadpole. (a-e) 3D depth coding views of the nerves. (a) lateral view of the ganglia of the anterior
cranial nerves. (b) dorsal view of the anteriorhead region. (c) lateral view of the anteriorhead region between the mouth opening and the
eye. (d) dorsal view of the levator mandibulae muscles. (e) dorsal view of the same area as in (d) showing the nerves innervating the levator
mandibulae muscles. (f–i) nerves are shown in green, muscles are shown in red. (f) merged image from (d) and (e). The white asterisks
indicate the innervation sites of the levator mandibulae muscles by ramuli of the trigeminal nerve. (g) lateral view of the ventralanteriorhead region. (h) magnification of the area surrounded by the strippled rectangle in (g). (i) ventral view of the anteriorhead region. The white
scale bar is 200 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 7 The facial and vestibulocochlear nerves. (a–h) Whole mount antibody staining of the nerves (anti-acetylated alpha-tubulin) and
muscles (anti-desmin) of a NF stage 47/48 X. laevis tadpole. (a–c) and (f–h) 3D depth coding views of the nerves. (a) lateral view of the ganglia
of the cranial nerves anterior to the otic capsule. (b) dorsal view of the anteriorhead region. (c) lateral view of the anteriorhead region. (d and e)
maximum intensity projections of the same digital stack. Nerves are shown in green, muscles are shown in red. (d) lateral view of the anteriorhead region close to the eye. The white asterisks indicate the innervation sites of the Musculus orbitohyoideus and the Musculus quadratohyoangularis
by ramuli of the facial nerve (VII). (e) ventral view of the anteriorhead region. The white asterisks indicate the innervations sites of
the Musculus interhyoideus by the ramulus interhyoideus of the VII. (f) lateral view of the anteriorhead region, anteroventral to the eye. (g) dorsal
view of the area of the otic capsule. The yellow arrows mark anastomosing fibers between the anterior and the posterior portions of the vestibulocochlear
nerve (VIII). (h) lateral view of the same area shown in (g). (i–k) 3D reconstructions of the labyrinth organ and the components of
the VIII, prepared from the z-stack of the whole mount antibody staining. The anterior branch of the VIII is colored in light green and the posterior
branch in dark green. The labyrinth organ is shown half-transparent and colored in yellow while the maculae are colored in turquoise. (i) dorsal
view. (j) dorsolateral view. (k) lateral view. The white scale bar is 200 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 8 The glossopharyngeal and vagal nerves. Whole mount antibody staining of the nerves (anti-acetylated alpha-tubulin) and
muscles (anti-desmin) of a NF stage 47/48 X. laevis tadpole. (a and b) 3D depth coding views of the nerves. (a) dorsal view of the region of
the otic capsule. (b) dorsal view of the distal branchial region. (c–l) maximum intensity projections of the same digital stack. Nerves are
shown in green, muscles are shown in red. (c) dorsal overview of head and branchial region. (d) ventral overview of the head and branchial
region. (e–l) magnifications of the areas marked by the strippled rectangles in (c) and (d). The white asterisks indicate the innervation sites
of the branchial muscles by rami/ramuli of the glossopharyngeal (IX) and vagal nerves (X). The yellow arrows indicate the route of the
ramulus constrictor arcus branchiarium III of the X. (l) dorsal view of the cucullaris muscle. The white scale bar in (c) and (d) is 200 mm, in (e)
to (l)50 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 9 The anterior spinal nerves. Whole mount antibody staining of the nerves (anti-acetylated alpha-tubulin) and muscles (anti-desmin)
of a NF stage 47/48 X. laevis tadpole. (a) 3D depth coding view of the nerves. Dorsal view of the posteriorhead region. The white arrows
indicate the ventral spinal roots while gray arrows indicate the dorsal spinal roots. The spinal nerve 1 has no dorsal root. (b) maximum
intensity projections of the same digital stack. Dorsal view of the posteriorhead region. Nerves are shown in green, muscles are shown in
red. The white asterisks mark the fibers of the spinal nerves innervating the myotomes of the epaxial trunk musculature. Spinal nerve 1 does
not innervate any myotome. The pink arrow indicates the point where the second and third spinal nerves fuse. (c) dorsal close-up of the roots
of the third to fifth spinal nerves. The white asterisks mark the fibers of the spinal nerves innervating the myotomes of the epaxial trunk musculature.
(d) 3D depth coding view of the nerves. Lateral overview of the trunk region. d1, magnification of the area surrounded by the
strippled rectangle in (d). The white arrows indicate the route of the cutaneous ramus of the fifth spinal nerve. (e) maximum intensity projections
of the same digital stack. lateral view of the ventralhead region. Nerves are shown in green, muscles are shown in red. The blue arrow
indicates the fibers of spinal nerve 2 (and maybe 3) joining spinal nerve 1 and becoming the hypoglossal nerve. The yellow arrow indicates
the anastomosis between fibers of the hypoglossal nerve and spinal nerve 2. The white asterisks indicate the innervation sites of the hypoglossal
muscles by the hypoglossal nerve. The white scale bar is 200 mm [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 10 Schematic diagrams illustrating the rami and ramuli of the cranial nerves V, VII, IX, and X and the anterior spinal nerves.
Components of the lateral line nerves are colored in gray, while components of the associated cranial nerves are colored in black. Lines
ending with arrowheads indicate a sensory cutaneous or mucous innervation. Lines ending with asterisks indicate a motor innervation. (a)
profundal and trigeminal nerves (V). (b) facial nerve (VII). (c) glossopharyngeal (IX) and vagal nerves (X). (d) anterior spinal nerves
FIGURE 11 Scheme of the developmental sequence of the mandibular muscles of Xenopus laevis and their innervation pattern compared
to the innervation pattern described for Discoglossus pictus. Black arrows indicate the sequence of differentiation. Dotted arrows with an
interrogation mark indicate an unsure or unknown origin of the muscle. Numbers in brackets indicate muscles which might be homologous
in both species. The names of the predicted homologous muscle are different since Schlosser and Roth (1995) used the terminology of
Edgeworth (1935) while Ziermann and Olsson (2007) used their own terminology
