First published online March 12, 2009
Journal of Experimental Biology 212, 914-921 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027250
Responses of hatchling Xenopus tadpoles to water currents: first function of lateral line receptors without cupulae
Alan Roberts*,
Ben Feetham,
Mark Pajak and
Tom Teare
School of Biological Sciences, University of Bristol, Bristol, UK
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Fig. 1. Tadpole responses to water jets and suction. (A) Diagram of centre of test
dish showing tadpole placed over crossed lines on target and position of
pipette. (B–D) Polar plots showing the direction of swimming; rings are
at 20% spacing. (B) Spontaneous swimming was mainly forward. (C) When a 10 ms
water jet from a 50 µm diameter pipette was applied, tadpoles swam towards
the pipette. (D) When suction was applied for 50 ms from a 5 mm diameter
pipette, tadpoles swam away from the pipette.
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Fig. 2. Responses to water currents as a function of age and developmental stage.
(A) Numbers swimming into a water jet (black bars); (B) numbers swimming away
from suction (black bars). Grey bars show numbers swimming in other directions
and white bars numbers not responding. Stage (st) numbers are given at the
top.
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Fig. 3. Responses to water jets in immobilised tadpoles and effects of skin
abrasions and neomycin on behaviour. (A) Diagram of the stage 37/38 tadpole
from the side to show placement of a suction electrode on muscle in an area
where skin has been removed (dashed square) to record motor nerve activity.
The skin was abraded in the grey shaded areas just rostral (r) and caudal (c)
to the eye. (B) Example recordings of motor nerve bursts (at dots) during
fictive swimming evoked by touch to the skin and a water jet stimulus to the
head region. (C,D) Behavioural tests on swimming responses. (C) Bar chart
showing effects of local skin abrasion on mean number of swimming responses to
a water jet. (D) Bar chart showing reduction in mean number of swimming
responses after neomycin treatment. Error bars indicate s.e.m.
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Fig. 4. Scanning EM views of the side of the head of a stage 37/38 tadpole to show
lateral-line neuromasts. (A) Whole head with many ciliated cells (black arrow
indicates an example), eye (e), nasal opening (n), cement gland (cg) and gills
(g). Two rows of neuromasts lie between the large white arrows just caudal to
the eye. (B) At higher magnification two rows of neuromasts (white arrows)
lying among skin cells (s) can be distinguished by their long kinocilia.
Ciliated cells (black arrow indicates an example) and mucus cells (asterisk)
are also present. The dashed rectangle shows area enlarged in C. (C) Area in
B, with three neuromasts, each with many long kinocilia. (D) A neuromast with
five long curved kinocilia emerging from bundles of stereocilia at their
bases.
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Fig. 5. High magnification images of individual neuromasts to show kinocilia and
stereocilia. (A) Neuromast of stage 37/38 tadpole with two kinocilia (marked
by arrows) just emerging from between skin cells. (B) Neuromast of stage 42
tadpole with three kinocilia, in which the apical ends of two hair cells
(arrows) are clearly visible with the kinoclia emerging next to the bases of a
group of stereocilia. (C) Neuromast of stage 37/38 tadpole with seven
kinocilia. Stereocilia can be seen in two cases, and the orientation of the
kinocilia and stereocilia (indicated by arrows) is nearly opposite.
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Fig. 6. Low magnification images of heads, in lateral view from the right, to show
rows of neuromasts (each marked by white arrow) at stages (A) 32, (B) 37/38
and (C) 42. Labels in C are as in Fig.
4. Scale bars, 100 µm.
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Fig. 7. Effects of water current on living kinocilia at stage 37/38. (A) Schematic
diagram of the tadpole head pinned dorsal side up into a Sylgard block.
Kinocilia were viewed on left side and stimulated by a water jet from a glass
pipette. (B–D) Images of the area in the rectangle in A with a group of
kinocilia emerging from the left side of the head (dark area bottom right).
(B) With no current; black arrowheads mark positions of the outside kinocilia
in the group at rest. (C) During head to tail water current (in direction of
the arrow) from pipette at top; kinocilia are deflected caudally (to positions
marked by open arrowheads). (D) After current stops kinocilia return to their
resting position.
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Fig. 8. Observations on living kinocilia. (A) Schematic diagram of the tadpole head
from above. Kinocilia were viewed on the right side and a tungsten probe
(moving in the direction of the arrow) was used to manipulate the kinocilia.
The small square shows the area of images below. (B) Diagram of an excised
neuromast with jelly cupula (light grey) surrounding four kinocilia. If probe
1 is moved into the cupula, the kinocilia should all move together before they
appear to be contacted directly. If probe 2 is moved beyond the ends of the
kinocilia it should also move the cupula and all kinocilia should move with
it. (C–F) A vertical tungsten probe is moved caudally (as indicated by
white arrows) into a group of kinocilia protruding from the right side of the
head. (D) More rostral kinocilia move when directly contacted, but more caudal
kinocilia remain in place. (E,F) Kinocilia only move when directly contacted
by the probe. (G–L) Moving the same probe past the ends of the kinocilia
does not move them. In all images top is rostral, bottom is caudal and dark
shadow on the left is the right side of the head from which kinocilia emerge.
Black and white arrowheads in C and G mark the outermost kinocilia.
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© The Company of Biologists Ltd 2009
