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A
A
In vivo motility of dendritic filopodia in 1 month mice
NM
Comm.
Auditory
nerve
1 ┬Ám
2 hours
NL
B
In vivo retraction and extension of dendritic spines
B
2 hours
24 hours
Control
Dorsal
dendrites
(innervated)
2 hours
Soma
Ventral
dendrites
(deafferented)
C
*
0.04
C
40
0.03
% Difference
(1-L 2 /L 1 )*100
30
0.02
20
L 1
0.01
10
0.0
L 2
Normal
Deprived
Normal
Deprived
Normal
Deprived
P21
P28
P42
0
Age and treatment
0
24
48
96
FIGURE 9.32 Two-photon imaging of dendritic spine and filopo-
dia motility in vivo. A. A set of time-lapse images (one hour inter-
vals) in a 1-month-old animal shows that filopodia undergo rapid
extension (arrows) and retraction (arrowheads). B. Dendritic spines
motility is more prominent at P21. Two time-lapse sequences are
shown (acquired over two hours). In the first, a spine is retracted
(top), and in the second a spine elongates (bottom). Binocular dep-
rivation from P14 significantly increases spine motility at P28 by
60%. However, there is no change in motility when deprivation
begins at P21. There is a slight reduction in motility in mice deprived
at P42. (From Grutzendler et al., 2002; Majewska and Sur, 2003)
Time after cut (hours)
FIGURE 9.31 Synaptic activity regulates dendrite length in the
chick auditory brain stem. A. Neurons of the nucleus laminaris (NL)
receive afferents from ipsilateral NM to their dorsal dendrites and
from the contralateral NM to their ventral dendrites. The ventral
dendrites of NL neurons were denervated by cutting NM afferent
axons at the midline. The dorsal dendrites remained fully inner-
vated. B. When NL neurons were stained with the Golgi technique,
the ventral dendrites were found to be significantly shorter than
those on the dorsal side within one hour of the manipulation. C. The
ventral dendrites shrunk by almost 40% by 96 hours after the lesion.
(Adapted from Deitch and Rubel, 1984)
Dendrite morphology can be studied in vivo by
imaging visual cortical neurons in transgenic mice that
express a fluorescent protein. Images obtained over a
two-hour period show that dendrites extend and
retract filopodial processes and spines while they are
developing (Figure 9.32A and B). However, the
number of filopodia declines dramatically, and the
spines become quite stable over the first two postnatal
months (Grutzendler et al., 2002). When animals are
visually deprived during the critical period, spine
ents to the ventral dendrites are cut. Even at the earliest
time point, there is a 14% decrease in the ventral den-
drites compared to the dorsal set (Deitch and Rubel,
1984). Since this is well before terminals are actually
removed from the postsynaptic neuron, the dendritic
atrophy probably results from the sudden cessation of
synaptic activity. Electron microscopy revealed that this
change in morphology was correlated with a dramatic
change in cytoskeletal structures, such as microtubules.
 
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