Long-term overexpression of GFP–TrkB.T1 causes neuronal atrophy and
dendritic beading in facial motor neurons. Transgene expression was detected with
GFP immunohistochemistry. A, Transduced cells at 2
weeks of expression of GFP–TrkB.T1 show typical motor neuron morphology
(arrows). B, At 4 weeks, some
GFP–TrkB.T1-expressing neurons exhibit a reduced soma size (arrowheads),
whereas other neurons are not affected (arrows).
C–E, Transgene expression at 2 months.
C, Example of a motor neuron with a rounded soma
(open arrowhead) and severe dendritic swelling (indicated with arrowheads).
Neighboring transduced neurons display regular soma contours and dendrites (arrows).
D, GFP–TrkB.T1-expressing motor neuron with
a rounded soma (open arrowhead). Dendrites contain large, spherical swellings
(arrowheads) separated by thin, atrophied segments. E,
Higher magnification of the boxed area in D. Open
arrowheads indicate dendritic varicosities, which appear as elongated enlargements
of dendrites connected by segments of normal caliber and also occur in intact motor
neurons. F, GFP–TrkB.T1 motor neuron morphology
at 4 months (arrows). The open arrowhead indicates transduced motor neuron with
rounded soma, eccentric nucleus, and thinned dendrites (arrowheads).
G, GFP-f-expressing motor neurons (arrows) show
regular soma contours and dendrites (arrowheads) 2 months after injection. Scale
bars: (in G) A–C,
F, G, 100 μm;
D, 25 μm; E,
10 μm.