B. Langenfeldoster et al., REGULAR AND PHOTODAMAGE-ENHANCED REMODELING IN VITALLY STAINED FROG AND MOUSE NEUROMUSCULAR-JUNCTIONS, Journal of neurocytology, 22(7), 1993, pp. 517-530
Repeated in vivo observations of vitally stained neuromuscular junctio
ns allow direct monitoring of ongoing structural changes, although, no
rmally occurring changes (remodelling) and those inflicted by the illu
mination itself (photodamage) need to be dissociated. In frog cutaneus
pectoris muscles, stained in vivo with 4Di-2ASP twice within four to
five weeks, growth only was observed in 14 out of 92 junctions (in 18
muscles), retraction only in 19, and both features simultaneously in 2
2 junctions, while 37 junctions showed no changes. The summed growth i
n a junction amounted to 5-42 mum, retraction to 5-52 mum, while overa
ll changes in synaptic length were absent. This and the simultaneous o
ccurrence of both, growth and retraction within a single junction, ind
icates junctional remodelling. Similar amounts of remodelling were obs
erved in junctions illuminated for 180, 60 or 10-30 s, indicating that
within this range and with the given optical system, blue light and 4
Di-2ASP fluorescence were not harmful. Remodelling was not induced by
the experimental procedure per se, since in in vitro preparations sign
s of sprouting (and retraction) were equally frequent in junctions of
totally untreated muscles, in junctions vitally stained four to five w
eeks previously or vitally stained but not light-exposed in the same m
uscle. In endplates of mouse gluteus maximus muscles double stained wi
th 4Di-2ASP and rhodamine-alpha-bungarotoxin, unusually large (>10 mum
) terminal sprouts and retraction with gain and loss of ACh-receptors
became prominent 9-29 days following illumination for more than 60 s.
Frequently also, muscle fibre damage with local contracture and acute
loss of stainability of axon terminals occurred; often followed by mus
cle fibre denervation. In contrast, no such changes occurred after low
er illumination intensities (12% emission filter for green) or shorter
exposure times (<60 s); even at a fourth exposure performed within 53
days. Previously reported smaller changes indicating regular remodell
ing were not investigated here.