<p class="first" id="P1">Pelvic nerve (PN) bladder primary afferent neurons were retrogradely
labeled by intraparenchymal
(IPar) microinjection of fluorescent tracer or intravesical (IVes) infusion of tracer
into the bladder lumen. IPar and IVes techniques labeled two distinct populations
of PN bladder neurons differentiated on the basis of dorsal root ganglion (DRG) soma
labeling, dye distribution within the bladder, and intrinsic electrophysiological
properties. IPar (Fast blue)- and IVes (DiI)-labeled neurons accounted for 91.5% (378.3
± 32.3) and 8% (33.0 ± 26.0) of all labeled neurons, respectively (p<0.01), with
only
2.0 ± 1.2 neurons labeled by both techniques. When dyes were switched, IPar (DiI)-
and IVes (Fast blue) labeled neurons accounted for 77.6% (103.0 ± 25.8) and 22.4%
(29.8 ± 10.5), respectively (P<0.05), with 6.0 ± 1.5 double-labeled neurons. Following
IPar labeling, DiI was distributed throughout non-urothelial layers of the bladder.
In contrast, dye was contained within the urothelium and occasionally the submucosa
after IVes labeling. Electrophysiological properties of DiI-labeled IPar and IVes
DRG neurons were characterized by whole-mount,
<i>in situ</i> patch-clamp recordings. IPar- and IVes-labeled neurons differed significantly
with
respect to rheobase, input resistance, membrane capacitance, amplitude of inactivating
and sustained K
<sup>+</sup> currents, and rebound action potential firing, suggesting that the IVes
population
is more excitable. This study is the first to demonstrate that IVes labeling is a
minimally invasive approach for retrograde labeling of PN bladder afferent neurons,
to selectively identify urothelial versus non-urothelial bladder DRG neurons, and
to elucidate electrophysiological properties of urothelial and non-urothelial afferents
in an intact DRG soma preparation.
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