Electrophysiological properties of lumbosacral primary afferent neurons innervating urothelial and non-urothelial layers of mouse urinary bladder

Abstract

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, in situ patch-clamp recordings. IPar- and IVes-labeled neurons differed significantly with respect to rheobase, input resistance, membrane capacitance, amplitude of inactivating and sustained K+ 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.

A biophysically detailed computational model of urinary bladder small DRG neuron soma

“…The observed R in from the model is in range of values reported in literature for dissociated bladder small DRG neurons i.e. 175 MΩ-581 MΩ [ 7 , 41 ] and is also close to the value reported for intact bladder DRG neurons (332 MΩ) [ 42 ].…”

“…In bladder small afferents neurons, among the many types K + channels expressed, transient A-type (K A ) channel (slowly-inactivating), delayed-rectifier (KDR) and KCNQ/M channels are the predominant ones [ 7 , 10 , 33 , 42 ]. Presence of Ca 2+ -activated K + (K Ca ) channels: large-conductance K Ca (BK Ca ) and small-conductance K Ca (SK Ca ) in bladder small DRG neurons have suggested by some studies [ 30 , 52 ].…”

Differential Regulation of Bladder Pain and Voiding Function by Sensory Afferent Populations Revealed by Selective Optogenetic Activation

“…The observed proportion of eYFP+ bladder afferents in Scn10a Cre ;Ai32 mice was slightly higher than previous reports of Na v 1.8 expression in 75% of mouse DRG neurons (Shields et al, 2012 ), and higher than the 70%–74% of bladder afferents in rat that exhibit TTX-resistant, Na v 1.8-mediated sodium currents (Yoshimura et al, 1996 , 2006 ; Masuda et al, 2006 ). It is important to note that in all of these studies and in the present study, retrograde labeling of afferent somata was achieved by microinjection of CTβ into the bladder parenchyma, which labels a distinct anatomical subset of non-urothelial, bladder-innervating primary afferents (Kanda et al, 2016 ; Clodfelder-Miller et al, 2017 ). Whether there are differences in the proportion of peri-urothelial afferents in Trpv1 Cre ;Ai32 vs. Scn10a Cre ;Ai32 mice and whether peri-urothelial afferents provide sensory input that is unique from that of the non-urothelial afferents studied here remains to be determined.…”

Morphological and functional diversity of first-order somatosensory neurons

“…For example, 90% of DRG neurons innervating the bladder are phasic (Kanda et al 2016), and capsaicin-sensitive bladder afferents change their firing pattern from phasic to tonic after spinal transection (Takahashi et al 2013). Similarly, Freisinger et al (2013) showed that a higher percentage of renal afferents are tonic (56%) compared to nonrenal afferents (12%).…”

“…Retrograde labeling allows characterization of the neurons that innervate specific organs. In some special cases, where the sensory modality is known a priori, this approach allows the study of a functionally defined population (Benson et al 1999;Silbert et al 2003;Connor et al 2005;Freisinger et al 2013;Kanda et al 2016). In addition, genetically modified animals that express a marker (for example, a fluorescent protein) under the control of a gene of interest are useful tools to study the properties of neurons that express that gene (Dussor et al 2008;Tang et al 2016;Le Pichon and Chesler 2014).…”