PTU - Polskie Towarzystwo Urologiczne
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Differences in the chemical coding of lumbar and sacral/coccygeal sensory neurons supplying porcine urinary bladder
Article published in Urologia Polska 2008/61/Supl. 1.

authors

Agnieszka Bossowska, Joanna Wojtkiewicz, Andrzej Borkowski, Piotr Radziszewski, Mariusz Majewski
Katedra Fizjologii Człowieka, Wydział Nauk Medycznych, Uniwersytet Warmińsko-Mazurski w Olsztynie
Klinika Urologii Ogólnej, Onkologicznej i Czynnościowej Warszawskiego Uniwersytetu Medycznego

summary

Introduction.

Sensory neurons of dorsal root ganglia (DRG) constitute one of the cardinal elements of the micturition-regulating neural circuit. As of now, the neurochemical characteristic of bladder-projecting sensory neurons has been well-documented in laboratory animals only. As domestic pig can be regarded as one of the better, even the best, animal model for human lower urinary tract, therefore, it appears to be of importance to establish in detail the chemical coding of sensory neurons supplying urinary bladder in this animal species, providing in this way a background for further physio-pharmacological studies based on this animal model.

Objectives.

The present study was aimed at revealing the detailed neurochemical characteristic of urinary bladder-projecting DRG sensory neurons in the pig, with special regard to differences in their phenotypes between the lumbar and sacral/coccygeal ones.

Materials and methods.

The study was performed on six juvenile female pigs, in which the retrograde tracer Fast Blue (FB) was injected into the urinary bladder wall in multiple injections. Three weeks later, all animals were sacrificed, transcardially perfused and DRGs of interest were collected. The neurochemical characterization was performed using routine single- and double-immunofluorescence labelling techniques on 10-μm-thick cryostat sections.

Results.

The vast majority (85%) of sensory neurons supplying porcine urinary bladder was located in sacral S3-S4 ganglia and in first coccygeal ganglion Cq1 (17%, 50% and 18%, respectively). The remaining 15% of FB+ nerve cells was found in lumbar ganglia from L3 to L6 (7%, 5%, 2% and 1%, respectively). Vast majority of the retrogradelly traced neurons in lumbar DRGs comprised of medium- (65%) and small-sized (40%) cells, while neurons belonging to the class of “large” DRG cells were not observed. On the other hand, FB+ cells located in sacral and coccygeal DRGs were mainly of small diameter (65%) while the medium-sized neurons constituted a less numerous subset (33%). Sporadically, single “large” afferent cells (2%) were also found in these ganglia. It has been found that bladder-projecting sensory neurons contained
substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating peptide (PACAP), nitric oxide synthase (NOS), galanin (GAL), calbindin (CB) and somatostatin (SOM), constituting 40%, 35%, 26%, 9%, 6%, 6%, of all retrogradelly traced DRG neurons, respectively. Approximately 40% of FB+ cells were immunonegative for any biological active substance studied. Significant differences in the number of neurons containing particular neurotransmitters were found between lumbar and sacral/ coccygeal DRGs: while the vast majority of FB+ cells were CGRP-, NOS-, GAL-, or SOM-IR (47%, 8%, 8% and 4.5%, respectively) in lumbar DRGs, such coded neurons comprised only 23%, 1.5%, 2% and 0.2% of FB+ neurons in the sacral/coccygeal ganglia, respectively. On the other hand, a higher number of retrogradely labelled S3 and S4 DRG neurons expressed PACAP (31%), when compared to FB+ neurons within the lumbar DRGs (23%). There were no significant differences in the number of SP- or CB-containing bladder sensory neurons between the lumbar and sacral/coccygeal DRGs studied.

Conclusions.

Thus, as may be judged from the results of the present study, the populations of lumbar and sacral/coccygeal bladder-projecting sensory neurons were heterogeneous both in terms of their chemical coding (and thus, in terms of neurotransmitters released from their nerve endings), as well as in terms of their exact function(s). Hence, taking into account also the distribution pattern of traced DRG neurons, it appears possible that the bladder filling phase is controlled by lumbar sensory cells (whose chemical coding distinctly differs from this of sacral/coccygeal ones), while the micturition phase (and also the mechanism(s) of detrusor-sphincter synergy) is under control
of sacral/coccygeal DRGs. However, this assumption has to be confirmed by further studies.