Functional segregation within the pelvic nerve of male rats: a meso‐ and microscopic analysis

Abstract

The pelvic splanchnic nerves are essential for pelvic organ function and have been proposed as targets for neuromodulation. We have focused on the rodent homologue of these nerves, the pelvic nerves. Our goal was to define within the pelvic nerve the projections of organ‐specific sensory axons labelled by microinjection of neural tracer (cholera toxin, subunit B) into the bladder, urethra or rectum. We also examined the location of peptidergic sensory axons within the pelvic nerves to determine whether they aggregated separately from sacral preganglionic and paravertebral sympathetic postganglionic axons travelling in the same nerve. To address these aims, microscopy was performed on the major pelvic ganglion (MPG) with attached pelvic nerves, microdissected from young adult male Sprague–Dawley rats (6–8 weeks old) and processed as whole mounts for fluorescence immunohistochemistry. The pelvic nerves were typically composed of five discrete fascicles. Each fascicle contained peptidergic sensory, cholinergic preganglionic and noradrenergic postganglionic axons. Sensory axons innervating the lower urinary tract (LUT) consistently projected in specific fascicles within the pelvic nerves, whereas sensory axons innervating the rectum projected in a complementary group of fascicles. These discrete aggregations of organ‐specific sensory projections could be followed along the full length of the pelvic nerves. From the junction of the pelvic nerve with the MPG, sensory axons immunoreactive for calcitonin gene‐related peptide (CGRP) showed several distinct patterns of projection: some projected directly to the cavernous nerve, others projected directly across the surface of the MPG to the accessory nerves and a third class entered the MPG, encircling specific cholinergic neurons projecting to the LUT. A subpopulation of preganglionic inputs to noradrenergic MPG neurons also showed CGRP immunoreactivity. Together, these studies reveal new molecular and structural features of the pelvic nerves and suggest functional targets of sensory nerves in the MPG. These anatomical data will facilitate the design of experimental bioengineering strategies to specifically modulate each axon class.

Recording of Electrically Evoked Neural Activity and Bladder Pressure Responses in Awake Rats Chronically Implanted With a Pelvic Nerve Array

“…Without more targeted physiological assays, we cannot discount an impact of pelvic nerve stimulation on non-LUT targets or the vasculature. It may also be possible to target pelvic nerve stimulation to particular neural populations, as afferents innervating the LUT have recently been identified as spatially segregated from rectal afferents (Bertrand et al, 2020). Another potential outcome of pelvic nerve stimulation is activation of nociceptive sensory axons projecting to the bladder.…”

An adeno‐associated viral labeling approach to visualize the meso‐ and microanatomy of mechanosensory afferents and autonomic innervation of the rat urinary bladder

“…Their peripheral projection to pelvic organs via the hypogastric and pelvic nerves could be identified in whole mounts of dissected pelvic ganglia with their primary connections. By immunostaining for CGRP and TH, we were able to distinguish myelinated nonpeptidergic axons from CGRP sensory axons and sympathetic postganglionic axons 41,57 . We did not identify any AAV‐positive preganglionic neurons in the spinal cord so do not consider any AAV‐positive axons in the pelvic or hypogastric nerves as preganglionic.…”

“…By immunostaining for CGRP and TH, we were able to distinguish myelinated nonpeptidergic axons from CGRP sensory axons and sympathetic postganglionic axons. 41,57 We did not identify any AAV-positive preganglionic neurons in the spinal cord so do not consider any AAV-positive axons in the pelvic or hypogastric nerves as preganglionic. Further examination of AAV-positive, TH-negative axons within pelvic nerve fascicles did not identify any overt clustering or other specific patterning of the sensory subclass, although further detailed spatial analyses may reveal this.…”

Lighting Up Mechanosensation: dyeing to see PIEZO2

“…In a preliminary effort to elucidate the molecular features of Torrey Pines neurons, we colocalized FM dye labeling with neuronal markers using whole-mount immunohistochemistry and genetic reporter mice. Despite dense peptidergic innervation of the urinary tract (Barry et al, 2018; Bertrand et al, 2020), Torrey pines neurons were not CGRP-positive (Supplemental Figure 6). We also found Torrey Pines neurons were beta-III tubulin- and neurofilament heavy (NFH)-positive, indicating that these are medium to large diameter neurons (Fig.…”