Regional Targeting of Bladder and Urethra Afferents in the Lumbosacral Spinal Cord of Male and Female Rats: A Multiscale Analysis

Abstract

Sensorimotor circuits of the lumbosacral spinal cord are required for lower urinary tract (LUT) regulation as well as being engaged in pelvic pain states. To date, no molecular markers have been identified to enable specific visualization of LUT afferents, which are embedded within spinal cord segments that also subserve somatic functions. Moreover, previous studies have not fully investigated the patterning within or across spinal segments, compared afferent innervation of the bladder and urethra, or explored possible structural sex differences in these pathways. We have addressed these questions in adult Sprague Dawley rats, using intramural microinjection of the tract tracer, B subunit of cholera toxin (CTB). Afferent distribution was analyzed within individual sections and 3D reconstructions from sections across four spinal cord segments (L5-S2), and in cleared intact spinal cord viewed with light sheet microscopy. Simultaneous mapping of preganglionic neurons showed their location throughout S1 but restricted to the caudal half of L6. Afferents from both LUT regions extended from L5 to S2, even where preganglionic motor pathways were absent. In L6 and S1, most afferents were associated with the sacral preganglionic nucleus (SPN) and sacral dorsal commissural nucleus (SDCom), with very few in the superficial laminae of the dorsal horn. Spinal innervation patterns by bladder and urethra afferents were remarkably similar, likewise the patterning in male and female rats. In conclusion, microscale to macroscale mapping has identified distinct features of LUT afferent projections to the lumbosacral cord and provided a new anatomic approach for future studies on plasticity, injury responses, and modeling of these pathways.

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

“…These terminations were prevalent in regions containing preganglionic neurons and interneurons involved in autonomic regulation. This concurs with recent studies using cholera toxin B subunit to map bladder‐ and urethra‐projecting afferents in male and female rats 50 . This tracer labels both myelinated and unmyelinated visceral afferents, 50,51 so would have included the population visualized by AAV in the current study.…”

“…This concurs with recent studies using cholera toxin B subunit to map bladder-and urethra-projecting afferents in male and female rats. 50 This tracer labels both myelinated and unmyelinated visceral afferents, 50,51 so would have included the population visualized by AAV in the current study. Further application of this approach will allow specific communication between myelinated afferents and specific components of the autonomic circuit to be probed.…”

“…Bladder afferents target the sacral preganglionic and dorsal commissural nuclei, demonstrated by c-fos activation studies [46][47][48][49] and tracing using cholera toxin B subunit 50 that both myelinated and unmyelinated afferents. 51 Here we had the opportunity to selectively visualize the myelinated component of spinally projecting afferents (target organ not defined), identifying them in the sacral preganglionic and dorsal commissural nuclei (Figure 11A,C,E-H).…”

Comparative localization of colorectal sensory afferent central projections in the mouse spinal cord dorsal horn and caudal medulla dorsal vagal complex

“…In accordance, projections of DMV neurons have been located with the myenteric ganglia along the length of the mouse colon (Tao et al., 2021). As for SPN neurons, tracer injections may have occurred within small microganglia localized in the rectal adventitia that are known to contain populations of rectospinal neurons (Fuller‐Jackson et al., 2021; Luckensmeyer et al., 1998; Olsson et al., 2006). This aligns with observing SPN neurons being labeled solely from caudal CTB injections, whereas DMV neurons were labeled from all injection sites.…”

A 3D atlas of sexually dimorphic lumbosacral motor neurons that control and integrate pelvic visceral and somatic functions in rats

“…Unlike humans and non-human primates, in this species these two functional classes are each located in a distinct nucleus within the lumbosacral cord (Nadelhaft and McKenna, 1987). These sections were immunolabelled for a previous study (Fuller-Jackson et al, 2021b), however in the current study this open dataset was reanalyzed to quantify the area of each motor nucleus in each section. Lumbosacral spinal cords (L5-S2) were cryoprotected overnight in 0.1 M PBS containing 30% sucrose prior to embedding in Tissue-Tek optimal cutting temperature compound (Sakura Finetek, CA, USA).…”