Neurons In Lumbosacral Dorsal Root Ganglia Research Articles

Retrograde Labeling of Different Distribution Features of DRG P2X2 and P2X3 Receptors in a Neuropathic Pain Rat Model.

The distributions of P2X subtypes during peripheral neuropathic pain conditions and their differential roles are not fully understood. To explore these characteristics, the lumbosacral dorsal root ganglion (DRG) in the chronic constriction injury (CCI) sciatic nerve rat model was studied. Retrograde trace labeling combined with immunofluorescence technology was applied to analyze the distribution of neuropathic nociceptive P2X1-6 receptors. Our results suggest that Fluoro-Gold (FG) retrograde trace labeling is an efficient method for studying lumbosacral DRG neurons in the CCI rat model, especially when the DRG neurons are divided into small, medium, and large subgroups. We found that neuropathic nociceptive lumbosacral DRG neurons (i.e., FG-positive cells) were significantly increased in medium DRG neurons, while they declined in the large DRG neurons in the CCI group. P2X3 receptors were markedly upregulated in medium while P2X2 receptors were significantly decreased in small FG-positive DRG neurons. There were no significant changes in other P2X receptors (including P2X1, P2X4, P2X5, and P2X6). We anticipate that P2X receptors modulate nociceptive sensitivity primarily through P2X3 subtypes that are upregulated in medium neuropathic nociceptive DRG neurons and/or via the downregulation of P2X2 cells in neuropathic nociceptive small DRG neurons.

SPARC: Building a Three‐Dimensional Atlas of Spinal Cord Circuits Regulating Lower Urinary Tract Function

Lumbar and sacral spinal cord circuits are critical for pelvic visceral regulation, as well as being engaged in pelvic pain states. Our study has focused on mapping two components of these circuits, the central projections of primary sensory neurons and the preganglionic neurons that drive motor activity via pelvic ganglia. These sensory pathways form a minority of lumbosacral dorsal root ganglion neurons. Likewise, although the parasympathetic preganglionic neurons are easily identified (aggregated in the sacral intermediolateral nucleus), the sympathetic preganglionic neurons comprise a minority of the thoracolumbar preganglionic neurons and are largely located outside of the intermediolateral nucleus. Our specific objectives were to map in adult male and female SD rats: (i) the terminal fields of primary sensory pathways that innervate distinct regions of the lower urinary tract; (ii) sympathetic and parasympathetic preganglionic neurons that innervate pelvic ganglion neurons, many of which regulate lower urinary tract tissues. To facilitate this, we have developed a spinal cord reference atlas, utilizing large volume immunostaining and clearing methods (iDISCO) to visualize primary neural classes throughout the entire lumbosacral cord. Region‐specific sensory neurons were identified by micro‐injection of CTB (B subunit of cholera toxin) into the bladder body, bladder trigone or urethra. In a separate group of animals, pelvic ganglion‐projecting preganglionic neurons were identified by microinjecting CTB bilaterally into the major pelvic ganglion (MPG). Four days later, spinal cord tissue was removed for immunohistochemical processing. We then combined several imaging approaches to reveal both mesoscopic and microscopic anatomical features of these pathways. Sensory terminals were mapped by constructing three‐dimensional representations, aligning alternate cryosections (TissueMaker, MicroBrightField) and relating CTB‐labelled terminals to specific chemoarchitectural features including spinal laminae and preganglionic neurons. Several molecular subclasses of sacral CTB‐labelled preganglionic neurons were mapped using the same strategy, while in other studies, the MPG‐projecting preganglionic neurons were mapped across the entire lumbosacral spinal cord, using immunohistochemistry of intact specimens and iDISCO clearing. Maps were constructed using 3D datasets obtained by light sheet microscopy or, for higher resolution analyses of neuronal connectivity and dendritic structure, ribbon scanning confocal microscopy. In conclusion, our tracing studies provide new insights into the complexity of sensory projections from defined pelvic visceral structures, and the location and structural properties of specific classes of pelvic viscera‐regulating preganglionic neurons. Our new spinal cord reference dataset provides a rich resource for mapping neural features following experimental intervention, for studies across the autonomic nervous system.Support or Funding InformationNIH SPARC 3OT2OD023872‐01S4

Characterization of bladder sensory neurons in the context of myelination, receptors for pain modulators, and acute responses to bladder inflammation

Bladder sensation is mediated by lumbosacral dorsal root ganglion neurons and is essential for normal voiding and nociception. Numerous electrophysiological, structural, and molecular changes occur in these neurons following inflammation. Defining which neurons undergo these changes is critical for understanding the mechanism underlying bladder pain and dysfunction. Our first aim was to define the chemical classes of bladder sensory neurons that express receptors for the endogenous modulators of nociceptor sensitivity, glial cell line-derived neurotrophic factor (GDNF), the related neurotrophic factor, artemin, and estrogens. Bladder sensory neurons of adult female Sprague-Dawley rats were identified with retrograde tracer. Diverse groups of neurons express these receptors, and some neurons express receptors for both neurotrophic factors and estrogens. Lumbar and sacral sensory neurons showed some distinct differences in their expression profile. We also distinguished the chemical profile of myelinated and unmyelinated bladder sensory neurons. Our second aim was to identify bladder sensory neurons likely to be undergoing structural remodeling during inflammation. Following systemic administration of cyclophosphamide (CYP), its renal metabolite acrolein causes transient urothelial loss, exposing local afferent terminals to a toxic environment. CYP induced expression of the injury-related immediate-early gene product, activating transcription factor-3 (ATF-3), in a small population of sacral nitrergic bladder sensory neurons. In conclusion, we have defined the bladder sensory neurons that express receptors for GDNF, artemin and estrogens. Our study has also identified a sub-population of sacral sensory neurons that are likely to be undergoing structural remodeling during acute inflammation of the bladder. Together these results contribute to increased understanding of the neurons that are known to be involved in pain modulation and hyperreflexia during inflammation.

Neurochemical features of boar lumbosacral dorsal root ganglion neurons and characterization of sensory neurons innervating the urinary bladder trigone

Porcine lumbosacral dorsal root ganglion (DRG) neurons were neurochemically characterized by using six neuronal markers: calcitonin gene-related peptide (CGRP), substance P (SP), neuronal nitric oxide synthase (nNOS), neurofilament 200kDa (NF200), transient receptor potential vanilloid 1 (TRPV1), and isolectin B4 (IB4) from Griffonia simplicifolia. In addition, the phenotype and cross-sectional area of DRG neurons innervating the urinary bladder trigone (UBT) were evaluated by coupling retrograde tracer technique and immunohistochemistry. Lumbar and sacral DRG neuronal subpopulations were immunoreactive (IR) for CGRP (30 ± 3% and 29 ± 3%, respectively), SP (26 ± 8% and 27 ± 12%, respectively), nNOS (21 ± 4% and 26 ± 7%, respectively), NF200 (75 ± 14% and 81 ± 7%, respectively), and TRPV1 (48 ± 13% and 43 ± 6%, respectively), and labeled for IB4 (56 ± 6% and 43 ± 10%, respectively). UBT sensory neurons, which were distributed from L2 to Ca1 DRG, had a segmental localization, showing their highest density in L4-L5 and S2-S4 DRG. Lumbar and sacral UBT sensory neurons expressed similar percentages of NF200 immunoreactivity (64 ± 33% and 58 ± 12%, respectively) but showed a significantly different immunoreactivity for CGRP, SP, nNOS, and TRPV1 (56 ± 9%, 39 ± 15%, 17 ± 13%, 62 ± 10% vs. 16 ± 6%, 16 ± 11%, 6 ± 1%, 45 ± 24%, respectively). Lumbar and sacral UBT sensory neurons also showed different IB4 labeling (67 ± 19% and 48 ± 16, respectively). Taken together, these data indicate that the lumbar and sacral pathways probably play different roles in sensory transmission from the UBT. The findings related to cell size also reinforced this hypothesis, because lumbar UBT sensory neurons were significantly larger than sacral ones (1,112 ± 624 μm(2) vs. 716 ± 421 μm(2) ).

17β-estradiol modifies TRPV1 mRNA expression in DRG neurons

While it has been demonstrated that women experience greater cancer pain and pain severity than men, the potential role of estrogen in regulating nociception particularly as it relates to tumor pain remains unclear. Current data indicate that estrogens act directly on the nervous system to affect the severity of pain, but the mechanisms underlying this effect are unclear. A major nociceptive mechanism associated with the development of cancer pain is activation of the transient receptor potential vanilloid-1 (TRPV1) channel. TRPV1 is a Ca2+-permeable ionotropic receptor activated by multiple sensory stimuli including heat, acid, and protons. Antagonism of the TRPV1 channel attenuates nociception in a mouse bone cancer pain model. Both estrogen (ER) and TRPV1 receptors are known to be expressed on dorsal root ganglion (DRG) neurons, whose axons transmit pain from the periphery to the spinal cord. This raises the question of whether estrogen can alter TRPV1 receptor expression or function particularly in pain states like cancer pain. The present study was designed to evaluate the effects of estrogen on pain sensitivity and TRPV1 expression in the DRG of male and female C3H mice in a mouse model of bone cancer pain. One goal was to determine whether estrogen modulates nociceptive receptors in the DRG in a manner consistent with its effects on pain sensitivity. This study demonstrated that exposure to 17β-estradiol in gonadectomized males (ORCH+E), but the lack of this same hormone in gonadectomized females (OVX), significantly reduced the mRNA levels of TRPV1 in lumbosacral DRG neurons and this correlated with a reduction in tumor-induced nociception. Our results suggest that modulation of 17β-estradiol causes a down regulation in TRPV1 expression in DRG neurons, which may be associated with a reduction in fibrosarcoma-induced mechanical allodynia in both male female mice.

Up-regulation of calcitonin gene-related peptide and receptor tyrosine kinase TrkB in rat bladder afferent neurons following TNBS colitis

Colonic inflammation has profound effects on the urinary bladder physiology and produces hypersensitivity of bladder afferent neurons and neurogenic bladder overactivity. Calcitonin gene-related peptide (CGRP) expressed in dorsal root ganglia (DRG) plays an important role in mediating sensory perception following visceral inflammation. In the present study, we determined that the expression of CGRP was increased in bladder afferent neurons in lumbosacral DRG following tri-nitrobenzene sulfonic acid (TNBS)-induced colitis in rat. After colitis, the percentage of bladder afferent neurons expressing CGRP was increased in L1 (61.2 ± 2.9% in colitis vs. 37.7 ± 5.1% in controls; p < 0.05) and S1 DRG (26.3 ± 2.3% in colitis vs. 15.5 ± 1.9% in controls; p < 0.01). We also demonstrated that the expression of tyrosine kinase receptor TrkB was increased in L1 (39.7 ± 2.9% in colitis vs. 25.2 ± 4.3% in controls; p < 0.05) and S1 DRG (45.6 ± 3.8% in colitis vs. 38.3 ± 3.6% in controls; p < 0.01) following colitis. CGRP and TrkB were co-stored in a subpopulation of DRG neurons in control and colitic animals and the number of DRG cells co-expressing CGRP and TrkB was significantly increased in L1 (2.7-fold, p < 0.01) and S1 DRG (2.4-fold, p < 0.01) following colitis. In cultured DRG, exogenous BDNF application significantly increased CGRP expression, which was blocked by TrkB selective inhibitor K252a. These results suggest that up-regulation of CGRP and TrkB in bladder afferent neurons may play a role in colon-to-bladder cross-sensitization following colitis.

Time of origin of substance P-positive neurons in chick dorsal root ganglia

The birthdates of substance P-positive neurons in chick dorsal root ganglia (DRGs) were determined by a combined immunohistochemical-autoradiographic method. Both substance P-positive and -negative neurons in lumbosacral DRGs were born between days E3 and E6 in ovo. Substance P-positive neurons were born relatively late in comparison to other neurons in the DRG, but did not have unique birthdays.