Percentage Of Dorsal Root Ganglion Neurons Research Articles

Augmented P2X response and immunolabeling in dorsal root ganglion neurons innervating skeletal muscle following femoral artery occlusion

The responsiveness of sensory neurons to muscle metabolites is altered under the conditions of insufficient limb blood supply in some diseases, such as peripheral artery disease. The purpose of this study was to examine ATP-induced current with activation of purinergic P2X subtypes P2X₃ and P2X₂/₃ in dorsal root ganglion (DRG) neurons of control limbs and limbs with 24 h of femoral artery occlusion using whole cell patch-clamp methods. Also, dual-labeling immunohistochemistry was employed to determine existence of P2X₃ expression in DRG neurons of thin-fiber afferents. DRG neurons from 4- to 6-wk-old rats were labeled by injecting the fluorescence tracer DiI into the hindlimb muscles 4-5 days before the recording experiments. Transient (P2X₃), mixed (P2X₃ and P2X₂/₃), and sustained (P2X₂/₃) current responses to α,β-methylene ATP (a P2X receptor agonist) are observed in small and medium DRG neurons, and size distribution of DRG neurons is similar in control and occluded limbs. However, the peak current amplitude of DRG neuron induced by stimulation of P2X₃ and/or P2X₂/₃ is larger in occluded limbs than that in control limbs. Moreover, the percentage of DRG neurons with P2X₃ transient currents is greater after arterial occlusion compared with control. In addition, a rapid desensitization was observed in DRG neurons with transient currents, but not with sustained currents in control and occluded groups. Furthermore, results from immunofluorescence experiments show that femoral artery occlusion primarily augments P2X₃ expression within DRG neurons projecting C-fiber afferents. Overall, these findings suggest that 1) greater ATP-induced currents with activation of P2X₃ and P2X₂/₃ are developed when hindlimb arterial blood supply is deficient under ischemic conditions and 2) increased P2X₃ expression is largely observed in C-fibers of DRG neurons after hindlimb vascular insufficiency.

Acid‐sensing ion channel subtype 3 function and immunolabelling increases in skeletal muscle sensory neurons following femoral artery occlusion

Sympathetic nerve activity and arterial blood pressure responses to static hindlimb muscle contractions are greater in rats with femoral arteries that were previously ligated (24-72 h earlier) than in control rats. Studies further demonstrate that acid-sensing ion channel subtype 3 (ASIC(3)) in thin-fibre muscle afferents contributes to the amplified reflex muscle responses observed in occluded rats, probably due to enhanced ASIC(3) expression in muscle sensory neurons. The purpose of this study was to characterize acid-induced current with activation of ASIC(3) in dorsal root ganglion (DRG) neurons of control rats and rats with 24 h of femoral occlusion using whole-cell patch clamp methods. Also, immunohistochemistry was employed to examine existence of ASIC(3) expression in DRG neurons of thin-fibre afferents. DRG neurons from 4- to 6-week-old rats were labelled by injecting the fluorescence tracer DiI into the hindlimb muscles 4-5 days prior to the recording experiments. The results of this study show that ∼90% of current responses evoked by pH 6.7 in DRG neurons innervating the hindlimb muscles are ASIC(3)-like. The peak current amplitude to pH 6.7 is significantly attenuated with application of rAPETx2, a specific ASIC(3) antagonist. In addition, ASIC(3)-like current responses to pH 6.7 are observed in small, medium and large DRG neurons, and size distribution of DRG neurons is similar in control and occluded animals. However, the peak current amplitude of DRG neuron response induced by ASIC(3) stimulation is larger in occluded rats than that in control rats. Moreover, the percentage of DRG neurons with ASIC(3)-like currents is greater after arterial occlusion compared with control. Furthermore, results from double immunofluorescence experiments show that femoral artery occlusion mainly augments ASIC(3) expression within DRG neurons projecting C-fibre afferents. Taken together, these data suggest that (1) the majority of current responses to pH 6.7 are ASIC(3)-like in DRG neurons with nerve endings in the hindlimb muscles, (2) a greater acid-induced current responding to pH 6.7 develops when hindlimb arterial blood supply is deficient under ischaemic conditions, and (3) increased ASIC(3) expression is largely observed in thin C-fibres of DRG neurons after hindlimb ischaemia.

Mechanical Allodynia Caused by Intraplantar Injection of P2X Receptor Agonist in Rats: Involvement of Heteromeric P2X2/3Receptor Signaling in Capsaicin-Insensitive Primary Afferent Neurons

Extracellular ATP has been known to activate sensory neurons via the ATP-gated ion channels P2X receptors, indicating that the P2X receptors may play a role in signal transduction of pain from the periphery to the spinal cord in vivo. Here, we found a novel nociceptive response induced by ATP, mechanical allodynia (hypersensitivity to innocuous mechanical stimulus). Injection of alpha,beta-methylene ATP (alpha(beta)meATP), an agonist to P2X receptor, into plantar surface in rats produced the mechanical allodynia along with previously described nocifensive behavior and thermal hyperalgesia. This allodynic response was blocked by pretreatment with the P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate. Interestingly, only the mechanical allodynia evoked by alpha(beta)meATP selectively remained in neonatal capsaicin-treated adult rats that had selectively lost the capsaicin-sensitive neurons. ATP has been shown to produce two distinguishable electrophysiological responses (inward currents with rapid and slow desensitization) in dorsal root ganglion (DRG) neurons. In the present electrophysiological experiment, the percentage of DRG neurons that responded to alpha(beta)meATP with slow desensitizing inward current remained constant in capsaicin-treated rats, whereas the percentage that responded with rapid desensitizing current dramatically decreased. Taken together with our previous finding that the alpha(beta)meATP-activated slow desensitizing current in DRG neurons is mediated by heteromeric P2X2/3 (P2X2 and P2X3) receptors, it is hypothesized that activation of heteromeric P2X2/3 receptors in peripheral terminals of capsaicin-insensitive primary afferent fibers leads to the induction of mechanical allodynia.

Restoration of substance P and calcitonin gene-related peptide in dorsal root ganglia and dorsal horn after neonatal sciatic nerve lesion.

Dorsal root ganglion (DRG) neurons decrease their substance P (SP) synthesis after peripheral nerve lesions. Levels in the dorsal horn also decline but return to normal if regeneration is successful. In adults, when regeneration is prevented, recovery of SP in the dorsal horn is slow and incomplete, whereas in newborns, recovery is rapid and complete even though retrograde cell death of DRG neurons is greater than in adults. We have examined the mechanisms that might account for the rapid and complete recovery of SP and calcitonin-gene related peptide (CGRP) in the dorsal horn after peripheral nerve injury in newborns. Peptides were compared in the L4 and L5 DRG and spinal cord segments of normal rats and in rats surviving 6 days to 4 months after sciatic nerve section/ligation within 24 hours of birth. Sciatic nerve section/ligation produced 50% neuron death in L4 and L5 DRGs, but immunocytochemical methods showed that both SP-immunoreactivity (-IR) and CGRP-IR recovered completely in dorsal horn. Radioimmunoassay confirmed that recovery of SP was not an artefact due to shrinkage. beta-Preprotachykinin (PPT)-mRNA hybridization and SP-IR were observed mostly in small neurons; alpha-CGRP-mRNA-hybridized and CGRP-IR neurons were more heterogeneous. The percentage of DRG neurons that contained SP (approximately 25%) or CGRP (approximately 50%) was the same in normal newborn and adult rats. Neither selective cell survival nor change in neuron phenotype was likely to contribute to the recovery seen in the dorsal horn, and DRG neurons ipsilateral to the lesion exhibited the same level of hybridized beta-PPT-mRNA and alpha-CGRP-mRNA as intact DRG neurons. Because neither the constitutive level of expression of the genes nor peptide levels increased above those observed in intact DRG neurons, these mechanisms were also not responsible. Axotomized DRG neurons, however, contributed to recovery. Recovery was also due to sprouting by neurons in intact DRGs rostral and caudal to L4 and L5.