Substance P In Dorsal Root Ganglia Research Articles

Effects of electroacupuncture on pain behavior and pain-related factors in spinal cord dorsal horn and dorsal root ganglia of rats with knee osteoarthritis

To observe the effect of electroacupuncture(EA) on the pain behavior and prostaglandin E2 (PGE2), calcitonin gene-related peptide (CGRP) and substance P (SP) in the spinal cord dorsal horn and dorsal root ganglia (DRG) of rats with knee osteoarthritis (KOA), so as to explore the mechanisms of EA underlying improvement of chronic pain in KOA rats. Thirty-two female SD rats were randomly divided into blank group, control group, model group and EA group, with 8 rats in each group. Rats in the control group were injected with 50 μL of 0.9% sodium chloride solution into the left knee joint cavity, and rats in the model and EA groups were injected with 50 μL of Monosodium iodoacetate in the left knee joint. EA(2 Hz/100 Hz, ＜2 mA) was applied to left "Yanglingquan"(GB34) and "Neixiyan" (EX-LE4) for 15 min, once daily, 5 days a course with a total of 2 courses. Paw withdrawal latency (PWL) and mechanical pain threshold (PWT) were tested by Plantar Test and Von Frey, separately. After the last pain test, the contents of PGE2, CGRP and SP in the left lumbar (L) 3-L5 DRG and L3-L5 spinal dorsal horn were detected by ELISA. Compared with the blank group, the PWL and PWT of the rats in the model group were significantly decreased (P<0.01), and the contents of PGE2, CGRP and SP in the DRG and spinal dorsal horn were significantly increased (P<0.01, P<0.05). There were no statistically significant differences in PWL, PWT, contents of PGE2, CGRP and SP in DRG and spinal dorsal horn between the blank group and the control group (P>0.05). Compared with the model group, the PWL and PWT of rats in the EA group were significantly increased (P<0.01), and the contents of PGE2, CGRP and SP in the DRG and spinal dorsal horn were significantly decreased (P<0.01, P<0.05). EA of GB34 and EX-LE4 can reduce the levels of pain-related factors PGE2, CGRP and SP in the DRG and spinal dorsal horn, thereby relieving spinal hyperalgesia in rats with KOA.

Association of down-regulation of calcitonin gene-related peptide and substance P with increase of myocardial vulnerability in diabetic neuropathic rats

Diabetic patients present high co-morbidities of neuropathy and severer consequences of coronary heart disease. But the pathological mechanism is still unclear. Here we investigated a potential association of diabetic impairment of sensory nerves with increase of vulnerability of myocardium in acute myocardial ischemia/reperfusion. A rat model of diabetes mellitus was induced by high fat and sugar diet plus a small dose of streptozotocin. Impairment of sensory nerves was evaluated by measurement of changes in tail flick latency to noxious thermal stimulation and calcitonin gene-related peptide (CGRP) and substance P (SP) in the dorsal root ganglia (DRG) and the myocardium of the heart were examined. The myocardial injury was examined by infarct size, apoptosis ratio of cardiomyocytes and cardiac troponin I in the animals underwent acute myocardial ischemia (for 30min) and reperfusion (for 120min). The effects of CGRP and SP on cardiomyocyte injury induced by high glucose and hypoxia/reoxygenation were tested in cultured myocytes. The diabetic animals presented significant elevation of noxious thermal threshold with obvious reduction of the contents of CGRP and SP in the DRG and the myocardium. Importantly, the diabetic animals showed significant increases of infarct size, myocyte apoptosis and serum cardiac troponin I after acute myocardial ischemia/reperfusion, compared to the non-diabetic control. Furthermore, exogenously administered CGRP and SP attenuated the myocyte injury induced by the high concentration of glucose and hypoxia/reoxygenation. These findings suggested that impairment of sensory nerves with significant reduction of CGRP and SP in DRG, ventricular myocardium and serum may be associated with increase of myocardial vulnerability in acute myocardial ischemia/reperfusion in streptozotocin-induced diabetic rats.

Effects of subcutaneous transfection of human beta-nerve growth factor gene on function of sensory nerve in a rat model of diabetic neuropathic pain

Objective To evalute the effects of subcutaneous transfection of human beta-nerve growth factor (Ad-hNGFβ) gene on the function of sensory nerve in a rat model of diabetic neuropathic pain (DNP).Methods Healthy male Sprague-Dawley rats,weighing 180-220 g,were used in this study.Ten rats were randomly collected as normal control without DNP (group C).DNP model was established by intraperitoneal injection of streptozocin (STZ) 75 mg/kg.Seventy-five rats with DNP were randomly divided into 3 groups (n =25 each):DNP group; Ad-hNGF group and Ad-LacZ group.Groups Ad-NGF and Ad-LacZ received subcutaneous transfection of 1.12 × 1011 PFU Ad-hNGFβ 10 ul and 1.12 × 1011 PFU Ad-LacZ 10 ul respectively after pain thresholds were measured on 21 days after STZ injection.The mechanical and thermal pain thresholds were measured before STZ injection (baseline) and at 21,35 and 49 days after STZ injection.The conduction velocity and latency of the sensory nerve and the expression of substance P (SP) in dorsal root ganglion (by immmuno-histpchemistry) were determined after measurement of pain threshold on 49 days after STZ injection.Results Compared with group C,the mechanical and thermal pain thresholds were significantly increased at each time point after STZ injection in groups DNP,Ad-NGF and Ad-Lacz,the conduction velocity of the sensory nerve was significantly decreased,the latency of the sensory nerve was prolonged,and the expression of SP in dorsal root ganglion was down-regulated in groups DNP and Ad-LacZ,the conduction velocity of the sensory nerve was significantly decreased (P ＜ 0.05),and no significant change was found in the latency of the sensory nerve and expression of SP in dorsal root ganglion in group Ad-NGF (P ＞ 0.05).Compared with group DNP,the thermal pain threshold was significantly increased at 49 days after STZ injection,the conduction velocity of the sensory nerve was decreased,the latency of the sensory nerve was shortened,and the expression of SP in dorsal root ganglion was down-regulated (P ＜ 0.05 or 0.01),while no significant change was found in the mechanical pain threshold in group Ad-NGF,and no significant change was found in the parameters mentioned above in group Ad-LacZ (P ＞ 0.05).Conclusion Subcutaneous transfection of Ad-hNGFβ can improve the function of sensory nerve in a rat model of DNP through up-regulat-ing of the SP expression in dorsal root ganglion. Key words: Nerve growth factor; Transfection ; Diabetes mellitus; Neuralgia; Neural conduction

TRESK gene recombinant adenovirus vector inhibits capsaicin-mediated substance P release from cultured rat dorsal root ganglion neurons

The present study was conducted to determine whether the activation of TRESK in the dorsal root ganglion (DRG) by the TRESK gene recombinant adenovirus vector inhibits the capsaicin-evoked substance P (SP) release using a radioimmunoassay. TRESK is an outwardly rectifying K+ current channel that contributes to the resting potential and is the most important background potassium channel in DRG. Previous studies have shown that neuropathic pain (NP) is closely related to the regulation of certain potassium channels in DRG neurons, while DRG-released SP is important in the peripheral mechanism of NP. In the present study, the TRESK gene adenovirus vector significantly enhanced the TRESK mRNA and protein of the cultured rat DRG neurons. Radioimmunoassay analysis revealed that the capsaicin-mediated SP release was significantly inhibited by the TRESK gene recombinant adenovirus vector in rat DRG neurons. These findings suggest that TRESK plays a role in adjusting the release of SP in DRG, which is related to NP.

Transient receptor potential vanilloid 1 is involved in the transfer of cardioprotection by remote limb ischemic postconditioning in rats

ObjectiveThis study aimed at investigating whether transient receptor potential vanilloid 1 (TRPV1) and its main neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), are responsible for the transfer of...

Effect of genetic deletion of the vanilloid receptor TRPV1 on the expression of Substance P in sensory neurons of mice with adjuvant-induced arthritis

The neuropeptide Substance P (SP), expressed by nociceptive sensory afferents in joints, plays an important role in the pathogenesis of arthritis. Capsaicin causes neurons in the dorsal root ganglia (DRG) to release SP from their central and peripheral axons, suggesting a functional link between SP and the capsaicin receptor, the transient receptor potential vanilloid 1 (TRPV1). The expression of both TRPV1 and SP have been reported to increase in several models of arthritis but the specific involvement of TRPV1-expressing articular afferents that can release SP is not completely understood. We here wanted to ascertain whether the increase in the number of SP-positive primary afferents in arthritis may be affected by genetic deletion of TRPV1. For this, we used immunohistochemistry to quantify the expression of SP in primary afferent neurons in wild-type mice (WT) vs. TRPV1-knockout (KO) mice with adjuvant-induced arthritis (AIA). We found that the expression of SP in DRG (1) increased significantly over naïve level in both WT and KO mice 3 weeks after AIA, (2) was significantly higher in KO mice than in WT mice in naïve mice and 2-3 weeks after AIA, (3) was significantly higher on the side of AIA than on the contralateral, vehicle-injected side at all time points in WT mice, but not in KO mice, and (4) increased predominantly in small-size neurons in KO mice and in small- and medium-size neurons in WT mice. Since the size distribution of SP-positive DRG neurons in arthritic TRPV1-KO mice was not significantly different from that in naïve mice, we speculate that the increased expression of SP is unlikely to reflect recruitment of A-fiber primary afferents and that the higher expression of SP in KO mice may represent a plastic change to compensate for the missing receptor in a major sensory circuit.

Substance P in the uterine cervix, dorsal root ganglia and spinal cord during pregnancy and the effect of estrogen on SP synthesis

Prior to parturition the non-pliable uterine cervix undergoes a ripening process (“softens” and dilates) to allow a timely passage of the fetus at term. The exact mechanism(s) triggering and involved in cervical ripening are unknown, though evidence for a role for sensory neurons and their contained neuropeptides is emerging. Moreover, an apparent increase in neuropeptide immunoreactive nerves occurs in the cervix during pregnancy, maternal serum estrogen levels rise at term and uterine cervix-related L6-S1 dorsal root ganglia (DRG) sensory neurons express estrogen receptor (ER) and neuropeptides. Thus, we sought to test the hypothesis that the neuropeptide substance P (SP) changes biosynthesis and release over pregnancy, that estrogen, acting via the ER pathway, increases synthesis of SP in DRG, and that SP is utilized in cervical ripening at late pregnancy. Using immunohistochemistry, in situ hybridization, reverse transcriptase–polymerase chain reaction (RT–PCR) and radioimmunoassay (RIA), we investigated coexpression of ER-α/β and SP; differential expression of ER-α and -β mRNA in DRG neurons; SP synthesis in DRG; and changes in SP concentration in the cervix, DRG and spinal cord over pregnancy. In addition, the effect of exogenous estrogen on SP synthesis in L6-S1 DRG of ovariectomized rats was examined. SP-immunoreactive neurons expressed ER-α and ER-β. SP synthesis (expressed as β-PPT mRNA label) was prominent in small DRG neurons. SP concentration increased in the L6-S1 DRG and spinal cord segments, with a peak at Day 20 of gestation, but decreased in the cervix during the first two trimesters, with a rise over the last trimester to Day 10 levels. SP and ER-α mRNA synthesis increased in DRG over pregnancy but ER-β mRNA levels were largely unchanged. When ovariectomized rats were treated with exogenous estrogen, SP mRNA synthesis in the DRG increased in a dose-related manner, an effect blocked by ER blocker ICI 182 780. From these results, we postulate that synthesis of SP in L6-S1 DRG and utilization in the cervix increase over pregnancy and this synthesis is under influence of the estrogen–ER system, most likely ER-α. We postulate that SP may play a role in cervical ripening and, consequently in the birth process.

Change in excitability and phenotype of substance P and its receptor in cat Aβ sensory neurons following peripheral inflammation

The effect of peripheral inflammation on spontaneous firing and level of substance P (SP) and its receptor in electrophysiologically identified cat Aβ neurons of dorsal root ganglion (DRG) was studied in vivo using a combination of intracellular recording, dye injection and immunohistochemical techniques. Following injection of carrageenan (Carg) into cat hindpaw, the number of Aβ neurons with spontaneous firing was enhanced significantly (42.9%, n=182) in comparison with control (16.8%, n=149, P<0.01). DRG Aβ neurons became less depolarized 2–4 h following Carg injection. After identifying the cell properties, Lucifer Yellow was injected and SP-like immunoreactivity (SP-LI) was then detected. A total of 17% of Aβ sensory neurons exhibited SP-LI in inflammatory cat. We also found in rat DRGs that the number of SP-LI positive large cells (>35 μm) was also significantly increased in Carg-treated DRG (11.8±1.2, n=8) compared with untreated DRG (1.8±0.8, n=8, P<0.01). In control cat, the topical use of SP in DRG did not induce any response of Aβ neurons. However, in Carg-treated cat, SP depolarized the membrane potential in most Aβ neurons (68.2%, n=22). L668,169, an antagonist of SP receptor, completely blocked the SP-induced responses. Furthermore, repeated application of SP did not induce obvious desensitization of Aβ neurons. These data suggest that peripheral inflammation increased the excitability, SP level and sensitivity of SP receptor of Aβ neurons. Therefore, we concluded that Aβ sensory neurons appear to contribute to inflammatory allodynia.