Reversal of ERK activation in the dorsal horn after decompression in chronic constriction injury

Systems and Circuits Linking Chronic Pain and Circadian Rhythms

Research over the last 20 years regarding the link between circadian rhythms and chronic pain pathology has suggested interconnected mechanisms that are not fully understood. Strong evidence for a bidirectional relationship between circadian function and pain has been revealed through inflammatory and immune studies as well as neuropathic ones. However, one limitation of many of these studies is a focus on only a few molecules or cell types, often within only one region of the brain or spinal cord, rather than systems-level interactions. To address this, our review will examine the circadian system as a whole, from the intracellular genetic machinery that controls its timing mechanism to its input and output circuits, and how chronic pain, whether inflammatory or neuropathic, may mediate or be driven by changes in these processes. We will investigate how rhythms of circadian clock gene expression and behavior, immune cells, cytokines, chemokines, intracellular signaling, and glial cells affect and are affected by chronic pain in animal models and human pathologies. We will also discuss key areas in both circadian rhythms and chronic pain that are sexually dimorphic. Understanding the overlapping mechanisms and complex interplay between pain and circadian mediators, the various nuclei they affect, and how they differ between sexes, will be crucial to move forward in developing treatments for chronic pain and for determining how and when they will achieve their maximum efficacy.

Peripheral Neuropathic Pain: From Experimental Models to Potential Therapeutic Targets in Dorsal Root Ganglion Neurons

Neuropathic pain exerts a global burden caused by the lesions in the somatosensory nerve system, including the central and peripheral nervous systems. The mechanisms of nerve injury-induced neuropathic pain involve multiple mechanisms, various signaling pathways, and molecules. Currently, poor efficacy is the major limitation of medications for treating neuropathic pain. Thus, understanding the detailed molecular mechanisms should shed light on the development of new therapeutic strategies for neuropathic pain. Several well-established in vivo pain models were used to investigate the detail mechanisms of peripheral neuropathic pain. Molecular mediators of pain are regulated differentially in various forms of neuropathic pain models; these regulators include purinergic receptors, transient receptor potential receptor channels, and voltage-gated sodium and calcium channels. Meanwhile, post-translational modification and transcriptional regulation are also altered in these pain models and have been reported to mediate several pain related molecules. In this review, we focus on molecular mechanisms and mediators of neuropathic pain with their corresponding transcriptional regulation and post-translational modification underlying peripheral sensitization in the dorsal root ganglia. Taken together, these molecular mediators and their modification and regulations provide excellent targets for neuropathic pain treatment.

Gene therapy by lentivirus-mediated RNA interference targeting extracellular-regulated kinase alleviates neuropathic pain in vivo

BACKGROUNDS

Neuropathic pain is an abnormal pain, which is related to the activation of extracellular-regulated kinase (ERK) signaling. This study was to investigate the effects of ERK knockdown via lentivirus-mediated RNA interference on allodynia in rats with chronic compression of the dorsal root ganglia (DRG) and to uncover the potential mechanisms.

METHODS

The model of chronic compression of the dorsal root ganglia (CCD) was established in rats by surgery. Gene silence was induced by injecting rats with lentivirus expressing ERK short hairpin RNA (shRNA). Behavioral test was performed by calculating paw withdrawal mechanical threshold (PWMT) and thermal paw withdrawal latency (TPWL).

RESULTS

We firstly generated lentivirus expressing ERK shRNA to downregulate ERK gene expression both in vitro and in vivo by using Western blot analysis and quantitative reverse transcription polymerase chain reaction. In CCD, ERK mRNA, and protein levels in DRG neurons were dramatically increased, accompanied with decreased PWMT and TPWL. Lentivirus-mediated RNA interference decreased ERK gene expression in DRG neurons and normalized the PWMT and TPWL in CCD rats, but not in rats infected with lentivirus expressing negative control shRNA. Further, calcium responses of DRG neurons to the hypotonic solution and 4α-phorbol 12,13-didecanoate were enhanced in CCD rats, which were suppressed by lentivirus-mediated ERK gene silence. Finally, the levels of transient receptor potential vanilloid 4 gene expressions in DRG neurons and L4 to L5 spinal cord isolated from CCD rats were dramatically upregulated, which were reversed by lentivirus-mediated ERK gene knockdown.

CONCLUSION

Lentivirus-mediated RNA interference (RNAi) silencing targeting ERK might reverse CCD-induced neuropathic pain in rats through transient receptor potential vanilloid 4.

Nerve Decompression Improves Spinal Synaptic Plasticity of Opioid Receptors for Pain Relief

Nerve decompression is an essential therapeutic strategy for pain relief clinically; however, its potential mechanism remains poorly understood. Opioid analgesics acting on opioid receptors (OR) within the various regions of the nervous system have been used widely for pain management. We therefore hypothesized that nerve decompression in a neuropathic pain model of chronic constriction injury (CCI) improves the synaptic OR plasticity in the dorsal horn, which is in response to alleviate pain hypersensitivity. After CCI, the Sprague-Dawley rats were assigned into Decompression group, in which the ligatures around the sciatic nerve were removed at post-operative week 4 (POW 4), and a CCI group, in which the ligatures remained. Pain hypersensitivity, including thermal hyperalgesia and mechanical allodynia, was entirely normalized in Decompression group within the following 4 weeks. Substantial reversal of mu- and delta-OR immunoreactive (IR) expressions in Decompression group was detected in primary afferent terminals in the dorsal horn. In Decompression group, mu-OR antagonist (CTOP, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 [Disulfide Bridge: 2-7]) and delta-OR antagonist (NTI, 17-(cyclopropylmethyl)-6,7-dehydro-4,5α-epoxy-3,14-dihydroxy-6,7-2',3'-indolomorphinan hydrochloride) re-induced pain hypersensitivity by intrathecal administration in a dose-responsive manner. Additionally, mu-OR agonist (DAMGO, [D-Ala2, NMe-Phe4, Gly-ol5]-enkephalin) and delta-OR agonist (SNC80, ((+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethyl-benzamide) were administrated intrathecally to attenuating CCI-induced chronic and acute pain hypersensitivity dose-dependently. Our current results strongly suggested that nerve decompression provides the opportunity for improving the synaptic OR plasticity in the dorsal horn and pharmacological blockade presents a novel insight into the therapeutic strategy for pain hypersensitivity.

MAPK Pathways Are Involved in Neuropathic Pain in Rats with Chronic Compression of the Dorsal Root Ganglion

The aim of the present study was to investigate whether the MAPK pathways were involved in the mechanism of neuropathic pain in rats with chronic compression of the dorsal root ganglion. We determined the paw withdrawal mechanical threshold (PWMT) of rats before and after CCD surgery and then after p38, JNK, or ERK inhibitors administration. Western blotting, RT-PCR, and immunofluorescence of dorsal root ganglia were performed to investigate the protein and mRNA level of MAPKs and also the alternation in distributions of positive neurons in dorsal root ganglia. Intrathecal administration of MAPKs inhibitors, SB203580 (p38 inhibitor), SP600125 (JNK inhibitor), and U0126 (ERK inhibitor), resulted in a partial reduction in CCD-induced mechanical allodynia. The reduction of allodynia was associated with significant depression in the level of both MAPKs mRNA and protein expression in CCD rats and also associated with the decreased ratios of large size MAPKs positive neurons in dorsal root ganglia. In conclusion, the specific inhibitors of MAPKs contributed to the attenuation of mechanical allodynia in CCD rats and the large size MAPKs positive neurons in dorsal root ganglia were crucial.

Determinants of nerve conduction recovery after nerve injuries: Compression duration and nerve fiber types

INTRODUCTION

The aims of this study were to determine the influences of: (1) timing of nerve decompression; and (2) nerve fiber types on the patterns of nerve conduction studies (NCS) after nerve injury.

METHODS

Nerve conduction studies (NCS) were performed on 3 models of nerve injury: (1) crush injury due to transient nerve compression (crush group); (2) chronic constriction injury (CCI), or permanent compression (CCI group); and (3) CCI with removal of ligatures, or delayed nerve decompression (De-CCI group).

RESULTS

There were distinct patterns of NCS recovery. The crush and De-CCI groups achieved similar motor nerve recovery, better than that of the CCI group. In contrast, recovery of sensory nerves was limited in the CCI and De-CCI groups and was lower than in the crush group.

CONCLUSIONS

Immediate relief of compression resulted in the best recovery of motor and sensory nerve conduction. In contrast, delayed decompression restored only motor nerve conduction.

Differential roles of hippocampal glutamatergic receptors in neuropathic anxiety-like behavior after partial sciatic nerve ligation in rats

BACKGROUND

Neuropathic pain evoked by nerve injury is frequently accompanied by deterioration of emotional behaviors, but the underlying signaling mechanisms remain elusive. Glutamate (Glu) is the major mediator of excitatory synaptic transmission throughout the brain, and abnormal activity of the glutamatergic system has been implicated in the pathophysiology of pain and associated emotional comorbidities. In this study we used the partial sciatic nerve ligation (PSNL) model of neuropathic pain in rats to characterize the development of anxiety-like behavior, the expression of glutamatergic receptors, and the phosphorylation of extracellular signal-regulated kinase (ERK) in the hippocampus, the region that encodes memories related to emotions.

RESULTS

We found that the mechanical withdrawal threshold was significantly reduced and an anxiety-like behavior was increased as determined via open field tests and elevated plus-maze tests at 28 days after injury. No significant differences were found in the ratio of sucrose preference and immobility time detected by sucrose preference tests and forced swimming tests respectively, possibly due to the timing factor. The expression of N-methyl-D-aspartate (NMDA) receptor subtypes NR1 and NR2B, but not NR2A, GluR1, or GluR2 (the main subtype of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] receptor) in the hippocampus of injured rats was significantly reduced. Moreover, PSNL resulted in decreased phosphorylation of ERK1/2 in the hippocampus. Intriguingly, treatment with D-serine (a co-agonist of NMDA receptor, 1 g/kg intraperitoneally) reduced the anxiety-like behavior but not the mechanical hypersensitivity induced by PSNL.

CONCLUSIONS

PSNL can induce significant anxiety-like but not depression-like behavior, and trigger down-regulation of NMDA but not AMPA receptors in the hippocampus at 28 days after injury.

Redistribution of voltage-gated sodium channels after nerve decompression contributes to relieve neuropathic pain in chronic constriction injury

Nerve decompression is an important therapeutic strategy to relieve neuropathic pain and promote the peripheral nerve regeneration. To address these issues, we investigated the effects of nerve decompression on relief of neuropathic pain behaviors, redistribution of voltage-gated sodium channels (VGSCs), and skin reinnervation with chronic constriction injury (CCI). At post-operative week (POW) 4, animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained. Thermal hyperalgesia and mechanical allodynia at POW 8 had distinct reductions in decompression group compared to CCI group. At that time in CCI group, morphological evidence of pan VGSCs (Pan Nav) and isoforms of VGSCs (Nav1.6, Nav1.9, except for Nav1.8) were shown the widely distribution along the injured sciatic nerve. All of the VGSCs in decompression group became clustering around the node of Ranvier, similar to the pattern of control sciatic nerve at POW 8. Skin reinnervation was demonstrated by epidermal nerve density (END) for protein gene product 9.5 (PGP 9.5)-immunoreactive (IR) nerve fibers and a significant difference between groups only at POW 24 (p=0.01). Growth-associated protein 43 (GAP-43) is participated in the nerve fiber growth and sprouting, a difference in END for GAP-43-IR nerve fibers at POW 24 between groups were also significant (p=0.02). These observations demonstrated that nerve decompression was accompanied with the disappearance of neuropathic pain behaviors after CCI. Morphological studies provided the evidence that redistribution of VGSCs along the injured sciatic nerve but still with an incomplete skin reinnervation. These significant findings demonstrated a role of VGSCs in the pathogenesis of neuropathic pain, and gave an approaching in pharmacological basis of therapeutics.

Curcumin could prevent the development of chronic neuropathic pain in rats with peripheral nerve injury

Background

Peripheral nerve injury results in chronic neuropathic pain characterized by allodynia and/or spontaneous pain. It has been suggested that activation of mitogen-activated protein kinases such as extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) contribute to the neuropathic pain.

Objectives

We investigated if curcumin could prevent the development of neuropathic pain in rats with chronic constriction injury (CCI) of the sciatic nerve.

Methods

The animals were divided into 3 groups. In the curcumin treatment group (n = 10), curcumin (50 mg/kg/d PO) was administered once daily from 1 day before CCI to 7 days after CCI. The rats in the sham group (n = 10) and CCI group (n = 10) received a control vehicle. The mechanical allodynia was assessed using von Frey at 1, 3, 5, and 7 days after nerve injury. Western blots were used to evaluate the levels of p-ERK, p-JNK, and phosphorylation of NR1 (p-NR1) subunits of N-methyl-D-aspartate in the spinal dorsal root ganglion.

Results

In the CCI group, mechanical allodynia was observed during 7 days after nerve injury. However, curcumin treatment reversed the mechanical allodynia 7 days after nerve ligation. There were no differences in the expression of p-ERK, p-JNK, and p-NR1 between the sham and curcumin groups. However, the expression of p-ERK, p-JNK, and p-NR1 in the CCI group were higher than the sham group and curcumin group, respectively (P < 0.05).

Conclusions

Treatment with curcumin during the early stages of peripheral neuropathy can prevent the development of chronic neuropathic pain.

The function of alpha-2-adrenoceptors in the rat locus coeruleus is preserved in the chronic constriction injury model of neuropathic pain

RATIONALE

Peripheral neuropathic pain is a chronic condition that may produce plastic changes in several brain regions. The noradrenergic locus coeruleus (LC) is a crucial component of ascending and descending pain pathways, both of which are frequently compromised after nerve injury.

OBJECTIVES

The objective of the study was to examine whether chronic constriction injury (CCI), a model of neuropathic pain, alters noradrenergic activity in the rat LC.

METHODS

Activity in the LC was assessed by electrophysiology and microdialysis, while protein expression was monitored in western blots and by immunohistochemistry.

RESULTS

The pain threshold had dropped in injured rats 7 days after inducing neuropathy. While alpha-2-adrenoceptors mediate activity in the LC and in its terminal areas, no alterations in either spontaneous neuronal activity or extracellular noradrenaline levels were observed following CCI. Moreover, alpha-2-adrenoceptor activity in the LC of CCI rats remained unchanged after systemic administration of UK14,304, RX821002 or desipramine. Accordingly, extracellular noradrenaline levels in the LC were similar in CCI and control animals following local administration of clonidine or RX821002. In addition, there were no changes in the expression of the alpha-2-adrenoceptors, Gαi/z subunits or the regulators of G-protein signaling. However, pERK1/2 (phosphorylated extracellular signal-regulated kinases 1/2) expression augmented in the spinal cord, paragigantocellularis nucleus (PGi) and dorsal raphe nucleus (DRN) following CCI.

CONCLUSIONS

Neuropathic pain is not accompanied by modifications in tonic LC activity after the onset of pain. This may indicate that the signals from the PGi and DRN, the excitatory and inhibitory afferents of the LC, cancel one another out.

Neuropathic pain as a process: reversal of chronification in an animal model

Peripheral neuropathic pain arises from trauma to sensory nerves. Other types of acute neurotrauma such as stroke and spinal cord injury are treated immediately, largely to prevent secondary damage. To pursue the possibility that neuropathic pain may also be amenable to early treatment, a rat model of neuropathic pain was induced using a 2-mm polyethylene cuff implanted around one sciatic nerve. Within 24 hours, hypersensitivity to von Frey hair stimulation appeared, as indicated by decreased paw withdrawal thresholds. When the cuff was removed 24 hours after implantation, readings returned to pre-implantation levels starting as early as day 18. When the cuff was removed after 4 days, there was a period of initial hypersensitivity, and then an increase toward baseline at two time points near the end of the study; therefore, only a partial recovery toward pre-implantation values occurred. Having established that a temporal reversal can occur, the next step examined possible pharmacological reversal. The tachykinin NK₁ receptor antagonist, CP-96,345, produced a minor increase in withdrawal thresholds in animals with the cuff left permanently implanted. To determine the effect of early and repeated administration of CP-96,345, it was given daily on days 1–4. The cuff was removed on day 4. Six days later, readings showed reversal of tactile hypersensitivity. We suggest that persistent neuropathic pain occurs from processes that develop over several hours and days, and that some of these processes may be prevented by early medical intervention. Thus, nerve injury in the context of chronic neuropathic pain should be treated in a similar manner to nerve injury resulting from stroke, spinal cord injury, and other types of neurotrauma. We suggest that effective medical intervention within the first few hours after nerve injury may spare a patient from a chronic debilitating pain that may be refractory to later therapies.

Extracellular signal-regulated kinases in pain of peripheral origin

Activation of members of the family of enzymes known as extracellular signal-regulated kinases (ERKs) is now known to be involved in the development and/or maintenance of the pain associated with many inflammatory conditions, such as herniated spinal disc pain, chronic inflammatory articular pain, and the pain associated with bladder inflammation. Moreover, ERKs are implicated in the development of neuropathic pain signs in animals which are subjected to the lumbar 5 spinal nerve ligation model and the chronic constriction injury model of neuropathic pain. The position has now been reached where all scientists working on pain subjects ought to be aware of the importance of ERKs, if only because certain of these enzymes are increasingly employed as experimental markers of nociceptive processing. Here, we introduce the reader, first, to the intracellular context in which these enzymes function. Thereafter, we consider the involvement of ERKs in mediating nociceptive signalling to the brain resulting from noxious stimuli at the periphery which will be interpreted by the brain as pain of peripheral origin.

Hypolocomotion, asymmetrically directed behaviors (licking, lifting, flinching, and shaking) and dynamic weight bearing (gait) changes are not measures of neuropathic pain in mice

BACKGROUND

Spontaneous (non-evoked) pain is a major clinical symptom of neuropathic syndromes, one that is understudied in basic pain research for practical reasons and because of a lack of consensus over precisely which behaviors reflect spontaneous pain in laboratory animals. It is commonly asserted that rodents experiencing pain in a hind limb exhibit hypolocomotion and decreased rearing, engage in both reflexive and organized limb directed behaviors, and avoid supporting their body weight on the affected side. Furthermore, it is assumed that the extent of these positive or negative behaviors can be used as a dependent measure of spontaneous chronic pain severity in such animals. In the present study, we tested these assumptions via blinded, systematic observation of digital video of mice with nerve injuries (chronic constriction or spared nerve injury), and automated assessment of locomotor behavior using photocell detection and dynamic weight bearing (i.e., gait) using the CatWalk system.

RESULTS

We found no deficits in locomotor activity or rearing associated with neuropathic injury. The frequency of asymmetric (ipsilaterally directed) behaviors were too rare to be seriously considered as representing spontaneous pain, and in any case did not statistically exceed what was blindly observed on the contralateral hind paw and in control (sham operated and unoperated) mice. Changes in dynamic weight bearing, on the other hand, were robust and ipsilateral after spared nerve injury (but not chronic constriction injury). However, we observed timing, pharmacological, and genetic dissociation of mechanical allodynia and gait alterations.

CONCLUSIONS

We conclude that spontaneous neuropathic pain in mice cannot be assessed using any of these measures, and thus caution is warranted in making such assertions.

SIP30 is regulated by ERK in peripheral nerve injury-induced neuropathic pain

ERK plays an important role in chronic neuropathic pain. However, the underlying mechanism is largely unknown. Here we show that in chronic constriction injury-treated rat spinal cords, up-regulation of SIP30 (SNAP25-interacting protein 30), which is involved in the development and maintenance of chronic constriction injury-induced neuropathic pain, correlates with ERK activation and that the up-regulation of SIP30 is suppressed by intrathecal delivery of the MEK inhibitor U0126. In PC12 cells, up-regulation of SIP30 by nerve growth factor is also dependent on ERK activation. We found that there is an ERK-responsive region in the rat sip30 promoter. Activation of ERK promotes the recruitment of the transcription factor cyclic AMP-response element-binding protein to the sip30 gene promoter. Taken together, our results provide a potential downstream target of ERK activation-mediated neuropathic pain.

Activation of the neuronal extracellular signal-regulated kinase 2 in the spinal cord dorsal horn is required for complete Freund's adjuvant-induced pain hypersensitivity

Extracellular signal-regulated kinase 1 (ERK1) and ERK2 signaling in the spinal cord dorsal horn (SCDH) has been implicated in injury-induced pain hypersensitivity. Available ERK pathway inhibitors cannot distinguish between ERK1 and ERK2, nor can they differentially target the expression of neuronal or glial ERK1/2. We selectively inhibited the expression of ERK2 in neurons of the adult mouse SCDH by use of an ERK2 small interfering RNA (siRNA) delivered by a neurotropic adenoassociated viral vector. In situ hybridization revealed a siRNA vector-induced decrease in ERK2 mRNA in the ipsilateral SCDH. Immunohistochemistry showed a decreased neuronal phospho-ERK1/2 (pERK1/2), and Western blot analysis revealed that both ERK2 expression and phosphorylation were reduced by the siRNA vector. In contrast, basal ERK1 expression was not affected, although pERK1 was slightly increased. The siRNA vector-induced knockdown of ERK2 expression in the SCDH did not alter the baseline mechanical or thermal paw withdrawal thresholds. Hindpaw intraplantar injection of complete Freund's adjuvant (CFA) produced peripheral inflammation, mechanical allodynia, and thermal hyperalgesia in vector control animals that persisted for at least 96 h. It also caused an increase in SCDH ERK1 and ERK2 levels at 96 h and pERK1 and pERK2 levels at 1 and 96 h. The ERK2 siRNA vector prevented changes in ERK1, ERK2, and pERK2. In addition, the siRNA vector protected the animals from developing mechanical allodynia and thermal hyperalgesia throughout the 96 h after CFA. These findings indicate that ERK2 in the SCDH neurons is critical for the development of inflammatory pain hypersensitivity.

Influences of surgical decompression on the dorsal horn after chronic constriction injury: changes in peptidergic and delta-opioid receptor (+) nerve terminals

To understand plastic changes in the dorsal horn related to neuropathic pain, we developed a model of decompression in rats with chronic constriction injury (CCI) and investigated corresponding changes in the dorsal horn. At postoperative week 4 (POW 4) of CCI, rats were divided into a decompression group, in which ligatures were removed, and a CCI group, in which ligatures remained. Spinal cords were immunostained for substance P (SP), the delta-opioid receptor (DOR), and calcitonin gene-related peptide (CGRP). Areas of immunoreactive nerve terminals in the dorsal horn were quantified and expressed as the dorsal horn index (immunoreactive areas of the operated side compared with those of the contralateral side). At POW 4, dorsal horn indexes of all of these molecules were significantly reduced in both groups to similar degrees (0.36-0.43). At POW 8, neuropathic pain behaviors had completely disappeared in the decompression group with significant reversal of the dorsal horn indexes compared with the CCI group (0.81+/-0.02 vs. 0.58+/-0.09, P < 0.001 for SP and 0.75+/-0.04 vs. 0.55+/-0.03, P < 0.001 for DOR). In the CCI group, neuropathic pain behaviors became normalized at POW 12 with corresponding changes in dorsal horn indexes for both SP and DOR similar to those of the decompression group. In contrast, changes in the dorsal horn indexes of CGRP were similar in both the CCI and decompression groups throughout the experimental period. These findings suggest that CCI and decompression cause different patterns in peptidergic and DOR (+) nerve terminals in the dorsal horn.

Depletion of peptidergic innervation in the gastric mucosa of streptozotocin-induced diabetic rats

Autonomic neuropathy affecting the gastrointestinal system is a major presentation of diabetic neuropathy. Changes in the innervation of gastric mucosa or muscle layers can contribute to gastrointestinal symptoms. The present study investigated this issue by quantitatively analyzing the immunohistochemical patterns of the gastric innervation in rats with streptozotocin (STZ)-induced diabetes. In control rats, calcitonin gene-related peptide (CGRP) and substance P (SP) (+) nerve fibers appeared in the gastric mucosa and muscle layers. Double immunohistochemical staining showed that immunoreactivities for SP and CGRP were co-localized with a pan-neuronal marker protein gene product 9.5. Both SP (+) nerve fibers (p<0.001) and CGRP (+) nerve fibers (p<0.005) were decreased in the gastric mucosa within 4 weeks of diabetes; the reduction persisted throughout 24 weeks. Diabetic rats treated with insulin did not show decrease of SP or CGRP (+) fibers in the mucosa 4 weeks after STZ injection (p>0.05). There was no significant change in SP (+) nerve fibers (p>0.05) or CGRP (+) nerve fibers (p>0.05) of the gastric muscle layers. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression levels of SP and CGRP mRNA in the thoracic dorsal root ganglia were similar between diabetic and control animals (p>0.05). Qualitative and quantitative ultrastructural examinations on the gastric mucosa documented unmyelinated nerve degeneration. These results suggest the existence of gastric sensory neuropathy in STZ-induced diabetes, and this pathology provides a foundation for understanding diabetic gastropathy.