Effects of histamine on spontaneous neuropathic pain induced by peripheral axotomy

Evaluation of the Effect of Loratadine versus Diosmin/Hesperidin Combination on Vinca Alkaloids-Induced Neuropathy: A Randomized Controlled Clinical Trial

Neurological injury is a crucial problem that interferes with the therapeutic use of vinca alkaloids as well as the quality of patient life. This study was conducted to assess the impact of using loratadine or diosmin/hesperidin on neuropathy induced by vinca alkaloids. Patients were randomized into one of three groups as follows: group 1 was the control group, group 2 received 450 mg diosmin and 50 mg hesperidin combination orally twice daily, and group 3 received loratadine 10 mg orally once daily. Subjective scores (numeric pain rating scale, douleur neuropathique 4, and functional assessment of cancer therapy/gynecologic oncology group-neurotoxicity (FACT/GOG-Ntx) scores), neuroinflammation biomarkers, adverse drug effects, quality of life, and response to chemotherapy were compared among the three groups. Both diosmin/hesperidin and loratadine improved the results of the neurotoxicity subscale in the FACT/GOG-Ntx score (p < 0.001, p < 0.01 respectively) and ameliorated the upsurge in neuroinflammation serum biomarkers. They also reduced the incidence and timing of paresthesia (p = 0.001 and p < 0.001, respectively) and dysuria occurrence (p = 0.042). Both loratadine and diosmin/hesperidin attenuated the intensity of acute neuropathy triggered by vinca alkaloids. Furthermore, they did not increase the frequency of adverse effects or interfere with the treatment response.

Strategies for Treating Traumatic Neuromas with Tissue-Engineered Materials

Neuroma, a pathological response to peripheral nerve injury, refers to the abnormal growth of nerve tissue characterized by disorganized axonal proliferation. Commonly occurring after nerve injuries, surgeries, or amputations, this condition leads to the formation of painful nodular structures. Traditional treatment options include surgical excision and pharmacological management, aiming to alleviate symptoms. However, these approaches often offer temporary relief without addressing the underlying regenerative challenges, necessitating the exploration of advanced strategies such as tissue-engineered materials for more comprehensive and effective solutions. In this study, we discussed the etiology, molecular mechanisms, and histological morphology of traumatic neuromas after peripheral nerve injury. Subsequently, we summarized and analyzed current nonsurgical and surgical treatment options, along with their advantages and disadvantages. Additionally, we emphasized recent advancements in treating traumatic neuromas with tissue-engineered material strategies. By integrating biomaterials, growth factors, cell-based approaches, and electrical stimulation, tissue engineering offers a comprehensive solution surpassing mere symptomatic relief, striving for the structural and functional restoration of damaged nerves. In conclusion, the utilization of tissue-engineered materials has the potential to significantly reduce the risk of neuroma recurrence after surgical treatment.

Exogenous histamine and H 2 receptor activation and H 3 receptor inhibition in nucleus accumbens modulate formalin-induced orofacial nociception through opioid receptors

It has been demonstrated that the nucleus accumbens (NAc) plays an important role in modulation of nociception due to its extensive connections with different regions of the brain. In addition, this nucleus receives histaminergic projections from tuberomammillary nucleus. Considering the role of the central histaminergic system in nociception, the effect of histamine and its H 2 and H 3 receptors agonist and antagonist microinjections into the NAc on orofacial formalin nociception was investigated. In male Wistar rats, using stereotaxic surgery, two guide cannulas were bilaterally implanted into the right and left sides of the NAc. Diluted formalin solution (1.5%, 50 µl) injection into the vibrissa pad led to orofacial nociception. Immediately after injection, face rubbing was observed at 3-min blocks for 45 min. Orofacial formalin nociception was characterized by a biphasic nociceptive response (first phase: 0-3 min and second phase: 15-33 min). Microinjections of histamine (0.5 and 1 μg/site), dimaprit (1 μg/site, H 2 receptor agonist) and thioperamide (2 μg/site, H 3 receptor antagonist) attenuated both phases of formalin orofacial nociception. Prior microinjection of famotidine (2 μg/site) inhibited the antinociceptive effects of dimaprit (1 μg/site). Furthermore, comicroinjection of thioperamide (2 μg/site) and immepip (1 μg/site) prevented thioperamide (2 μg/site)-induced antinociception. Naloxone (2 μg/site) also prevented histamine, dimaprit- and thioperamide-induced antinociception. The results of this study demonstrate that at the level of the NAc, histamine and its H 2 and H 3 receptors are probably involved in the modulation of orofacial nociception with an opioid system-dependent mechanism.

Biology and pathophysiology of symptomatic neuromas

ABSTRACT

Neuromas are a substantial cause of morbidity and reduction in quality of life. This is not only caused by a disruption in motor and sensory function from the underlying nerve injury but also by the debilitating effects of neuropathic pain resulting from symptomatic neuromas. A wide range of surgical and therapeutic modalities have been introduced to mitigate this pain. Nevertheless, no single treatment option has been successful in completely resolving the associated constellation of symptoms. While certain novel surgical techniques have shown promising results in reducing neuroma-derived and phantom limb pain, their effectiveness and the exact mechanism behind their pain-relieving capacities have not yet been defined. Furthermore, surgery has inherent risks, may not be suitable for many patients, and may yet still fail to relieve pain. Therefore, there remains a great clinical need for additional therapeutic modalities to further improve treatment for patients with devastating injuries that lead to symptomatic neuromas. However, the molecular mechanisms and genetic contributions behind the regulatory programs that drive neuroma formation-as well as the resulting neuropathic pain-remain incompletely understood. Here, we review the histopathological features of symptomatic neuromas, our current understanding of the mechanisms that favor neuroma formation, and the putative contributory signals and regulatory programs that facilitate somatic pain, including neurotrophic factors, neuroinflammatory peptides, cytokines, along with transient receptor potential, and ionotropic channels that suggest possible approaches and innovations to identify novel clinical therapeutics.

Antihistamine promotes electroacupuncture analgesia in healthy human subjects: A pilot study

Background and aim

We have previously reported that histamine H₁ receptor antagonists facilitate electroacupuncture (EA) analgesia in experimental animals. In this pilot study, we sought to determine whether the histamine H₁ receptor antagonist dexchlorpheniramine (DCPA) facilitates EA analgesia in healthy human subjects.

Experimental procedure

Forty healthy subjects aged 20–30 years were randomly allocated to 1 of 4 groups: (1) sham EA at acupoints Zusanli (ST36) and Yanglingquan (GB34) (sham EA; n = 10); (2) EA at ST36 and GB34 (n = 10); (3) EA at ST36 and GB34 plus low-dose DCPA (2 mg, n = 10); (4) EA at ST36 and GB34 plus high-dose DCPA (4 mg, n = 10). Before and after acupuncture treatment, pain thresholds were determined by transcutaneous electrical stimuli on the glabrous skin of the left upper arm.

Results

After the acupuncture session, subjects in the EA plus high-dose DCPA group had a significantly higher pain threshold elevation compared with the other 3 study groups. The change from baseline in pain threshold in the EA plus high-dose DCPA group was significantly greater than the change in pain threshold with EA only, indicating that DCPA 4 mg facilitated EA analgesia.

Conclusion

The results suggest that combining H₁ receptor antagonist treatment with EA appears to relieve pain to a greater extent compared with EA alone. This study is registered with ClinicalTrials.gov (https://clinicaltrials.gov/), number NCT03805035 (https://clinicaltrials.gov/ct2/show/NCT03805035).

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Histamine H₁ receptor antagonist treatment appears to augment the pain-relieving effects of EA in healthy subjects.

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EA increased the pain thresholds in EA treated groups.

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Combination of EA and high-dose of DCPA further increased pain thresholds.

Polydopamine-coated polycaprolactone/carbon nanotubes fibrous scaffolds loaded with brain-derived neurotrophic factor for peripheral nerve regeneration

Carbon nanotubes (CNTs) have attracted increasing attention in the field of peripheral nerve tissue engineering owing to their unique structural and physical characteristics. In this study, a novel type of aligned conductive scaffolds composed of polycaprolactone (PCL) and CNTs were fabricated via electrospinning. Utilizing the mussel-inspired polydopamine (PDA) surface modification, brain-derived neurotrophic factor (BDNF) was loaded onto PCL/CNTs fibrous scaffolds to obtain PCL/CNTs-PDA-BDNF fibrous scaffolds capable of the sustained release of BDNF over 28 days. Schwann cells were cultured on these scaffolds, and the effects of the scaffolds on peripheral nerve regeneration in vitro were assessed by studying cell proliferation, morphology and the expressions of myelination-related genes S100, P0 and myelin basic protein (MBP). Furthermore, the effects of these scaffolds on peripheral nerve regeneration in vivo were investigated using a 10-mm rat sciatic nerve defect model. Both the in vitro and in vivo results indicated that PCL/CNTs-PDA-BDNF fibrous scaffolds could effectively promote sciatic nerve regeneration and functional recovery. Therefore, PCL/CNTs-PDA-BDNF fibrous scaffolds have great potential for peripheral nerve restoration.

Pharmacometabolomics by NMR in Oncology: A Systematic Review

Pharmacometabolomics (PMx) studies aim to predict individual differences in treatment response and in the development of adverse effects associated with specific drug treatments. Overall, these studies inform us about how individuals will respond to a drug treatment based on their metabolic profiles obtained before, during, or after the therapeutic intervention. In the era of precision medicine, metabolic profiles hold great potential to guide patient selection and stratification in clinical trials, with a focus on improving drug efficacy and safety. Metabolomics is closely related to the phenotype as alterations in metabolism reflect changes in the preceding cascade of genomics, transcriptomics, and proteomics changes, thus providing a significant advance over other omics approaches. Nuclear Magnetic Resonance (NMR) is one of the most widely used analytical platforms in metabolomics studies. In fact, since the introduction of PMx studies in 2006, the number of NMR-based PMx studies has been continuously growing and has provided novel insights into the specific metabolic changes associated with different mechanisms of action and/or toxic effects. This review presents an up-to-date summary of NMR-based PMx studies performed over the last 10 years. Our main objective is to discuss the experimental approaches used for the characterization of the metabolic changes associated with specific therapeutic interventions, the most relevant results obtained so far, and some of the remaining challenges in this area.

Alterations in the gut microbiota and metabolite profiles in the context of neuropathic pain

The aim of this study was to explore the relationships among gut microbiota disturbances and serum and spinal cord metabolic disorders in neuropathic pain. 16S rDNA amplicon sequencing and serum and spinal cord metabolomics were used to identify alterations in the microbiota and metabolite profiles in the sham rats and the chronic constriction injury (CCI) model rats. Correlations between the abundances of gut microbiota components at the genus level, the levels of serum metabolites, and pain-related behavioural parameters were analysed. Ingenuity pathway analysis (IPA) was applied to analyse the interaction networks of the differentially expressed serum metabolites. First, we found that the composition of the gut microbiota was different between rats with CCI-induced neuropathic pain and sham controls. At the genus level, the abundances of Helicobacter, Phascolarctobacterium, Christensenella, Blautia, Streptococcus, Rothia and Lactobacillus were significantly increased, whereas the abundances of Ignatzschineria, Butyricimonas, Escherichia, AF12, and Corynebacterium were significantly decreased. Additionally, 72 significantly differentially expressed serum metabolites and 17 significantly differentially expressed spinal cord metabolites were identified between the CCI rats and the sham rats. Finally, correlation analysis showed that changes in the gut microbiota was significantly correlated with changes in serum metabolite levels, suggesting that dysbiosis of the gut microbiota is an important factor in modulating metabolic disturbances in the context of neuropathic pain. In conclusion, our research provides a novel perspective on the potential roles of the gut microbiota and related metabolites in neuropathic pain.

Histamine, histamine receptors, and neuropathic pain relief

Histamine, acting via distinct histamine H₁, H₂, H₃, and H₄ receptors, regulates various physiological and pathological processes, including pain. In the last two decades, there has been a particular increase in evidence to support the involvement of H₃ receptor and H₄ receptor in the modulation of neuropathic pain, which remains challenging in terms of management. However, recent data show contrasting effects on neuropathic pain due to multiple factors that determine the pharmacological responses of histamine receptors and their underlying signal transduction properties (e.g., localization on either the presynaptic or postsynaptic neuronal membranes). This review summarizes the most recent findings on the role of histamine and the effects mediated by the four histamine receptors in response to the various stimuli associated with and promoting neuropathic pain. We particularly focus on mechanisms underlying histamine‐mediated analgesia, as we aim to clarify the analgesic potential of histamine receptor ligands in neuropathic pain.

Linked Articles

This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc

Evaluation of different classes of histamine H1 and H2 receptor antagonist effects on neuropathic nociceptive behavior following tibial nerve transection in rats

It seems that histamine release in the site of neuronal injury could contribute to the neuropathic pain mechanism. In the present study, we investigated the anti-allodynic effects of chronic administration of different classes of histamine H₁ and H₂ receptor antagonists on neuropathic nociceptive behavior following tibial nerve transection (TNT) in rats. Peripheral neuropathy was induced by TNT surgery. We performed acetone tests (AT) to record cold allodynia, Von Frey tests (VFT) to measure mechanical allodynia, double plate test (DPT) to evaluate thermal place preference/avoidance and open field test (OFT) for evaluation of animal activity. TNT rats showed a significant mechanical and cold allodynia compared to the sham group. Chlorpheniramine (5 and 15 mg/kg, i.p) significantly attenuated cold allodynia and prevented cold plate avoidance behavior and at the dose of 15 mg/kg remarkably decreased mechanical allodynia. Fexofenadine (10 and 30 mg/kg, p.o) significantly attenuated the mechanical allodynia and prevented cold plate avoidance. Ranitidine (5 and 15 mg/kg, i.p) significantly prevented cold plate avoidance behavior and at the dose of 15 mg/kg notably improved mechanical and cold allodynia. Famotidine (1 and 3 mg/kg, p.o) was ineffective on all nociceptive tests. Gabapantin (100 mg/kg, p.o) significantly improved all types of nociceptive behaviors. These results indicate that both blood brain barrier penetrating (chlorpheniramine) and poorly penetrating (fexofenadine) histamine H₁ receptor antagonists could improve the neuropathic pain sign, but only the blood brain barrier penetrating histamine H₂ receptor antagonist (ranitidine) could produce anti-allodynic effects in the TNT model of neuropathic pain in rats.

Pharmacometabolomics reveals a role for histidine, phenylalanine, and threonine in the development of paclitaxel-induced peripheral neuropathy

PURPOSE

Approximately 25% of breast cancer patients experience treatment delays or discontinuation due to paclitaxel-induced peripheral neuropathy (PN). Currently, there are no predictive biomarkers of PN. Pharmacometabolomics is an informative tool for biomarker discovery of drug toxicity. We conducted a secondary whole blood pharmacometabolomics analysis to assess the association between pretreatment metabolome, early treatment-induced metabolic changes, and the development of PN.

METHODS

Whole blood samples were collected pre-treatment (BL), just before the end of the first paclitaxel infusion (EOI), and 24 h after the first infusion (24H) from sixty patients with breast cancer receiving (80 mg/m²) weekly treatment. Neuropathy was assessed at BL and prior to each infusion using the sensory subscale (CIPN8) of the EORTC CIPN20 questionnaire. Blood metabolites were quantified from 1-D-¹H-nuclear magnetic resonance spectra using Chenomx® software. Metabolite concentrations were normalized in preparation for Pearson correlation and one-way repeated measures ANOVA with multiple comparisons corrected by false discovery rate (FDR).

RESULTS

Pretreatment histidine, phenylalanine, and threonine concentrations were inversely associated with maximum change in CIPN8 (ΔCIPN8) (p < 0.02; FDR ≤ 25%). Paclitaxel caused a significant change in concentrations of 2-hydroxybutyrate, 3-hydroxybutyrate, pyruvate, o-acetylcarnitine, and several amino acids from BL to EOI and/or 24H (p < 0.05; FDR ≤ 25%), although these changes were not associated with ΔCIPN8.

CONCLUSIONS

Whole blood metabolomics is a feasible approach to identify potential biomarker candidates of paclitaxel-induced PN. The findings suggest that pretreatment concentrations of histidine, phenylalanine, and threonine may be predictive of the severity of future PN and paclitaxel-induced metabolic changes may be related to disruption of energy homeostasis.

Toll-like receptor 4 contributes to chronic itch, alloknesis, and spinal astrocyte activation in male mice

Increasing evidence suggests that Toll-like receptor 4 (TLR4) contributes importantly to spinal cord glial activation and chronic pain sensitization; however, its unique role in acute and chronic itch is unclear. In this study, we investigated the involvement of TLR4 in acute and chronic itch models in male mice using both transgenic and pharmacological approaches. Tlr4 mice exhibited normal acute itch induced by compound 48/80 and chloroquine, but these mice showed substantial reductions in scratching in chronic itch models of dry skin, induced by acetone and diethylether followed by water (AEW), contact dermatitis, and allergic contact dermatitis on the neck. Intrathecal (spinal) inhibition of TLR4 with lipopolysaccharide Rhodobacter sphaeroides did not affect acute itch but suppressed AEW-induced chronic itch. Compound 48/80 and AEW also produced robust alloknesis, a touch-elicited itch in wild-type mice, which was suppressed by intrathecal lipopolysaccharide R sphaeroides and Tlr4 deletion. Acetone and diethylether followed by water induced persistent upregulation of Tlr4 mRNA and increased TLR4 expression in GFAP-expressing astrocytes in spinal cord dorsal horn. Acetone and diethylether followed by water also induced TLR4-dependent astrogliosis (GFAP upregulation) in spinal cord. Intrathecal injection of astroglial inhibitor L-α-aminoadipate reduced AEW-induced chronic itch and alloknesis without affecting acute itch. Spinal TLR4 was also necessary for AEW-induced chronic itch in the cheek model. Interestingly, scratching plays an essential role in spinal astrogliosis because AEW-induced astrogliosis was abrogated by putting Elizabethan collars on the neck to prevent scratching the itchy skin. Our findings suggest that spinal TLR4 signaling is important for spinal astrocyte activation and astrogliosis that may underlie alloknesis and chronic itch.

A critical time window for the analgesic effect of central histamine in the partial sciatic ligation model of neuropathic pain

Background

It is known that histamine participates in pain modulation. However, the effect of central histamine on neuropathic pain is not fully understood. Here, we report a critical time window for the analgesic effect of central histamine in the partial sciatic nerve ligation model of neuropathic pain.

Methods

Neuropathic pain was induced by partial sciatic nerve ligation (PSL) in rats, wild-type (C57BL/6J) mice and HDC^−/− (histidine decarboxylase gene knockout) and IL-1R^−/− (interleukin-1 receptor gene knockout) mice. Histidine, a precursor of histamine that can increase the central histamine levels, was administered intraperitoneally (i.p.). Histidine decarboxylase (HDC) enzyme inhibitor α-fluoromethylhistidine was administered intracerebroventricularly (i.c.v.). Histamine H₁ receptor antagonist mepyramine and H₂ receptor antagonist cimetidine were given intrathecally (i.t.) and intracisternally (i.c.). Withdrawal thresholds to tactile and heat stimuli were measured with a set of von Frey hairs and infrared laser, respectively. Immunohistochemistry and Western blot were carried out to evaluate the morphology of microglia and IL-1β production, respectively.

Results

Histidine (100 mg/kg, i.p.) administered throughout days 0–3, 0–7, or 0–14 postoperatively (PO) alleviated mechanical allodynia and thermal hyperalgesia in the hindpaw following PSL in rats. Intrathecal histamine reversed PSL-induced thermal hyperalgesia in a dose-dependent manner and intracisternal histamine alleviated both mechanical allodynia and thermal hyperalgesia. Moreover, α-fluoromethylhistidine (i.c.v.) abrogated the analgesic effect of histidine. However, histidine treatment initiated later than the first postoperative day (treatment periods included days 2–3, 4–7, and 8–14 PO) did not show an analgesic effect. In addition, histidine treatment initiated immediately, but not 3 days after PSL, inhibited microglial activation and IL-1β upregulation in the lumbar spinal cord, in parallel with its effects on behavioral hypersensitivity. Moreover, the inhibitory effects on pain hypersensitivity and spinal microglial activation were absent in HDC^−/− mice and IL-1R^−/− mice. H₁ receptor antagonist mepyramine (200 ng/rat i.t. or i.c.), but not H₂ receptor antagonist cimetidine (200, 500 ng/rat i.t. or 500 ng/rat i.c.), blocked the effects of histidine on pain behavior and spinal microglia.

Conclusions

These results demonstrate that central histamine is analgesic within a critical time window in the PSL model of neuropathic pain via histamine H₁ receptors. This effect may partly relate to the inhibition of microglial activation and IL-1β production in the spinal cord following nerve injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0637-0) contains supplementary material, which is available to authorized users.

Pressure algometry and enzyme-linked immunosorbent assay of natural antibodies in the evaluation of pain syndrome

The dynamics of possible markers of pain syndrome: pain pressure thresholds of intolerance (PTI) and natural antibodies to mediators of pain processing (nAbs) in blood serum at dorsalgia was studied. We have shown that most men and women had reduced PTIs. Night PTIs were lower than daytime PTIs regardless of the gender. The study of the content of nAbs to opioids and biogenic amines by ELISA have shown a prolonged maintenance of their elevated and high levels that could evoke long-term effect in pain chronization. Thus, the pressure algometry and ELISA of nAbs to pain processing mediators make it possible to assess the individual pain status objectively and, on this bases, to propose personal schemes of treatment.

Pharmacologically inhibiting GluR2 internalization alleviates neuropathic pain

Neuropathic pain is of serious clinical concern and only about half of patients achieve partial relief with currently-available treatments, so it is critical to find new drugs for this condition. Recently, the cellsurface trafficking of pain-related receptors has been suggested as an important mechanism underlying persistent neuropathic pain. Here, we used the short peptide GluA2-3y, which specifically inhibits the GluA2-dependent endocytosis of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and tested its anti-nociceptive effect in the periaqueductal grey (PAG) of intact rats and rats with neuropathic pain. Intra-PAG injection of 0.15, 1.5, 7.5, and 15 pmol of GluA2-3y induced dose-dependent increases in hindpaw withdrawal latencies to noxious thermal and mechanical stimuli in intact rats, suggesting that GluA2 cell-surface trafficking in the PAG is involved in pain modulation. Furthermore, GluA2-3y had much stronger anti-nociceptive effects in rats with neuropathic pain induced by sciatic nerve ligation. Interestingly, the intra-PAG injection of 15 pmol GluA2-3y had an analgesic effect similar to 10 μg (35 nmol) morphine in rats with neuropathic pain. Taken together, our results suggested that GluA2 trafficking in the PAG plays a critical role in pain modulation, and inhibiting GluA2 endocytosis with GluA2-3y has potent analgesic effects in rats with neuropathic pain. These findings strongly support the recent hypothesis that targeting receptor trafficking could be a new strategy for the treatment of neuropathic pain.

Histamine upregulates Nav1.8 expression in primary afferent neurons via H2 receptors: involvement in neuropathic pain

INTRODUCTION

The upregulation of Nav1.8 in primary afferents plays a critical role in the development and persistence of neuropathic pain. The mechanisms underlying the upregulation are not fully understood.

AIMS

The present study aims to investigate the regulatory effect of histamine on the expression of Nav1.8 in primary afferent neurons and its involvement in neuropathic pain.

RESULTS

Histamine at 10(-8) M increased the expression of Nav1.8 in cultured DRG neurons. This effect could be blocked by H2 receptor antagonist cimetidine or famotidine, but not by H1 receptor antagonist pyrilamine or dual H3 /H4 antagonist thioperamide. Peri-sciatic administration of histamine increased Nav1.8 expression in the sciatic nerve and L4/L5 DRG neurons in a dose-dependent manner, accompanied with remarkable mechanical allodynia and heat hyperalgesia in the ipsilateral hindpaw. Famotidine but not pyrilamine or thioperamide inhibited Nav1.8 upregulation and pain hypersensitivity. In addition, famotidine (40 mg/kg, i.p.) not only suppressed autotomy behavior in the rat neuroma model of neuropathic pain but also attenuated mechanical allodynia and thermal hyperalgesia following partial sciatic nerve ligation. Moreover, famotidine inhibited Nav1.8 upregulation in the neuroma and ligated sciatic nerve.

CONCLUSIONS

Our findings indicate that histamine increases Nav1.8 expression in primary afferent neurons via H2 receptor-mediated pathway and thereby contributes to neuropathic pain. H2 receptor antagonists may potentially be used as analgesics for patients with neuropathic pain.

SIP30 is required for neuropathic pain-evoked aversion in rats

SIP30 (SNAP25 interacting protein of 30) is a SNAP25 interaction protein of 30 kDa that functions in neurotransmitter release. Using a chronic constriction injury (CCI) model of neuropathic pain, we profiled gene expression in the rat spinal cord and brain and identified sip30, which was upregulated after CCI. Here, we show that CCI induced a bilateral increase of SIP30 in the rostral anterior cingulate cortex (rACC), a key brain region that has been implicated in pain affect. We put rats in a chamber with one half painted white (light area) and the other half painted black (dark area), and measured neuropathic pain-evoked place escape/avoidance paradigm (PEAP) to quantify the level of negative emotion evoked by painful stimuli using a Von Frey hair. Inhibition of CCI-mediated induction of SIP30 by intra-rACC injection of shRNA targeting the rat sip30 gene reduced PEAP. Interestingly, knockdown of SIP30 did not affect CCI-induced evoked pain such as heat hyperalgesia and mechanical allodynia. Neither did it affect general learning and memory. CCI-induced upregulation of SIP30 was correlated with activation of ERK, PKA, and CREB in the rACC. Intra-rACC administration of PKA or ERK inhibitors suppressed CCI-induced SIP30 upregulation and blocked the induction of PEAP. Additionally, knockdown of SIP30 suppressed the frequency of mEPSCs and increased paired-pulse ratios in rACC slices and decreased extracellular glutamate concentrations. Together, our results highlight SIP30 as a target of PKA and ERK in the rACC to mediate neuropathic pain-evoked negative emotion via modulation of glutamate release and excitatory synaptic transmission.

Gender differences in histamine-induced depolarization and inward currents in vagal ganglion neurons in rats

Evidence has shown gender differences regarding the critical roles of histamine in the prevalence of asthma, anaphylaxis, and angina pectoris. Histamine depolarizes unmyelinated C-type neurons without any effects on myelinated A-type vagal ganglion neurons (VGNs) in male rats. However, little is known if VGNs from females react to histamine in a similar manner. Membrane depolarization and inward currents were tested in VGNs isolated from adult rats using a whole-cell patch technique. Results from males were consistent with the literature. Surprisingly, histamine-induced depolarization and inward currents were observed in both unmyelinated C-type and myelinated A- and Ah-type VGNs from female rats. In Ah-type neurons, responses to 1.0 μM histamine were stronger in intact females than in males and significantly reduced in ovariectomized (OVX) females. In C-type neurons, histamine-induced events were significantly smaller (pA/pF) in intact females compared with males and this histamine-induced activity was dramatically increased by OVX. Female A-types responded to histamine, which was further increased following ovariectomy. Histamine at 300 nM depolarized Ah-types in females, but not Ah-types in OVX females. In contrast, the sensitivity of A- and C-types to histamine was upregulated by OVX. These data demonstrate gender differences in VGN chemosensitivity to histamine for the first time. Myelinated Ah-types showed the highest sensitivity to histamine across female populations, which was changed by OVX. These novel findings improve the understanding of gender differences in the prevalence of asthma, anaphylaxis, and pain. Changes in sensitivity to histamine by OVX may explain alterations in the prevalence of certain pathophysiological conditions when women reach a postmenopausal age.