Histaminergic Involvement in Neuropathic Pain Produced by Partial Ligation of the Sciatic Nerve in Rats:

Microinjection of histamine and its H3 receptor agonist and antagonist into the agranular insular cortex influence sensory and affective components of neuropathic pain in rats

Many areas of the brain along with neurotransmitters involve in processing of nociceptive, emotional and cognitive dimensions of neuropathic pain. Brian neuronal histamine through H₁, H₂, H₃ and H₄ receptors mediates many physiological functions such as cognition, emotion and pain. In the present study we investigated the effects of intra-agranular insular cortex microinjection of histamine and its H₃ receptor agonist and antagonist on sensory and affective aspects of neuropathic pain. Spared nerve injury model of neuropathic pain was used. Two guide cannulas were surgically implanted in the right and left sides of agranular insular cortex. Sensory component (mechanical hyperalgesia) was recorded by application of von Frey filaments onto the plantar surface of the hind paw. Area under curve of mechanical hyperalgesia was calculated. Affective aspect (place escape avoidance paradigm) was recorded using an inverse white/black chamber. Histamine (0.5, 1 and 2 μg/site) and thioperamide (a histamine H₃ receptor antagonist, 4 μg/site) decreased, whereas immepip (a histamine H₃ receptor agonist, 2 μg/site) increased the percentages of paw withdrawal frequency and time spent in white side of white/black box. Prior administration of thioperamide (4 μg/site) increased the suppressive effects induced by histamine and inhibited immepip (2 μg/site)-induced hyperalgesia and aversion. Based on the present results, it is concluded that histamine and its H₃ receptor at the agranular insular cortex level may involve in modulation of sensory and affective components of 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

Development of an AmpliSeqTM Panel for Next-Generation Sequencing of a Set of Genetic Predictors of Persisting Pain

Background: Many gene variants modulate the individual perception of pain and possibly also its persistence. The limited selection of single functional variants is increasingly being replaced by analyses of the full coding and regulatory sequences of pain-relevant genes accessible by means of next generation sequencing (NGS).

Methods: An NGS panel was created for a set of 77 human genes selected following different lines of evidence supporting their role in persisting pain. To address the role of these candidate genes, we established a sequencing assay based on a custom AmpliSeq^TM panel to assess the exomic sequences in 72 subjects of Caucasian ethnicity. To identify the systems biology of the genes, the biological functions associated with these genes were assessed by means of a computational over-representation analysis.

Results: Sequencing generated a median of 2.85 ⋅ 10⁶ reads per run with a mean depth close to 200 reads, mean read length of 205 called bases and an average chip loading of 71%. A total of 3,185 genetic variants were called. A computational functional genomics analysis indicated that the proposed NGS gene panel covers biological processes identified previously as characterizing the functional genomics of persisting pain.

Conclusion: Results of the NGS assay suggested that the produced nucleotide sequences are comparable to those earned with the classical Sanger sequencing technique. The assay is applicable for small to large-scale experimental setups to target the accessing of information about any nucleotide within the addressed genes in a study cohort.

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.

Effects of S 38093, an antagonist/inverse agonist of histamine H3 receptors, in models of neuropathic pain in rats

BACKGROUND

Histamine H3 receptors are mainly expressed on CNS neurons, particularly along the nociceptive pathways. The potential involvement of these receptors in pain processing has been suggested using H3 receptor inverse agonists.

METHODS

The antinociceptive effect of S 38093, a novel inverse agonist of H3 receptors, has been evaluated in several neuropathic pain models in rat and compared with those of gabapentin and pregabalin.

RESULTS

While S 38093 did not change vocalization thresholds to paw pressure in healthy rats, it exhibited a significant antihyperalgesic effect in the Streptozocin-induced diabetic (STZ) neuropathy model after acute and chronic administration and, in the chronic constriction injury (CCI) model only after chronic administration, submitted to the paw-pressure test. Acute S 38093 administration at all doses tested displayed a significant cold antiallodynic effect in a model of acute or repeated administration of oxaliplatin-induced neuropathy submitted to cold tail immersion, cold allodynia being the main side effect of oxaliplatin in patients. The effect of S 38093 increased following chronic administration (i.e. twice a day during 5 days) in the CCI and STZ models except in the oxaliplatin models where its effect was already maximal from the first administration The kinetics and size of effect of S 38093 were similar to gabapentin and/or pregabalin. Finally, the antinociceptive effect of S 38093 could be partially mediated by α2 adrenoreceptors desensitization in the locus coeruleus.

CONCLUSIONS

These results highlight the interest of S 38093 to relieve neuropathic pain and warrant clinical trials especially in chemotherapeutic agent-induced neuropathic pain.

SIGNIFICANCE

S 38093, a new H3 antagonist/inverse agonist, displays antiallodynic and antihyperalgesic effect in neuropathic pain, especially in oxaliplatin-induced neuropathy after chronic administration. This effect of S 38093 in neuropathic pain could be partly mediated by α2 receptors desensitization in the locus coeruleus.

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.

Effects of an H3R antagonist on the animal model of autism induced by prenatal exposure to valproic acid

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders primarily characterized by impaired social interaction and communication, and by restricted repetitive behaviors and interests. Ligands of histamine receptor 3 (H3R) are considered potential therapeutic agents for the treatment of different brain disorders and cognitive impairments. Considering this, the aim of the present study is to evaluate the actions of ciproxifan (CPX), an H3R antagonist, on the animal model of autism induced by prenatal exposure to valproic acid (VPA). Swiss mice were prenatally exposed to VPA on embryonic day 11 and assessed for social behavior, nociceptive threshold and repetitive behavior at 50 days of life. The treatment with CPX (3 mg/kg) or saline was administered 30 minutes before each behavioral test. The VPA group presented lower sociability index compared to VPA animals that were treated with CPX. Compared to the Control group, VPA animals presented a significantly higher nociceptive threshold, and treatment with CPX was not able to modify this parameter. In the marble burying test, the number of marbles buried by VPA animals was consistent with markedly repetitive behavior. VPA animals that received CPX buried a reduced amount of marbles. In summary, we report that an acute dose of CPX is able to attenuate sociability deficits and stereotypies present in the VPA model of autism. Our findings have the potential to help the investigations of both the molecular underpinnings of ASD and of possible treatments to ameliorate the ASD symptomatology, although more research is still necessary to corroborate and expand this initial data.

Effects of histamine on spontaneous neuropathic pain induced by peripheral axotomy

The present study was designed to investigate the effects of histamine on spontaneous neuropathic pain (NP) induced by peripheral axotomy. Rats and mice were subjected to complete transection of the left sciatic and saphenous nerves to induce spontaneous NP (the neuroma model). Rats were then treated with drugs once daily for 30 days (histidine and loratadine, i.p.) or 21 days (histamine, i.c.v.). Autotomy behavior was scored daily until day 50 post-operation (PO). On days 14 to 21 PO, some rats in the control group were subjected to single-fiber recording. Autotomy behavior was also monitored daily in histidine decarboxylase (the key enzyme for histamine synthesis) knockout (HDC(-/-)) and wild-type mice for 42 days. We found that both histidine (500 mg/kg) (a precursor of histamine that increases histamine levels in the tissues) and histamine (50 μg/5 μL) significantly suppressed autotomy behavior in rats. HDC(-/-) mice lacking endogenous histamine showed higher levels of autotomy than the wild-type. In addition, the analgesic effect of histidine was not antagonized by loratadine (a peripherally-acting H1 receptor antagonist), while loratadine alone significantly suppressed autotomy. Electrophysiological recording showed that ectopic spontaneous discharges from the neuroma were blocked by systemic diphenhydramine (an H1 receptor antagonist). Our results suggest that histamine plays an important role in spontaneous NP. It is likely that histamine in the central nervous system is analgesic, while in the periphery, via H1 receptors, it is algesic. This study justifies the avoidance of a histamine-rich diet and the use of peripherally-acting H1 receptor antagonists as well as agents that improve histamine action in the central nervous system in patients with spontaneous NP.

Overdose of the histamine H₃ inverse agonist pitolisant increases thermal pain thresholds

OBJECTIVE AND DESIGN

Pitolisant (BF2.649) is a selective inverse agonist for the histamine H(3) receptor and was developed for the treatment of excessive daytime sleepiness in Parkinson disease, narcolepsy, and schizophrenia. Since H(3)-ligands can decrease inflammatory pain, we tested Pitolisant in inflammatory and neuropathic pain models. MATERIALS AND TREATMENTS: Behavioral effects of pitolisant and the structural different H(3) receptor inverse agonists ciproxifan and ST-889 were tested in zymosan-induced inflammation and the spared nerve injury model for neuropathic pain.

METHODS

Responses to mechanical and thermal stimuli were determined. Calcium imaging was performed with primary neuronal cultures of dorsal root ganglions.

RESULTS

Clinically relevant doses of pitolisant (10 mg/kg) had no relevant effect on mechanical or thermal pain thresholds in all animal models. Higher doses (50 mg/kg) dramatically increased thermal but not mechanical pain thresholds. Neither ciproxifan nor ST-889 altered thermal pain thresholds. In peripheral sensory neurons high concentrations of pitolisant (30-500 μM), but not ciproxifan, partially inhibited calcium increases induced by capsaicin, a selective activator of transient receptor potential vanilloid receptor 1 (TRPV1). High doses of pitolisant induced a strong hypothermia.

CONCLUSION

The data show a dramatic effect of high dosages of pitolisant on the thermosensory system, which appears to be H(3) receptor-independent.

Interaction between histamine and morphine at the level of the hippocampus in the formalin-induced orofacial pain in rats

The present study explored the interaction between histaminergic and opioidergic systems at the level of the hippocampus in modulation of orofacial pain by intra-hippocampal microinjections of histamine, pyrilamine (an antagonist of histamine H(1) receptors), ranitidine (an antagonist of histamine H(2) receptors), morphine (an opioid receptor agonist) and naloxone (an opioid receptor antagonist) in separate and combined treatments. Orofacial pain was induced by subcutaneous (sc) injection of formalin (50 μl, 1%) in the upper lip region and the time spent face rubbing was recorded in 3 min blocks for 45 min. Formalin (sc) produced a marked biphasic (first phase: 0-3 min, second phase: 15-33 min) pain response. Histamine and morphine suppressed both phases of pain. Histamine increased morphine-induced antinociception. Pyrilamine and ranitidine had no effects when used alone, whereas pretreatments with pyrilamine and ranitidine prevented histamine- and morphine-induced antinociceptive effects. Naloxone alone non-significantly increased pain intensity and inhibited the antinociceptive effects of morphine and histamine. The results of the present study indicate that at the level of the hippocampus, histamine through its H(1) and H(2) receptors, mediates orofacial region pain. Moreover, morphine via a naloxone-reversible mechanism produces analgesia. In addition, both histamine H(1) and H(2) receptors, as well as opioid receptors may be involved in the interaction between histamine and morphine in producing analgesia.

H3 receptors and pain modulation: peripheral, spinal, and brain interactions

Histamine H(3) receptors (H(3)Rs), distributed within the brain, the spinal cord, and on specific types of primary sensory neurons, can modulate pain transmission by several mechanisms. In the skin, H(3)Rs are found on certain Aβ fibers, and on keratinocytes and Merkel cells, as well as on deep dermal, peptidergic Aδ fibers terminating on deep dermal blood vessels. Activation of H(3)Rs on the latter in the skin, heart, lung, and dura mater reduces calcitonin gene-related peptide and substance P release, leading to anti-inflammatory (but not antinociceptive) actions. However, activation of H(3)Rs on the spinal terminals of these sensory fibers reduces nociceptive responding to low-intensity mechanical stimuli and inflammatory stimuli such as formalin. These findings suggest that H(3)R agonists might be useful analgesics, but these drugs have not been tested in clinically relevant pain models. Paradoxically, H(3) antagonists/inverse agonists have also been reported to attenuate several types of pain responses, including phase II responses to formalin. In the periaqueductal gray (an important pain regulatory center), the H(3) inverse agonist thioperamide releases neuronal histamine and mimics histamine's biphasic modulatory effects in thermal nociceptive tests. Newer H(3) inverse agonists with potent, selective, and brain-penetrating properties show efficacy in several neuropathic and arthritis pain models, but the sites and mechanisms for these actions remain poorly understood.