Enhanced antinociception by intrathecally-administered morphine in histamine H1 receptor gene knockout mice

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

Histamine and Delirium: Current Opinion

Delirium is a very common, but refractory clinical state, notably present in intensive care and in the growing aging community. It is characterized by fluctuating disturbances in a number of key behavioral features, namely cognition, mood, attention, arousal, and self-awareness. Histamine is arguably the most pleotropic neurotransmitter in the human brain, and this review provides a rationale, and proposes that this neuroactive amine plays a role in modulating the characteristic features of delirium. While centrally permeable H1 and H2 histamine receptor antagonists have pro-delirium potential, we propose that centrally permeable H3 histamine receptor antagonists may provide an exciting new strategy to combat delirium. The Histamine H4 receptor may also have an indirect inflammatory neuroglial role which requires further exploration.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

The role of histamine in neurogenic inflammation

The term 'neurogenic inflammation' has been adopted to describe the local release of inflammatory mediators, such as substance P and calcitonin gene-related peptide, from neurons. Once released, these neuropeptides induce the release of histamine from adjacent mast cells. In turn, histamine evokes the release of substance P and calcitonin gene-related peptide; thus, a bidirectional link between histamine and neuropeptides in neurogenic inflammation is established. The aim of this review is to summarize the most recent findings on the role of histamine in neurogenic inflammation, with particular regard to nociceptive pain, as well as neurogenic inflammation in the skin, airways and bladder.

Histamine produces opposing effects to serotonin in the knee joint of rats

Formalin injected in the knee joint of rats produces concentration-dependent nociception, edema, and plasma leakage (PL). Herein, we investigated the effect of histamine H1 receptor (H1R) antagonists in this model. Articular nociception was inferred from the paw elevation time (PET; seconds) during 1-minute periods of stimulated walking, determined every 5 minutes, throughout a 60-minute experimental session. Edema was evaluated by the increase in articular diameter (AD; mm), and PL was measured by the amount of Evans blue dye in the synovial fluid (PL; μg/mL). Loratadine and cetirizine, given systemically, both increased the PET. None of the treatments changed the AD and PL. Loratadine given locally with formalin increased the PET but was without effect when given in the contralateral knee. Systemic loratadine was also without effect when formalin was coinjected with sodium cromoglycate. Histamine and the selective H1R agonist 2-pyridylethylamine decreased the PET and potentiated morphine spinal analgesia, but did not affect the AD and PL. Cetirizine prevented the antinociceptive effect of the H1R agonist. The N-methyl-D-aspartate/histamine-site agonist tele-methylhistamine coinjected with formalin only increased PET. Serotonin alone had no effect on the PET and increased the AD, and the highest dose increased the PL. When coinjected with formalin, serotonin only caused hypernociception, and the highest dose also increased AD. NAN 190, cyproheptadine, and ondansetron (respectively, 5-HT1, 5-HT2, and 5-HT3 receptor antagonists) decreased the PET without changing the AD or PL. Collectively, these results suggest that in rats, the H1R plays an antinociceptive role within the knee joint, while serotonin receptors play a pronociceptive role.

PERSPECTIVE

The present study revealed an antinociceptive mechanism that has previously not been detected by traditional nociceptive tests. Our observations may help to improve the development of new pharmacological strategies for the treatment of clinically relevant pains that generally originate in deep structures.

Effects of dexamethasone and pheniramine hydrogen maleate on stress response in patients undergoing elective laparoscopic cholecystectomy

BACKGROUND

Laparoscopic cholecystectomy (LC) still leads to significant postoperative nausea and vomiting (PONV) and pain. Our aim was to evaluate the efficacy of dexamethasone or pheniramine hydrogen maleate, either alone or combined, in reducing the stress response and symptoms after LC.

METHODS

Patients were randomly assigned to 1 of 4 groups, each consisting of 20 patients: control, dexamethasone (8 mg/2 mL), pheniramine hydrogen maleate (45.5 mg/2 mL), and the combined group. The drugs were given before anesthesia induction.

RESULTS

C-reactive protein levels (CRP) and visual analog scale (VAS) scores were significantly less in the dexamethasone (P = .003) and combined groups (P < .001). Both dexamethasone (P < .001) and pheniramine hydrogen maleate (P = .005) significantly reduced PONV.

CONCLUSIONS

Dexamethasone significantly reduced postoperative pain and the systemic acute-phase response, whereas these effects were only partially attained with pheniramine hydrogen maleate. Both dexamethasone and pheniramine hydrogen maleate significantly reduced PONV. An additive effect seemed to occur if these drugs were used in combination.

Role of spinal neurotransmitter receptors in itch: new insights into therapies and drug development

Targets for antipruritic therapies are now expanding from the skin to the central nervous system. Recent studies demonstrate that various neuronal receptors in the spinal cord are involved in pruritus. The spinal opioid receptor is one of the best-known examples. Spinal administration of morphine is frequently accompanied by segmental pruritus. In addition to μ-opioid receptor antagonists, κ-opioid receptor agonists have recently come into usage as novel antipruritic drugs, and are expected to suppress certain subtypes of itch such as hemodialysis- and cholestasis-associated itch that are difficult to treat with antihistamines. The gastrin-releasing peptide receptor in the superficial dorsal horn of the spinal cord has also received recent attention as a novel pathway of itch-selective neural transmission. The NMDA glutamate receptor appears to be another potential target for the treatment of itch, especially in terms of central sensitization. The development of NMDA receptor antagonists with less undesirable side effects on the central nervous system might be beneficial for antipruritic therapies. Drugs suppressing presynaptic glutamate-release such as gabapentin and pregabalin also reportedly inhibit certain subtypes of itch such as brachioradial pruritus. Spinal receptors of other neuromediators such as bradykinin, substance P, serotonin, and histamine may also be potential targets for antipruritic therapies, given that most of these molecules interfere not only with pain, but also with itch transmission or regulation. Thus, the identification of itch-specific receptors and understanding itch-related circuits in the spinal cord may be innovative strategies for the development of novel antipruritic drugs.

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.

Differential responding of autonomic function to histamine H₁ antagonism in irritable bowel syndrome

BACKGROUND

The role of histamine in the pathophysiology of irritable bowel syndrome (IBS) is largely unknown. Dysfunction of the autonomic nervous system (ANS) in IBS patients is also not fully confirmed. We hypothesized that blockade of histamine H₁ receptors affects ANS responses differently between IBS subjects and controls.

METHODS

Subjects were 12 IBS subjects and 12 age- and sex-matched controls. Either 100 μg kg⁻¹ chlorphenamine or the same amount of saline was administered on different days. The rectum was stimulated with electrical currents of 0 mA (sham) or 30 mA. Autonomic nervous system function was measured using mean arterial pressure (MAP), heart rate (HR), high frequency (HF) component of HR variability, low frequency/high frequency ratio (LF/HF ratio) and plasma catecholamines and histamine. Subjective perceived stress during the examination was evaluated on an ordinate scale.

KEY RESULTS

Mean arterial pressure showed significant effects of diagnosis (P < 0.05) and drug × diagnosis interaction (P < 0.05). The MAP significantly increased after chlorphenamine administration in IBS subjects, but not in controls. Heart rate revealed a significant drug effect (P < 0.001), which decreased after chlorphenamine administration in controls, but not in IBS subjects. Perceived stress significantly increased by rectal stimulation (P < 0.001) and a significant stimulus × diagnosis interaction (P < 0.05) was revealed, indicating greater reduction in IBS subjects by chlorphenamine.

CONCLUSION & INFERENCES

Sympathetic vasomotor tone in IBS subjects differentially responded on administration of a histamine H₁ antagonist to that of controls. These findings suggest an increased histaminergic activity in IBS subjects.

Effects of chlorpheniramine and ranitidine on the visceral nociception induced by acetic acid in rats: role of opioid system

In this study, effects of chlorpheniramine (H1-receptor blocker), ranitidine (H2-receptor blocker), morphine (an opioid agonist) and naloxone (an opioid antagonist) in separate and combined treatments were investigated on the visceral nociception in rats. Visceral nociception was induced by intraperitoneal injection of acetic acid (1 mL, 1%). The latency time to the beginning of the first abdominal wall contraction (first writhe) was measured and the numbers of writhes were counted for 1 h after acetic acid injection. Intraperitoneal injections of chlorpheniramine and ranitidine significantly (p < 0.05) increased the latency time to the beginning of the first writhe and also significantly (p < 0.05) decreased the numbers of writhes. The same results were obtained after subcutaneous injection of morphine. Subcutaneous injection of naloxone did not change the intensity of visceral nociception, but significantly (p < 0.05) prevented the morphine-induced antinociception. Intraperitoneal injection of chlorpheniramine significantly (p < 0.05) enhanced the morphine-induced analgesia, but did not reverse the effect of naloxone on nociceptive responses. Intraperitoneal injection of ranitidine, with no effect on the morphine-induced antinociception, significantly (p < 0.05) reversed the effect of naloxone on pain responses. These results suggest that both chlorpheniramine and ranitidine exert antinociceptive effect in the visceral nociception. In addition, morphine through a naloxone-dependent mechanism produces visceral antinociception. Moreover, the endogenous opioid system may participate in the chlorpheniramine- but not in the ranitidine-induced antinociception.

Role of histaminergic neurons in hypnotic modulation of brain processing of visceral perception

Modulating visceral sensation of the body is important to the understanding of emotion formation. Molecules that act during hypnosis and modify visceral pain perception are not known. We tested our hypothesis that hypnotic suggestion changes electrophysiological processing of visceroafferent signals in the human brain and that these conditions are in part dependent on histaminergic neurons. Twelve healthy male subjects were studied on two separate days: a day of treatment with histamine H1 receptor antagonist (d-chlorpheniramine 100 microg kg(-1), intravenously) and another day of that with placebo (saline, the same amount) in a randomized order. We recorded cortical evoked potentials to 100 rectal electrical stimuli after neutral, hyperalgesic or analgesic hypnotic suggestions as given to modulate the visceral perception. Analgesic suggestion reduced the amplitude of the deepest positive peak of viscerosensory evoked potential. Administration of histamine H1 antagonist diminished the attenuation of viscerosensory evoked potential by analgesic suggestion. Our results suggest that central pain modulatory system in the brain is activated by hypnotic suggestion and that brain histamine is a mediator in the hypnotic modulation of visceral sensory pathway as well as in the control of consciousness level. These findings lead us to possible new treatment for control of visceral perception.

Neurotensin-produced antinociception in the rostral ventromedial medulla is partially mediated by spinal cord norepinephrine

Microinjection of neurotensin (NT) into the rostral ventromedial medulla (RVM) produces dose-dependent antinociception. Here we show that antinociception produced by intra-RVM microinjection of neurotensin (NT) or the selective NT receptor subtype 1 (NTR1) agonist PD149163 can be partially blocked by intrathecal (i.t.) yohimbine, an alpha2-adrenoceptor antagonist and by methysergide, a serotonin receptor antagonist. Antinociception produced by the NTR2 agonist beta-lactotensin (beta-LT) is blocked by intrathecal (i.t.) yohimbine, but not by methysergide i.t. It is not known which noradrenergic cell group is involved in this newly identified noradrenergic component of NTR-mediated antinociception. These experiments provide the first evidence that selective activation of NTR2 in the RVM produces antinociception. These results also provide evidence that activation of NTR1 in the RVM produces antinociception through spinal release of norepinephrine (NE) and serotonin, and that activation of NTR2 in the RVM produces antinociception mediated by spinal release of NE.

Antidepressants enhance the antinociceptive effects of carbamazepine in the acetic acid-induced writhing test in mice

Some antidepressants, as well as antiepileptics, are effective for treating pain of varying etiology. The present study was designed to characterize the antinociceptive effects of imipramine, a tricyclic antidepressant, fluvoxamine, a selective serotonin reuptake inhibitor, milnacipran, a serotonin noradrenaline reuptake inhibitor, and carbamazepine, an antiepileptic drug, using the acetic acid-induced writhing test in mice. Imipramine (1.25-10 mg/kg, i.p.), fluvoxamine (5-40 mg/kg, i.p.) and milnacipran (2.5-20 mg/kg, i.p.) all dose-dependently and significantly reduced the number of writhes induced by the injection of acetic acid (0.8% (v/v)), although the maximal effect of milnacipran was weaker than those of imipramine and fluvoxamine. Similarly, carbamazepine (5-20 mg/kg, i.p.) also showed a dose-dependent and significant antinociceptive effect. In combination studies, the co-administration of a sub-effective dose of carbamazepine (5 mg/kg, i.p.) with imipramine (1.25 and 2.5 mg/kg, i.p.), fluvoxamine (10 mg/kg, i.p.) or milnacipran (1.25 and 2.5 mg/kg, i.p.) significantly reduced the number of writhes. Additionally, the hole-board test revealed that the medications with significant antinociceptive effects barely produced changes in motor activity that could possibly affect writhing behavior. Thus, the present study demonstrated that the antinociceptive effect of carbamazepine is enhanced by combination with imipramine, fluvoxamine and milnacipran. Therefore, the combined therapy using antidepressants and carbamazepine may be useful clinically for the control of pain.

Altered emotional behavioral responses in mice lacking brain-type fatty acid-binding protein gene

Brain-type fatty acid-binding protein (B-FABP) belongs to a family of intracellular lipid-binding proteins. B-FABP exhibits a binding affinity to long-chain fatty acids (FAs) whose effects on brain functions including development, emotion, learning and memory have been proposed. B-FABP is localized in the ventricular germinal cells in embryonic brain and astrocytes in developing and mature brain of rodents. In the present study we generated the mouse harboring a null mutation in the B-FABP gene and studied its phenotype. B-FABP mutant mice exhibited the enhanced anxiety and increased fear memory as well as the decreased content of docosahexaenoic acid (DHA) in their brain during the neonatal period without detection of any histological changes in the brain. In the adult brain, B-FABP was localized more numerously to the astrocytes in the amygdala and septal area than to those in the hippocampal area. Analysis of FA content in the amygdala of adult brain revealed that arachidonic and palmitic acids increased significantly in the mutant mice compared with wild-type. Furthermore, the response of N-methyl-d-aspartate receptor-mediated current to DHA in isolated neurons from B-FABP mutant brain was significantly decreased compared with that of wild-type, while no significant differences were detected in behavioral responses related to the spatial learning/memory or in the hippocampal long-term potentiation. These data indicate that B-FABP is crucially involved in the fear memory and anxiety through its binding with FAs and/or its own direct effects on pertinent metabolism/signaling of FAs.

Enhanced antinociceptive effects of morphine in histamine H2 receptor gene knockout mice

We have previously shown that antinociceptive effects of morphine are enhanced in histamine H1 receptor gene knockout mice. In the present study, involvement of supraspinal histamine H2 receptor in antinociception by morphine was examined using histamine H2 receptor gene knockout (H2KO) mice and histamine H2 receptor antagonists. Antinociception was evaluated by assays for thermal (hot-plate, tail-flick and paw-withdrawal tests), mechanical (tail-pressure test) and chemical (formalin and capsaicin tests) stimuli. Thresholds for pain perception in H2KO mice were higher than wild-type mice. Antinociceptive effects of intracerebroventricularly administered morphine were enhanced in the H2KO mice compared to wild-type mice. Intracerebroventricular co-administration of morphine and cimetidine produced significant antinociceptive effects in the wild-type mice when compared to morphine or cimetidine alone. Furthermore, zolantidine, a selective and hydrophobic H2 receptor antagonist, enhanced the effects of morphine in all nociceptive assays examined. These results suggest that histamine exerts inhibitory effects on morphine-induced antinociception through H2 receptors at the supraspinal level. Our present and previous studies suggest that H1 and H2 receptors cooperatively function to modulate pain perception in the central nervous system.

Enhanced antinociception by intracerebroventricularly administered orexin A in histamine H1 or H2 receptor gene knockout mice

Orexins are neuropeptides that are mostly expressed in the posterior and lateral hypothalamus, and related to the central control of appetite, arousal, and antinociception. Orexin neurons projected to the tuberomammillary nucleus and orexins may release histamine from the histamine neurons in this nucleus. Histamine is known to cause hypernociception. The roles of histamine H1 and H2 receptors in the orexin A-induced antinociception, however, have not been clarified yet. Here we studied the effects of histamine H1 and H2 receptors on orexin A-produced antinociception using histamine receptor knockout mice in four assays of nociception; the hot-plate, the tail-flick, the tail-pressure and the capsaicin tests. Furthermore we studied effects of histamine H1 and H2 receptor antagonists on orexin A-produced antinociception in C57BL/6 mice. The antinociceptive effects of i.c.v. orexin A were greater in histamine H1 receptor or H2 receptor knockout mice than in the wild-type mice in all four assays of pain. Furthermore, treatment of C57BL/6 mice with a combination of i.c.v. orexin A and d-chlorpheniramine (a histamine H1 receptor antagonist) or cimetidine (a histamine H2 receptor antagonist) showed a greater antinociception than i.c.v. orexin A alone in all four assays. These findings suggest the possibility that orexin A may activate H1 and H2 receptors in the supraspinal levels through the release of histamine from neurons, which might attenuate the antinociceptive effects of orexin A. Thus, the blocking of the histamine H1 or H2 receptor may produce antinociception and enhance the orexin A-induced antinociception.

Intrathecally-administered histamine facilitates nociception through tachykinin NK1 and histamine H1 receptors: A study in histidine decarboxylase gene knockout mice

Intrathecal injection of histamine elicited behavioral responses consisting of scratching, biting and licking in conscious mice. To study the participation of histamine in pain perception, histidine decarboxylase knockout mice were examined for pain threshold by means of three different kinds of noxious stimuli: thermal nociception (hot-plate, tail-flick, and paw-withdrawal), mechanical nociception (tail-pressure), and chemical nociception (formalin test and capsaicin test). Mutant mice lacking histidine decarboxylase showed significantly fewer nociceptive responses to the hot-plate, tail-flick, paw-withdrawal, tail-pressure, formalin and capsaicin tests. Sensitivity to noxious stimuli in the histidine decarboxylase knockout mice was significantly lower when compared to the wild-type mice. The intrathecally-administered histamine (400 pmol) significantly shortened the latency in the histidine decarboxylase knockout mice, but not in the wild-type mice in tail-flick tests. Pyrilamine, a histamine H(1) receptor antagonist, but not ranitidine, a histamine H(2) receptor antagonist, produced inhibition of the induced behavioral responses in the tail-flick test when co-administered with histamine. Sendide, a tachykinin NK(1) receptor antagonist, inhibited histamine-induced nociceptive behavior in the histidine decarboxylase knockout mice. In contrast, the treatment with D-(-)-2 amino-5-phosponovaleric acid (D-APV), an N-methyl-D-aspartate (NMDA) receptor antagonist, did not prevent the induction of the behavioral responses by histamine. These studies substantiate the evidence that nociceptive behavior induced by intrathecal injection of histamine is largely mediated through tachykinin NK(1) and histamine H(1) receptors in the spinal cord.

Enhanced antinociception by intracerebroventricularly and intrathecally-administered orexin A and B (hypocretin-1 and -2) in mice

Orexins are neuropeptides located exclusively in neurons of the lateral hypothalamic area, which send projections to most monoaminergic nuclei, such as noradrenergic locus coeruleus, dopaminergic ventral tegmental areas, and histaminergic tuberomammillary nuclei. The present work was carried out to examine the role of orexins in nociception in mice. C57BL/6 mice were administered with orexin A and B intracerebroventricularly (i.c.v.), intrathecally (i.t.) and subcutaneously (s.c.) to reveal the sites of action of these peptides and to examine the pain thresholds using four kinds of nociceptive tasks. Orexins showed antinociceptive effects in all four types of assays for thermal (hot-plate, tail-flick, paw-withdrawal), mechanical (tail-pressure), chemical (formalin, capsaicin and abdominal stretch) nociceptions and nociceptin-induced behavioral responses, when administered i.c.v. or i.t., whereas the s.c. administration was ineffective. The antinociceptive effects of orexin A were more remarkable than those of orexin B. The i.c.v. administration of orexin A was as effective as, or more potent than the i.t. administration. The effects of orexin A were completely blocked by adenosine type 1 receptor antagonists, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and theophylline, but not by naloxone, suggesting a possible involvement of the adenosine-containing neurons and/or the adenosine pathway in these orexin actions. The i.c.v. administration of nociceptin had no significant effects on orexin expression in the brain and spinal cord. The present findings suggest that orexins have an antinociceptive role in at least four different types of pains, probably acting on both the brain and spinal cord.

Effects of activation of central nervous histamine receptors in cardiovascular regulation; studies in H(1) and H(2) receptor gene knockout mice

To elucidate the central roles of histamine receptors in cardiovascular regulatory system, systolic, mean, and diastolic blood pressures (BPs) and heart rate (HR) were examined in conscious H(1) receptor gene knockout (H(1)KO) mice, H(2) receptor gene knockout (H(2)KO) mice, H(1) and H(2) receptor gene double knockout (DKO) mice, and their respective control mice by the tail-cuff system. Histamine, histamine-trifluoromethyl-toluidine derivative (HTMT, an H(1) agonist), dimaprit (an H(2) agonist), and immepip (an H(3) agonist) were intrathecally administered to these KO mice and control mice. Basal BPs and HR were not different among these three KO mice and their control or wild-type mice. Intrathecal administration of histamine significantly increased BPs and decreased HR in control mice. The increases in BPs were produced by histamine in H(1)KO and H(2)KO mice and by HTMT and dimaprit in C57BL mice. The pressor responses by HTMT and dimaprit in C57BL mice were greater than those by histamine in H(1)KO and H(2)KO mice, although the same decreases in HR were induced by histamine in C57BL and H(1)KO mice and by dimaprit in C57BL mice. The selective stimulation of H(3) receptors by immepip produced a consistent decrease in BPs in control mice. These results obtained with the exogenous selective agonists of three histamine receptors suggest that the pressor responses to histamine are mediated through the stimulation of both H(1) and H(2) receptors, whereas the atropine-sensitive decrease in heart rate is mainly due to H(2) receptors which activate the vagal output to the heart.

Analgesic effects of preincisional administration of dextromethorphan and tenoxicam following laparoscopic cholecystectomy

BACKGROUND

Pre-incisional treatment with either N-methyl-D-aspartate (NMDA) receptor antagonists or non-steroidal anti-inflammatory drugs (NSAIDs) improves postoperative pain relief. This study examines the effect on postlaparoscopic cholecystectomy (LC) pain of a combination of dextromethorphan (DM), a NMDA-receptor antagonist, and tenoxicam, a NSAID, given preoperatively.

METHODS

Eighty-eight ASA I or II patients scheduled for LC were entered into a randomized, double-blind study and randomly allocated to one of four groups. Controls received 20 mg (4 ml) of chlorpheniramine maleate (CPM) IM and 4 ml of normal saline (N/S) IV. Group DM received 40 mg of DM (containing 20 mg of CPM) IM and 4 ml of N/S IV. Group T were given CPM 20 mg IM, and tenoxicam 40 mg (4 ml) IV. Group DM + T were given DM 40 mg (containing 20 mg of CPM) IM, and tenoxicam 40 mg IV. All treatments were given 30 min before skin incision. Analgesic effects were evaluated by Visual Analog Scale (VAS) pain scores at rest and during coughing, at 1, 2, 4, 12, 24 and 48 h after surgery. The time to the first request for meperidine for pain relief, and total meperidine consumption, were recorded for 48 h after surgery.

RESULTS

Compared to controls, patients given DM and DM + T first requested meperidine significantly later, had lower meperidine consumption, made fewer requests for meperidine, and had lower pain scores. There were significant differences between the DM + T and T groups at 2 and 4 h in both resting and incident VAS pain scores, the incidence of meperidine requests and the time to first meperidine injection. There were significant differences between groups DM and T at 1 h for resting pain and at 2 and 4 h for incident pain. Except for a significant difference in the incident pain score 1 h after surgery, there were no other differences in pain scores between the DM and DM + T groups. Neither synergistic nor antagonistic interaction was observed between DM and tenoxicam.

CONCLUSIONS

The results suggest that pretreatment with DM, but not tenoxicam, provides significant pre-emptive analgesia for postoperative pain management in patients after LC surgery. Combining DM and tenoxicam also gives good pain relief.

The effect of promethazine on postoperative pain: a comparison of preoperative, postoperative, and placebo administration in patients following total abdominal hysterectomy

BACKGROUND

Histamine receptors are involved in the development of inflammatory pain and hyperalgesia, and the use of antihistamines is advocated as an alternative for pain therapy and treatment of postoperative nausea and vomiting. We investigated the influence of timing of promethazine administration on postoperative pain outcomes.

METHODS

Ninety female patients undergoing total abdominal hysterectomy were randomly divided into three groups. All individuals received infusions of promethazine and normal saline before anaesthesia induction, and postoperatively the Pre group received promethazine 0.1 mg kg(-1) before anaesthesia and saline postoperatively, and the Post group received saline before anaesthesia and promethazine 0.1 mg kg(-1) postoperatively, while the Control group received two equivalent volumes of saline. Patients were treated using patient-controlled intravenous analgesia (PCA). The primary endpoint was pain intensity and morphine consumption. The secondary endpoint was postoperative nausea and vomiting.

RESULTS

Postoperative morphine usage was significantly lower in the Pre group (24.1 +/- 3.9 mg) relative to the Post (30.0 +/- 4.6 mg) and Control groups (32.1 +/- 4.8 mg) during the first 24 h postoperatively (P<0.05). The number and incidence of patients suffering from postoperative nausea in the first 24 h was six (21%), seven (23%), and 15 (47%) in the Pre, Post, and Control groups, respectively (P<0.05). The number and incidence of patients vomiting in the first 24 h was three (10%), two (7%), and 10 (32%) in the Pre, Post, and Control groups, respectively (P<0.05). The number of patients asking for rescue antiemetic in the first 24 h was one (3%), two (7%), and seven (22%) in the Pre, Post, and Control groups, respectively (P<0.05).

CONCLUSIONS

Our results suggest that preoperative administration of promethazine 0.1 mg kg(-1) reduces postoperative morphine consumption compared with postoperative and placebo administration, and that use of promethazine reduces PONV and the number of patients asking for rescue antiemetic in the first 24 h after surgery when compared with placebo.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Improgan antinociception does not require neuronal histamine or histamine receptors

Improgan, a chemical congener of the H(2) antagonist cimetidine, induces antinociception following intracerebroventricular (i.c.v.) administration in rodents, but the mechanism of action of this compound remains unknown. Because the chemical structure of improgan closely resembles those of histamine and certain histamine blockers, and because neuronal histamine is known to participate in pain-relieving responses, the antinociceptive actions of improgan were evaluated in mice containing null mutations in the genes for three histamine receptors (H(1), H(2), and H(3)) and also in the gene for histidine decarboxylase (the histamine biosynthetic enzyme). Similar to earlier findings in Swiss-Webster mice, improgan induced maximal, reversible, dose-related reductions in thermal nociceptive responses in ICR mice, but neither pre-improgan (baseline) nor post-improgan nociceptive latencies were changed in any of the mutant mice as compared with wild-type controls. Improgan also had weak inhibitory activity in vitro (pK(i)=4.7-4.9) on specific binding to three recently-discovered, recombinant isoforms of the rat H(3) receptor (H(3A), H(3B), and H(3C)). The present findings strongly support the hypothesis that neuronal histamine and its receptors fail to play a role in improgan-induced antinociception.

Roles of histamine receptors in pain perception: A study using receptors gene knockout mice

To study the participation of histamine H1- and H2-receptors in pain perception, H1 and H2 receptor knockout (KO) mice were examined for pain threshold by means of three kinds of nociceptive tasks. These included assays for thermal, mechanical, and chemical nociception. H1KO mice showed significantly fewer nociceptive responses to the hot-plate, tail-flick, tail-pressure, paw-withdrawal, formalin, capsaicin, and abdominal constriction tests. Sensitivity to noxious stimuli in H1KO mice was significantly decreased when compared to wild-type mice. The antinociceptive phenotypes of H2KO were relatively less prominent when compared to H1KO mice. We also examined the antinociceptive effects of intrathecally-, intracerebroventricularly-, and subcutaneously-administered morphine in H1KO and H2KO mice. In these nociceptive assays, the antinociceptive effects produced by morphine were more enhanced in both H1KO and H2KO mice. The effects of histamine H1- and H2-receptor antagonists on morphine-induced antinociception were studied in ICR mice. The intrathecal, intracerebroventricular and subcutaneous co-administrations of d-chlorpheniramine enhanced the effects of morphine in all nociceptive assays examined. In addition, intrathecal co-administrations of cimetidine enhanced the antinociception of morphine in the hot plate tests. These results suggest that existing H1 and H2 receptors play an inhibitory role in morphine-induced antinociception in the spinal and supra-spinal levels.