5-HT1D Receptor Research Articles

Distribution of 5-HT 1B, 5-HT 1D and 5-HT 1F receptor expression in rat trigeminal and dorsal root ganglia neurons: Relevance to the selective anti-migraine effect of triptans

Triptans, acting as serotonin, 5-HT 1B/1D/1F, receptor agonists, provide an effective and established treatment option in migraine and cluster headache. Clinical observations suggest a relatively specific effect of these compounds on primary headache disorders, but not in other pain syndromes. The mechanism of this specificity, however, is not well understood. Hence, we systematically studied primary sensory ganglia in rat to determine if the peripheral distribution of 5HT 1B/1D/1F receptors showed any anatomical difference that would account for the specificity of clinical effect. Rat primary afferent and sensory ganglia neurons—trigeminal ganglia (Vg), and dorsal root ganglia (DRG): C 2, C 5, T 5, L 5—were examined using paraffin-embedded, slide-bound tissue sections reacted with specific primary antibodies for rat 5-HT 1B, 1D and 1F receptors in a peroxidase-based immunohistochemical method. Immunoreactivity specific for all three serotonergic receptor subtypes was demonstrated in the five peripheral nervous system regions examined and quantitated. There was a good agreement for 5-HT 1B and 5-HT 1D receptors to that previously demonstrated in Vg and DRG L 5, while this was the first characterisation for 5-HT 1F receptor in any of the five regions, as well as for 5-HT 1B and 5HT 1D receptors in DRG C 2, C 5 and T 5. In summary, all three 5-HT receptors are equally represented in Vg and the DRGs examined. We conclude that the triptans are theoretically able to bind to receptors at each level of the peripheral neuraxis without any apparent anatomical preference for the head.

ChemInform Abstract: Binding of Indolylalkylamines at 5-HT2 Serotonin Receptors: Examination of a Hydrophobic Binding Region.

Taking advantage of a proposed hydrophobic region on 5-HT2 receptors previously identified by radioligand-binding studies utilizing various phenylisopropylamine derivatives, we prepared and evaluated several N1 - and/or C7-alkyl-substituted derivatives of alpha-methyltryptamine in order to improve its affinity and selectivity. It was determined that substitution of an n-propyl or amyl group has similar effect on affinity regardless of location (i.e., N1 or C7). The low affinity of several N1-alkylpyrroleethylamines suggests that the benzene portion of the alpha-methyltryptamines is necessary for significant affinity. Whereas tryptamine derivatives generally display little selectivity for the various populations of 5-HT receptors, N1-n-propyl-5-methoxy-alpha-methyltryptamine (3h) binds with significant affinity (Ki = 12 nM) and selectivity at 5-HT2 receptors relative to 5-HT1A (Ki = 7100 nM), 5-HT1B (Ki = 5000 nM), 5-HT1C (Ki = 120 nM), and 5-HT1D (Ki greater than 10,000 nM) receptors. As a consequence, this is the most 5-HT2-selective indolylalkylamine derivative reported to date.

5-Hydroxyptryptamine 1F (5-HT1F) receptor agonism. A possible new treatment principle for acute migraine attacks

This editorial prefaces two papers addressing the possibility that 5-hydroxyptryptamine 1F(5-HT1F) receptor agonism may be a valuable new treatment principle for acute migraine attacks. Nelson et al. (1) describe the preclinical pharmacological profile of the selective 5HT1F receptor agonist Lasmiditan and Ferrari et al. (2) present the first proof-of-concept study. Several years ago, an indole-based 5-HT1F receptor agonist, LY334370, showed promise in the treatment of acute migraine attacks (3), but was not further developed due to compound-related toxicity. Subsequently, the Eli Lilly Company launched a search for an improved molecule. It was requested that this molecule be more selective for the 5-HT1F receptor than LY334370, that it should not have affinity to other 5-HT receptors, in particular 5-HT1B and 5-HT1D receptors, and that it should be based on a new non-indole skeleton. The result of this search was Lasmiditan. In vitro binding studies showed a high binding affinity to the 5-HT1F receptor compared with the binding to the 5-HT1B and 5-HT1D receptors. The molecule also had a relatively low binding affinity to the 5-HT1A receptor. It did not bind to a host of other receptors and ion channels. In agreement with this profile, Lasmiditan did not constrict rabbit saphenous vein rings. Lasmiditan potently inhibited dural plasma protein extravassation and also inhibited electrically stimulated induction of the immediate early gene c-fos in the trigeminal nucleus caudalis. Finally, Lasmiditan was based on a scaffold not found in any other antimigraine drug. After preclinical development, Lasmiditan was taken over by the CoLucid company for clinical development. Ferrari et al. (2) present the first clinical study where Lasmiditan has been tested in the treatment of acute migraine attacks. A slow intravenous infusion of the drug was used, possibly in order to avoid variation in absorption and better to be able to do pharmacokinetic–pharmacodynamic modelling. This route of administration required patients to come to the hospital for treatment, a notoriously difficult approach as many patients do not come despite initial expression of interest. The difficulty in recruiting to in-patient treatment were overcome partly by using the relatively novel, highly effective group-sequential adaptive treatment assignment design. This resulted in the selection of an effective dose of 20mg after testing a wide range of doses despite treating only 130 patients. Interestingly, this is very similar to the number needed to demonstrate efficacy of a calcitonin gene-related peptide (CGRP) receptor antagonist (4). The study by Ferrari et al. (2) proves beyond doubt that 5-HT1F receptor agonism has efficacy in the treatment of acute migraine attacks. While the last word has not been said about the most effective dosing of Lasmiditan, the study allows a very good guess at the doses to be tested in the future development of the compound. After CGRP antagonists, 5-HT1F agonists are the second class of substance to prove that migraine attacks can be treated with a drug that has no vascular activity. Does this mean the end of the vascular hypothesis of migraine? As the only mechanism of migraine, vasodilatation has definitely been ruled out. However, could vasodilatation perhaps play a more limited role? Previous studies using transcranial Doppler demonstrated a slight dilatation on the painful side of a migraine attack compared to the non-painful side (5). It was stated that this amount of dilatation was not itself enough to be the cause of migraine pain but that, combined with sensitisation of peripheral sensory

Preclinical pharmacological profile of the selective 5-HT1F receptor agonist lasmiditan

Lasmiditan (also known as COL-144 and LY573144; 2,4,6-trifluoro-N-[6-[(1-methylpiperidin-4-yl)carbonyl]pyridin-2yl]benzamide) is a high-affinity, highly selective serotonin (5-HT) 5-HT(1F) receptor agonist. In vitro binding studies show a K(i) value of 2.21 nM at the 5-HT(1F) receptor, compared with K(i) values of 1043 nM and 1357 nM at the 5-HT(1B) and 5-HT(1D) receptors, respectively, a selectivity ratio greater than 470-fold. Lasmiditan showed higher selectivity for the 5-HT(1F) receptor relative to other 5-HT(1) receptor subtypes than the first generation 5-HT(1F) receptor agonist LY334370. Unlike the 5-HT(1B/1D) receptor agonist sumatriptan, lasmiditan did not contract rabbit saphenous vein rings, a surrogate assay for human coronary artery constriction, at concentrations up to 100 µM. In two rodent models of migraine, oral administration of lasmiditan potently inhibited markers associated with electrical stimulation of the trigeminal ganglion (dural plasma protein extravasation, and induction of the immediate early gene c-Fos in the trigeminal nucleus caudalis). Lasmiditan presents a unique pyridinoyl-piperidine scaffold not found in any other antimigraine class. Its chemical structure and pharmacological profile clearly distinguish it from the triptans. The potency and selectivity of lasmiditan make it ideally suited to definitively test the involvement of 5-HT(1F) receptors in migraine headache therapy.

Homeostasis of glucose in the rainbow trout (Oncorhynchus mykiss Walbaum): the role of serotonin

In this study, we evaluated, for the first time, the 5-HT (serotonin)-mediated control of glucose homeostasis in the rainbow trout Oncorhynchus mykiss. Intraperitoneal administration of 5-HT increased plasma levels of glucose, adrenaline and noradrenaline. By contrast, intracerebroventricular administration of 5-HT did not cause any significant variation in plasma levels of glucose. The release of endogenous 5-HT following intraperitoneal administration of d-fenfluramine led to a significant increase in plasma levels of glucose and adrenaline. Intraperitoneal administration of (1) MIAN (a 5-HT2 receptor antagonist) did not block either the hyperglycaemic action or the increase in plasma levels of adrenaline induced by 5-HT, but did block the increase in plasma levels of noradrenaline, and (2) 5-CT (a 5-HT1 agonist) increased the plasma levels of glucose and of adrenaline, without altering those of noradrenaline. Administration of TFMPP (a 5-HT1B agonist) did not increase the plasma levels of glucose, and the hyperglycaemic action of 5-HT was not blocked by antagonists of 5-HT1A (WAY 100635), 5-HT1D (BRL 15572), 5-HT2B (SB 204741) or 5-HT7 (pimozide) receptors. It was demonstrated that, in rainbow trout, peripheral 5-HT, but not brain 5-HT intervenes in the modulation of glucose homeostasis with a hyperglycaemic effect. This effect is associated with the release of adrenaline and activation of 5-HT1-like receptors. As far as could be determined in the present study, these 5-HT1-like receptors are unrelated to either the 5-HT1A, 5-HT1B or 5-HT1D receptor subtypes of mammals. The 5-HT2-type receptors may mediate the release of noradrenaline, but not of adrenaline, and furthermore, do not appear to play an important role in the hyperglycaemic effect exerted by 5-HT.

Identification of genetic modifiers of behavioral phenotypes in serotonin transporter knockout rats

BackgroundGenetic variation in the regulatory region of the human serotonin transporter gene (SLC6A4) has been shown to affect brain functionality and personality. However, large heterogeneity in its biological effects is observed, which is at least partially due to genetic modifiers. To gain insight into serotonin transporter (SERT)-specific genetic modifiers, we studied an intercross between the Wistar SERT-/- rat and the behaviorally and genetically divergent Brown Norway rat, and performed a QTL analysis.ResultsIn a cohort of >150 intercross SERT-/- and control (SERT+/+) rats we characterized 12 traits that were previously associated with SERT deficiency, including activity, exploratory pattern, cocaine-induced locomotor activity, and abdominal and subcutaneous fat. Using 325 genetic markers, 10 SERT-/--specific quantitative trait loci (QTLs) for parameters related to activity and exploratory pattern (Chr.1,9,11,14), and cocaine-induced anxiety and locomotor activity (Chr.5,8) were identified. No significant QTLs were found for fat parameters. Using in silico approaches we explored potential causal genes within modifier QTL regions and found interesting candidates, amongst others, the 5-HT1D receptor (Chr. 5), dopamine D2 receptor (Chr. 8), cannabinoid receptor 2 (Chr. 5), and genes involved in fetal development and plasticity (across chromosomes).ConclusionsWe anticipate that the SERT-/--specific QTLs may lead to the identification of new modulators of serotonergic signaling, which may be targets for pharmacogenetic and therapeutic approaches.

Marine indole alkaloids: potential new drug leads for the control of depression and anxiety.

The marine environment has been explored in the search for new bioactive compounds over the last 50 years, becoming a highly important and rich source of potent molecules and drug leads reported to possess a wide scope of activities. Alkaloids constitute one of the largest classes of natural products and are synthesized by terrestrial and marine organisms on all evolutionary levels. Alkaloids are usually present in an organism as a mixture consisting of several major and a few minor compounds of the same biosynthetic origin and differing only in functional groups. This group of compounds has apparently evolved as a defense mechanism against predators and as a result alkaloids are often highly potent and toxic molecules.1 Marine invertebrates have proven to be an outstanding source of active molecules, one of the most promising being indole alkaloids. Although many of these marine alkaloids closely resemble the endogenous amines (serotonin, dopamine or histamine), their potential affinity to various neurological targets and consequential impact on animal behavior is virtually unexplored. Indole alkaloids, their activity, synthesis and potential use in medicine have been already reviewed in several articles.2 In this review we provide information on current and potential pharmaceuticals including small molecule natural indole alkaloids, their biological properties, structure-activity relationship studies, and especially their potential for the treatment of neurological disorders. 1.1. The indole moiety in drugs The indole moiety is present in a number of drugs currently on the market. Most of these belong to triptans which are used mainly in the treatment of migraine headaches (Fig. 1). All members of this group are agonists of migraine associated 5HT1B and 5HT1D serotonin receptors. Sumatriptan (Imitrex) was developed by Glaxo for the treatment of migraines and introduced into the market as the first member of the triptan family.3 Relative to the second generation triptans, sumatriptan has lower oral bioavailability and a shorter half-life. Frovatriptan (FROVA®) was developed by Vernalis for the treatment of menstruation associated headaches. Frovatriptan's affinity for migraine specific serotonin receptors 5HT1B is believed to be the highest among all triptans.4 In addition, frovatriptan binds to 5HT1D and 5HT7 receptor subtypes.5 Zolmitriptan marketed by AstraZeneca is used to treat acute migraine attacks and cluster headaches. GlaxoSmithKline's naratriptan (Amerge) is also used in the treatment of migraines and some of its side effects include dizziness, tiredness, tingling of the hands and feet and dry mouth. All available triptans are well tolerated and effective.6 The highest incidence of central nervous system (CNS) related side effects (dizziness, drowsiness) was reported for zolmitriptan (5 mg), rizatriptan (10 mg) and eletriptan (40 mg, 80 mg).7 The differences in side-effect profiles for triptans are not likely caused by their different affinity towards serotonin receptors or other neurological receptors in the CNS. There is a positive correlation between the lipophilicity coefficient and CNS side effects; these undesired effects are also dose-dependent. Figure 1 Currently available drugs from the triptan group. 1.2. Serotonin receptors – possible targets for neurologically active marine indole alkaloids Given that depression affects approximately 18 million Americans annually,8 it is crucial to develop new effective treatments for this disorder. Intensive studies are being conducted in the area of new targets for antidepressant drugs,9,10 but most antidepressant drugs still target the neurotransmitter systems, mainly serotonin, dopamine and noradrenaline. Serotonin is one of the neurotransmitters present in the central and peripheral nervous system which plays an important role in normal brain function and regulates sleep, mood, appetite, sexual function, memory, anxiety and many others.11 Serotonin exerts its effects through seven families of receptors (5-HT1 – 5-HT7) further divided into several subclasses. Except for 5-HT3 receptor which is a ligand-gated ion channel, the serotonin receptors belong to the G-protein coupled receptor family. Due to a lack of selective ligands, there is still little known about several 5-HT receptor subclasses.12 Marine monoindole alkaloids, sharing structure similarities with serotonin, are certain to become useful tools to facilitate the understanding of serotonin receptor function and generate new drug leads for the treatment of depression, anxiety, migraines and other 5HT receptor related disorders.

Recent Advances in the Discovery of Selective and Non-Selective 5-HT1D Receptor Ligands

This article highlights recent advances in the discovery of new agonists, antagonists and partial agonists of the 5-HT(1D) receptor. The field of 5-HT(1D) agonists continues to deliver a number of new potential therapeutic agents, although advances in this field are now more focussed on the clinical evaluation phase. The identification of novel compounds is greater for the 5-HT(1D) receptor antagonists, and whilst few truly selective ligands have been identified, a number of approaches are discussed towards defined mixed-pharmacology profiles. An overview is also given of recent advances in biological and clinical understanding of the receptor.

Transcriptional expression of serotonergic regulators in laser‐captured microdissected dorsal raphe neurons of subjects with major depressive disorder: sex‐specific differences

The relationship between serotonin (5-HT) and major depressive disorder (MDD) has been extensively studied but certain aspects are still ambiguous. Given the evidence that 5-HT neurotransmission is reduced in depressed subjects, it is possible that one or more of the 5-HT regulators may be altered in the dorsal raphe nucleus (DR) of depressed subjects. Candidates that regulate 5-HT synthesis and neuronal activity of 5-HT neurons include intrinsic regulators such as tryptophan hydroxylase 2, 5-HT autoreceptors, 5-HT transporter and transcription factors, as well as afferent regulators such as estrogen and brain-derived neurotrophic factor. The present study was designed to quantify mRNA concentrations of the above 5-HT regulators in an isolated population of 5-HT-containing DR neurons of MDD subjects and gender-matched psychiatrically normal control subjects. We found that mRNA concentrations of the 5-HT1D receptor and the transcription factors, NUDR and REST, were significantly increased in DR-captured neurons of female MDD subjects compared to female control subjects. No significant differences were found for the transcripts in male MDD subjects compared to male controls. This study reveals sex-specific alterations in gene expression of the pre-synaptic 5-HT1D autoreceptors and 5-HT-related transcription factors, NUDR and REST, in DR neurons of women with MDD.

Effect of serotonergic system on AVP secretion induced by physical exercise

The present study was undertaken in order to establish the possible involvement of serotonergic receptors in the control of physical exercise-stimulated vasopressin secretion. Twenty-one healthy men (divided in three groups of seven) underwent bicycle-ergometer tests until exhaustion: exercise control test (n=21), exercise plus ondansetron, selective 5-HT3 antagonist (n=7), exercise plus buspirone, selective 5-HT1A receptor agonist (n=7), exercise plus sumatriptan, selective 5-HT1D receptor agonist (n=7). AVP levels, physiological and biochemical variables were measured and compared during tests. Results showed that exercise-induced AVP rise did not change after the administration of buspirone and sumatriptan. In contrast, the administration of ondansetron significantly reduced physical exercise-induced AVP rise. Mean peak levels during physical exercise were 4.9 times higher than basal values in the control test and 2.6 times higher than basal values in the ondansetron plus exercise test. These data demonstrate that 5-HT3 serotonergic receptors at least partially mediate the AVP response to physical exercise. On the other hand, 5-HT1A and 5-HT1D serotonergic receptors do not appear to be involved in the control of AVP secretion during exercise.

Plasma membrane depolarization and activation of receptors for endogenous vasoconstrictors as possible mechanisms of potentiation of vasoconstrictive response to serotonin in traumatic shock in rats

The goal of this work was to study possible mechanisms underlying the potentiation of vasopressor response to serotonin observed in traumatic shock. Experiments with isolated aorta and mesenteric artery of the rat showed that vasoconstriction is caused by the activation of 5HT2A receptors. Agonists of 5HT1B, 5HT1D, 5HT2B, and 5HT4 receptors induced vasodilation. Agonists of 5HT1A receptors had a dual effect determined by interaction with alpha1-adrenergic receptors and 5HT1A receptors. Plasma membrane depolarization with 15 mM KCl increased the vasoconstrictive force in response to serotonin. This effect was determined by the ability of KCl to activate voltage-gated calcium channels, as a result of which the intracellular calcium stores are replenished. Inhibition of serotonin response by ketanserin, a 5HT2A receptor blocker, did not depend on the presence of 15 mM KCl. Constriction in response to serotonin was potentiated after its addition to vessels preconstricted with noradrenaline or endothelin-1. The constriction response partially retained in the presence of 2 x 10(-7) M ketanserin, which completely suppressed the serotonin-induced constriction of dilated vessels both at normal membrane potential and after plasma membrane depolarization. It can be assumed that noradrenalin and endothelin-1 alter the characteristics of 5HT2A receptors and possibly 5HT1A receptors as a result of their heterodimerization with the receptors for these vasoconstrictive hormones or interreceptor interaction at the level of signaling systems. Along with the potentiating effect of KCl, this mechanism may underlie the enhancement of vasopressor response to serotonin in shock.

Synephrine, a Component of Evodiae Fructus, Constricts Isolated Rat Aorta via Adrenergic and Serotonergic Receptors

We investigated the effects of Evodiae Fructus and synephrine, one of the components of Evodiae Fructus, on blood vessels. We found that Evodiae Fructus (1 × 10−4 g/mL) had constrictive effects on rat aorta. The vasoconstrictive effects of Evodiae Fructus were significantly inhibited by pretreatment with prazosin (adrenergic α1-receptor antagonist), BRL15572 [5-hydroxytryptamine (5-HT)1D antagonist], and ketanserin (5-HT2A antagonist), but its vasoconstrictive effects were not inhibited by pretreatment with SB216641 (5-HT1B antagonist) or propranolol (adrenergic β-receptor antagonist). These results suggest that Evodiae Fructus constricts rat aorta via adrenergic and serotonergic receptors. We also investigated the constrictive effects of synephrine on blood vessels. The vasoconstrictive effects of synephrine (1 × 10−7– 3 × 10−5 mol /L) were significantly inhibited by pretreatment with prazosin, BRL15572, and ketanserin. However, its constrictive effects were not inhibited by pretreatment with SB216641 and propranolol. The pA2 values of prazosin or ketanserin were nearly equal between Evodiae Fructus and synephrine. Because the constrictive effects of both Evodiae Fructus and synephrine were exerted via adrenergic α1-receptors and serotonergic (5-HT1D and 5-HT2A) receptors, synephrine may be one of the important components in the constrictive effects of Evodiae Fructus.

Central Nervous System Networks Involved in the Processing of Meningeal and Cutaneous Inputs From the Ophthalmic Branch of the Trigeminal Nerve in the Rat

This study analysed the organization of central nervous system networks involved in the processing of meningeal inputs in the male, Sprague-Dawley rat. We injected the anterograde tracer, biotin dextran, into areas of the medullary trigeminal nucleus caudalis (Sp5C), which receive inputs from the ophthalmic division of the trigeminal nerve. Double-labelling immunohistochemical studies were then performed to compare calcitonin gene-related peptide (CGRP) or serotonin 1D (5HT1(D)) receptor distributions in the areas innervated by Sp5C neurons. Dense, topographically organized intratrigeminal connections were observed. Sp5C neurons projected to the commissural subnucleus of the solitary tract, A5 cell group region/superior salivatory nucleus, lateral periaqueductal grey matter, inferior colliculus and parabrachial nuclei. Trigeminothalamic afferents were restricted to the posterior group and ventroposteromedial thalamic nuclei. Some of these areas are also immunoreactive for 5HT1(D) and CGRP and thus remain potential central targets of triptan molecules and other antimigraine drugs.

Alcohol and Cluster Headaches

Alcohol and Cluster Headaches

Sumatriptan Inhibits Synaptic Transmission in the Rat Midbrain Periaqueductal Grey

BackgroundThere is evidence to suggest that the midbrain periaqueductal grey (PAG) has a role in migraine and the actions of the anti-migraine drug sumatriptan. In the present study we examined the serotonergic modulation of GABAergic and glutamatergic synaptic transmission in rat midbrain PAG slices in vitro.ResultsSerotonin (5-hydroxytriptamine, 5-HT, IC50 = 142 nM) and the selective serotonin reuptake inhibitor fluoxetine (30 μM) produced a reduction in the amplitude of GABAA-mediated evoked inhibitory postsynaptic currents (IPSCs) in all PAG neurons which was associated with an increase in the paired-pulse ratio of evoked IPSCs. Real time PCR revealed that 5-HT1A, 5-HT1B, 5-HT1D and 5-HT1F receptor mRNA was present in the PAG. The 5-HT1A, 5-HT1B and 5-HT1D receptor agonists 8-OH-DPAT (3 μM), CP93129 (3 μM) and L694247 (3 μM), but not the 5-HT1F receptor agonist LY344864 (1 – 3 μM) inhibited evoked IPSCs. The 5-HT (1 μM) induced inhibition of evoked IPSCs was abolished by the 5-HT1B antagonist NAS181 (10 μM), but not by the 5-HT1A and 5-HT1D antagonists WAY100135 (3 μM) and BRL15572 (10 μM). Sumatriptan also inhibited evoked IPSCs with an IC50 of 261 nM, and reduced the rate, but not the amplitude of spontaneous miniature IPSCs. The sumatriptan (1 μM) induced inhibition of evoked IPSCs was abolished by NAS181 (10 μM) and BRL15572 (10 μM), together, but not separately. 5-HT (10 μM) and sumatriptan (3 μM) also reduced the amplitude of non-NMDA mediated evoked excitatory postsynaptic currents (EPSCs) in all PAG neurons tested.ConclusionThese results indicate that sumatriptan inhibits GABAergic and glutamatergic synaptic transmission within the PAG via a 5-HT1B/D receptor mediated reduction in the probability of neurotransmitter release from nerve terminals. These actions overlap those of other analgesics, such as opioids, and provide a mechanism by which centrally acting 5-HT1B and 5-HT1D ligands might lead to novel anti-migraine pharmacotherapies.

Characterization of the human basilar artery contractile response to 5‐HT and triptans

To study the contractile responses of the human basilar artery to 5-hydroxytryptamine (5-HT), sumatriptan, zolmitriptan and naratriptan, and to characterize the 5-HT receptor subtypes involved on those responses, human basilar artery rings were prepared for isometric contraction, protein isolation and Western blotting analysis. Concentration-response (CR) curves were made for all agonists in the absence or in the presence of selective antagonists at 5-HT1B (cyanopindolol), 5-HT1D (BRL 15,572) and 5-HT2 (ketanserin) receptors. We also used anti-5-HT1B and 5-HT1D receptor antibodies to search for the expression of protein of these receptor subtypes. From the CR curves, the relative intrinsic activity and potency of these agonists were determined. The ranking order for the intrinsic activity was 5-HT > or = sumatriptan > zolmitriptan > or = naratriptan, whereas that for the potency was zolmitriptan > or = 5-HT > or = sumatriptan > naratriptan. Our results also show that the human basilar artery seems to have a mixed population of 5-HT1B/1D receptors mediating the contractile response to triptans, which is also suggested by the expression of both receptor subtypes. There is also a population of 5-HT2 receptors for which the antimigraine drugs used have no apparent affinity. From this study, one can conclude that the second generation triptans have lower contractile capacity than sumatriptan, suggesting that they have a better cerebrovascular safety profile.

Actions of sumatriptan on myenteric neurones: relief from an old headache in the enteric nervous system?

Actions of sumatriptan on myenteric neurones: relief from an old headache in the enteric nervous system?

Gene expression and molecular changes in cerebral arteries following subarachnoid hemorrhage in the rat

The authors investigated early changes in the cerebral arteries of rats that occur after subarachnoid hemorrhage (SAH). Messenger RNA was investigated by performing microarray and quantitative real-time polymerase chain reaction (PCR) analyses, and protein expression was shown by performing immunohistochemical studies. The array data indicated that the initial processes that occur after SAH involve activation of genes involved in angiogenesis, inflammation, and extracellular matrix (ECM) remodeling. The real-time PCR investigation confirmed upregulation of genes that were observed using the microarray to be regulated, including iNOS, MMP13, and cxcl2. The authors also verified the upregulation of previously implicated genes for G-protein-coupled receptors (endothelin B [ETB], angiotensin 1 [AT1], and AT2) and metalloproteinase 9. The results of an immunohistochemical study confirmed that receptor genes that were seen to be regulated produced an increase in protein expression. Double immunostaining of rat cerebral arteries with endothelial cell- or smooth-muscle cell-specific antibodies verified that an increase in ETB, 5-hydrotryptamine (5-HT1B), and 5-HT1D receptor expression occurs in smooth-muscle cells. Processes occurring after SAH lead to enhanced arterial contractility and ECM remodeling either directly or through angiogenesis and inflammation. These processes are active via an increase in metalloproteinase expression, the presence of proangiogenic factors, and the expression of proinflammatory genes.

GLC756 decreases TNF-α via an alpha2 and beta2 adrenoceptor related mechanism

GLC756, a polyvalent anti-glaucoma drug showed in an endotoxin-induced-uveitis model (EIU) in rats a significant tumor necrosis factor-α (TNF-α) decrease in serum, indicating an additional anti-inflammatory potential of this compound. The receptors on which GLC756 binds (D1, D2, D4, α-1, α-2, 5-HT1A, 5-HT2C, 5-HT1D, 5-HT2 A, β-1, and β-2) were suggested to play a role. In order to identify a receptor type mediating the TNF-α lowering response, GLC756 was combined with various counteracting compounds (CP). For EIU, 8 week old Lewis rats were intravenously injected at 160 μg lipopolysaccharide (LPS) from Salmonella typhimurium. Before EIU-induction animals received either one of the CP's or GLC756 alone, or GLC756 in combination with one of the CP's. TNF-α was determined in serum 2 h post EIU-induction. Treatment with CP's alone indicated that agonistic effects on β-2 adrenoceptors and antagonistic effects on α-2, 5-HT1A and 5-HT1D receptors resulted in statistically significant decreased TNF-α levels in comparison to the LPS-control group. In combination with GLC756, the counteracting CP's domitor (α-2 adrenoceptor agonist) and ICI 118551 (β-2 adrenoceptor antagonist) inhibited completely the TNF-α decreasing effect of GLC756. Counteracting the 5-HT1A receptor with the 5-HT1A agonist 8-OH-DPAT could not prevent the TNF-α decreasing effect of GLC756. In conclusion, the antagonistic effect on α-2 adrenoceptors and the agonistic effect on β-2 adrenoceptors were identified as mechanism for the TNF-α decreasing effect of GLC756.

Tissue Injury Regulates Serotonin 1D Receptor Expression: Implications for the Control of Migraine and Inflammatory Pain

The anti-migraine action of "triptan" drugs involves the activation of serotonin subtype 1D (5-HT1D) receptors expressed on "pain-responsive" trigeminal primary afferents. In the central terminals of these nociceptors, the receptor is concentrated on peptidergic dense core vesicles (DCVs) and is notably absent from the plasma membrane. Based on this arrangement, we hypothesized that in the resting state the receptor is not available for binding by a triptan, but that noxious stimulation of these afferents could trigger vesicular release of DCVs, thus externalizing the receptor. Here we report that within 5 min of an acute mechanical stimulus to the hindpaw of the rat, there is a significant increase of 5-HT1D-immunoreactivity (IR) in the ipsilateral dorsal horn of the spinal cord. We suggest that these rapid immunohistochemical changes reflect redistribution of sequestered receptor to the plasma membrane, where it is more readily detected. We also observed divergent changes in 5-HT1D-IR in inflammatory and nerve-injury models of persistent pain, occurring at least in part through the regulation of 5-HT1D-receptor gene expression. Finally, we found that 5-HT1D-IR is unchanged in the spinal cord dorsal horn of mice with a deletion of the gene encoding the neuropeptide substance P. This result differs from that reported for the partial differential-opioid receptor, which is also sorted to DCVs, but is greatly reduced in preprotachykinin mutant mice. We suggest that a "pain"-triggered regulation of 5-HT1D-receptor expression underlies the effectiveness of triptans for the treatment of migraine. Moreover, the widespread expression of 5-HT1D receptor in somatic nociceptive afferents suggests that triptans could, in certain circumstances, treat pain in nontrigeminal regions of the body.