5-HT1B Receptor Polymorphism and Clinical Response to Sumatriptan

The 5-HT₁ receptor agonist, sumatriptan, is highly effective in the treatment of migraine. Some patients, however, do not respond or experience recurrence of the headache. In addition, some patients report chest symptoms after sumatriptan. We investigated whether these different responses could be attributed to genetic diversity of the 5-HT_1B receptor, which most likely mediates the therapeutic action and the coronary side effects of sumatriptan. Allele frequencies of two polymorphisms in the 5-HT_1B receptor gene ( G861C and T-261G ) were investigated in migraine patients with consistently good response to sumatriptan (n=14), with no response (n=12), with recurrence of the headache (n=12), with chest symptoms (n=13), and in patients without chest symptoms (n=27). Allele frequencies (G:0.74; C:0.26 at nt 861 and T:0.39; G:0.61 at nt -261) did not differ between patient groups, indicating that genetic diversity of the 5-HT_1B receptor does not seem to be involved in the different clinical responses to sumatriptan.     

Pharmacology of the Selective 5-HT1B/1D Agonist Frovatriptan

Objective.—To determine the pharmacological profile of frovatriptan.
Background.—Frovatriptan is a new 5-HT_1B/1D agonist developed for the treatment of migraine.
Methods.—Pharmacological studies were performed using in vitro and in vivo techniques.
Results.—Radioligand-binding studies showed that frovatriptan has a high affinity for 5-HT_1B and 5-HT_1D receptors, and moderate affinity for 5-HT_1A, 5-HT_1F, and 5-HT₇ receptors. In vitro, frovatriptan acts as a potent full agonist at human cloned 5-HT_1B and 5-HT_1D receptors, and as a moderately potent full agonist at 5-HT₇ receptors. Studies of frovatriptan in isolated human arteries demonstrated a lower threshold for constriction of cerebral than coronary vasculature and a bell-shaped dose-response curve was apparent in the coronary arteries. In anesthetized dogs, frovatriptan administration produced no measurable effect on cardiac function or on blood pressure. Frovatriptan had no effects on coronary blood flow following transient coronary artery occlusion, whereas sumatriptan produced a prolonged and significant decrease in coronary blood flow.
Conclusion.—The pharmacology of frovatriptan suggests that it should be an effective agent for the acute treatment of migraine, with a low potential for undesirable peripheral effects.     

Stress-induced alterations of somatodendritic 5-HT1A autoreceptor sensitivity in the rat dorsal raphe nucleus — in vitro electrophysiological evidence

Summary— Somatodendritic 5-HT_1A autoreceptors play a key role in the control of the electrical and metabolic activity of serotoninergic neurons in the dorsal raphe nucleus. These neurons also possess intracellular glucocorticoid receptors which may be involved in the well established modulation of serotonin (5-hydroxytryptamine, 5-HT) metabolism by corticosterone in stressed animals. The possible mediation by somatodendritic 5-HT_1A autoreceptors of such corticosterone-dependent changes in serotoninergic neuron activity was investigated using an in vitro electrophysiological approach. 5-HT_1A autoreceptor-mediated inhibition of the firing of serotoninergic neurons was examined in brain stem slices from rats whose serum corticosterone concentrations had been markedly increased (+ 100–200%) by two different stressful conditions. Immobilization for 30 or 90 min (restraint stress) did not modify the concentration-dependent inhibition of the firing of serotoninergic neurons by the 5-HT_1A receptor agonist ipsapirone. In contrast, placing the rats in novel uncontrolled environmental conditions for 16 h significantly reduced the cell response to ipsapirone, indicating a decreased sensitivity of somatodendritic 5-HT_1A autoreceptors. Such a change was not observed in adrenalectomized rats subjected to the same stressful conditions. These data show that some forms of stress can reduce the 5-HT_1A autoreceptor-dependent inhibitory control of the electrophysiological activity of serotoninergic neurons in the dorsal raphe nucleus. Both the nature and duration of stress seem to be critical factors for triggering the (corticosterone-dependent) mechanism(s) responsible for the functional desensitization of 5-HT_1A autoreceptors in stressed rats.     

Up-regulation of 5-HT2 Serotonin Receptor: A Possible Mechanism of Transformed Migraine

SYNOPSIS
Transformation of episodic migraine to chronic daily headache (so called transformed migraine) ia now a well recognized phenomenon. Although several factors, i.e. analgesic overuse, increasing age, psychiatric disorders are reported to play some roles in this transformation, the precise cascade is still unclear. Further suppression of an already abnormal antinociceptive system with up-regulation of post-synaptic receptors is one of the possible explanation. In order to understand the mechanism underlying this condition, 5-HT₂ serotonin receptors on platelets were assayed by the radioligand binding technique. Six transformed migraine patients (67.67 ± 1.52 years) and seven healthy controls (72.86 ± 1.82 years) were studied. [³H]-spiperone and ketanserin were used to determine the specific binding. We found a significant increase (P <0.05) in the maximal receptor numbers (B_max ) on platelet membrane of the migraine patients when compared to the controls (64.31 ± 11.06 end 39.96 ± 5.42 fmol/mg protein, respectively), whereas the dissociation equilibrium constant (K D ) values remained unchanged (3.63 ± 0.78 nM and 2.84 ± 0.48 nM for the migraine patients and controls, respectively). The up-regulation of serotonin receptors found in this study provided further support to the "serotonergic hypofunction" theory of migraine pathogenesis and may explain the unusual loss of episodicity seen in the transformed migraine patients.     

Stress-induced 5-HT1A receptor desensitization: protective effects of Ginkgo biloba extract (EGb 761)

Summary— The effects of sub-chronic cold stress on the functioning of hippocampal 5-HT_1A receptors in old isolated rats and the possible protective effects of Ginkgo biloba extract (EGb 761) were investigated. Cold exposure during five days, produced a significant reduction of the inhibitory effect of 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) on forskolin-stimulated adenylyl cyclase activity. In contrast, neither the affinity nor the density of hippocampal [³H]8-OH-DPAT binding sites were affected indicating that the reduced sensitivity of 5-HT_1A receptors induced by stress is probably due to a modification of their coupling mechanisms to adenylyl cyclase. The stress-induced desensitization of 5-HT_1A receptors was prevented by the administration of EGb 761 (50 mg/kg per os /14 days). These results clearly indicate that 5-HT_1A receptors are desensitized by stress and point out the reduced capacity of old rats to cope with the adverse effects of a chronic stressor. EGb 761 appears to restore the age-related decreased capacity to adapt to a chronic stressor.     

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

Summary.  Background:  Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents. Objective:  The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction. Methods:  We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin. Results:  Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT_2A receptor, and sarpogrelate, a selective 5-HT_2A receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries. Conclusions:  These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT_2A receptor and the Rho-kinase pathway.     

Biochemical and electrophysiological properties of SR 57746A, a new, potent 5-HT1A receptor agonist

Summary— SR 57746A (1-[2-(naphth-2-yl) ethyl]-4-(3-trifluoromethylphenyl)-1, 2, 5, 6 tetra-hydropyridine hydrochloride) binds competitively, and with high affinity (K_i = 2.0 ± 0.7 nM) to 5-HT_1A receptors from rat hippocampus in vitro , but has much less affinity for other 5-HT receptor subtypes (IC₅₀ > 650 nM). SR 57746A produces a concentration-dependent inhibition of forskolin-stimulated adenylate cyclase activity in rat hippocampal homogenates, with a maximal effect identical to that of 8-OH-DPAT, suggesting that SR 57746A behaves as a full agonist in tthis experimental model. SR 57746A potently displaces [³H]8-OH-DPAT binding to rat hippocampal membranes ex vivo , with an ID₅₀ of 11.1 mg/kg po, 30 min after administration, and 2.8 mg/kg po, 2 h after administration. This effect of SR 57746A is long-lasting (at least 24 hours at 10 mg/kg po). SR 57746A does not modify the levels of 5-HT or DA in various brain areas, but decreases the concentrations of 5-HIAA, and increases those of DOPAC, HVA and 3-MT. Following iv administration, SR 57746A (0.095 to 0.25 mg/kg) inhibits the spontaneous firing of dorsal raphe neurones, but does not modify the activity of DA neurones in the substantia nigra or ventral tegmental area. Thus, SR 57746A is a potent, selective and full agonist at 5-HT_1A receptors in vitro and vivo.     

Migraine association and linkage analyses of the human 5-hydroxytryptamine (5HT2A) receptor gene

5-Hydroxytryptamine (5HT), commonly known as serotonin, which predominantly serves as an inhibitory neurotransmitter in the brain, has long been implicated in migraine pathophysiology. This study tested an Mspl polymorphism in the human 5HT_2A receptor gene ( HTR2A ) and a closely linked microsatellite marker (D13S126), for linkage and association with common migraine. In the association analyses, no significant differences were found between the migraine and control populations for both the Mspl polymorphism and the D13S126 microsatellite marker. The linkage studies involving three families comprising 36 affected members were analysed using both parametric (FASTLINK) and non-parametric (MFLINK and APM) techniques. Significant close linkage was indicated between the Mspl polymorphism and the D13S126 microsatellite marker at a recombination fraction (θ) of zero (lod score=7.15). Linkage results for the Mspl polymorphism were not very informative in the three families, producing maximum and minimum lod scores of only 0.35 and 0.39 at recombination fractions (θ) of 0.2 and 0.00, respectively. However, linkage analysis between the D13S126 marker and migraine indicated significant non-linkage (lod2) up to a recombination fraction (θ) of 0.028. Results from this study exclude the HTR2A gene, which has been localized to chromosome 13q14-q21, for involvement with common migraine.     

5HT2 receptors in cerebral cortex of migraineurs studied using PET and 18F-fluorosetoperone

Since the brain 5HT₂ receptors might be implicated in migraine pathogenesis, we have used positron emission tomography and ¹⁸F-fluorosetoperone, a 5HT₂ specific radioligand, to investigate in vivo the cortical 5HT₂ receptors in migraine subjects. Nine migraineurs who had either migraine with and without aura ( n = 5) or only migraine without aura ( n = 4) were studied between attacks. Twelve unmedicated healthy subjects of similar mean age were used as controls. Brain radioactivity was measured after ¹⁸F-setoperone IV injection for 90 min. A decrease of the regional specific distribution volumes (SDV) of the ligand was observed both in migraineurs and in controls. The age adjusted group means of SDV did not differ between patients and controls for the whole and for the right or left frontal, temporal, parietal and occipital cortex. These results suggest that cortical 5HT₂ receptors may be unaltered between attacks in migraine sufferers.     

The role of 5-hydroxytryptamine (5-HT) receptor subtypes and plasticity in the 5-HT systems in the regulation of nociceptive sensitivity

This review shows that the role of 5-hydroxytryptamine (5-HT) in the regulation of nociception depends on the 5-HT receptor subtypes involved and on long-term functional changes in the 5-HT receptors. Stimulation of the 5-HT₁ receptors, as well as of the 5-HT₂ and 5-HT₃ receptors, may reduce nociceptive sensitivity. In addition, activation of 5-HT₂ and 5-HT₃ receptors may also enhance nociceptive sensitivity. Up- or down-regulation of the 5-HT receptors may result in long-lasting changes, plasticity, in the 5-HT systems. Lesioning of 5-HT neurons induces denervation supersensitivity to 5-HT, and prolonged stimulation of 5-HT receptors may produce subsensitivity to 5-HT. In the spinal cord denervation supersensitivity to 5-HT may depend on reduced release of substance P (SP). An increase in the release of SP, on the other hand, may reduce the effects of 5-HT receptor activation. Long-term treatment with antidepressants which are used in clinical pain therapy appears to up-regulate the 5-HT₁ receptors and to down-regulate the 5-HT₂ receptors.     

Mechanical, thermal and formalin-induced nociception is differentially altered in 5-HT1A-/-, 5-HT1B-/-, 5-HT2A-/-, 5-HT3A-/- and 5-HTT-/- knock-out male mice

Extensive studies in rodents suggest that serotonin (5-HT) modulates nociceptive responses through the stimulation of several receptor types. However, it remains to demonstrate that these receptors participate in the control of nociception under physiological conditions. Pain behaviors of mutants which do not express 5-HT_1A, 5-HT_1B, 5-HT_2A or 5-HT_3A receptors, or lacking the 5-HT transporter, compared to paired wild-type mice of the same genetic background, were examined using validated tests based on different sensory modalities. Mechanical (von Frey filaments, tail pressure, tail clip tests), thermal (radiant heat, 46 °C water bath, hot-plate test) and formalin-induced nociception were determined in 2- to 3-month-old males. 5-HT_1A knock-out mice differed from wild-types by higher thermal sensitivity (hot-plate test only), and 5-HT_1B knock-out mice by higher thermal and formalin sensitivity. Both 5-HT_2A and 5-HT_3A knock-out mice differed from wild-types by a dramatic decrease in the formalin-induced nociceptive responses for phase II (16–45 min after injection/inflammatory phase). In contrast, neither mechanical, thermal nor formalin-induced nociception differed between mutants lacking the 5-HT transporter and paired wild-type mice. Although differences in spontaneous locomotor activity in 5-HT_1B−/− (increase) and 5-HT_3A−/− (decrease) knock-out mice versus paired wild-types might have confounded differences in nociception, acute 5-HT receptor blockade by selective antagonists was found to replicate in wild-type mice the effects on pain behavior, but not on locomotor activity, of the respective gene knock-out in mutants. These results support the conclusion that the complex control of pain mechanisms by 5-HT, acting at multiple receptors, is physiologically relevant in mice.     

Effects of pretreatment with clonidine, lithium and quinine on the activities of antidepressant drugs in the mouse tail suspension test

Summary— The aim of the present study was the investigation of pretreatment effects with clonidine (0.06 mg/kg, intraperitoneal [ip]), lithium (1 mEq, ip) or quinine (0.5 mg/kg, ip) on the activities of various drugs acting on noradrenergic and/or serotonergic systems in the mouse tail suspension test. Drugs used in the present study included: the tricyclic antidepressants imipramine and dothiepin, the heterocyclic antidepressant trazodone, the 5-HT reuptake inhibitor (SSRI) fluoxetine, the atypical antidepressants mianserin and iprindole, the 5-HT_1A receptor agonist ipsapirone, the 5-HT_2A/2C receptor antagonist ritanserin, and the 5-HT₃ receptor antagonist ondansetron. Clonidine, lithium and quinine differentially enhanced the effects of several psychotropic drugs administered at sub-active doses. The activity of iprindole (32 mg/kg, ip) was not potentiated by pretreatment with clonidine, lithium or quinine. Our results suggest that lithium exerted additive effects via postsynaptic 5-HT_1A receptor activation, quinine via potassium ion channel blockade of 5-HT₃ receptors, while clonidine did so primarily via action at 5-HT₂ receptors.     

Thromboxane A2 and related prostaglandins in airways

Summary— Asthma is now thought to be a chronic inflammatory disease of the airways. The roles of prostanoids, thromboxane A₂ (TXA₂) and the prostaglandins (PGs) in the pathogenesis and pathophysiology of asthma have fostered a wealth of studies but remain controversial. TXA₂ and the bronchoconstrictor PGs, PGD₂ and PGF_2α, are generated in greater amounts in asthmatic than in normal subjects. TXA₂ is a potent constrictor of airway smooth muscle, an inducer of acetylcholine release and of airway microvascular leakage. It may participate in the thickening and the remodeling of the airway wall which may contribute to the airway hyperresponsiveness, a typical feature of asthma. Strategies for inhibition of TXA₂ effects include antagonism of the TXA₂ receptor (TP receptor) and inhibition of the thromboxane synthase. TP receptor antagonists could block the effects of all the bronchoconstrictor prostanoids because TXA₂ as well as the bronchoconstrictor PGs act through activation of lung TP receptor. The recent development of specific and potent TP receptor antagonists and inhibitors of thromboxane synthase has provided tools to assess the role of TXA₂ and bronchoconstrictor PGs in the pathophysiology of asthma.     

5-HT 2 Serotonin Receptor on Blood Platelet of Migraine Patients

Several lines of evidence have previously suggested that platelets might play a primary or secondary role in migraine pathogenesis, and that in addition serotonin receptors on human platelets might be involved in those processes. By using [3H]-spiperone as a radioligand and ketanserin to determine the non-specific binding, the numbers of 5-HT2 serotonin receptors on platelet membrane obtained from normal healthy and migraine subjects were determined. We found a significant decrease (p < 0.02) in the maximal receptor numbers (Bmax) on platelet membrane of migraine patients (Bmax = 33.01 +/- 5.57 fmol/mg protein) when compared to the normal healthy group (Bmax = 86.59 +/- 9.09 fmol/mg protein) whereas the dissociation equilibrium constant (Kd) values (2.47 +/- 0.44 nM and 3.41 +/- 0.95 nM for the normal and migraine subjects, respectively) remained unchanged. The platelet response showed a higher degree of aggregability in migraine subjects, whereas the platelet counts were the same. This finding implies that serotonin receptors on the platelet may reflect some aspect of the pathogenesis of migraine headache.     

5-HYDROXYTRYPTAMINE STIMULATES TWO DISTINCT ADENYLATE CYCLASE ACTIVITIES IN RAT BRAIN: HIGH-AFFINITY ACTIVATION IS RELATED TO A 5-HT1 SUBTYPE DIFFERENT FROM 5-HT1A, 5-HT1B, AND 5-HT1C

5-HT binding sites of the 5-HT1 type are heterogeneous and appear to comprise several subtypes (5-HT1A, 5-HT1B and 5-HT1C); their physiological role is as yet unclear. The stimulation of adenylate cyclase induced by 5-HT has been investigated in membrane fractions prepared from rat brain cortex. Enzymatic activity was determined by measuring cAMP production with an HPLC technique. It was shown that 5-HT stimulates adenylate cyclase activity with 2 activation constants (Kact): one shows a high apparent affinity (Kact = 0.8 nM) and the other a lower apparent affinity (Kact = 0.30 microM). The latter activity, induced by micromolar concentrations of 5-HT, was inhibited by spiperone at concentrations that block 5-HT1A binding. 5-Methoxytryptamine, bufotenin, and LSD also had a stimulatory biphasic effect on adenylate cyclase activity, whereas trifluoromethylphenylpiperazine, 5-carboxyamidotryptamine, 8-hydroxy-(2-di-n-propylamino)tetralin, RU 24969 had a monophasic effect. Enzyme activation by drugs acting in the micromolar range was inhibited by spiperone (1 microM), suggesting a link between this activation and 5-HT1A sites. On the other hand, the high-affinity activation of the enzyme induced by 5-HT, 5-methoxytryptamine, bufotenin, LSD, and the activation induced by TFMPP were not inhibited by spiperone (1 microM), by propranolol (3 microM), or by mesulergine (0.1 microM), which selectively block 5-HT1A, 5-HT1B, and 5-HT1C sites. Inhibition was produced by dihydroergotamine, methysergide, cinanserin, and mianserin, but not by naloxone, phenoxybenzamine, and phentolamine. Therefore, these activations seem related to 5-HT1 receptors but not to 5-HT1A, 5-HT1B, or 5-HT1C sites. Accordingly, binding of [3H]5-HT to 5-HT1-like sites was examined in the presence of spiperone (1 microM) and propranolol (3 microM); in these conditions, a high-affinity site (KD = 3.4 nM) was indeed revealed. The relative potencies of a series of drugs that stimulate or inhibit the activation of the adenylate cyclase with a high affinity and their ability to inhibit this binding of [3H]5-HT showed a positive correlation, strongly suggesting a direct relation between this recognition site for 5-HT and the production of a second messenger (cAMP). Moreover, this potential receptor is shown to be heterogeneously distributed within the brain, and was localized postsynaptically at serotonergic synapses.     

Efficacy and Safety of Rizatriptan Versus Standard Care During Long-term Treatment for Migraine

Rizatriptan is a novel, selective 5-HT_1B/1D receptor agonist with a rapid onset of action after oral dosing for the acute treatment of migraine. We conducted a long-term (up to 1 year), multicenter, randomized study in 1831 patients treating more than 46 000 attacks to compare the efficacy and tolerability of rizatriptan 5 mg and 10 mg to standard care medications routinely used for the acute treatment of migraine attacks. Both doses of rizatriptan were highly effective, without evidence of tachyphylaxis. Rizatriptan 10 mg was consistently superior ( P <0.05), both to the 5-mg dose and to standard care, in providing relief in 90% of attacks, with 50% pain-free by 2 hours after dosing. The most common dose-related adverse events were nausea, somnolence, and asthenia/fatigue. Based on this large, multicenter, long-term trial, rizatriptan is an important new oral agent for the acute treatment of migraine.     

Extracellular recordings of membrane potential from guinea-pig isolated trigeminal ganglion: lack of effect of sumatriptan

The aim of this study was to investigate the effect of the anti-migraine drug and selective 5-HT₁ receptor agonist, sumatriptan, on membrane potential of guinea-pig isolated trigeminal ganglion. Ganglia were divided into three longitudinally, placed in two-compartment baths and the d.c. potential between compartments was recorded extracellularly. Drugs were applied to the Krebs superfusion fluid of one compartment. KCl (3 mmol/1) and GABA (0.1 mmol/l) caused depolarization (0.30 ± 0.05 and 0.55± 0.08 mV respectively, n = 11–19). 5-HT (1–10 mmol/1) caused small depolarizations (0.06 ± 0.02. mV, n = 8) but sumatriptan (0.1–10 mmol/l) had no effect on trigeminal ganglion membrane potential. Collagenase pretreatment, to enhance desheathing, or modification of the composition of the Krebs solution failed to reveal any effect of sumatriptan. These data provide no evidence to suggest that sumatriptan inhibits neurotransmission in trigeminal ganglion. However, 5-HT₁ receptors may be present in insufficient numbers in the trigeminal ganglion to elicit a change in membrane potential. Further studies are required to investigate the effect of sumatriptan at the level of the sensory nerve terminals within the intracranial vasculature, where 5-HT₁ receptors may be concentrated.     

Anti-Migraine Drug Interactions with Cloned Human 5-Hydroxytryptamine 1 , Receptor Subtypes

SYNOPSIS
Multiple 5-hydroxytryptamine (5-HT) receptors have been identified in humans. A subgroup of these receptors (designated 5-HT ₁ receptors) have been hypothesized to be involved in the mechanism of action of acute anti-migraine drugs. At present, this hypothesis cannot be tested directly in human tissues due to technical limitations. However, recent molecular biological advances have allowed for the development of assays employing cloned human 5-HT ₁ receptors expressed in cells by DNA transfection. This study analyzed the ability of ergotamine, dihydroergotamine, 5-HT and sumatriptan to interact with the four known human 5-HT ₁ receptor subtypes. The four acute anti-migraine agents interacted with all 4 human 5-HT ₁ receptor subtypes with less than 1 μM affinity. However, drug affinities for the human 5-HT _1B and 5-HT _1D receptors correlate most closely with the rank order of clinical dosages used to treat a migraine attack. Therefore, these data indicate that human 5-HT _1B and/or 5-HT _1D receptors are likely to mediate the therapeutic efficacy of acute anti-migraine drugs.