Exclusion of 5-HT2A and 5-HT2C Receptor Genes as Candidate Genes for Migraine

Several lines of investigation suggest that the serotonergic system may be involved in the pathogenesis of migraine. In particular, drugs which block 5-HT₂ receptor subtypes appear to be effective migraine prophylactic agents. Therefore, chromosomal DNA regions overlapping the 5-HT_2A (13q14-q22) and 5-HT_2c (Xq22-25) receptor loci were analyzed for possible linkage to the clinical diagnosis of migraine. No evidence for linkage to either chromosomal region was found, although a small subset of migrainous families showed positive likelihood of odds (LOD) scores. However, a homogeneity (HOMOG) analysis provided no statistical evidence for locus heterogeneity. The coding region of the 5-HT_2A and 5-HT_2c receptor genes was also analyzed in migraine patients and unaffected controls using polmerase chain reaction and direct sequencing. No mutations were found in the deduced amino acid sequence of either receptor in the sample of migraineurs tested. These results indicate that DNA-based mutations in the 5-HT_2A and 5-HT_2c receptors are not generally involved in the pathogenesis of migraine.     

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.     

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.     

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.     

The phe-124-Cys and A-161T variants of the human 5-HT1B receptor gene are not major determinants of the clinical response to sumatriptan

BACKGROUND: The 5-HT(1B/1D) receptor agonist sumatriptan is highly effective in the treatment of migraine. However, some patients do not respond to sumatriptan or experience recurrence of the headache after initial relief. In addition, some patients report chest symptoms after the use of sumatriptan. OBJECTIVE: To assess whether 2 genetic variants (F124C changing a phenylalanine for a cysteine and polymorphism A/T at nucleotide position -161 in the 5' regulatory region) of the 5-HT(1B) receptor play a major role in the therapeutic response to sumatriptan. The 5-HT(1B) receptor most likely mediates the therapeutic action and coronary side effects of sumatriptan, and both F124C and A-161T have relevant functional consequences on either the affinity of sumatriptan to bind to the 5-HT(1B) receptor or on receptor expression level itself, respectively. METHOD: Genomic DNA of a relatively small but very well-characterized set of 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 patients without chest symptoms (n = 27) was available for the genetic analyses and screened for the F124C variant and the A-161T polymorphism in the human 5-HT(1B) receptor gene. RESULTS: F124C was not detected in any of the patients studied. In addition, we did not observe drastic changes in allele frequencies of the A-161T polymorphism that might hint to a causal relation with the therapeutic effect of sumatriptan. CONCLUSION: We have not obtained any evidence that variants F124C and A-161T of the 5-HT(1B) receptor are major determinants in the clinical response to sumatriptan.     

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.     

First Clinical Study of the Selective 5-HT3 Antagonist, Granisetron (BRL 43694), in the Acute Treatment of Migraine Headache

Granisetron (BRL 43694), a selective 5-HT3 receptor antagonist, was assessed as acute therapy for the first time in migraine patients. In an open pilot study 7 migraine attacks were treated in 6 patients. All but 1 patient experienced marked and rapid relief from the headache, and nausea and vomiting were rapidly resolved in the 6 cases where these symptoms accompanied the attack. No side effects were recorded. Development of granisetron for migraine was suspended during the study for extraneous reasons.     

Sumatriptan is a potent vasoconstrictor of human dural arteries via a 5-HT1-like receptor

The action of sumatriptan, putatively a selective 5-HT1D or 5-HT1-like receptor agonist which is effective in the treatment of migraine, has been studied on fresh human dural (middle meningeal) arteries. In low concentrations (10(-8)-10(-7) M) it was found to be a significantly stronger vasoconstrictor of dural arteries compared to cerebral and temporal arteries. However, its potency was less than that of 5-HT. The sumatriptan-induced vasoconstriction was antagonized by methiothepin (10(-9)-10(-8) M), but not by ketanserin (10(-7) M). The observations suggest that the sumatriptan-induced contraction of the dural artery is mediated via activation of 5-HT1D or 5-HT1-like receptors, whereas it does not appear to activate the 5-HT2 receptors.     

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.     

5-Hydroxytryptamine(1B/1D) and 5-hydroxytryptamine1F receptors inhibit capsaicin-induced c-fos immunoreactivity within mouse trigeminal nucleus caudalis

In order to investigate the c-fos response within the trigeminal nucleus caudalis (Sp5C) after noxious meningeal stimulation, capsaicin (0.25, 0.5, 1 and 5 nmol) was administered intracisternally in urethane (1 g/kg) and alpha-chloralose (20 mg/kg) anaesthetized male mice. Capsaicin induced a robust and dose-dependent c-fos-like immunoreactivity (c-fos LI) within Sp5C. C-fos LI was observed within laminae I and II of the entire brain stem from the area postrema to C2 level, being maximum at the decussatio pyramidum level. The area postrema, solitary tract, medullary and lateral reticular nuclei were also labelled. The 5-hydroxytryptamine(1B/1D/1F) receptor agonist sumatriptan (0.01, 0.1, 1 and 10 mg/kg), administered intraperitoneally 15 min before capsaicin stimulation (1 nmol), decreased the c-fos response within Sp5C, but not within solitary tract. The novel specific 5-hydroxytryptamine1F agonist LY 344864 (0.1 and 1 mg/kg, i.p.) significantly decreased the c-fos LI within the Sp5C as well. These findings suggest that intracisternally administered capsaicin activates the trigeminovascular system and that the pain neurotransmission can be modulated by 5-hydroxytryptamine(1B/1D/1F) receptors in mice. Thus, the availability of this model in mice, taken together with the possibility of altering the expression of specific genes in this species, may help to investigate further the importance of distinct proteins in the neurotransmission of cephalic pain.     

Differential distribution of 5HT1D- and 5HT1B-immunoreactivity within the human trigemino-cerebrovascular system: implications for the discovery of new antimigraine drugs

Sumatriptan, a 5HT_1B/1D-receptor agonist, is clinically effective as an antimigraine agent. Its therapeutic action may result partly from vasoconstriction of excessively dilated cranial blood vessels (a 5HT_1B-receptor mediated response). The antimigraine activity of sumatriptan may also result from inhibition of the release of vasoactive neuropeptides from trigeminal sensory fibres within the meninges. The identity of the 5HT_1B/1D-receptor subtype mediating this effect is unknown. Using 5HT_1D- and 5HT_1B-receptor-specific antibodies we have demonstrated a differential distribution of these receptor subtypes within the human trigemino-cerebrovascular system. Only 5HT_1B-receptor protein was detected on dural arteries. In contrast, only 5HT_1D-receptor protein was detected on trigeminal sensory neurones including peripheral and central projections to dural blood vessels and to the medulla. Within the medulla 5HT_1D-receptor protein was confined to discrete areas associated with the trigeminal sensory system. These findings have important implications for the design of new antimigraine drugs.     

Comparative tolerability of oral 5-HT1B/1D agonists

OBJECTIVES: To compare the relative tolerability of 5-HT1B/1D agonists and to investigate the relationships (if any) among systemic exposure, lipophilicity, and clinical tolerability for 5-HT1B/1D agonists. METHODS: Post hoc correlations were sought among the following variables: absolute dose (= administered dose x oral bioavailability), Cmax, LogDpH7.4 (LogD), frequencies of all, neurological and dizziness/somnolence/drowsiness adverse events, adjusted for corresponding placebo-associated frequencies. RESULTS: For effective doses of all drugs with available data, absolute dose-response relationships exist for adverse event frequencies. The overall rank order of the frequency of adverse events was as follows: naratriptan < sumatriptan = rizatriptan < zolmitriptan. With the exception of eletriptan, 5-HT1B/1D agonists exhibit correlations between absolute dose, Cmax (R = 0.97), and LogD (R = 0. 71). For neurological and dizziness/somnolence/drowsiness adverse event frequencies, the overall rank order was sumatriptan < naratriptan < rizatriptan < zolmitriptan. Neither LogD nor absolute dose size predicted adverse event frequencies. CONCLUSIONS: Triptans may be distinguished in terms of their tolerability. Effectiveness, absolute dose size, and lipophilicity are related for the 5-HT1B/1D agonists considered here, except eletriptan. Adverse event frequencies cannot be predicted from in vitro measures of lipophilicity, in vivo estimates of absolute bioavailability, dose size, or any combination of these variables. Since these drugs are all agonists at 5-HT1B/1D receptors in the low nanomolar range, but differ in their tolerability profiles, adverse effects are not likely to be mediated through 5-HT1B/1D receptors. Drugs of this class must be studied individually and on a reasonably large scale in clinical development programs.     

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.     

Role of 5-HT1A autoreceptors in the mechanism of action of serotoninergic antidepressant drugs: recent findings from in vivo microdialysis studies

Summary— Although a new generation of selective serotonin reuptake inhibitors (SSRIs) has been introduced in therapeutics as antidepressant drugs, a two to four week lag period still occurs between starting treatment with SSRIs and the onset of therapeutic effects in man. In vivo cerebral microdialysis can be used to measure extracellular concentrations of serotonin (5-hydroxytryptamine, 5-HT), which reflect intrasynaptic events. With the coupling of this new experimental method to very sensitive analytical assays such as liquid chromatography with electrochemical detection, it has recently been possible to obtain two major arguments supporting the hypothesis that somatodendritic 5-HT_1A autoreceptors situated in the raphe nuclei play an important role in the mechanism of action of SSRIs. First, in the rat, single administration of SSRIs at low doses comparable to those used therapeutically increases extracellular 5-HT concentrations in the vicinity of the cell body and the dendrites of serotoninergic neurones of the raphe nuclei. This effect is more marked than that observed in regions rich in nerve endings (frontal cortex). The magnitude of the activation of the serotoninergic neurotransmission depends on the brain area studied and the dose of the SSRIs administered to rats. This could be explained by simultaneous activation of somatodendritic 5-HT_1A autoreceptors by endogenous 5-HT in the raphe nuclei, thereby limiting the corticofrontal effects of the antidepressant. Second, SSRIs cause a larger increase in extracellular 5-HT concentrations in the nerve endings when administered chronically: 5-HT autoreceptors may have gradually desensitized during the 2–4 weeks of treatment with SSRIs. Preliminary studies of patients with depression appear to confirm these experimental results, as co-administration of a 5-HT_1A autoreceptor antagonist and a SSRI accelerated the onset of the antidepressant effect (< 1 week).     

Onset of effect of 5-HT1B/1D agonists: a model with pharmacokinetic validation

OBJECTIVE: To quantitate onset of effect of all formulations of sumatriptan, and to investigate whether this is related to rate, not extent, of drug absorption. METHODS: From published literature, for 4 formulations of sumatriptan and matching placebos, response rates were modeled using a simple logarithmic equation, with a being a parameter of curve convexity and B, a location parameter (equal to response rate at 2 hours [the standard regulatory parameter]). The average rate of drug absorption (A) was estimated by dividing the maximal drug concentration by the time needed to achieve it (Cmax/Tmax). Least mean square correlation was then performed between the therapeutic gains and therapeutic ratios of curve convexity and rate of drug absorption. RESULTS:-Models closely fitted observed response rates (2 hours or less). Curve convexity correlated with rate of drug absorption. Sumatriptan response rates (0 to 2 hours) for formulations correlated with rate, not extent, of drug absorption. The range of rates of onset of effect among different routes of administration was greater than that for tablets with 4-fold differences in dose size. CONCLUSION: Onset of effect is related to rate of absorption of sumatriptan. There is greater scope for improving onset of effect using an alternative route of administration than by increasing the oral dose.     

Migraine, serum serotonin and platelet 5-HT2 receptors

In spite of recent theories about the aetiopathogenesis of migraine, serotonin continues to play a central role, explaining the efficacy of almost all migraine prophylactic drugs. In migraineurs with and without aura we measured (by HPLC-EC) the serum serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels between as well as during headache attacks. Between attacks of migraine with aura and at the beginning of attacks of both types of migraine the serum 5-HT and 5-HIAA concentration was significantly increased. These results were corroborated by 3H-spiperone binding to platelet membranes: in migraineurs with aura in the attack-free interval, there was a significant decrease in its Bmax, which suggests down-regulation of 5-HT2 receptors. In conclusion, we have verified that migraine with aura differs biochemically from migraine without aura.     

Lack of efficacy of 5-HT2A receptor antagonists to reduce brain damage after 3 minutes of transient global cerebral ischaemia in gerbils

Summary— Stimulation of the 5-HT_2A receptors by serotonin has been reported to exert an excitatory effect on neocortical neurons in rats and mice, to facilitate ischaemia-induced release of excitatory amino acids and to mediate the vasomotor constrictor component of the response of blood vessels to 5-HT. 5-HT_2A receptor antagonists have, therefore, been proposed as potential protectants against the effects of cerebral ischaemia. The aim of this study was to evaluate the effects of two relatively selective 5-HT_2A receptor antagonists, ketanserin and ritanserin, on delayed hyperactivity and the ensuing neuronal degeneration induced by 3 minutes of bilateral carotid artery ligation in Mongolian gerbils. Effects were compared to that of flunarizine, which blocks calcium overload and served as a positive control in this paradigm. Temporal and/or rectal temperatures were measured and strictly controlled during the ischaemia and the early reperfusion phase. Locomotor activity was measured one day after the ischaemia and neuronal degeneration quantified 7 days later using an image analysis system (Quantimet 570, Leica). Global ischaemia in gerbils elicits hyperactivity associated with a delayed neuronal degeneration predominantly in the CA1 zone of the hippocampus. Ketanserin and ritanserin (3 and 10 mg/kg ip, twice daily for 3 days, pre- and postischaemia) did not protect the CA1 neurons against ischaemic damage. The postischaemic hyperactivity was inhibited only with the higher dose of ketanserin. As previously reported, flunarizine (30 mg/kg po) markedly reduced neuronal degeneration (-44.2%, p < 0.01) and totally abolished the ischaemia-induced hyperactivity. These data demonstrate that ketanserin and ritanserin are not effective protectants of the gerbil hippocampus against ischaemic damage when the body temperature of the animals is controlled, thus suggesting that 5-HT_2A receptors are not directly implicated in the pathogenesis of global cerebral ischaemia in this model.     

Naratriptan has a selective inhibitory effect on trigeminovascular neurones at central 5-HT1A and 5-HT(1B/1D) receptors in the cat: implications for migraine therapy

The triptans are agonists at serotonin (5-HT)1B/1D receptors; however, they are also active at 5-HT1A and 5-HT1F receptors. We conducted this series of experiments to further elucidate the site of action of naratriptan using a well-established animal model of trigeminovascular stimulation. Following electrical stimulation of the superior sagittal sinus of the cat, single cell responses (n=83) were recorded in the trigeminal nucleus caudalis. Most cells (91%) also responded to electrical and mechanical stimulation of cutaneous or mucosal facial receptive fields. The microiontophoretic application of naratriptan resulted in a significant suppression of the response to sagittal sinus stimulation (response suppressed by 47 +/- 4%, P<0.001). The effect of naratriptan was significantly attenuated by application of either the 5-HT(1B/1D) receptor antagonist GR-127935 (P<0.001) or the 5-HT1A antagonist WAY-100635 (P<0.05). The response of single cells to receptive field stimulation was also suppressed by microiontophoretic application of naratriptan, but by only 20 +/- 3%. Intravenous administration of naratriptan resulted in a similar selective suppression of sagittal sinus vs. receptive field responses in trigeminal neurones. These results indicate that naratriptan has a central effect in the trigeminovascular system, selectively inhibiting afferent activity in craniovascular neurones, via both 5-HT(1B/1D) and 5-HT1A receptors.