5-HT1D Receptor Research Articles

Effect of Third Ventricle Administration of L-694,247, a Selective 5-HT1 D Receptor Agonist, on Water Intake in Rats

DE CASTRO-E-SILVA, E., C. SARMENTO, T. A. NASCIMENTO, C. P. LUZ, T. SOARES, C. A. MARINHO, M. CUNHA, C. BULCÃO, I. R. DE OLIVEIRA AND J. B. FREGONEZE. Effect of third ventricle administration of L-694,247, a selective 5-HT1D receptor agonist, on water intake in rats. PHARMACOL BIOCHEM BEHAV 57 [4]749–754, 1997.—L-694,247, a selective 5-HT1 D receptor agonist, injected directly into the third ventricle (2.5, 5.0, and 10.0 μg/rat) of dehydrated rats induced a dose-dependent partial blockade of water intake. Injected in this way, the compound abolishes drinking behavior induced by third ventricle administration of carbachol (2 μg/rat), angiotensin II (5 ng/rat), and isoproterenol (40 μg/rat). In addition, intraventricular injections of L-694,247 did not modify water intake in normohydrated rats. The effects of L-694,247 are due to a specific interaction with 5-HT1 D receptors, because its inhibitory effect on water intake in dehydrated rats is blocked by the previous administration of a 5-HT1 D antagonist, GR 127935 (5 μg/rat), directly into the third ventricle. It is concluded that central 5-HT1 D receptor activation disrupts the functional integrity of central pathways related to drinking behavior.

5-HT1F receptor agonists inhibit neurogenic dural inflammation in guinea pigs.

The serotonin (5-HT) receptor subtype mediating inhibition of neurogenic dural inflammation in guinea pigs was investigated using a series of serotonin agonists with differing affinities for the 5-HT1B, 5-HT1D and 5-HT1F receptors. When agonist potencies for inhibiting neurogenic inflammation were compared with affinities for these receptor subtypes, a significant positive correlation was seen only with the 5-HT1F receptor. The potency of agonists in inhibiting adenylate cyclase in cells transfected with human 5-HT1F receptor was also highly correlated with their potency in the animal model of migraine. In situ hybridization demonstrated 5-HT1F receptor mRNA in guinea pig trigeminal ganglion neurons. These data suggest that the 5-HT1F receptor is a rational target for migraine therapeutics.

Growth hormone response to sumatriptan (5-HT1D agonist) challenge in seasonal affective disorder: Effects of light therapy

To explore the role of serotonergic system in seasonal affective disorder (SAD), we compared growth hormone (GH) responses to a challenge with a novel 5-HT1D receptor agonist sumatriptan between 11 patients with SAD and nine healthy controls. Of the 11 patients with SAD, nine had repeat sumatriptan challenge following treatment with light therapy. The results showed that GH responses were significantly blunted during winter depression in patients with SAD compared to healthy controls. The GH responses normalized following treatment with light therapy to similar levels in controls. The results of this study provide a support for the role of serotonergic system in pathophysiology of SAD and in the mechanism of action of light therapy.

5-HT1D and 5-HT1E/1F binding sites in depressed suicides: increased 5-HT1D binding in globus pallidus but not cortex.

5-HT1D and 5-HT1E/1F receptor binding sites were measured in brain samples obtained at postmortem from suicide victims with a firm retrospective diagnosis of depression, and matched controls. In antidepressant-free suicides a significantly higher number of 5-HT1D receptors was found in globus pallidus. This was largely restricted to those suicides who died by violent means. This effect was not observed in antidepressant-treated suicides. No differences or trends in 5-HT1D binding were found in putamen, parietal or frontal cortex, in antidepressant-free or antidepressant-treated suicides. There were no differences in the number of 5-HT1E/1F receptors in any of the regions studied.

(+)-WAY 100135, a partial agonist, at native and recombinant 5-HT1B/1D receptors.

1. We have studied the effects of the purportedly selective 5-HT1A receptor antagonist (+)-WAY 100135 on electrically stimulated 5-hydroxytryptamine (5-HT) efflux in the ventrolateral geniculate nucleus (vLGN), and its affinity at human 5-HT1B and 5-HT1D receptors stably expressed in Chinese hamster ovary (CHO) cells. 2. On short 'pseudo single pulse' stimulations (20 pulses at 100 Hz, 190 ms train duration), (+)-WAY 100135 (1.0 microM) decreased 5-HT efflux in the vLGN to 68 +/- 8% of pre-drug values (P < 0.01). This decrease could be blocked by the 5-HT1D/1B receptor antagonist GR 127935 (50 nM). Conversely, when long stimulations (20 pulses at 20 Hz, 950 ms train) were used, (+)-WAY 100135 had no effect on 5-HT efflux (84 +/- 8% of pre-drug values) although both methiothepin (200 nM) and GR 127935 (50 nM) caused significant increases (to 175 +/- 18 and 130 +/- 10% of pre-drug values, respectively). 3. Paroxetine (100 nM), the selective 5-HT reuptake inhibitor, increased stimulated 5-HT efflux and reuptake half-life (to 145 +/- 18% and 649 +/- 121%, respectively) on pseudo single pulse stimulations. When (+)-WAY 100135 was added in combination with the uptake blocker, the effect of paroxetine on stimulated 5-HT efflux was potentiated to 282 +/- 48% (P < 0.01) without further effect on the 5-HT reuptake half-life. 4. The affinity and intrinsic activity of (+)-WAY 100135 were determined at recombinant human 5-HT1B and 5-HT1D receptors expressed in CHO cells, by use of radioligand binding and [35S]-GTP gamma S binding (+)-WAY 100135 was a partial agonist at human 5-HT1B and 5-HT1D receptors with moderately high affinity for 5-HT1D receptors (pEC50 = 7.61). 5. In conclusion, (+)-WAY 100135 was found to be not a selective 5-HT1A autoreceptor antagonist but may act as a partial agonist at the 5-HT1B/1D receptor, displaying agonist or antagonist properties depending on the stimulation protocol used and the resultant 5-HT 'tone' at the receptor.

Effect of a serotonin agonist (sumatriptan) on the peptidergic innervation of the rat cerebral dura mater and on the expression of c-fos in the caudal trigeminal nucleus in an experimental migraine model

The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation including nociceptive axons and their terminals, which display intense calcitonin gene-related peptide (CGRP) immunoreactivity both in the connective tissue and around blood vessels. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, induces marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura. Intravenous administration of sumatriptan, prior to electrical stimulation, prevents disintegration of perivascular terminals and induces accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increase in size; accumulation of axoplasmic organelles results in a "hollow" appearance of many varicosities. Since sumatriptan exerts its anti-migraine effect by virtue of its agonist action on 5-HT1D receptors, we suggest that sumatriptan prevents the release of CGRP from dural perivascular terminals by an action at 5-HT1D receptors. In the caudal trigeminal nucleus electrical stimulation of the trigeminal ganglion induces, in interneurons, increased expression of the oncoprotein c-fos which is not prevented by intravenous application of sumatriptan. Disparate findings regarding this effect are partly due to the fact that sumatriptan very poorly passes the blood-brain barrier and partly to different experimental paradigms used by different authors.

Naratriptan: biological profile in animal models relevant to migraine.

The biological profile of naratriptan (N-methyl-3-(1-methyl-4-piperidinyl)-1H-indole-5-ethane-sulphonamide), a novel 5HT1B/1D receptor agonist, was investigated in a variety of experimental models of relevance to migraine. Naratriptan has high affinity for human recombinant 5HT1B and 5HT1D receptors (pKi = 8.7 +/- 0.03 and 8.3 +/- 0.1, respectively) and causes contractions of dog isolated basilar and middle cerebral artery (EC50 values of 0.11 and 0.07 microM, respectively). Naratriptan causes small contractions of human isolated coronary arteries (EC50 value of 0.17 microM; maximum contraction equivalent to 33% of 5HT maximum). In anaesthetized dogs, naratriptan causes selective vasoconstriction of the carotid arterial bed (CD50 dose = 19 +/- 3 micrograms kg-1) and, in anaesthetized rats, naratriptan selectively inhibits neurogenic plasma protein extravasation in the dura (ID50 = 4.1 micrograms kg-1). In a variety of antinociceptive tests, naratriptan has no effect even at high doses. In conscious rats and dogs, naratriptan has high oral bioavailability (71% and 95%, respectively). The data show that naratriptan is a selective agonist at 5HT1B/1D receptors, with a pharmacological profile very similar to that of sumatriptan, albeit 2-3 fold more potent. These observations, coupled with high oral bioavailability in animals, suggest that naratriptan has the profile of an orally effective anti-migraine drug.

Receptor specificity and trigemino-vascular inhibitory actions of a novel 5-HT1B/1D receptor partial agonist, 311C90 (zolmitriptan).

1. 311C90 (zolmitriptan zomig: (S)-4[[3-[2-(dimethylamino)ethyl]-1H-indol-5-yl]methyl]-2-oxazolidinone) is a novel 5-HT1B/1D receptor agonist with proven efficacy in the acute treatment of migraine. Here, we describe the receptor specificity of the drug and its actions on trigeminal-evoked plasma protein extravasation into the dura mater of the anaesthetized guinea-pig. 2. At the "5-HT1B-like' receptor mediating vascular contraction (rabbit saphenous vein), the compound was a potent (p[A50] = 6.79 +/- 0.06) partial agonist achieving 77 +/- 4% of the maximum effect to 5-hydroxytryptamine (5-HT). In the same experiments, sumatriptan (p[A50] = 6.48 +/- 0.04) was half as potent as 311C90 and produced 97 +/- 2% of the 5-HT maximum effect. Studies in which receptor inactivation methods were used to estimate the affinity (pKA) and efficacy relative to 5-HT (tau rel) for each agonist confirmed that 311C90 exhibits higher affinity than sumatriptan (pKA = 6.63 +/- 0.04 and 6.16 +/- 0.03, respectively) and that both drugs are partial agonists relative to 5-HT (tau rel = 0.61 +/- 0.03 and 0.63 +/- 0.10, respectively, compared to 5-HT = 1.0). 3. Consistent with its effects in rabbit saphenous vein, 311C90 also produced concentration-dependent contractions of primate basilar artery and human epicardial coronary artery rings. In basilar artery, agonist potency (p[A50] = 6.92 +/- 0.07) was similar to that demonstrated in rabbit saphenous vein, again being 2-3 fold higher than for sumatriptan (p[A50] = 6.46 +/- 0.03). Both agonists produced about 50% of the maximum response obtained with 5-HT in the same preparations. In rings of human coronary artery, the absolute potency of 311C90 and sumatriptan was higher than in primate basilar artery (p[A50] = 7.3 +/- 0.1 and 6.7 +/- 0.1, respectively), but maximum effects relative to 5-HT were lower (37 +/- 8% and 35 +/- 7%, respectively). In both types of vessel, the inability of 5-HT1B/1D agonists to achieve the same maximum as the endogenous agonist 5-HT is explained by the additional presence of 5-HT2A receptors. 4. 311C90 displayed high affinity at human recombinant 5-HT1D (formerly 5-HT1D alpha) and 5-HT1B (formerly 5-HT1D beta) receptors in transfected CHO-K1 cell membranes (pIC50 values = 9.16 +/- 0.12 and 8.32 +/- 0.09, respectively). In intact cells, the drug produced concentration-dependent inhibition of forskolin-stimulated adenylyl cyclase (p[A50] = 9.9 and 9.5, respectively) achieving the same maximum effect as 5-HT. Excepting human recombinant 5-HT1A and 5-ht1F receptors at which the drug behaved as an agonist with modest affinity (pIC50 = 6.45 +/- 0.11 and 7.22 +/- 0.12, respectively), 311C90 exhibited low, or no detectable affinity (pKi or pKB < or = 5.5) at numerous other monoamine receptors, including other 5-HT receptor subtypes. 5. When administered to anaesthetized guinea-pigs ten minutes before unilateral electrical stimulation of the trigeminal ganglion (1.2 mA, 5 Hz, 5 ms, 5 min), 311C90 (3-30 micrograms kg-1, i.v.) caused a dose-dependent inhibition of [125I]-albumin extravasation within the ipsilateral dura mater. At the same doses, the drug also produced dose-dependent falls in cranial vascular conductance (32.3 +/- 7.5% at 30 micrograms kg-1), as measured in the ear by laser doppler flowmetry. 6. These results show that 311C90, a novel member of the 5-HT1B/1D agonist drug class, exhibits a high degree of pharmacological specificity. Its potent partial agonist action at "5-HT1B-like' receptors in intracranial arteries, coupled with potent agonism at 5-HT1D and 5-HT1B receptors and an ability to inhibit neurogenic plasma protein extravasation in the dura, are consistent with its utility as an effective acute treatment for migraine.

5-Hydroxytryptamine1B receptors modulate the effect of cocaine on c-fos expression: converging evidence using 5-hydroxytryptamine1B knockout mice and the 5-hydroxytryptamine1B/1D antagonist GR127935.

Serotonergic transmission has been suggested to modulate the effects of cocaine. However, the specific receptors and brain structures underlying this phenomenon have not been identified. To test the possible contribution of the 5-hydroxytryptamine1B (5-HT1B) receptor, we studied the induction of the immediate-early gene c-fos elicited by cocaine in knockout mice lacking this receptor. 5-HT1B knockout mice display a markedly reduced effect of cocaine on c-fos induction in different brain structures, most notably in the striatum. In addition, the administration to wild-type mice of the 5-HT1B receptor agonist RU24969 results in a striatal induction of c-fos expression very similar to that induced by cocaine in its time course, cellular and anatomical distribution, and pharmacology. Here, we also report the ability of a 5-HT1D receptor antagonist, GR127935, to antagonize 5-HT1B receptors in vivo. Finally, when administered to wild-type mice, GR127935 reduces the increase in striatal c-fos expression elicited by cocaine. These converging lines of evidence obtained with the knockout mice and 5-HT(1B/1D) antagonist indicate that cocaine acts as an indirect agonist of 5-HT1B receptors in vivo and demonstrate that activation of 5-HT1B receptors contributes to the cellular responses elicited by cocaine.

Molecular Cloning and Pharmacological Characterization of Guinea Pig 5-HT1B and 5-HT1D Receptors

Human 5-HT1B and 5-HT1D receptors have been implicated as molecular targets for the treatment of acute migraine based upon the pharmacological actions and clinical efficacy of sumatriptan, an agonist for human 5-HT1B/1D receptors. The guinea pig has served as an animal model to assess 5-HT1B/1D receptor function, most recently in evaluating 5-HT1B/1D receptor agonists as potential anti-migraine agents. Since two distinct, but closely-related receptors displaying “5-HT1D receptor pharmacology” have been cloned previously from most mammalian species, the genes encoding these receptors were isolated from a guinea pig liver genomic DNA library using oligonucleotide probes targeted to nonconserved regions of recombinant human 5-HT1B and 5-HT1D receptors. Sequence analysis indicates that guinea pig 5-HT1B and 5-HT1D receptors are comprised 390 and 378 amino acids, respectively. Comparison of the deduced amino acid sequences of guinea pig 5-HT1B and 5-HT1D receptor subtypes show that they display overall and transmembrane (TM) identities of 63% and 77%, respectively. Both clones contain a conserved threonine residue in TM7, a structural feature imparting “5-HT1D receptor pharmacology”. Guinea pig 5-HT1B and 5-HT1D receptor genes were transiently expressed in Cos-7 cells and their binding properties were evaluated using [3H]5-HT. Both cloned receptor subtypes displayed “5-HT1D receptor pharmacology” with the following rank order of binding affinities: 5-CT > 5-HT > sumatriptan > 8-OH-DPAT > (−)-pindolol. Ketanserin displayed modest (five-fold) 5-HT1D receptor selectivity, while methiothepin exhibited a similar selectivity for the 5-HT1B subtype. In particular, ketanserin exhibits profound differences in 5-HT1D receptor affinity (and selectivity) across species. High correlations were observed between the binding affinities of serotonergic ligands for 5-HT1D binding sites measured in guinea pig cortical membranes and both cloned guinea pig 5-HT1B (r2 = 0.88) and 5-HT1D (r2 = 0.80) receptors, indicating that the development of subtype selective compounds (i.e. 5-HT1B versus 5-HT1D) using native tissues may be more difficult to achieve without the advantage of using recombinant receptor subtypes. Additionally, there is a good correspondence between binding profiles of recombinant guinea pig 5-HT1B and 5-HT1D receptor subtypes and to their respective cloned human homologs. However, species differences in binding affinities of a subset of compounds are evident. These data extend previous observations that subtype selective (i.e. 5-HT1D) compounds identified in one species may not discriminate between closely related receptors (i.e. 5-HT1B and 5-HT1D) in all animal model systems. © 1997 Elsevier Science Ltd.

Differential Distribution of [3H]Sumatriptan Binding Sites (5-HT1B, 5-HT1D and 5-HT1F Receptors) in Human Brain: Focus on Brainstem and Spinal Cord

We report on the autoradiographic distribution of 5-HT1B, 5-HT1D and 5-HT1F receptor subtypes in human brain, focusing on the brainstem and cervical spinal cord. We have used [3H]sumatriptan as a radioligand in the presence of suitable concentrations of 5-CT (5-carboxamidotryptamine) to define 5-HT1F receptors, and ketanserin, to discriminate between 5-HT1B and 5-HT1D receptors. In the brainstem the highest concentrations of [3H]sumatriptan binding sites were seen in substantia nigra. The spinal trigeminal nucleus, substantia gelatinosa of the spinal cord, nucleus of the tractus solitarius and periaqueductal grey, also showed significant levels of [3H]sumatriptan binding sites. In the brainstem and spinal cord the total population of 5-CT-insensitive receptors, corresponding to 5-HT1F receptors, ranged from 9.8% in the periaqueductal grey to 53.4% in the substantia gelatinosa. This population represented 67.0% of binding in layer V of the frontal cortex. The decrease in [3H]sumatriptan binding in the presence of 200 nM ketanserin, indicative of the presence of 5-HT1D receptors, was very limited throughout the human brain, only reaching 20% of total specific binding over the periaqueductal grey. The proportion of [3H]sumatriptan binding sites displaced by 5-CT and insensitive to ketanserin, corresponding to 5-HT1B receptors, was, in general, the most abundant, ranging from 43.8% in substantia gelatinosa to 69.9% in the periaqueductal grey. Significant levels of 5-HT1B and 5-HT1F receptors found in migraine control pain areas suggest their involvement in antinociceptive mechanisms. © 1997 Elsevier Science Ltd.

Importance of h5-HT1B Receptor Selectivity for 5-HT Terminal Autoreceptor Activity: an In Vivo Microdialysis Study in the Freely-moving Guinea-pig

The importance of h5-HT1B receptor selectivity for 5-HT terminal autoreceptor activity was investigated with the selective h5-HT1B receptor ligands SB 219085, SB 220272, SB 224289 and SB 216641. The studies employed measurement of compound affinity and efficacy in vitro and the measurement of extracellular 5-HT in the frontal cortex of the freely-moving guinea-pig using in vivo microdialysis. All compounds had high affinity and selectivity for the h5-HT1B receptor, with SB 224289 the most selective for h5-HT1B over h5-HT1D receptors. Compounds exhibited a range of efficacies at both receptors: SB 224289 and SB 219085 were inverse agonists, SB 220272 was an antagonist and SB 216641 was a partial agonist. SB 220272, SB 216641 and SB 224289 had no effect on extracellular 5-HT following systemic administration, however, SB 219085 produced a significant increase. The SB 219085-induced increase in extracellular 5-HT was attributed to the compounds non-specific releasing properties as it was also demonstrated to increase basal release of [3H]5-HT from pre-loaded guinea-pig cortical slices. The lack of effect of the above h5-HT1B receptor selective compounds and the decrease in extracellular 5-HT elicited by the non-selective compounds GR 127935, GR125743 and methiothepin suggest that antagonism of 5-HT1D receptors may mediate this decrease in 5-HT levels. It is plausible that blockade of 5-HT1D receptors increases 5-HT levels in the raphe, this activates 5-HT1A receptors which results in an overall decrease in terminal 5-HT release. Definitive proof now awaits elucidation of the action of a selective 5-HT1D receptor antagonist. © 1997 Elsevier Science Ltd.

Identification of 5-HT Receptor Sub-types in a Homogeneous Population of Presumptive Serotoninergic Neurones

The expression of the known rat 5-HT receptor sub-types has been analyzed in a presumptive serotoninergic cell line derived from the rat raphé nuclei, using reverse transcription followed by polymerase chain reaction. By manipulating the activity of the oncogene (ts-SV40T) product used to immortalize the serotoninergic precursors, it has been possible to compare the expression of the 5-HT receptors in either replicative or differentiating cells. 5-HT1B, 5-HT1D, 5-HT3, 5-HT6 and 5-HT7 receptor gene expression were all observed in the replicating cells. However, under differentiation conditions, expression of all except the 5-HT1B receptor was lost. Only one novel amplification product appeared during early differentiation, in the 5-HT2B lane; its smaller than expected size was suggestive of a previously undescribed alternate splicing of the mRNA in brain. The curtailment of 5-HT receptor expression in differentiating neurones in vitro may reflect the normal ongoing restriction in the phenotypic potential during embryogenesis in vivo.The serotonin cells, therefore, constitute a pristine cell line in which to study the receptor pharmacology of one or more 5-HT receptor sub-types in isolation. © 1997 Elsevier Science Ltd.

Differential Effects of 5-HT1B/1D Receptor Agonists on Neurogenic Dural Plasma Extravasation and Vasodilation in Anaesthetized Rats

These studies compared the effects of the 5-HT1B/1D receptor agonists sumatriptan, CP-122 288 ((R)-N-methyl-[3-(1-methyl-2-pyrrolidinylmethyl)-1H-indol-5-yl]methanesulphonamide succinate) and CP-93 129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride) on neurogenic dural extravasation and vasodilation in anaesthetized rats. Dural extravasation, evoked by high intensity (1.2 mA) stimulation of the trigeminal ganglion, was measured using the radioactive plasma marker 125I-labelled bovine serum albumin. Dural vasodilation produced by lower intensity (50–300 μA) stimulation of trigeminal fibres, was measured through a closed cranial window using intravital microscopy. All compounds inhibited dural extravasation (rank order of potency: CP-122 288 ⪢ sumatriptan > CP-93 129) and dural vasodilation (rank order of potency: CP-93 129 ⪢ sumatriptan = CP-122 288). Comparison of the potency of these compounds with their potencies in an in vitro functional model, agonist-induced [35S]GTPγS binding, suggests that blockade of dural extravasation was consistent with an action at rat 5-HT1D receptors, but activity at another, unknown, “extravasation receptor” could also be involved. In contrast, inhibition of dural vasodilation was consistent with an action at rat 5-HT1B receptors. We suggest that in our preparations, production of dural vasodilation involves activation of trigeminal Aδ-fibres whereas production of dural extravasation involves activation of trigeminal C-fibres. The differential effects of compounds on dural extravasation and vasodilation may therefore be due to the different receptor subtypes involved and to the selective localization of these subtypes on different populations of trigeminal sensory fibre. © 1997 Elsevier Science Ltd.

Cloning and Characterization of The Guinea Pig 5-HT1F Receptor Subtype: a Comparison of the Pharmacological Profile to the Human Species Homolog

The anti-migraine compound, sumatriptan, has been shown to have substantial affinity for the cloned human 5-HT1F receptor suggesting that, in addition to 5-HT1B/5-HT1D receptor subtypes, the 5-HT1F receptor may be a therapeutic target for the treatment of migraine. Several investigators have used the guinea pig plasma extravasation model to evaluate potential anti-migraine drugs. Since species differences in the pharmacology of serotonin receptors are well known, we compared the pharmacological profiles of the cloned human and guinea pig 5-HT1F receptors in order to validate the usefulness of the in vivo model in predicting anti-migraine activity of compounds targeted for humans. We have cloned the guinea pig 5-HT1F by homology to the human 5-HT1F receptor and evaluated its pharmacological profile using radioligand binding assays. The cloned guinea pig 5-HT1F gene exhibited 94% amino acid identity to the corresponding human homolog. High affinity (Kd ∼ 10 nM) [3H]5-HT binding was detected to membranes obtained from Cos-7 cells transiently expressing the guinea pig 5-HT1F receptor. The cloned guinea pig receptor displayed typical 5-HT1F receptor pharmacology with the following rank order of binding affinities: 5-HT > sumatriptan > 1-NP = DHE > α-methyl 5-HT > metergoline > methiothepin > 5-CT. The pharmacological profiles of the cloned guinea pig and human 5-HT1F receptors were very similar as reflected by the high correlation (r2 = 0.72, slope = 0.76) observed between the binding affinities of compounds for these two species homologs. In situ hybridization studies in guinea pig tissue revealed 5-HT1F receptor mRNA expression in the neurons of the trigeminal ganglion, suggesting that the 5-HT1F receptor may play a role in the presynaptic inhibition of neuropeptide release at the level of the intracranial vasculature, thereby blocking the development of neurogenic inflammation. Dorsal root ganglion cells also moderately expressed the 5-HT1F transcripts. The localization of the 5-HT1F receptor to areas involved in the mediation and transfer of nociceptive information implies a role for this receptor in pain processing. These findings indicate that a selective 5-HT1F agonist may be a novel approach to treat migraine. © 1997 Elsevier Science Ltd.

CURRENT CONCEPTS OF THE PATHOPHYSIOLOGY OF MIGRAINE

An understanding of the basic anatomy and physiology of the cranial circulation facilitates the assessment and management of patients with headache, particularly vascular-type headaches, such as migraine. At the very least, all pain is perceived and processed in the brain. With migraine it is likely that the fundamental problem and its clinical expression are driven by the CNS; thus study of the brain regarding headache is warranted. As therapy evolves during the 1900s, such an understanding will be necessary, as new and highly specific receptor-targeted compounds allow treatment and improvement of headache in many patients. Since writing this article, the nomenclature for serotonin (5HT) receptors has changed so that any reference herein to 5HTID alpha is now 5HTID and 5HTID beta is now 5HTI beta. This change in nomenclature is discussed in Martig PR, Hoyer D, Humphrey PPA, et al: Alignment of receptor nomenclature with the human genome: Classification of 5HT-1 beta and 5HT-1D receptor subtypes. Trends in the Pharmacological Sciences 17:103, 1996.

Modulation of the firing activity of noradrenergic neurones in the rat locus coeruleus by the 5‐hydroxtryptamine system

1. The aim of the present study was to investigate the putative modulation of locus coeruleus (LC) noradrenergic (NA) neurones by the 5-hydroxytryptaminergic (5-HT) system by use of in vivo extracellular unitary recordings and microiontophoresis in anaesthetized rats. To this end, the potent and selective 5-HT1A receptor antagonist WAY 100635 (N-[2-[4(2-methoxyphenyl)-1-piperazinyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydroxychloride) was used. 2. In the dorsal hippocampus, both local (by microiontophoresis, 20 nA) and systemic (100 micrograms kg-1, i.v.) administration of WAY 100635 antagonized the suppressant effect of microiontophorectically-applied 5-HT on the firing activity of CA3 pyramidal neurones, indicating its antagonistic effect on postsynaptic 5-HT1A receptors. 3. WAY 100635 and 5-HT failed to modify the spontaneous firing activity of LC NA neurones when applied by microiontophoresis. However, the intravenous injection of WAY 100635 (100 micrograms kg-1) readily suppressed the spontaneous firing activity of LC NA neurones. 4. The lesion of 5-HT neurones with the neurotoxin 5,7-dihydroxytryptamine increased the spontaneous firing activity of LC NA neurones and abolished the suppressant effect of WAY 100635 on the firing activity of LC NA neurones. 5. In order to determine the nature of the 5-HT receptor subtypes mediating the suppressant effect of WAY 100635 on NA neurone firing activity, several 5-HT receptor antagonists were used. The selective 5-HT3 receptor antagonist BRL 46470A (10 and 100 micrograms kg-1, i.v.), the 5-HT1D receptor antagonist GR 127935 (100 micrograms kg-1, i.v.) and the 5-HT1A/1B receptor antagonist (-)-pindolol (15 mg kg-1, i.p.) did not prevent the suppressant effect of WAY 100635 on the firing activity of LC NA neurones. However, the suppressant effect of WAY 100635 was prevented by the non-selective 5-HT receptor antagonists spiperone (1 mg kg-1, i.v.) and metergoline (1 mg kg-1, i.v.), by the 5-HT2 receptor antagonist ritanserin (500 micrograms kg-1, i.v.). It was also prevented by the 5-HT1A receptor/alpha 1D-adrenoceptor antagonist BMY 7378 (1 mg kg-1, i.v.) and by the alpha 1-adrenoceptor antagonist prazosin (100 micrograms kg-1, i.v.). 6. These data support the notion that the 5-HT system tonically modulates NA neurotransmission since the lesion of 5-HT neurones enhanced the LC NA neurones firing activity and the suppressant effect of WAY 100635 on the firing activity of NA neurones was abolished by this lesion. However, the location of the 5-HT1A receptors involved in this complex circuitry remains to be elucidated. It is concluded that the suppressant effect of WAY 100635 on the firing activity of LC NA neurones is due to an enhancement of the function of 5-HT neurones via a presynaptic 5-HT1A receptor. In contrast, the postsynaptic 5-HT receptor mediating this effect of WAY 100635 on NA neurones appears to be of the 5-HT2A subtype.

Sequence and functional analysis of cloned guinea pig and rat serotonin 5-HT1D receptors: common pharmacological features within the 5-HT1D receptor subfamily.

This study was undertaken to investigate the pharmacology of cloned guinea pig and rat 5-hydroxytryptamine (serotonin; 5-HT)1D receptor sites. Guinea pig, rat, and mouse 5-HT1D receptor genes were cloned, and their amino acid sequences were compared with those of the human, dog, and rabbit. The overall amino acid sequence identity between these 5-HT1D receptors is high and varies between 86 and 99%. The sequence homology is slightly more divergent (13-27%) in the N-terminal extracellular region of these 5-HT1D receptors. Guinea pig and rat 5-HT1D receptors, stably and separately expressed in rat C6 glial cells, are negatively coupled to cyclic AMP formation upon stimulation with agonists, as previously found for cloned human 5-HT1D receptor sites. The cyclic AMP data show some common pharmacological features for the 5-HT1D receptors of guinea pig, rat, and human: an almost similar rank order of potency for the investigated 5-HT1D receptor agonists, stereoselectivity for the binding affinity and agonist potency of R(+)-8-hydroxy-2-(di-n-propylamino)tetralin, and equal 5-HT1D receptor-mediated antagonist potency for methiothepin and the 5-HT2 receptor antagonists ritanserin and ketanserin. In conclusion, the pharmacology of the cloned 5-HT1D receptor subtype seems, unlike the 5-HT1B receptor subtype, conserved among various mammal species such as the human, guinea pig, and rat.

Synthesis, binding affinity and intrinsic activity of new anilide derivatives of serotonin at human 5-HT 1D receptors

The design and synthesis of a new series of anilide derivatives of serotonin is described. Binding affinity and intrinsic activity were evaluated at cloned human 5-HTIDα, 5-HTIDβ and 5-HTIA receptors. Modification of the terminal substituent on the aromatic moiety (R1) was investigated and optimal affinity, activity and selectivity for 5-HT1D versus 5-HTIA receptors were obtained for the sulfonamide derivatives 9 and 10. Functional activity was also assessed in the New Zealand white rabbit saphenous vein contraction model, in which most of the compounds behaved as full agonists. Further structural modifications are also described, eg, replacement of the oxygen for carbon atom at the 5-position of the tryptamine moiety or terminal N-dimethylation.

Pharmacological profile of LY301317, a potent and selective 5-HT1A agonist

LY301317 ((4r)-(−)-4-(dipropylamino)-6-(5-oxazolinyl)-1,3,4,5-tetrahydrobenz[c,d]indole) has high affinity for the 5-HT1A receptor and weak affinity for the 5-HT1D and histamine-H1 receptors. No significant affinity was found for the other amine receptors studied. In rats, LY301317 produced potent in vivo effects that are characteristic of compounds with agonist activity at the 5-HT1A receptor, such as an increase in serum corticosterone concentration, a reduction in 5-HIAA concentration in brain tissue, induction of flat body posture and lower lip retraction (components of a serotonin syndrome), and a decrease of core body temperature. In pigeons trained to discriminate 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) from saline, full generalization to LY301317 was observed. LY301317 increased punished responding in both the pigeon and rat conflict tests for anxiolytic activity. LY301317 reduced immobility in the rat forced swim model used to indicate potential antidepressant activity. In pigeons, LY301317 blocked emesis induced by a chemical (ditolyguanidine), by a 5-HT3 agonist (m-(chlorophenyl)-biguanide), and by an oncolytic agent (cisplatin), as well as vomiting induced by conditioning to environmental stimuli (a model of anticipatory nausea and vomiting). In addition, LY301317 blocked cisplatin- and ipecac-induced vomiting in the dog and motion-induced emesis in the cat. It was concluded that LY301317 is an orally active, potent, and selective agonist for the 5-HT1A receptor with potential clinical utility as an anxiolytic, an antidepressant, and a broad-spectrum antiemetic. Drug Dev. Res. 40:17–34, 1997. © 1997 Wiley-Liss, Inc.