A pharmacological analysis of the 5-HT receptor mediating inhibition of 5-HT release in the guinea-pig frontal cortex

doi:10.1016/0014-2999(88)90476-1

European Journal of Pharmacology

Volume 157, Issue 1, 15 November 1988, Pages 101-107

https://doi.org/10.1016/0014-2999(88)90476-1 Get rights and content

Abstract

The release of [³H]5-HT from guinea-pig frontal cortex slices was elicited by continuous exposure to Krebs solution containing elevated K⁺ ions (30 mM) and 10 μM fluvoxamine. K⁺-stimulated release was inhibited by 5-carboxamidotryptamine (pIC₂₅ 8.1), 5-HT (7.4), RU 24969 (6.5) and GR 43175 (6.4). 8-OH-DPAT was without effect on K⁺-evoked release of [³H]5-HT at concentrations up to 1 μM. The inhibitory effects of 5-HT were antagonised by metitepine (pA₂ 8.2), metergoline (7.0), methysergide (6.5), cyanopindolol (6.5), yohimbine (6.5) and mesulergine (6.2) but not by the 5-HT₃ antagonist, ICS 205–930 (1 μM). The results are discussed in the context of the known pharmacology of 5-HT receptor subtypes. It is concluded that the 5-HT receptor modulating 5-HT release in the guinea-pig frontal cortex does not correspond to any of the 5-HT₁-subtype recognition sites of the 5-HT₂ or 5-HT₃ receptors.

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Characterisation of the selective 5-HT<inf>1B</inf> receptor antagonist SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]- 1-[2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl ]methanone hydrochloride): In vivo neurochemical and behavioural evidence of anxiolytic/antidepressant activity
2006, Neuropharmacology
Citation Excerpt :
Those that reside on somatodendritic regions of the cell bodies within the dorsal and median raphe regions are predominantly of the 5-HT1A receptor subtype (Blier and De Montigny, 1987), whereas those located on nerve terminals are thought to be of the 5-HT1B receptor subtype (Roberts et al., 1997a,b; Davidson and Stamford, 1996; Middlemiss et al., 1999). Thus, 5-HT1B receptors are the principal terminal autoreceptors in rat, guinea pig and human (Middlemiss et al., 1988; Hoyer and Middlemiss, 1989; Middlemiss and Hutson, 1990). However, despite the high homology of the 5-HT1B receptor across species the rodent receptor, which possesses a single amino acid difference (in the seventh transmembrane domain), exhibits altered pharmacology to the human receptor that is most marked for molecules such as pindolol and propranolol (Adham et al., 1994).
The 5-HT_1B receptor has attracted significant interest as a potential target for the development of therapeutics for the treatment of affective disorders such as anxiety and depression. Here we present the in vivo characterisation of a novel, selective and orally bioavailable 5-HT_1B receptor antagonist, SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride). SB-616234-A reversed the 5-HT_1/7 receptor agonist, SKF-99101H-induced hypothermia in guinea pigs in a dose related manner with an ED₅₀ of 2.4 mg/kg p.o. Using in vivo microdialysis in freely moving guinea pigs, SB-616234-A (3–30 mg/kg p.o.) caused a dose-related increase in extracellular 5-HT in the dentate gyrus. Evaluation of antidepressant- and anxiolytic-like effects of this 5-HT_1B receptor antagonist was performed in a variety of models and species. SB-616234-A produced a decrease in immobility time in the mouse forced swim test; an effect suggestive of antidepressant activity. Furthermore, SB-616234-A produced dose-related anxiolytic effects in both rat and guinea pig maternal separation-induced vocalisation models with an ED₅₀ of 1.0 and 3.3 mg/kg i.p., respectively (vs fluoxetine treatment ED₅₀ = 2.2 mg/kg i.p. in both species). Also a significant reduction in posturing behaviours was observed in the human threat test in marmosets; an effect indicative of anxiolytic activity. In summary, SB-616234-A is a novel, potent and orally bioavailable 5-HT_1B receptor antagonist which exhibits a neurochemical and behavioural profile that is consistent with both anxiolytic- and antidepressant-like activity in a variety of species. Taken together these data suggest that SB-616234-A may have therapeutic efficacy in the treatment of affective disorders.
Effects of sustained administration of the serotonin and norepinephrine reuptake inhibitor venlafaxine: I. In vivo electrophysiological studies in the rat
2000, Neuropharmacology
The effect of a 21-day treatment with the dual 5-HT and NE reuptake blocker venlafaxine (delivered s.c. by osmotic minipumps) was assessed on the time required for a 50% recovery (RT₅₀) of the firing activity of dorsal hippocampus CA₃ pyramidal neurons from the suppression induced by microiontophoretic applications of 5-HT and NE. The RT₅₀ values for 5-HT were increased by both 10 and 40 mg/kg/day regimens of venlafaxine, whereas those for NE were increased only by the 40 mg/kg/day regimen, indicative of a greater potency of venlafaxine in blocking 5-HT reuptake. The sensitivity of the postsynaptic 5-HT_1A and α₂-adrenergic receptors was altered by neither regimen of venlafaxine. Using a paradigm by which the 5-HT_1A antagonist WAY 100635 can induce a dishinbition of firing activity of CA₃ pyramidal neurons, it was demonstrated that the high, but not the low, dose of venlafaxine led to an enhanced tonic activation of postsynaptic 5-HT_1A receptors in the dorsal hippocampus. The duration of the suppressant effect of the firing activity of CA₃ hippocampus pyramidal neurons produced by the electrical stimulation of the ascending 5-HT pathway was significantly reduced when the frequency of the stimulation was enhanced from 1 Hz to 5 Hz in control rats and in rats treated with 10 mg/kg/day, but not with 40 mg/kg/day of venlafaxine. Hence, venlafaxine induced a desensitization of the terminal 5-HT_1B autoreceptor only at the high dose. A 2-day treatment with 10 mg/kg/day of venlafaxine induced a suppression of the firing activity of 5-HT neurons of the dorsal raphe. The firing activity of these neurons was back to control level in rats that had been treated for 21 days with the same dose of venlafaxine. The suppressant effect of the i.v. administration of the 5-HT autoreceptor agonist LSD on the firing activity of dorsal raphe 5-HT neurons was reduced in rats that had been treated for 21 days with 10 mg/kg/day of venlafaxine. A 2-day treatment with 40 mg/kg/day of venlafaxine, unlike the 10 mg/kg/day regimen, induced a marked suppression of the firing activity of locus coeruleus NE neurons. However, in contrast to 5-HT neurons, NE neurons did not recover their firing activity after a 21-day treatment. Taken together, the results from this study indicate that the low dose of venlafaxine blocked selectively the reuptake of 5-HT, whereas the high dose blocked the reuptake of both 5-HT and NE. Moreover, an enhancement of serotonergic neurotransmission by venlafaxine was only achieved under conditions whereby the desensitization of the terminal 5-HT_1B autoreceptor is appended to that of the somatodendritic 5-HT_1A receptor.
5-HT-moduline controls serotonergic activity: Implication in neuroimmune reciprocal regulation mechanisms
2000, Progress in Neurobiology
Citation Excerpt :
On the other hand, electrical activity is controlled by the autoreceptor 5-HT1A whose activity decreases the frequency of discharge of the neuron (Aghajanian, 1978; Sprouse and Aghajanian, 1987). Alternatively, the amount of 5-HT released by the terminals is controlled by serotonergic autoreceptors (5-HT1B) (Middlemiss, 1984; Engel et al., 1986; Göthert et al., 1987; Chaput and De Montigny, 1988; Middlemiss et al., 1988; Galzin et al., 1992) (Fig. 3). Thus, if we consider the activity of a single neuron originating from the raphe area and projecting to different brain areas via its arborizations, this neuron may release 5-HT from the multiple varicosities located in all innervated areas.
The serotonergic neurotransmission is known as a neuromodulatory system exerting its activity in the central nervous system (CNS) as well as at the periphery. The anatomical and morphological organization of the system based on a marked centralization of the cellular bodies and the large, almost ubiquitary, presence of axonal projections of the neurons is in good agreement with this modulatory role. Furthermore, a very high number of varicosities located along the axonal branches are capable of releasing serotonin (5-HT).
The amine stimulates a number of different specific receptor types which allows 5-HT to exert different activities on its various cellular targets. Among these receptors, the 5-HT_1B subtypes play a particular role as they are autoreceptors located on 5-HT neurons terminals and heteroreceptors located on non-serotonergic terminals where they control the release of the neurotransmitter.
5-HT-moduline, an endogenous tetrapeptide, regulates the efficacy of these 5-HT_1B receptors, hence, is able to control the serotonergic activity in a synchronous manner for the various varicosities from a single neuron and thus may favour the differential effect of that neuron on distinct cerebral functions. Accordingly, the peptide allows the `fine tuning' of the cerebral activity by the serotonergic system to elaborate the response given by the brain to a particular stimulus, that is, stress situations.
At the periphery, the serotonergic system also appears to possess a regulatory activity via 5-HT_1B receptors. In particular, the receptors located on immunocompetent cells control their activity and are themselves regulated by 5-HT-moduline likely originating from adrenal medulla and released after acute stress.
The serotonergic system appears to play a major role in the reciprocal signalling existing between the neuronal and the immune system. The participation of 5-HT-moduline is likely in physiological functions as well as in pathological disorders affecting central and peripheral activities.
Two amino acids within the helix of Gα(i1) mediate coupling with 5- hydroxytryptamine(1B) receptors
1999, Journal of Biological Chemistry
We previously reported that residues 299–318 in Gα_i1 participate in the selective interaction between Gα_i1 and the 5-hydroxytryptamine_1B(5-HT_1B) receptor (Bae, H., Anderson, K., Flood, L. A., Skiba, N. P., Hamm, H. E., and Graber, S. G. (1997)J. Biol. Chem. 272, 32071–32077). The present study more precisely defines which residues within this domain are critical for 5-HT_1B receptor-mediated G protein activation. A series of Gα_i1/Gα_t chimeras and point mutations were reconstituted with Gβγ and Sf9 cell membranes containing the 5-HT_1B receptor. Functional coupling to 5-HT_1B receptors was assessed by 1) [³⁵S]GTPγS binding and 2) agonist affinity shift assays. Replacement of the α4 helix of Gα_i1 (residues 299–308) with the corresponding sequence from Gα_tproduced a chimera (Chi22) that only weakly coupled to the 5-HT_1B receptor. In contrast, substitution of residues within the α4-β6 loop region of Gα_i1 (residues 309–318) with the corresponding sequence in Gα_t either permitted full 5-HT_1B receptor coupling to the chimera (Chi24) or only minimally reduced coupling to the chimeric protein (Chi25). Two mutations within the α4 helix of Gα_i1 (Q304K and E308L) reduced agonist-stimulated [³⁵S]GTPγS binding, and the effects of these mutations were additive. The opposite substitutions within Chi22 (K300Q and L304E) restored 5-HT_1B receptor coupling, and again the effects of the two mutations were additive. Mutations of other residues within the α4 helix of Gα_i1 had minimal to no effect on 5-HT_1B coupling behavior. These data provide evidence that α4 helix residues in Gα_i participate in directing specific receptor interactions and suggest that Gln³⁰⁴ and Glu³⁰⁸ of Gα_i1 act in concert to mediate the ability of the 5-HT_1B receptor to couple specifically to inhibitory G proteins.
Magnitude of 5-HT(1B) and 5-HT(1A) receptor activation in guinea-pig and rat brain: Evidence from sumatriptan dimer-mediated [<sup>35</sup>S]GTPγS binding responses
1999, Molecular Brain Research
The present study reports on G-protein activation by recombinant 5-HT receptors and by native 5-HT_1A and 5-HT_1B receptors in guinea-pig and rat brain using agonist-stimulated [ $^{35} S$ ]GTPγS binding responses mediated by a new 5-HT ligand, a dimer of sumatriptan. Dimerization of sumatriptan increased the binding affinity for h 5-HT_1B (pK_i: 9.22 vs. 7.79 for sumatriptan), h 5-HT_1D (9.07 vs. 8.08) and also h 5-HT_1A receptors (7.80 vs. 6.40), while the binding affinity for h 5-ht_1E (6.67 vs. 6.19) and h 5-ht_1F (7.37 vs. 7.78) receptors was not affected. Sumatriptan dimer (10 μM) stimulated [ $^{35} S$ ]GTPγS binding mainly in the superficial gray layer of the superior colliculi, hippocampus and substantia nigra of guinea-pig and rat coronal brain sections. This fits with the labelling by the 5-HT_1B/1D receptor antagonist [ $^{3} H$ ] GR 125743. The observed [ $^{35} S$ ]GTPγS binding responses in the substantia nigra are likely to be mediated by stimulation of the 5-HT_1B receptor subtype, since they were antagonized by the 5-HT_1B inverse agonist SB 224289 (10 μM), and not by the 5-HT_2A/1D antagonist ketanserin (10 μM). Quantitative assessment of the [ $^{35} S$ ]GTPγS binding responses in the substantia nigra of rat showed highly efficacious responses for both sumatriptan dimer and its monomer. In contrast, less efficacious agonist responses (51±10% and 35±13%, respectively) were measured in the guinea-pig substantia nigra. This may suggest that the G-protein coupling efficacy of 5-HT_1B receptors is different between the substantia nigra of both species. In addition, the sumatriptan dimer also activated guinea-pig and rat hippocampal 5-HT_1A receptors with high efficacy in contrast to sumatriptan. Therefore, dimerization of sumatriptan can be considered as a new approach to transform a partial 5-HT_1A agonist into a more efficacious agonist. In conclusion, the sumatriptan dimer stimulates G-protein activation via 5-HT_1B receptors besides 5-HT_1A receptors in guinea-pig and rat brain. The magnitude of the 5-HT_1B receptor responses is superior for sumatriptan and its dimer in rat compared to guinea-pig substantia nigra.
Mapping of 5-HT-moduline binding sites in guinea-pig brain by film and digital autoradiography
1998, Brain Research
5-HT-moduline is a cerebral tetrapeptide [Leu-Ser-Ala-Leu] that was recently isolated from bovine brain tissue and shown to interact specifically with 5-HT_1B receptors, particularly in rodents. The pharmacological properties of 5-HT_1B receptors in rodents are different from those in other species. In order to better understand the role of this peptide in non-rodent species, we determined the distribution of 5-HT-moduline binding sites in guinea-pig brain using both the film autoradiography and digital autoradiography with a newly developed high resolution β-imaging techniques. We found that 5-HT-moduline binding sites were expressed in various brain regions. Quantitative analysis showed that densities of binding sites were similar to those observed previously in rat brain. Regions with the highest labelling included cortex, septum, hippocampus and some regions of basal ganglia. Our results extend previous data and show that 5-HT-moduline interacts with the two forms of 5-HT_1B receptors that are distinct pharmacologically. By this interaction, 5-HT-moduline may play an important role in regulating the functional activity of 5-HT_1B receptors, thereby contributes to the pathophysiology of serotonergic transmission.

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A pharmacological analysis of the 5-HT receptor mediating inhibition of 5-HT release in the guinea-pig frontal cortex

Abstract

Neuropharmacology

European J. Pharmacol.

Naunyn-Schmiedeb. Arch. Pharmacol.

Neuropharmacology

Trends Pharmacol. Sci.

European J. Pharmacol.

Neuropharmacology

European J. Pharmacol.

Brain Res.

European J. Pharmacol.

Trends Pharmacol. Sci.

European J. Pharmacol.

Ann. Rep. Med. Chem.

Brain Res.

Evidence for two different types of receptor for 5-hydroxytryptamine in dog isolated vasculature

Br. J. Pharmacol.

An inhibitory prejunctional 5-HT1-like receptor in the isolated perfussed rat kidney

Naunyn-Schmiedeb. Arch. Pharmacol.

5-Carboxamidotryptamine receptors mediating vasodilation and tachycardia in anaesthetised cats

Br. J. Pharmacol.

An inhibitory prejunctional 5-HT₁-like receptor in the isolated perfussed rat kidney