Genetic knockout and pharmacological blockade studies of the 5-HT7 receptor suggest therapeutic potential in depression
Introduction
The 5-HT7 receptor is one of 14 distinct receptor subtypes thought to mediate the diverse range of CNS effects of the neurotransmitter, serotonin (reviewed in Barnes and Sharp, 2000). The 5-HT7 receptor is the most recent addition to the 5-HT receptor family having been cloned from a variety of species, including man, rat, mouse and guinea-pig (Plassat et al., 1993, Ruat et al., 1993, Shen et al., 1993, Tsou et al., 1994, Gelernter et al., 1995). The 5-HT7 receptor exhibits only low (40%) homology with other Gs coupled 5-HT receptors and is encoded by a single gene on human chromosome 10 (Krobert et al., 2001). Although it is found in four different isoforms (5-HT7a, 5-HT7b, 5-HT7c, and 5-HT7d), only two (5-HT7a and 5-HT7b) are present in both rat and human, and there appears to be no pharmacological differences between them (Gustafson et al., 1996). In situ hybridisation studies revealed CNS expression in amygdala, cortex, hippocampus, thalamus, septum, hypothalamus and suprachiasmatic nucleus (Gustafson et al., 1996). 5-HT7 receptors are defined pharmacologically by their high affinity for 5-CT, 5-HT, 5-MeOT and methiothepin, moderate affinity for 8-OH-DPAT and ritanserin and low affinity for pindolol, sumatriptan and buspirone (Sleight et al., 1995).
This CNS distribution, coupled with the receptor's relatively high affinity for several psychoactive drugs, including hallucinogenics (e.g. LSD), antipsychotics (e.g. clozapine) and antidepressants (e.g. amitriptyline), have implicated the 5-HT7 receptor as a potential therapeutic target in psychosis and depression. In support of this, chronic antidepressant treatment down regulates 5-HT7 receptor expression in rat hypothalamus (Mullins et al., 1999). Recent evidence also suggests that 5-HT7 receptors may be involved in the regulation of circadian rhythms (Lovenberg et al., 1993; Ehlen et al., 2001). Thus in rat SCN slices, 8-OH-DPAT-induced phase advances in spontaneous cell firing were attenuated by ritanserin, but not pindolol, suggestive of a 5-HT7 receptor pharmacology (Lovenberg et al., 1993, Thomas et al., 1998). However, until now little direct evidence of receptor function in vivo has been available to support any of these proposals.
In this study, we have examined the in vivo role of the 5-HT7 receptor in mice in which the receptor gene has been deleted by testing the mice in a range of behavioural assays sensitive to potential psychotic states. In addition, where a behavioural phenotype was observed, we also determined the effect of treating the wild type mice with the selective 5-HT7 receptor antagonist, SB-258719 (Forbes et al., 1998, Lovell et al., 2000). The data from both approaches provide the first, direct, preclinical validation of the 5-HT7 receptor as a therapeutic target for depression and add further support to its potential role in circadian/sleep disorders.
Section snippets
Compound synthesis
SB-258719 was synthesised and used for behavioural studies. (R)-[35S]-1-[2-(1-benzenesulfonyl-pyrrolidin-2-yl)-ethyl]-4-methyl-piperidine (termed compound A) was made following a reported generic synthetic route for such compounds (Collinson et al., 2002), and confirmed to be a high affinity 5-HT7 receptor antagonist suitable for use in autoradiography experiments. Desipramine HCl (DMI; 20 mg/kg; i.p.; Sigma–Aldrich, Poole, U.K.) was dissolved in 0.9% saline and administered in a dosing volume
Generation of 5-HT7 receptor knockout mice
5-HT7 receptor knockout mice were generated using a targeting vector to knockout exon 1 of the 5-HT7 gene (Fig. 1a). This vector was transfected into 129SvEv embryonic stem cells and six positive ES clones showing the targeted mutation were identified (Fig. 1b) and subsequently injected into C57Bl/6 blastocysts. A single independent line (line 3) was bred to generate homozygotic animals and all behavioural assessments have been carried out in male mice from the F3 or F4 generation of this line.
Characterisation of 5-HT7 receptor knockout mice and the selective 5-HT7 receptor antagonist, SB-258719
5-HT7 receptor knockout mice were generated by knocking out exon 1 of the 5-HT7 gene A single independent line (line 3) was bred to generate homozygotic animals and all behavioural assessments have been carried out in male mice from the F3 or F4 generation of this line. PCR analysis of tail DNA confirmed the successful generation of homozygous knockout mice at the genome level (Fig. 1c) while RT-PCR (data not shown) and autoradiographic studies (Fig. 1d) confirmed that functional 5-HT7 receptor
Acknowledgments
We would like to thank Dennis Dean and colleagues in the Labeled Compound Synthesis Group (LCS) at MRL Basic Research, Rahway for assistance in the generation of (R)-[35S]-1-[2-(1-benzenesulfonyl-pyrrolidin-2-yl)-ethyl]-4-methyl-piperidine.
References (46)
- et al.
A proposed test battery and constellations of specific behavioral paradigms to investigate the behavioral phenotypes of transgenic and knockout mice
Horm. Behav.
(1997) - et al.
Aging and SB-269970-A, a selective 5-HT7 receptor antagonist, attenuate circadian phase advances induced by microinjections of serotonergic drugs in the hamster dorsal raphe nucleus
Brain Res.
(2004) - et al.
Assignment of the 5HT7 receptor gene (HTR7) to Chromosome 10q and exclusion of genetic linkage with Tourette syndrome
Genomics
(1995) - et al.
The hypothermic effect of 5-CT in mice is mediated by the 5-HT7 receptor
Neuropharmacology
(2003) - et al.
Influence of circadian phase and test illumination on pre-clinical models of anxiety
Physiol. Behav.
(2001) Sleep research in depressive illness: clinical implications – a tasting menu
Biol. Psychiatry
(1995)- et al.
A novel adenylyl cyclase-activating serotonin receptor (5-HT7) implicated in the regulation of mammalian circadian rhythms
Neuron
(1993) - et al.
Effects of antidepressants on 5-HT7 receptor regulation in the rat hypothalamus
Neuropsychopharmacology
(1999) - et al.
Localization of 5-HT(7) receptors in rat brain by immunocytochemistry, in situ hybridization, and agonist stimulated cFos expression
J. Chem. Neuroanat.
(2001) - et al.
Effects of the 5-HT(7) receptor antagonist SB-258741 in animal models for schizophrenia
Pharmacol. Biochem. Behav.
(2002)
A 5-HT(1B) receptor agonist inhibits light-induced suppression of pineal melatonin production
Brain Res.
Molecular cloning and expression of a 5-hydroxytryptamine7 serotonin receptor subtype
J. Biol. Chem.
WAY-100635, a specific 5-HT1A antagonist, can increase the responsiveness of the mammalian circadian pacemaker to photic stimuli
Neurosci. Lett.
Effects of 5-HT1A receptor agonists on the circadian rhythm of wheel-running activity in hamsters
Eur. J. Pharmacol.
Response of the mouse circadian system to serotonin 1A/2/7 agonists in vivo: surprisingly little
J. Biol. Rhythms
A review of central 5-HT receptors and their function
Neuropharmacology
Subcellular distribution of 5-HT1B and 5-HT7 receptors in the mouse suprachiasmatic nucleus
J. Comp. Neurol.
Enhanced learning and memory and altered GABAergic synaptic transmission in mice lacking the alpha 5 subunit of the GABAA receptor
J. Neurosci.
Endogenous regulation of serotonin release in the hamster suprachiasmatic nucleus
J. Neurosci.
In vivo resetting of the hamster circadian clock by 5-HT7 receptors in the suprachiasmatic nucleus
J. Neurosci.
(R)-3,N-dimethyl-N-[1-methyl-3-(4-methyl-piperidin-1-yl) propyl]benzenesulfonamide: the first selective 5-HT7 receptor antagonist
J. Med. Chem.
Pharmacological studies of prepulse inhibition models of sensorimotor gating deficits in schizophrenia: a decade in review
Psychopharmacology (Berl.)
A receptor autoradiographic and in situ hybridization analysis of the distribution of the 5-ht7 receptor in rat brain
Br. J. Pharmacol.
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MG and LJB contributed equally to this work.