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Serotonin 2A receptors are a stress response system: implications for post-traumatic stress disorder. Behav Pharmacol 2020; 30:151-162. [PMID: 30632995 DOI: 10.1097/fbp.0000000000000459] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Serotonin, one of the first neurotransmitters to be identified, is an evolutionarily old molecule that is highly conserved across the animal kingdom, and widely used throughout the brain. Despite this, ascribing a specific set of functions to brain serotonin and its receptors has been difficult and controversial. The 2A subtype of serotonin receptors (5-HT2A receptor) is the major excitatory serotonin receptor in the brain and has been linked to the effects of drugs that produce profound sensory and cognitive changes. Numerous studies have shown that this receptor is upregulated by a broad variety of stressors, and have related 5-HT2A receptor function to associative learning. This review proposes that stress, particularly stress related to danger and existential threats, increases the expression and function of 5-HT2A receptors. It is argued that this is a neurobiological adaptation to promote learning and avoidance of danger in the future. Upregulation of 5-HT2A receptors during stressful events forms associations that tune the brain to environmental cues that signal danger. It is speculated that life-threatening situations may activate this system and contribute to the symptoms associated with post-traumatic stress disorder (PTSD). 3,4-Methylenedioxymethamphetamine, which activates 5-HT2A receptors, has been successful in the treatment of PTSD and has recently achieved status as a breakthrough therapy. An argument is presented that 3,4-methylenedioxymethamphetamine may paradoxically act through these same 5-HT2A receptors to ameliorate the symptoms of PTSD. The central thematic contention is that a key role of serotonin may be to function as a stress detection and response system.
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Fantoni ER, Dal Ben D, Falzoni S, Di Virgilio F, Lovestone S, Gee A. Design, synthesis and evaluation in an LPS rodent model of neuroinflammation of a novel 18F-labelled PET tracer targeting P2X7. EJNMMI Res 2017; 7:31. [PMID: 28374288 PMCID: PMC5378566 DOI: 10.1186/s13550-017-0275-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 03/08/2017] [Indexed: 01/08/2023] Open
Abstract
Background The P2X7 receptor has been shown to play a fundamental role in the initiation and sustenance of the inflammatory cascade. The development of a novel fluorine-18 PET tracer superior and with a longer half-life to those currently available is a promising step towards harnessing the therapeutic and diagnostic potential offered by this target. Inspired by the known antagonist A-804598, the present study outlines the design via molecular docking, synthesis and biological evaluation of the novel P2X7 tracer [18F]EFB. The tracer was radiolabelled via a three-step procedure, in vitro binding assessed in P2X7-transfected HEK293 and in B16 cells by calcium influx assays and an initial preclinical evaluation was performed in a lipopolysaccharide (LPS)-injected rat model of neuroinflammation. Results The novel tracer [18F]EFB was synthesised in 210 min in 3–5% decay-corrected radiochemical yield (DC RCY), >99% radiochemical purity (RCP) and >300 GBq/μmol and fully characterised. Functional assays showed that the compound binds with nM Ki to human, rat and mouse P2X7 receptors. In vivo, [18F]EFB displayed a desirable distribution profile, and while it showed low blood–brain barrier penetration, brain uptake was quantifiable and displayed significantly higher mean longitudinal uptake in inflamed versus control rat CNS regions. Conclusions [18F]EFB demonstrates strong in vitro affinity to human and rodent P2X7 and limited yet quantifiable BBB penetration. Considering the initial promising in vivo data in an LPS rat model with elevated P2X7 expression, this work constitutes an important step in the development of a radiotracer useful for the diagnosis and monitoring of clinical disorders with associated neuroinflammatory processes. Electronic supplementary material The online version of this article (doi:10.1186/s13550-017-0275-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Enrico Raffaele Fantoni
- Department of Imaging Sciences and Biomedical Engineering, King's College London, St Thomas' Hospital, 4th floor Lambeth Wing, SE1 7EH, London, UK
| | - Diego Dal Ben
- School of Pharmacy, Medicinal Chemistry Unit, University of Camerino, via S. Agostino 1, 62032, Camerino, MC, Italy
| | - Simonetta Falzoni
- Prof Francesco Di Virgilio and Dr Simonetta Falzoni, Dipartimento di Morfologia, Chirurgia e Medicina Sperimentale, Sezione di Patologia, Oncologia e Biologia Sperimentale, University of Ferrara, Ferrara, Italy
| | - Francesco Di Virgilio
- Prof Francesco Di Virgilio and Dr Simonetta Falzoni, Dipartimento di Morfologia, Chirurgia e Medicina Sperimentale, Sezione di Patologia, Oncologia e Biologia Sperimentale, University of Ferrara, Ferrara, Italy
| | - Simon Lovestone
- Department of Psychiatry, Warneford Hospital, University of Oxford, Warneford Lane, Oxford, OX3 7JX, UK
| | - Antony Gee
- Department of Imaging Sciences and Biomedical Engineering, King's College London, St Thomas' Hospital, 4th floor Lambeth Wing, SE1 7EH, London, UK.
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Couch Y, Martin CJ, Howarth C, Raley J, Khrapitchev AA, Stratford M, Sharp T, Sibson NR, Anthony DC. Systemic inflammation alters central 5-HT function as determined by pharmacological MRI. Neuroimage 2013; 75:177-186. [PMID: 23473937 PMCID: PMC4004801 DOI: 10.1016/j.neuroimage.2013.02.046] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2012] [Revised: 02/18/2013] [Accepted: 02/20/2013] [Indexed: 02/02/2023] Open
Abstract
Considerable evidence indicates a link between systemic inflammation and central 5-HT function. This study used pharmacological magnetic resonance imaging (phMRI) to study the effects of systemic inflammatory events on central 5-HT function. Changes in blood oxygenation level dependent (BOLD) contrast were detected in selected brain regions of anaesthetised rats in response to intravenous administration of the 5-HT-releasing agent, fenfluramine (10 mg/kg). Further groups of rats were pre-treated with the bacterial lipopolysaccharide (LPS; 0.5 mg/kg), to induce systemic inflammation, or the selective 5-HT2A receptor antagonist MDL100907 prior to fenfluramine. The resultant phMRI data were investigated further through measurements of cortical 5-HT release (microdialysis), and vascular responsivity, as well as a more thorough investigation of the role of the 5-HT2A receptor in sickness behaviour. Fenfluramine evoked a positive BOLD response in the motor cortex (+15.9±2%) and a negative BOLD response in the dorsal raphe nucleus (-9.9±4.2%) and nucleus accumbens (-7.7±5.3%). In all regions, BOLD responses to fenfluramine were significantly attenuated by pre-treatment with LPS (p<0.0001), but neurovascular coupling remained intact, and fenfluramine-evoked 5-HT release was not affected. However, increased expression of the 5-HT2A receptor mRNA and decreased 5-HT2A-dependent behaviour (wet-dog shakes) was a feature of the LPS treatment and may underpin the altered phMRI signal. MDL100907 (0.5 mg/kg), 5-HT2A antagonist, significantly reduced the BOLD responses to fenfluramine in all three regions (p<0.0001) in a similar manner to LPS. Together these results suggest that systemic inflammation decreases brain 5-HT activity as assessed by phMRI. However, these effects do not appear to be mediated by changes in 5-HT release, but are associated with changes in 5-HT2A-receptor-mediated downstream signalling pathways.
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Affiliation(s)
- Yvonne Couch
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK; CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Chris J Martin
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Clare Howarth
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Josie Raley
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Alexandre A Khrapitchev
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Michael Stratford
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Trevor Sharp
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK
| | - Nicola R Sibson
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK.
| | - Daniel C Anthony
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK
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Baisley SK, Fallace KL, Rajbhandari AK, Bakshi VP. Mutual independence of 5-HT(2) and α1 noradrenergic receptors in mediating deficits in sensorimotor gating. Psychopharmacology (Berl) 2012; 220:465-79. [PMID: 21947334 PMCID: PMC4090044 DOI: 10.1007/s00213-011-2490-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Accepted: 09/05/2011] [Indexed: 12/20/2022]
Abstract
RATIONALE Prepulse inhibition (PPI), a preattentional information-filtering mechanism, is disrupted by serotonin (5-HT) or norepinephrine (NE) agonists to model deficits seen in schizophrenia, but whether this effect occurs through interactions between these systems is not known. OBJECTIVES These studies investigated whether PPI/activity changes induced by agonists of one system were dependent on neurotransmission within the other. METHODS Male Sprague-Dawley rats received the 5-HT(2) receptor agonist DOI (1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane) (0, 0.3 mg/kg), with or without antagonists for α1 (prazosin:0, 0.3, or 1 mg/kg) or β (timolol:0, 3, or 10 mg/kg) receptors or their combination (0 or 0.3 mg/kg prazosin + 3 mg/kg timolol), or the 5-HT(2) antagonist ritanserin (0, 2 mg/kg). Separately, the α1-adrenergic receptor agonist cirazoline (0, 0.68 mg/kg) was given with and without ritanserin (0, 0.5, or 2 mg/kg) or the NE antagonists (0 or 0.3 mg/kg prazosin + 3 mg/kg timolol). Finally, combinations of subthreshold doses of DOI (0, 0.01, 0.025 mg/kg) and cirazoline (0, 0.1, 0.25 mg/kg) were tested for their ability to disrupt PPI, and concomitant administration of all three antagonists (0 vs. 0.3 mg/kg prazosin + 3 mg/kg timolol + 2 mg/kg ritanserin) was assessed for its ability to modify PPI. Locomotion was assessed in an additional set of experiments. RESULTS Doses/combinations of prazosin and timolol that reversed cirazoline-induced effects did not alter DOI-induced effects, and ritanserin did not affect cirazoline at doses that blocked DOI-mediated effects. Concomitant antagonism of α1 + β + 5-HT(2) receptors did not modify PPI, nor did combinations of subthreshold doses of cirazoline and DOI. CONCLUSIONS 5-HT(2) receptors and α1 and β NE receptors may act through independent mechanisms to modulate sensorimotor gating and locomotor activity.
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Affiliation(s)
- Sarah K. Baisley
- Department of Psychiatry, UW-Madison, Madison, WI, USA,Neuroscience Training Program, UW-Madison, Madison, WI, USA
| | | | - Abha K. Rajbhandari
- Department of Psychiatry, UW-Madison, Madison, WI, USA,Neuroscience Training Program, UW-Madison, Madison, WI, USA
| | - Vaishali P. Bakshi
- Department of Psychiatry, UW-Madison, Madison, WI, USA,Neuroscience Training Program, UW-Madison, Madison, WI, USA,Department of Psychiatry, University of Wisconsin School of Medicine and Public Health, 6001 Research Park Blvd, Madison, WI 53719, USA
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Effects of LPS and serotonergic drugs on hygienic behavior in mice. Pharmacol Biochem Behav 2011; 98:392-7. [DOI: 10.1016/j.pbb.2011.02.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Revised: 02/03/2011] [Accepted: 02/05/2011] [Indexed: 11/18/2022]
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Weiland TJ, Voudouris NJ, Kent S. CCK2 receptor nullification attenuates lipopolysaccharide-induced sickness behavior. Am J Physiol Regul Integr Comp Physiol 2007; 292:R112-23. [PMID: 16857893 DOI: 10.1152/ajpregu.00156.2006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Systemic infection produces a highly regulated set of responses such as fever, anorexia, adipsia, inactivity, and cachexia, collectively referred to as sickness behavior. Although the expression of sickness behavior requires immune-brain communication, the mechanisms by which peripheral cytokines signal the brain are unclear. Several mechanisms have been proposed for neuroimmune communication, including the interaction of cytokines with peripheral nerves. A critical role has been ascribed to the vagus nerve in mediating sickness behavior after intraperitoneally delivered immune activation, and converging evidence suggests that this communication may involve neurochemical intermediaries afferent and/or efferent to this nerve. Mice lacking functional CCK2/gastrin receptors (CCK2KO) and wild-type (WT) controls were administered LPS (50, 500, or 2,500 μg/kg; serotype 0111:B4; ip). Results indicate a role for CCK2 receptor activation in the initiation and maintenance of LPS-induced sickness behavior. Compared with WT controls, CCK2KO mice were significantly less affected by LPS on measures of body temperature, activity, body weight, and food intake, with the magnitude of effects increasing with increasing LPS dose. Although activation of CCK2 receptors at the level of the vagus nerve cannot be excluded, a possible role for these receptors in nonvagal routes of immune-brain communication is suggested.
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Affiliation(s)
- Tracey J Weiland
- School of Psychological Science, La Trobe University, Bundoora, Victoria, Australia.
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