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Tzeng NS, Chung JY, Lin CC, Cheng PY, Liu YP. Effects of Subchronic Buspirone Treatment on Depressive Profile in Socially Isolated Rats: Implication of Early Life Experience on 5-HT1A Receptor-Related Depression. Pharmaceuticals (Basel) 2024; 17:717. [PMID: 38931384 PMCID: PMC11206366 DOI: 10.3390/ph17060717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 05/15/2024] [Accepted: 05/18/2024] [Indexed: 06/28/2024] Open
Abstract
The heterogeneity of etiology may serve as a crucial factor in the challenges of treatment, including the low response rate and the delay in establishing therapeutic effect. In the present study, we examined whether social experience since early life is one of the etiologies, with the involvement of the 5-HT1A receptors, and explored the potentially therapeutic action of the subchronic administration of buspirone, a partial 5-HT1A agonist. Rats were isolation reared (IR) since their weaning, and the depressive profile indexed by the forced-swim test (FST) was examined in adulthood. Nonspecific locomotor activity was used for the IR validation. Buspirone administration (1 mg/kg/day) was introduced for 14 days (week 9-11). The immobility score of the FST was examined before and after the buspirone administration. Tissue levels of serotonin (5-HT) and its metabolite 5-HIAA were measured in the hippocampus, the amygdala, and the prefrontal cortex. Efflux levels of 5-HT, dopamine (DA), and norepinephrine (NE) were detected in the hippocampus by brain dialysis. Finally, the full 5-HT1A agonist 8-OH-DPAT (0.5 mg/kg) was acutely administered in both behavioral testing and the dialysis experiment. Our results showed (i) increased immobility time in the FST for the IR rats as compared to the social controls, which could not be reversed by the buspirone administration; (ii) IR-induced FST immobility in rats receiving buspirone was corrected by the 8-OH-DPAT; and (iii) IR-induced reduction in hippocampal 5-HT levels can be reversed by the buspirone administration. Our data indicated the 5-HT1A receptor-linked early life social experience as one of the mechanisms of later life depressive mood.
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Affiliation(s)
- Nian-Sheng Tzeng
- Department of Psychiatry, Tri-Service General Hospital, Taipei 114, Taiwan;
- Student Counseling Center, National Defense Medical Center, Taipei 114, Taiwan
| | - Jing-Yi Chung
- Laboratory of Cognitive Neuroscience, Department of Physiology and Biophysics, National Defense Medical Center, Taipei 114, Taiwan; (J.-Y.C.); (C.-C.L.); (P.-Y.C.)
| | - Chen-Cheng Lin
- Laboratory of Cognitive Neuroscience, Department of Physiology and Biophysics, National Defense Medical Center, Taipei 114, Taiwan; (J.-Y.C.); (C.-C.L.); (P.-Y.C.)
| | - Pao-Yun Cheng
- Laboratory of Cognitive Neuroscience, Department of Physiology and Biophysics, National Defense Medical Center, Taipei 114, Taiwan; (J.-Y.C.); (C.-C.L.); (P.-Y.C.)
| | - Yia-Ping Liu
- Laboratory of Cognitive Neuroscience, Department of Physiology and Biophysics, National Defense Medical Center, Taipei 114, Taiwan; (J.-Y.C.); (C.-C.L.); (P.-Y.C.)
- Department of Psychiatry, Cheng Hsin General Hospital, Taipei 112, Taiwan
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Yaman B, Bal R. Pindolol potentiates the antidepressant effect of venlafaxine by inhibiting 5-HT1A receptor in DRN neurons of mice. Int J Neurosci 2020; 132:23-30. [DOI: 10.1080/00207454.2020.1797723] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Burak Yaman
- Medicine Faculty, Department of Physiology, Gaziantep University, Gaziantep, Turkey
| | - Ramazan Bal
- Medicine Faculty, Department of Physiology, Gaziantep University, Gaziantep, Turkey
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3
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Fitzgerald PJ, Watson BO. In vivo electrophysiological recordings of the effects of antidepressant drugs. Exp Brain Res 2019; 237:1593-1614. [PMID: 31079238 PMCID: PMC6584243 DOI: 10.1007/s00221-019-05556-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 05/06/2019] [Indexed: 12/11/2022]
Abstract
Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.
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Affiliation(s)
- Paul J Fitzgerald
- Department of Psychiatry, University of Michigan, Ann Arbor, MI, 48109-5720, USA.
| | - Brendon O Watson
- Department of Psychiatry, University of Michigan, Ann Arbor, MI, 48109-5720, USA.
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Zaretsky DV, Zaretskaia MV, Dimicco JA, Durant PJ, Ross CT, Rusyniak DE. Independent of 5-HT1A receptors, neurons in the paraventricular hypothalamus mediate ACTH responses from MDMA. Neurosci Lett 2013; 555:42-6. [PMID: 23933156 DOI: 10.1016/j.neulet.2013.07.053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 07/19/2013] [Accepted: 07/30/2013] [Indexed: 12/12/2022]
Abstract
Acute and chronic complications from the substituted amphetamine 3,4-methylenedioxymethamphetamine (MDMA) are linked to activation of the hypothalamic-pituitary-adrenal (HPA) axis. How MDMA activates the HPA axis is not known. HPA responses to stress are known to be mediated through the paraventricular (PVH) hypothalamus and to involve serotonin-1a (5-HT1A) receptors. We sought to determine if the PVH and 5-HT1A receptors were also involved in mediating HPA responses to MDMA. Rats were pretreated with either saline or a 5-HT1A antagonist, WAY-100635 (WAY), followed by a systemic dose of MDMA (7.5mg/kg i.v.). Animals pretreated with WAY had significantly lower plasma ACTH concentrations after MDMA. To determine if neurons in the PVH were involved, and if their involvement was mediated by 5-HT1A receptors, rats implanted with guide cannulas targeting the PVH were microinjected with the GABAA receptor agonist muscimol, aCSF, or WAY followed by MDMA. Compared to aCSF, microinjections of muscimol significantly attenuated the MDMA-induced rise in plasma ACTH (126 vs. 588pg/ml, P=<0.01). WAY had no effect. Our data demonstrates that neurons in the PVH, independent of 5-HT1A receptors, mediate ACTH responses to MDMA.
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Affiliation(s)
- Dmitry V Zaretsky
- Department of Emergency Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, United States
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Saijo T, Maeda J, Okauchi T, Maeda JI, Morio Y, Kuwahara Y, Suzuki M, Goto N, Fukumura T, Suhara T, Higuchi M. Presynaptic selectivity of a ligand for serotonin 1A receptors revealed by in vivo PET assays of rat brain. PLoS One 2012; 7:e42589. [PMID: 22880045 PMCID: PMC3413639 DOI: 10.1371/journal.pone.0042589] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 07/10/2012] [Indexed: 11/19/2022] Open
Abstract
A novel investigational antidepressant with high affinity for the serotonin transporter and the serotonin 1A (5-HT(1A)) receptor, called Wf-516 (structural formula: (2S)-1-[4-(3,4-dichlorophenyl)piperidin-1-yl]-3-[2-(5-methyl-1,3,4-oxadiazol-2-yl)benzo[b]furan-4-yloxy]propan-2-ol monohydrochloride), has been found to exert a rapid therapeutic effect, although the mechanistic basis for this potential advantage remains undetermined. We comparatively investigated the pharmacokinetics and pharmacodynamics of Wf-516 and pindolol by positron emission tomographic (PET) and autoradiographic assays of rat brains in order to elucidate their molecular interactions with presynaptic and postsynaptic 5-HT(1A) receptors. In contrast to the full receptor occupancy by pindolol in PET measurements, the binding of Wf-516 to 5-HT(1A) receptors displayed limited capacity, with relatively high receptor occupancy being achieved in regions predominantly containing presynaptic receptors. This selectivity was further proven by PET scans of neurotoxicant-treated rats deficient in presynaptic 5-HT(1A) receptors. In addition, [(35)S]guanosine 5'-O-[γ-thio]triphosphate autoradiography indicated a partial agonistic ability of Wf-516 for 5-HT(1A) receptors. This finding has lent support to reports that diverse partial agonists for 5-HT(1A) receptors exert high sensitivity for presynaptic components. Thus, the present PET data suggest a relatively high capacity of presynaptic binding sites for partial agonists. Since our in vitro and ex vivo autoradiographies failed to illustrate these distinct features of Wf-516, in vivo PET imaging is considered to be, thus far, the sole method capable of pharmacokinetically demonstrating the unique actions of Wf-516 and similar new-generation antidepressants.
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Affiliation(s)
- Takeaki Saijo
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
- Department of Molecular Neuroimaging, Tohoku University School of Medicine, Sendai, Japan
- DMPK Research Laboratory, Mitsubishi Tanabe Pharma Corporation, Kisarazu, Japan
| | - Jun Maeda
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
| | - Takashi Okauchi
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
| | - Jun-ichi Maeda
- Research Quality Assurance Department, Mitsubishi Tanabe Pharma Corporation, Yokohama, Japan
| | - Yasunori Morio
- Development Project Management Department, Mitsubishi Tanabe Pharma Corporation, Tokyo, Japan
| | - Yasuhiro Kuwahara
- Advanced Medical Research Laboratory, Mitsubishi Tanabe Pharma Corporation, Yokohama, Japan
| | - Masayuki Suzuki
- DMPK Research Laboratory, Mitsubishi Tanabe Pharma Corporation, Kisarazu, Japan
| | - Nobuharu Goto
- Early Stage Clinical Research Center, Mitsubishi Tanabe Pharma Corporation, Tokyo, Japan
| | - Toshimitsu Fukumura
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
| | - Tetsuya Suhara
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
- Department of Molecular Neuroimaging, Tohoku University School of Medicine, Sendai, Japan
| | - Makoto Higuchi
- Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
- Department of Molecular Neuroimaging, Tohoku University School of Medicine, Sendai, Japan
- * E-mail:
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SK channel blocker apamin attenuates the effect of SSRI fluoxetine upon cell firing in dorsal raphe nucleus: A concomitant electrophysiological and electrochemical in vivo study reveals implications for modulating extracellular 5-HT. Brain Res 2010; 1334:1-11. [DOI: 10.1016/j.brainres.2010.03.081] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Revised: 03/22/2010] [Accepted: 03/23/2010] [Indexed: 11/23/2022]
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Guilloux JP, David DJP, Guiard BP, Chenu F, Repérant C, Toth M, Bourin M, Gardier AM. Blockade of 5-HT1A receptors by (+/-)-pindolol potentiates cortical 5-HT outflow, but not antidepressant-like activity of paroxetine: microdialysis and behavioral approaches in 5-HT1A receptor knockout mice. Neuropsychopharmacology 2006; 31:2162-72. [PMID: 16452992 DOI: 10.1038/sj.npp.1301019] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Selective serotonin reuptake inhibitors like paroxetine (Prx) often requires 4-6 weeks to achieve clinical benefits in depressed patients. Pindolol shortens this delay and it has been suggested that this effect is mediated by somatodendritic 5-hydroxytryptamine (5-HT) 1A autoreceptors. However clinical data on the beneficial effects of pindolol are conflicting. To study the effects of (+/-)-pindolol-paroxetine administration, we used genetical and pharmacological approaches in 5-HT1A knockout mice (5-HT1A-/-). Two assays, in vivo intracerebral microdialysis in awake mice and the forced swimming test (FST), were used to assess the antidepressant-like effects of this drug combination. Basal levels of extracellular serotonin, 5-HT ([5-HT]ext) in the frontal cortex (FCX) and the dorsal raphe nucleus (DRN) did not differ between the two strains of mice, suggesting a lack of tonic control of 5-HT1A autoreceptors on nerve terminal 5-HT release. Prx (1 and 4 mg/kg) dose-dependently increased cortical [5-HT]ext in both genotypes, but the effects were greater in mutants. The selective 5-HT1A receptor antagonist, WAY-100635 (0.5 mg/kg), or (+/-)-pindolol (5 and 10 mg/kg) potentiated the effects of Prx (4 mg/kg) on cortical [5-HT]ext in 5-HT1A+/+, but not in 5-HT1A-/- mice. Similar responses were obtained following local intra-raphe perfusion by reverse microdialysis of either WAY-100635 or (+/-)-pindolol (100 microM each). In the FST, Prx administration dose-dependently decreased the immobility time in both strains of mice, but the response was much greater in 5HT1A-/- mice. In contrast, (+/-)-pindolol blocked Prx-induced decreases in the immobility time while WAY-100635 had no effect in both genotypes. These findings using 5-HT1A-/- mice confirm that (+/-)-pindolol behaves as an antagonist of 5-HT1A autoreceptor in mice, but its blockade of paroxetine-induced antidepressant-like effects in the FST may be due to its binding to other neurotransmitter receptors.
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Affiliation(s)
- Jean-Philippe Guilloux
- Laboratoire de Neuropharmacologie EA 3544, Faculté de Pharmacie, Université Paris-Sud, Châtenay-Malabry Cedex, France
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8
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Bosker FJ, Westerink BHC, Cremers TIFH, Gerrits M, van der Hart MGC, Kuipers SD, van der Pompe G, ter Horst GJ, den Boer JA, Korf J. Future antidepressants: what is in the pipeline and what is missing? CNS Drugs 2004; 18:705-32. [PMID: 15330686 DOI: 10.2165/00023210-200418110-00002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Monoamine reuptake inhibitors still reign in the treatment of major depression, but possibly not for long. While medicinal chemists have been able to reduce the side effects of these drugs, their delayed onset of action and considerable non-response rate remain problematic. Of late, serious questions have been raised regarding the efficacy of monoamine reuptake inhibitors. The present review presents an inventory of what is (and until recently was) in the antidepressant pipeline of pharmaceutical companies. Novel antidepressant compounds can be categorised into four groups depending on their target(s): (i) monoamine receptors; (ii) non-monoamine receptors; (iii) neuropeptide receptors; and (iv) hormone receptors. Other possible targets include components of post-receptor intracellular processes and elements of the immune system; to date, however, compounds specifically aimed at these targets have not been the subject of clinical trials. Development of several compounds targeted at monoamine receptors has recently been discontinued. At least five neurokinin-1 (NK(1)) receptor antagonists were until recently in phase II of clinical testing. However, the apparent interest in the NK(1) receptor should not be interpreted as representing a departure from the monoamine hypothesis since neurokinins also modulate monoaminergic systems. In the authors' view, development of future antidepressants will continue to rely on the serendipity-based monoamine hypothesis. However, an alternative approach, based on the hypothesis that chronic stress precipitates depressive symptoms, might be more productive. Unfortunately, clinical results using drugs targeted at components of the HPA axis have not been very encouraging to date. In the short run, the authors believe that augmentation strategies offer the best hope for improving the efficacy of antidepressant treatment. Several approaches to improve the efficacy of SSRIs are conceivable, such as concurrent blockade of monoamine autoreceptors and the addition of antipsychotics, neuromodulators or hormones (HPA axis and gender related). In the long-term, however, construction of a scientifically verified conceptual framework will be needed before more effective antidepressants can be developed. It can be argued that it is not depression itself that should be treated, but rather that its duration should be reduced by pharmacological means. Animal models that take this concept into consideration and identify mechanisms for acceleration of recovery from the effects of stress need to be developed.
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Affiliation(s)
- Fokko J Bosker
- Department of Psychiatry, University and University Hospital of Groningen, Hanzeplein 1, PO Box 30 001, Groningen, 9700 RB, The Netherlands.
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9
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Rabiner EA, Bhagwagar Z, Gunn RN, Cowen PJ, Grasby PM. Preferential 5-HT1A autoreceptor occupancy by pindolol is attenuated in depressed patients: effect of treatment or an endophenotype of depression? Neuropsychopharmacology 2004; 29:1688-98. [PMID: 15127080 DOI: 10.1038/sj.npp.1300472] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Using positron emission tomography and the selective 5-HT1A receptor radioligand [11C]WAY100635, we previously demonstrated a preferential occupancy of 5-HT1A autoreceptors, compared to postsynaptic receptors by pindolol in healthy volunteers. We have speculated that preferential occupancy may be clinically important for the purported actions of pindolol in accelerating the antidepressant effects of selective serotonin re-uptake inhibitors (SSRIs). In this study, we have examined the preferential occupancy by pindolol of 5-HT1A autoreceptors, following three different pindolol regimes (10 mg single dose, 2.5 mg t.i.d., and 5 mg t.i.d., in 15 depressed patients on SSRIs. In addition, seven healthy volunteers were examined following a single 10 mg dose of pindolol. We found a preferential occupancy of 22.6+/-7.7% following a single dose of 10 mg of pindolol, in the healthy volunteers, which was attenuated in depressed patients on the same dose of pindolol to 2.9+/-10.8% (Student's t=3.94, df=12, p=0.002). In addition, we found a significant negative correlation between the degree of preferential occupancy and the severity of depression as assessed by the Hamilton depression rating score (HAM-D), Spearman's rho=-0.728, N=14, p=0.003, in the depressed sample. A possible mechanism underlying preferential occupancy and the attenuation of this phenomenon in depressed patients on SSRIs may include changes in the proportion of high affinity 5-HT1A sites in the autoreceptor region of the midbrain raphe. Speculatively, the degree of preferential occupancy may serve as a surrogate marker for depression, or the pharmacological effects of antidepressants.
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Affiliation(s)
- Eugenii A Rabiner
- PET Psychiatry, Translational Medicine and Technologies, GlaxoSmithKline, Cambridge, UK.
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Abstract
Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.
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Affiliation(s)
- Mark J Millan
- Psychopharmacology Department, Centre de Rescherches de Croissy, Institut de Recherches (IDR) Servier, 125 Chemin de Ronde, 78290 Croissy-sur-Seine, Paris, France.
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11
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Farvolden P, Kennedy SH, Lam RW. Recent developments in the psychobiology and pharmacotherapy of depression: optimising existing treatments and novel approaches for the future. Expert Opin Investig Drugs 2003; 12:65-86. [PMID: 12517255 DOI: 10.1517/13543784.12.1.65] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Effective antidepressants include monoamine oxidase inhibitors and tricyclic antidepressants, selective serotonin re-uptake inhibitors and novel agents, including serotonin and noradrenaline re-uptake inhibitors. Although effective, current treatments most often produce partial symptomatic improvement (response) rather than symptom resolution and optimal functioning (remission). While current pharmacotherapies target monoaminergic systems, different symptoms of major depressive disorder (MDD) may have distinct neurobiological underpinnings and other neurobiological systems are likely involved in the pathogenesis of MDD. In this article a review of current pharmacotherapeutic options for MDD, current understanding of the neurobiology and pathogenesis of MDD and a review of new and promising directions in pharmacological research will be provided. It is generally accepted that no single neurotransmitter or system is responsible for the dysregulation found in MDD. While agents that affect monoaminergic systems will likely continue to be first-line treatments for MDD for the foreseeable future, a number of new and novel agents, including corticotropin-releasing factor antagonists, substance P antagonists and antiglucocorticoids show considerable promise for refining treatment options. In order to better understand the neurobiology and treatment response of MDD, it is probable that more sophisticated theory-driven typologies of MDD will have to be developed.
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Affiliation(s)
- P Farvolden
- Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada.
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12
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Johnson DA, Gartside SE, Ingram CD. 5-HT1A receptor-mediated autoinhibition does not function at physiological firing rates: evidence from in vitro electrophysiological studies in the rat dorsal raphe nucleus. Neuropharmacology 2002; 43:959-65. [PMID: 12423665 DOI: 10.1016/s0028-3908(02)00116-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
5-HT(1A)-mediated autoinhibition of neurones in the dorsal raphe nucleus (DRN) is considered to be the principal inhibitory regulator of 5-HT neuronal activity. The activation of this receptor by endogenous 5-HT was investigated using electrophysiological recordings from the rat DRN in vitro. At a concentration which blocked the inhibitory effect of exogenous 5-HT, the 5-HT(1A) antagonist WAY 100635 did not alter basal firing rate or modulate the excitatory response to the alpha(1)-agonist phenylephrine. Blockade of 5-HT reuptake by a concentration of fluoxetine, which enhanced the inhibitory effect of exogenous 5-HT, lowered phenylephrine-induced basal firing presumably due to potentiation of the effect of endogenous 5-HT. However, this effect was not firing rate dependent and neither the proportional increase nor the time-course of the response to a higher concentration of phenylephrine were altered in the presence of fluoxetine. These data suggest that the inhibitory 5-HT(1A) receptor on raphe neurones is neither tonically activated nor plays any role in modulating the response to excitatory transmitters. Thus, at physiological firing rates this receptor does not appear to function as an autoreceptor of serotonergic neurones of the DRN.
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Affiliation(s)
- D A Johnson
- Psychobiology Research Group, University of Newcastle upon Tyne, School of Neurosciences and Psychiatry, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
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13
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Papp M, Nalepa I, Antkiewicz-Michaluk L, Sánchez C. Behavioural and biochemical studies of citalopram and WAY 100635 in rat chronic mild stress model. Pharmacol Biochem Behav 2002; 72:465-74. [PMID: 11900821 DOI: 10.1016/s0091-3057(01)00778-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Reversal of chronic mild stress (CMS)-induced decrease of sucrose consumption has been studied in rats after 2, 7, 14, and 35 days treatment with imipramine, citalopram (both 10 mg/kg per day, i.p.), WAY 100635 (0.2 mg/kg sc, b.i.d.), and citalopram plus WAY 100635. Bmax, Kd, and functional status [cyclic AMP (cAMP) generation] of beta1-adrenoceptors were assessed in cortical tissue at the same time points. Citalopram reversed CMS-induced reduction of sucrose intake at an earlier time point than imipramine. WAY 100635 was not effective and did not potentiate the effect of citalopram. CMS produced increase of Bmax. Imipramine decreased Bmax in controls (Days 2, 7, 14, and 35) and normalised Bmax in stressed animals (Day 35). Citalopram, WAY 100635, and the combination increased Bmax in stressed animals and controls (Days 14 and 35). Inconsistent changes of Kd values and of cAMP responses to noradrenaline (NA) stimulation were observed. Thus stress- and drug-induced effects on beta1-adrenoceptors do not appear to be a common biochemical marker of antidepressant-like activity in the CMS model.
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Affiliation(s)
- Mariusz Papp
- Institute of Pharmacology, Polish Academy of Sciences, 31-343 Cracow, Poland
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Szabo ST, Blier P. Functional and pharmacological characterization of the modulatory role of serotonin on the firing activity of locus coeruleus norepinephrine neurons. Brain Res 2001; 922:9-20. [PMID: 11730697 DOI: 10.1016/s0006-8993(01)03121-3] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Previous studies, using in vivo extracellular unitary recordings in anaesthetized rats, have shown that the selective 5-HT(1A) receptor antagonist WAY 100,635 suppressed the firing rate of locus coeruleus (LC) norepinephrine (NE) neurons and that this effect was abolished by lesioning 5-HT neurons. In the present experiments, the selective 5-HT(2A) receptor antagonist MDL 100,907, while having no effect on the spontaneous firing activity of LC neurons in controls, was able to restore NE neuronal discharges following the injection of WAY 100,635. The 5-HT(1A) receptor agonist 8-OH-DPAT enhanced the firing activity of NE neurons and this action was entirely dependent on intact 5-HT neurons, unlike the inhibitory effect of the 5-HT(2) receptor agonist DOI. Taken together, these data indicate that 5-HT(2A) but not 5-HT(1A) receptors controlling LC firing activity are postsynaptic to 5-HT neurons. Prolonged, but not subacute, administration of selective 5-HT reuptake inhibitors (SSRIs) produces a decrease in the spontaneous firing activity of LC NE neurons. MDL 100,907 partially reversed this suppressed firing activity of LC neurons in paroxetine-treated rats. Although the alpha(2)-adrenoceptor antagonist idazoxan also enhanced the firing activity of NE neurons in paroxetine-treated rats, this increase was similar to that obtained in controls. In conclusion, prolonged SSRI treatment enhances a tonic inhibitory influence by 5-HT on LC neurons through postsynaptic 5-HT(2A) receptors that are not located on NE neurons. A speculative neuronal circuitry accounting for these phenomena on LC NE activity is proposed.
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Affiliation(s)
- S T Szabo
- Neurobiological Psychiatry Unit, McGill University, Montréal, Quebec, Canada H3A 1A1
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Abstract
Since 1994, the beta-adrenoceptor and 5-HT(1A/1B) receptor ligand pindolol has been used to accelerate or enhance the clinical effects of antidepressant drugs, such as the selective 5-HT reuptake inhibitors (SSRIs), that act primarily on 5-HT-containing neurones. Pindolol was initially thought to act by preventing the inhibition of 5-HT release, elicited by SSRIs and other 5-HT-acting drugs, as a result of its ability to antagonize the action of 5-HT at midbrain raphe 5-HT(1A) autoreceptors that control the activity of ascending 5-HT-mediated pathways. However, the partial agonist properties of pindolol at 5-HT(1A) receptors and beta-adrenoceptors suggest that other explanations for its action are also possible. In this article, recent controversial data on the mechanism of action of pindolol, which are crucial for the development of more rapid and efficient antidepressant therapies, will be discussed.
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Affiliation(s)
- F Artigas
- Dept of Neurochemistry, Institut d'Investigacions Biomèdiques de Barcelona (CSIC-IDIBAPS) Rosselló 161, 08036 Barcelona, Spain.
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Kinney GG, Taber MT, Gribkoff VK. The augmentation hypothesis for improvement of antidepressant therapy: is pindolol a suitable candidate for testing the ability of 5HT1A receptor antagonists to enhance SSRI efficacy and onset latency? Mol Neurobiol 2000; 21:137-52. [PMID: 11379796 DOI: 10.1385/mn:21:3:137] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The development of selective serotonin reuptake inhibitors (SSRIs) provided a major advancement in the treatment of depression. However, these drugs suffer from a variety of drawbacks, most notably a delay in the onset of efficacy. One hypothesis suggests that this delay in efficacy is due to a paradoxical decrease in serotonergic (5-HT) neuronal impulse flow and release, following activation of inhibitory presynaptic 5-HT1A autoreceptors, following acute administration of SSRIs. According to the hypothesis, efficacy is seen only when this impulse flow is restored following desensitization of 5-HT1A autoreceptors and coincident increases in postsynaptic 5-HT levels are achieved. Clinical proof of this principal has been suggested in studies that found a significant augmenting effect when the beta-adrenergic/5-HT1A receptor antagonist, pindolol, was coadministered with SSRI treatment. In this article, we review preclinical electrophysiological and microdialysis studies that have examined this desensitization hypothesis. We further discuss clinical studies that utilized pindolol as a test of this hypothesis in depressed patients and examine preclinical studies that challenge the notion that the beneficial effect of pindolol is due to functional antagonism of the 5-HT1A autoreceptors.
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Affiliation(s)
- G G Kinney
- Bristol-Myers Squibb Pharmaceutical Research Institute, Neuroscience and Genitourinary Drug Discovery, Wallingford, CT 06492, USA.
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