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Leibold NK, van den Hove DLA, Weidner MT, Buchanan GF, Steinbusch HWM, Lesch KP, Schruers KRJ. Effect of serotonin transporter genotype on carbon dioxide-induced fear-related behavior in mice. J Psychopharmacol 2020; 34:1408-1417. [PMID: 33103571 PMCID: PMC7708670 DOI: 10.1177/0269881120959611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Inhaling 35% carbon dioxide induces an emotional and symptomatic state in humans closely resembling naturally occurring panic attacks, the core symptom of panic disorder. Previous research has suggested a role of the serotonin system in the individual sensitivity to carbon dioxide. In line with this, we previously showed that a variant in the SLC6A4 gene, encoding the serotonin transporter, moderates the fear response to carbon dioxide in humans. To study the etiological basis of carbon dioxide-reactivity and panic attacks in more detail, we recently established a translational mouse model. AIM The purpose of this study was to investigate whether decreased expression of the serotonin transporter affects the sensitivity to carbon dioxide. METHODS Based on our previous work, wildtype and serotonin transporter deficient (+/-, -/-) mice were monitored while being exposed to carbon dioxide-enriched air. In wildtype and serotonin transporter +/- mice, also cardio-respiration was assessed. RESULTS For most behavioral measures under air exposure, wildtype and serotonin transporter +/- mice did not differ, while serotonin transporter -/- mice showed more fear-related behavior. Carbon dioxide exposure evoked a marked increase in fear-related behaviors, independent of genotype, with the exception of time serotonin transporter -/- mice spent in the center zone of the modified open field test and freezing in the two-chamber test. On the physiological level, when inhaling carbon dioxide, the respiratory system was strongly activated and heart rate decreased independent of genotype. CONCLUSION Carbon dioxide is a robust fear-inducing stimulus. It evokes inhibitory behavioral responses such as decreased exploration and is associated with a clear respiratory profile independent of serotonin transporter genotype.
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Affiliation(s)
- Nicole K Leibold
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,Department of Neurology, Yale School of Medicine, New Haven, USA,Nicole K Leibold, Department of Psychiatry and Neuropsychology, Maastricht University, P.O. Box 616 (Vijverdal), 6200 MD Maastricht, The Netherlands.
| | - Daniel LA van den Hove
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, The Netherlands,Division of Molecular Psychiatry, Center of Mental Health, University of Wuerzburg, Wuerzburg, Germany
| | - Magdalena T Weidner
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, The Netherlands,Division of Molecular Psychiatry, Center of Mental Health, University of Wuerzburg, Wuerzburg, Germany,Department of Psychiatry and Psychotherapy, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Gordon F Buchanan
- Department of Neurology, Yale School of Medicine, New Haven, USA,Department of Neurology, University of Iowa, Iowa City, USA,University of Iowa Graduate College, Iowa City, USA
| | - Harry WM Steinbusch
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, The Netherlands,Department of Brain and Cognitive Sciences, Daegu Gyeongbuk Institute of Science and Technoglogy (DGIST), Daegu, South Korea
| | - Klaus-Peter Lesch
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, The Netherlands,Division of Molecular Psychiatry, Center of Mental Health, University of Wuerzburg, Wuerzburg, Germany,Laboratory of Psychiatric Neurobiology, I.M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Koen RJ Schruers
- Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands,School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, The Netherlands,Department of Psychology, University of Leuven, Leuven, Belgium
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Differential behavioral sensitivity to carbon dioxide (CO 2) inhalation in rats. Neuroscience 2017; 346:423-433. [PMID: 28087339 DOI: 10.1016/j.neuroscience.2017.01.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 12/14/2016] [Accepted: 01/03/2017] [Indexed: 01/21/2023]
Abstract
Inhalation of carbon dioxide (CO2) is frequently employed as a biological challenge to evoke intense fear and anxiety. In individuals with panic disorder, CO2 reliably evokes panic attacks. Sensitivity to CO2 is highly heterogeneous among individuals, and although a genetic component is implicated, underlying mechanisms are not clear. Preclinical models that can simulate differential responsivity to CO2 are therefore relevant. In the current study we investigated CO2-evoked behavioral responses in four different rat strains: Sprague-Dawley (SD), Wistar (W), Long Evans (LE) and Wistar-Kyoto, (WK) rats. We also assessed tryptophan hydroxylase 2 (TPH-2)-positive serotonergic neurons in anxiety/panic regulatory subdivisions of the dorsal raphe nucleus (DR), as well as dopamine β hydroxylase (DβH)-positive noradrenergic neurons in the locus coeruleus, implicated in central CO2-chemosensitivity. Behavioral responsivity to CO2 inhalation varied between strains. CO2-evoked immobility was significantly higher in LE and WK rats as compared with W and SD cohorts. Differences were also observed in CO2-evoked rearing and grooming behaviors. Exposure to CO2 did not produce conditioned behavioral responses upon re-exposure to CO2 context in any strain. Reduced TPH-2-positive cell counts were observed specifically in the panic-regulatory dorsal raphe ventrolateral (DRVL)-ventrolateral periaqueductal gray (VLPAG) subdivision in CO2-sensitive strains. Conversely, DβH-positive cell counts within the LC were significantly higher in CO2-sensitive strains. Collectively, our data provide evidence for strain dependent, differential CO2-sensitivity and potential differences in monoaminergic systems regulating panic and anxiety. Comparative studies between CO2-vulnerable and resistant strains may facilitate the mechanistic understanding of differential CO2-sensitivity in the development of panic and anxiety disorders.
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Abstract
During exercise by healthy mammals, alveolar ventilation and alveolar-capillary diffusion increase in proportion to the increase in metabolic rate to prevent PaCO2 from increasing and PaO2 from decreasing. There is no known mechanism capable of directly sensing the rate of gas exchange in the muscles or the lungs; thus, for over a century there has been intense interest in elucidating how respiratory neurons adjust their output to variables which can not be directly monitored. Several hypotheses have been tested and supportive data were obtained, but for each hypothesis, there are contradictory data or reasons to question the validity of each hypothesis. Herein, we report a critique of the major hypotheses which has led to the following conclusions. First, a single stimulus or combination of stimuli that convincingly and entirely explains the hyperpnea has not been identified. Second, the coupling of the hyperpnea to metabolic rate is not causal but is due to of these variables each resulting from a common factor which link the circulatory and ventilatory responses to exercise. Third, stimuli postulated to act at pulmonary or cardiac receptors or carotid and intracranial chemoreceptors are not primary mediators of the hyperpnea. Fourth, stimuli originating in exercising limbs and conveyed to the brain by spinal afferents contribute to the exercise hyperpnea. Fifth, the hyperventilation during heavy exercise is not primarily due to lactacidosis stimulation of carotid chemoreceptors. Finally, since volitional exercise requires activation of the CNS, neural feed-forward (central command) mediation of the exercise hyperpnea seems intuitive and is supported by data from several studies. However, there is no compelling evidence to accept this concept as an indisputable fact.
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Affiliation(s)
- Hubert V Forster
- Medical College of Wisconsin, Department of Physiology, Milwaukee, Wisconsin, USA.
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Annerbrink K, Olsson M, Hedner J, Eriksson E. Acute and chronic treatment with serotonin reuptake inhibitors exert opposite effects on respiration in rats: possible implications for panic disorder. J Psychopharmacol 2010; 24:1793-801. [PMID: 19825902 DOI: 10.1177/0269881109106908] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Prompted by the suggested importance of respiration for the pathophysiology of panic disorder, we studied the influence of serotonin reuptake inhibitors (SRIs) as well as other serotonin-modulating compounds on respiration in freely moving rats. The effect on respiration after acute administration of compounds enhancing synaptic levels of serotonin, that is, the serotonin reuptake inhibitors paroxetine and fluoxetine, the serotonin-releasing agents m-chlorophenylpiperazine and d-fenfluramine, and the selective 5-HT1A antagonist WAY-100635, were investigated. All serotonin-releasing substances decreased respiratory rate in unrestrained, awake animals, suggesting the influence of serotonin on respiratory rate under these conditions to be mainly inhibitory. In line with a previous study, rats administered fluoxetine for 23 days or more, on the other hand, displayed an enhanced respiratory rate. The results reinforce the assumption that the effect of subchronic administration of a serotonin reuptake inhibitor on certain serotonin-regulated parameters may be opposite to that obtained after acute administration. We suggest that our observations may be of relevance for the fact that acute administration of SRIs, d-fenfluramine, or m-chlorophenylpiperazine often is anxiogenic in panic disorder patients, and that weeks of administration of an SRI leads to a very effective prevention of panic.
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Affiliation(s)
- Kristina Annerbrink
- Department of Pharmacology, Institute of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
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Hodges MR, Tattersall GJ, Harris MB, McEvoy SD, Richerson DN, Deneris ES, Johnson RL, Chen ZF, Richerson GB. Defects in breathing and thermoregulation in mice with near-complete absence of central serotonin neurons. J Neurosci 2008; 28:2495-505. [PMID: 18322094 PMCID: PMC6671195 DOI: 10.1523/jneurosci.4729-07.2008] [Citation(s) in RCA: 258] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 01/21/2008] [Accepted: 01/21/2008] [Indexed: 01/28/2023] Open
Abstract
Serotonergic neurons project widely throughout the CNS and modulate many different brain functions. Particularly important, but controversial, are the contributions of serotonin (5-HT) neurons to respiratory and thermoregulatory control. To better define the roles of 5-HT neurons in breathing and thermoregulation, we took advantage of a unique conditional knock-out mouse in which Lmx1b is genetically deleted in Pet1-expressing cells (Lmx1b(f/f/p)), resulting in near-complete absence of central 5-HT neurons. Here, we show that the hypercapnic ventilatory response in adult Lmx1b(f/f/p) mice was decreased by 50% compared with wild-type mice, whereas baseline ventilation and the hypoxic ventilatory response were normal. In addition, Lmx1b(f/f/p) mice rapidly became hypothermic when exposed to an ambient temperature of 4 degrees C, decreasing core temperature to 30 degrees C within 120 min. This failure of thermoregulation was caused by impaired shivering and nonshivering thermogenesis, whereas thermosensory perception and heat conservation were normal. Finally, intracerebroventricular infusion of 5-HT stimulated baseline ventilation, and rescued the blunted hypercapnic ventilatory response. These data identify a previously unrecognized role of 5-HT neurons in the CO(2) chemoreflex, whereby they enhance the response of the rest of the respiratory network to CO(2). We conclude that the proper function of the 5-HT system is particularly important under conditions of environmental stress and contributes significantly to the hypercapnic ventilatory response and thermoregulatory cold defense.
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Affiliation(s)
- Matthew R Hodges
- Department of Neurology, Yale University, New Haven, Connecticut 06520, USA.
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Melchior LK, Ho HP, Olsson M, Annerbrink K, Hedner J, Eriksson E. Association between estrus cycle-related aggression and tidal volume variability in female Wistar rats. Psychoneuroendocrinology 2004; 29:1097-100. [PMID: 15219662 DOI: 10.1016/j.psyneuen.2003.10.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2003] [Revised: 10/13/2003] [Accepted: 10/28/2003] [Indexed: 10/26/2022]
Abstract
Premenstrual dysphoria is characterized by symptoms such as irritability and depressed mood, present during the luteal phase of the menstrual cycle, and disappearing shortly after the onset of menstruation. Subjects with premenstrual dysphoria have previously been reported to display enhanced respiratory variability, and to experience anxiety when exposed to panicogens, such as CO2. In the present study, the possible influence of the estrus cycle and estrus cycle-related aggression on respiratory variability was investigated in female rats of the Wistar strain. The rats were subdivided into two groups: those displaying estrus cycle-related aggression, as evaluated using the resident intruder paradigm, and those not showing aggression throughout the estrus cycle. This model has been developed to serve as an animal model of premenstrual irritability. The former group was found to display higher tidal volume variability in diestrus, as compared to the non-aggressive rats. There was no effect of estrus cycle phase on respiratory variability. These results are well in line with the clinical observation that women with premenstrual dysphoria display higher respiratory variability than controls, and the notion that respiratory variability is a parameter of interest in this context. In our opinion, they also strengthen the concept of this animal model as a model of premenstrual irritability.
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Affiliation(s)
- Lydia K Melchior
- Department of Pharmacology, Göteborg University, Göteborg, Sweden.
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