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Willadsen M, Uengoer M, Sługocka A, Schwarting RK, Homberg JR, Wöhr M. Fear Extinction and Predictive Trait-Like Inter-Individual Differences in Rats Lacking the Serotonin Transporter. Int J Mol Sci 2021; 22:ijms22137088. [PMID: 34209318 PMCID: PMC8268876 DOI: 10.3390/ijms22137088] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 06/24/2021] [Accepted: 06/28/2021] [Indexed: 11/28/2022] Open
Abstract
Anxiety disorders are associated with a failure to sufficiently extinguish fear memories. The serotonergic system (5-hydroxytryptamine, 5-HT) with the 5-HT transporter (5-HTT, SERT) is strongly implicated in the regulation of anxiety and fear. In the present study, we examined the effects of SERT deficiency on fear extinction in a differential fear conditioning paradigm in male and female rats. Fear-related behavior displayed during acquisition, extinction, and recovery, was measured through quantification of immobility and alarm 22-kHz ultrasonic vocalizations (USV). Trait-like inter-individual differences in novelty-seeking, anxiety-related behavior, habituation learning, cognitive performance, and pain sensitivity were examined for their predictive value in forecasting fear extinction. Our results show that SERT deficiency strongly affected the emission of 22-kHz USV during differential fear conditioning. During acquisition, extinction, and recovery, SERT deficiency consistently led to a reduction in 22-kHz USV emission. While SERT deficiency did not affect immobility during acquisition, genotype differences started to emerge during extinction, and during recovery rats lacking SERT showed higher levels of immobility than wildtype littermate controls. Recovery was reflected in increased levels of immobility but not 22-kHz USV emission. Prominent sex differences were evident. Among several measures for trait-like inter-individual differences, anxiety-related behavior had the best predictive quality.
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Affiliation(s)
- Maria Willadsen
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; (M.W.); (R.K.W.S.)
| | - Metin Uengoer
- Associative Learning, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany;
| | - Anna Sługocka
- Department for Experimental Medicine, Faculty of Medical Sciences in Katowice, Medical University of Silesia, Medyków 4, 40-752 Katowice, Poland;
- Department of Physiology, Faculty of Medical Sciences in Katowice, Medical University of Silesia, Medyków 18, 40-752 Katowice, Poland
| | - Rainer K.W. Schwarting
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; (M.W.); (R.K.W.S.)
- Center for Mind, Brain and Behavior, Philipps-University of Marburg, Hans-Meerwein-Str. 6, D-35032 Marburg, Germany
| | - Judith R. Homberg
- Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, Kapittelweg 29, 6525 EN Nijmegen, The Netherlands;
| | - Markus Wöhr
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; (M.W.); (R.K.W.S.)
- Center for Mind, Brain and Behavior, Philipps-University of Marburg, Hans-Meerwein-Str. 6, D-35032 Marburg, Germany
- KU Leuven, Faculty of Psychology and Educational Sciences, Research Unit Brain and Cognition, Laboratory of Biological Psychology, Social and Affective Neuroscience Research Group, B-3000 Leuven, Belgium
- KU Leuven, Leuven Brain Institute, B-3000 Leuven, Belgium
- Correspondence: ; Tel.: +32–16–19–45–57
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Willadsen M, Uengoer M, Schwarting RKW, Homberg JR, Wöhr M. Reduced emission of alarm 22-kHz ultrasonic vocalizations during fear conditioning in rats lacking the serotonin transporter. Prog Neuropsychopharmacol Biol Psychiatry 2021; 108:110072. [PMID: 32800867 DOI: 10.1016/j.pnpbp.2020.110072] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/02/2020] [Accepted: 08/09/2020] [Indexed: 12/19/2022]
Abstract
Rats display a rich social behavioral repertoire. An important component of this repertoire is the emission of whistle-like calls in the ultrasonic range, so-called ultrasonic vocalizations (USV). Long low-frequency 22-kHz USV occur in aversive situations, including aggressive interactions, predator exposure, and electric shocks during fear conditioning. They are believed to reflect a negative affective state akin to anxiety and fear. A prominent theory suggests that 22-kHz USV function as alarm calls to warn conspecifics. Serotonin (5-hydroxytryptamine, 5-HT) is strongly implicated in the regulation of affective states, particularly anxiety and fear. A key component of the system is the 5-HT transporter (5-HTT, also known as SERT), regulating 5-HT availability in the synaptic cleft. In the present experiment, we studied the effects of SERT deficiency on overt fear-related behavior and alarm 22-kHz USV during fear conditioning in male and female rats. While overt fear-related behavior was not affected by SERT deficiency and sex, the emission of alarm 22-kHz USV was clearly reduced in homozygous SERT-/- but not heterozygous SERT+/- mutants, as compared to their wildtype SERT+/+ littermate controls. Genotype effects were particularly prominent in females. Females in general emitted fewer alarm 22-kHz USV than males. This supports the view that 22-kHz USV are, at least partly, independently regulated from anxiety or fear and as socially mediated alarm calls do not simply express a negative affective state. Reduced 22-kHz USV emission in rats lacking SERT might be due to social deficits in the use of 22-kHz USV as a socio-affective signal to warn conspecifics about threats.
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Affiliation(s)
- Maria Willadsen
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany
| | - Metin Uengoer
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; Center for Mind, Brain and Behavior, Philipps-University of Marburg, Hans-Meerwein-Str. 6, D-35032 Marburg, Germany
| | - Rainer K W Schwarting
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; Center for Mind, Brain and Behavior, Philipps-University of Marburg, Hans-Meerwein-Str. 6, D-35032 Marburg, Germany
| | - Judith R Homberg
- Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands
| | - Markus Wöhr
- Behavioral Neuroscience, Experimental and Biological Psychology, Faculty of Psychology, Philipps-University of Marburg, Gutenberg-Str. 18, D-35032 Marburg, Germany; Center for Mind, Brain and Behavior, Philipps-University of Marburg, Hans-Meerwein-Str. 6, D-35032 Marburg, Germany; Laboratory for Behavioral Neuroscience, Department of Biology, Faculty of Science, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
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