Abstract
Because of the important roles of both serotonin (5-HT) and the cerebellum in regulating anxiety, we asked whether 5-HT signaling within the cerebellum is involved in anxiety behavior. Physiological 5-HT levels were measured in vivo by expressing a fluorescent sensor for 5-HT in lobule VII of the cerebellum, while using fiber photometry to measure sensor fluorescence during anxiety behavior on the elevated zero maze. Serotonin increased in lobule VII when male mice were less anxious and decreased when mice were more anxious. To establish a causal role for this serotonergic input in anxiety behavior, we photostimulated or photoinhibited serotonergic terminals in lobule VII while mice were in an elevated zero maze. Photostimulating these terminals reduced anxiety behavior in mice, while photoinhibiting them enhanced anxiety behavior. Our findings add to evidence that cerebellar lobule VII is a topographical locus for anxiety behavior and establish that 5-HT input into this lobule is necessary and sufficient to bidirectionally influence anxiety behavior. These results represent progress toward understanding how the cerebellum regulates anxiety behavior and provide new evidence for a functional connection between the cerebellum and the serotonin system within the anxiety circuit.
Significance Statement This is the first analysis of the involvement of the neuromodulator, serotonin, in the cerebellum during anxiety behavior. Our results reveal that serotonin regulates anxiety behavior. This offers new insight into the role of serotonin in the cerebellum, as well as illuminating how the cerebellum interacts with the rest of the brain to produce anxiety. Our results are important for future use of serotonin-related pharmacological therapeutics, such as selective serotonin-reuptake inhibitors, in treating anxiety in humans.
Footnotes
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank Karen Chung for her invaluable technical support, Drs. Jinsook Kim and Arong Jung for their help with cerebellar slice imaging, and Drs. Jinxia Wan and Yulong Li (Peking University) for kindly providing us with their GRAB5HT2h sensor prior to its publication. The experimental work described in this paper represents part of Ph.D. thesis of P.W.C. at Nanyang Technological University. This work was supported by research grant MOE2017-T3-1-002 from the Singapore Ministry of Education and by the Temasek Life Sciences Laboratory.
↵*Current address: School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA.
