Journal
BEHAVIOURAL BRAIN RESEARCH
Volume 379, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.bbr.2019.112394
Keywords
Htr2c; 5-HT1C; Motor activity; Freezing behavior
Categories
Funding
- Ministry of Education, Culture, Sports, Science and Technology of Japan [18K07545, 16H05371]
- Grants-in-Aid for Scientific Research [16H05371, 18K07545] Funding Source: KAKEN
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Pharmacological studies have suggested that the serotonin 5-HT2C receptor is involved in locomotor activity, anxiety, and fear memory. However, the results of locomotor activity and anxiety in 5-HT2C receptor knockout mice have been mixed, and the effects of 5-HT2C receptor knockout on contextual fear memory have not yet been addressed. In the present study, we reconcile these inconsistent results by analyzing behavioral data in detail and by examining the effects of 5-HT2C receptor knockout on contextual fear memory. We demonstrated that the higher locomotor activity in 5-HT2C receptor knockout mice was observed only in the late phase of the test, indicating that the analyses in the previous study using the total locomotor activity would lead to variable results. Moreover, by analyzing mouse behavior in detail, we found that 5-HT2C receptor knockout mice displayed a hesitating attitude by staying in the central area as well as risk assessment behavior in the elevated plusmaze test. However, the time spent in the open arms was longer in 5-HT2C receptor knockout mice than in wildtype littermates when a zero-maze test lacking the central area was used. In the contextual fear conditioning test, 5-HT2C receptor knockout mice showed rapid within-session extinction of fear, but not between-session extinction, compared with wild-type littermates. However, this remains inconclusive because the facilitation of extinction might be confounded with higher locomotor activity in 5-HT2C receptor knockout mice. Taken together, the present results provide reasonable explanations about previous inconsistent findings and partially filled the gaps between pharmacological and genetic findings.
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