title: Melatonin facilitates extinction, but not acquisition or expression, of conditional cued fear in rats.
abstract: BACKGROUND
  Previous studies have shown that melatonin is involved in the processes that contribute to learning and memory. At present study, we tested the effects of exogenous melatonin (2.5 mg/kg) on the acquisition, expression and extinction of cued fear in rats.
  
  
  RESULTS
  Results showed that a single afternoon administration 30 min before conditioning has no effect on the acquisition of cued fear. Compared to rats injected with vehicle, rats injected with melatonin 30 min before extinction training presented a significant lower freezing during both extinction training and extinction test phases, however, freezing response did not differ for the initial four trials during extinction training. Melatonin injected immediately after extinction training was ineffective on extinction learning.
  
  
  CONCLUSIONS
  These results suggest that melatonin, at the dose applied in this study, facilitates the extinction of conditional cued fear without affecting its acquisition or expression, and melatonin facilitates cued fear extinction only when it is present during extinction training. These findings extend previous research on the melatonin effects on learning and memory and suggest that melatonin may serve as an agent for the treatment of anxiety disorders such as posttraumatic stress disorder (PTSD).
authors.forename: Fulian
authors.initials: F
authors.lastname: Huang
authors.forename: Zehua
authors.initials: Z
authors.lastname: Yang
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Anatomy and Neurobiology, School of Basic Medical Sciences, Central South University, Tongzipo Road 172, Changsha, Hunan 410013, P,R China. changqili@csu.edu.cn.
authors.forename: Chang-Qi
authors.initials: CQ
authors.lastname: Li
mesh_terms: D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects*; D003463:Cues; D005108:Extinction, Psychological / Q000187:drug effects*; D005239:Fear / Q000187:drug effects*; D046352:Freezing Reaction, Cataleptic / Q000187:drug effects; D008297:Male; D008550:Melatonin / Q000008:administration & dosage*; D018697:Nootropic Agents / Q000008:administration & dosage*; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D018697:Nootropic Agents; D008550:Melatonin