The International Journal of Neuropsychopharmacology

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The International Journal of Neuropsychopharmacology (2009), 12:83-93 Cambridge University Press
Copyright © 2008 CINP

Research Article

We are in the dark here: induction of depression- and anxiety-like behaviours in the diurnal fat sand rat, by short daylight or melatonin injections

Tal Ashkenazya1, Haim Einata2 and Noga Kronfeld-Schora1 c1

a1 Department of Zoology, Tel-Aviv University, Ramat-Aviv, Israel
a2 College of Pharmacy, University of Minnesota, Duluth, MN, USA
Article author query
ashkenazy t [PubMed]  [Google Scholar]
einat h [PubMed]  [Google Scholar]
kronfeld-schor n [PubMed]  [Google Scholar]


Circadian rhythms are considered an important factor in the aetiology, expression and treatment of major affective disorders, including seasonal affective disorder (SAD). However, data on the effects of daylight length manipulation or melatonin administration are complex. It has been suggested that since diurnal and nocturnal mammals differ significantly in their physiological and behavioural responses to daylight, diurnal rodents offer a preferable model of disorders related to circadian rhythms in the diurnal human. We previously found that diurnal fat sand rats maintained under short daylight (SD), show depression-like behaviour in the forced swim test (FST). The present study was designed to test additional behaviours related to affective disorders and study the involvement of melatonin in these behaviours. Sand rats were divided into short-daylight (SD, 5 h light:19 h dark) and long-daylight (LD, 12 h light:12 h dark) groups, and received 100 μg melatonin or vehicle administration for 3 wk (5 h and 8.5 h after light onset in the LD room). Animals were then tested for reward-seeking behaviour (saccharin consumption), anxiety (elevated plus-maze), aggression (resident-intruder test), and depression-like behaviour (FST). SD or melatonin administration resulted in a depressed/anxious-like behavioural phenotype including reduced reward seeking, increased anxiety, decreased aggression and decreased activity in the FST, supporting the notion that in a diurnal animal, reduced light results in a variety of behavioural changes that may model depression and anxiety; and that melatonin may be a significant factor in these changes. We suggest that the sand rat may offer an excellent model species to explore the interactions between daylight, affective behaviour and the related underlying mechanisms.

(Received January 21 2008)

(Reviewed February 17 2008)

(Revised June 01 2008)

(Accepted June 13 2008)

(Online publication July 17 2008)

Key Words:Depression; diurnal; fat sand rat; melatonin; photoperiod


c1 Address for correspondence: Dr N. Kronfeld-Schor, Department of Zoology, Tel-Aviv University, Tel Aviv 69978, Israel. Tel.: +972-3-640-5740 Fax: +972-3-640-9403 E-mail: nogaks@tauex

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