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First published online February 27, 2009
Journal of Experimental Biology 212, 867-877 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027003

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Roles of PER immunoreactive neurons in circadian rhythms and photoperiodism in the blow fly, Protophormia terraenovae

Sakiko Shiga^* and Hideharu Numata

Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Sumiyoshi, Osaka 558-8585, Japan

^* Author for correspondence (e-mail: shigask{at}sci.osaka-cu.ac.jp)

Accepted 24 December 2008

Several hypothetical models suggest that the circadian clock system is involved in the photoperiodic clock mechanisms in insects. However, there is no evidence for this at a neuronal level. In the present study, whether circadian clock neurons were involved in photoperiodism was examined by surgical ablation of small area in the brain and by immunocytochemical analysis in the blow fly Protophormia terraenovae. Five types of PER-immunoreactive cells, dorsal lateral neurons (LN_d), large ventral lateral neurons (l-LN_v), small ventral lateral neurons (s-LN_v), lateral dorsal neurons (DN_l) and medial dorsal neurons (DN_m) were found, corresponding to period-expressing neurons in Drosophila melanogaster. Four l-LN_vs and four s-LN_vs were bilaterally double-labelled with antisera against pigment-dispersing factor (PDF) and PER. When the anterior base of the medulla in the optic lobe, where PDF-immunoreactive somata (l-LN_v and s-LN_v) are located, was bilaterally ablated, 55% of flies showed arrhythmic or obscure activity patterns under constant darkness. Percentages of flies exhibiting a rhythmic activity pattern decreased along with the number of small PDF-immunoreactive somata (i.e. s-Ln_v). When regions containing small PDF somata (s-LN_v) were bilaterally ablated, flies did not discriminate photoperiod, and diapause incidences were 48% under long-day and 55% under short-day conditions. The results suggest that circadian clock neurons, s-LN_vs, driving behavioural rhythms might also be involved in photoperiodism, and that circadian behavioural rhythms and photoperiodism share neural elements in their underlying mechanisms.

Key words: activity rhythm, diapause, lateral neurons, pigment-dispersing factor, photoperiodic response

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