Significance of the clock gene period in photoperiodism in larval development and production of diapause eggs in the silkworm Bombyx mori.

Many insects living in seasonal environments sense seasonal changes from photoperiod and appropriately regulate their development and physiological activities. Genetic researches have indicated the importance of a circadian clock system in photoperiodic time-measurement for photoperiodic regulations. However, most previous studies have focused on the effects on a single photoperiodic phenotype, without elucidating whether the circadian clock is involved in the core photoperiodic mechanism or only in the production of one target phenotype, such as diapause. Here, we focused on two different phenotypes in a bivoltine Kosetsu strain of the silkworm Bombyx mori, namely, embryonic diapause and larval development, and examined their photoperiodic responses and relationship to the circadian clock gene period. Photoperiod during the larval stage clearly influenced the induction of embryonic diapause and duration of larval development in the Kosetsu strain; short-day exposure leaded to the production of diapause eggs and shortened the larval duration. Genetic knockout of period inhibited the short-day-induced embryonic diapause. Conversely, in the period-knockout silkworms, the larval duration was shortened, but the photoperiodic difference was maintained. In conclusion, our results indicate that the period gene is not causally involved in the photoperiodic response of larval development, while that is essential for the short-day-induced embryonic diapause.

Pain-like behavior in mice can be induced by the environmental context in which the pain stimulus was previously given.

It has been known for decades that classical conditioning influences pain perception. However, the precise mechanism of pain modified by conditioning remains unclear, partly because of the lack of dedicated behavioral tests. In the present study, we aimed to develop a new method to detect conditioned pain using mice that were injected with formalin as an unconditioned nociceptive stimulus into the hind paw repetitively under a neutral environment. On the test day, the mice exhibited a pain-like behavior without the application of a pain stimulus in the environment. These results demonstrate that a conditioned nociceptive response can be induced by exposure alone to the environmental context in which the pain was previously experienced. The conditioned nociceptive response was sustained for at least 2 weeks. Furthermore, the conditioned nociceptive response was reduced by fentanyl but not by ibuprofen, pregabalin or fluvoxamine. This method may be useful for studying the mechanisms of irritable chronic pain and for the development of novel therapeutic strategies.