Lack of circadian regulation of in vitro melatonin release from the pineal organ of salmonid teleosts

doi:10.1016/j.ygcen.2007.06.013

General and Comparative Endocrinology

Volume 154, Issues 1–3, October–December 2007, Pages 91-97

https://doi.org/10.1016/j.ygcen.2007.06.013 Get rights and content

Abstract

In many teleost species, the photoreceptive pineal organ harbors the circadian clock that regulates melatonin release in the pineal organ itself. However, the pineal organ of three salmonids (rainbow trout Oncorhynchus mykiss, masu salmon Oncorhynchus masou, and sockeye salmon Oncorhynchus nerka) did not exhibit circadian rhythms in melatonin release when maintained under constant darkness (DD) in vitro, suggesting that the pineal organs of all salmonids lack the circadian regulation of melatonin production. To test this hypothesis, the pineal organ of seven salmonids (common whitefish Coregonus lavaretus, grayling Thymallus thymallus, Japanese huchen Hucho perryi, Japanese charr Salvelius leucomaenis pluvius, brook trout Salvelius fontinalis, brown trout Salmo trutta and chum salmon Oncorhynchus keta) and closely related osmerids (ayu Plecoglossus altivelis altivelis and Japanese smelt Hypomesus nipponensis) were individually maintained in flow-through culture at 15 °C under several light conditions. Under light–dark cycles, the pineal organ of all species showed a rhythmic melatonin release with high rates during the dark phase. Under DD, the osmerid pineal organs exhibited circadian rhythms in melatonin release with high rates only during the subjective-night but the salmonid pineal organs constantly released melatonin at high rates. Under constant light, melatonin release was suppressed in all species. The pineal organ of rainbow trout maintained at different temperature (15, 20 or 25 °C) under DD released melatonin with high rates but the amount of melatonin released was temperature-sensitive (highest at 20 °C). Thus, melatonin release from the pineal organ of osmerids is regulated by both light and circadian clock but the circadian regulation is lacking in salmonids. These results indicate that ancestral salmonids lost the circadian regulation of melatonin production after the divergence from osmerid teleosts.

Introduction

The pineal organ of teleosts is directly photosensitive and transduces photoperiod into rhythmic secretion of melatonin (N-acetyl-5-methoxytryptamine). Melatonin production in the pineal organ is high during the dark phase and low during the light phase under light–dark (LD) cycles (Iigo et al., 1994, Iigo et al., 1997, Ekström and Meissl, 1997, Falcón, 1999). As a result, plasma melatonin levels exhibit similar profiles (Gern et al., 1978, Kezuka et al., 1988, Kezuka et al., 1992, Iigo and Aida, 1995, Iigo et al., 1997, Sánchez-Vázquez et al., 1997, Pavlidis et al., 1999, Garcia-Allegue et al., 2001, Masuda et al., 2003b). The duration of the nocturnal elevations in circulating melatonin under short photoperiods is longer than those under long photoperiods (Kezuka et al., 1988, Kezuka et al., 1992, Iigo and Aida, 1995, Garcia-Allegue et al., 2001, Masuda et al., 2003b). Thus, melatonin is considered as the chemical mediator of darkness (Yu and Reiter, 1992).

Light is the principal regulator of melatonin production in the fish pineal organ (Iigo et al., 1994, Iigo et al., 1997, Ekström and Meissl, 1997, Falcón, 1999). However, in vitro studies have demonstrated the involvement of an intra-pineal circadian clock in the regulation of melatonin synthesis: rhythmic melatonin release from the pineal organ in organ or cell culture persisted even under constant darkness (DD) with higher rates during the subjective-night than those during the subjective-day. The pineal organs of a number of teleosts have been proved to harbor intra-pineal circadian clocks (Falcón et al., 1989, Kezuka et al., 1989, Iigo et al., 1991, Iigo et al., 2003, Iigo et al., 2004, Zachmann et al., 1991; Bolliet et al., 1996, Cahill, 1996, Molina-Borja et al., 1996, Okimoto and Stetson, 1999a, Okimoto and Stetson, 1999b, Masuda et al., 2003a), indicating that the pineal organ is an important component of the teleostean circadian system. These suggest that the presence of a circadian clock in the pineal organ is common among fish. However, lack of the circadian regulation of melatonin production in the pineal organ was first reported for the rainbow trout Oncorhynchus mykiss and subsequently for the masu salmon Oncorhynchus masou and sockeye salmon Oncorhynchus nerka: melatonin release from the pineal organ of these three salmonids was constantly activated both during the subjective-day and the subjective-night under DD in vitro (Gern and Greenhouse, 1988, Max and Menaker, 1992, Meissl and Brandstätter, 1992, Iigo et al., 1998, Iigo et al., 2007a). It is still controversial whether or not these salmonids are exceptions among teleost species. However, these strongly suggest that the pineal organs of all salmonids lack the circadian regulation of melatonin production.

In the present study, to examine when the pineal organ of salmonids lost the circadian regulation of melatonin production and to obtain more insights into the evolution of the pineal circadian clock system, the pineal organ of salmonids and osmerids, close relative of salmonids, were cultured under several conditions and melatonin secretory profiles were monitored. In addition, the pineal organ of rainbow trout was maintained at different temperature in vitro to test whether temperature affects the expression of circadian rhythms in melatonin release.

Section snippets

Experimental fish

Two osmerid species (ayu Plecoglossus altivelis altivelis and Japanese smelt Hypomesus nipponensis) and seven salmonid species (common whitefish Coregonus lavaretus, grayling Thymallus thymallus, Japanese huchen Hucho perryi, Japanese charr Salvelius leucomaenis pluvius, brook trout Salvelius fontinalis, brown trout Salmo trutta and chum salmon O. keta) were used in Experiment 1 (Table 1). Ayu, common whitefish, and grayling were purchased from local dealers. Japanese smelt was caught by

Melatonin secretory profiles from the pineal organ of osmerids

Melatonin secretory profiles from the pineal organ of osmerids under LD/DD/LL/LD conditions are shown in Fig. 1 and characteristics of the secretory profiles are depicted in Table 1. Under LD, all the pineal organs released melatonin according to the LD alternation. Even under DD, robust free-running rhythm in melatonin release was evident. The free-running period was 24.7 ± 0.5 h for ayu and 22.3 ± 0.3 h for Japanese smelt (mean ± SEM; Table 1), indicating circadian rhythms. Under LL, melatonin

Discussion

The pineal organs of many teleost species are assumed to contain circadian clocks that regulate rhythmic melatonin release (Falcón et al., 1989, Kezuka et al., 1989, Iigo et al., 1991, Iigo et al., 2003, Iigo et al., 2004, Zachmann et al., 1991, Bolliet et al., 1996, Cahill, 1996, Molina-Borja et al., 1996, Okimoto and Stetson, 1999a, Okimoto and Stetson, 1999b). However, the pineal organ of salmonids such as rainbow trout, masu salmon, and sockeye salmon lacks the circadian regulation of

Acknowledgments

We express our thanks to Prof. K. Wakabayashi (Gunma University, Maebashi, Gunma, Japan), for providing the melatonin antiserum, and to Prof. E. Yamaha (Nanae Fresh-Water Laboratory, Field Science Center for Northern Biosphere, Hokkaido University, Nanae, Hokkaido, Japan), for providing Japanese huchen. We also thank Fuji Trout Hatchery, Shizuoka Prefectural Fisheries Experimental Station, Shizuoka Prefecture, for supplying the rainbow trout. We also thank Toshio Shikama, Koji Muto and Hidefumi

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¹: Present address: Wilmer Institute, Johns Hopkins University School of Medicine, 600 North Wolfe Street, Maumenee 809, Baltimore, MD 21287, USA.

²: Present address: School of Fisheries Sciences, Kitasato University, Sanriku, Ofunato, Iwate 022-0101, Japan.

³: Present address: Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan.

⁴: Present address: Freshwater Fisheries Research Division, National Research Institute of Fisheries Science, Chugushi, Nikko, Tochigi 321-1661, Japan.

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Lack of circadian regulation of in vitro melatonin release from the pineal organ of salmonid teleosts

Abstract

Introduction

Section snippets

Experimental fish

Melatonin secretory profiles from the pineal organ of osmerids

Discussion

Acknowledgments

Brain Res.

Mol. Brain Res.

Prog. Neurobiol.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Neurosci. Biobehav. Rev.

Brain Res.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Gen. Comp. Endocrinol.

Rhythmic melatonin secretion in different teleost species: an in vitro study

J. Comp. Physiol. B

The pineal organ of teleost fishes

Rev. Fish. Biol. Fisheries

Regulation of melatonin secretion in a photoreceptive pineal organ: an in vitro study in the pike

J. Neurosci.

Melatonin rhythms in European sea bass plasma and eye: influence of seasonal photoperiod and water temperature

J. Pineal Res.