Pinealectomy does not affect the entrainment to light nor the generation of the circadian demand-feeding rhythms of rainbow trout

Author(s): Iigo, M., Madrid, J. A., Tabata, M.

Journal/Book: Physiol Behav. 2000; 69: the Boulevard Langford Lane, Kidlington, Oxford Ox5 1GB, England. Pergamon-Elsevier Science Ltd. 455-461.

Abstract: The pint al organ and its secretory product melatonin an regarded as synchronizers of daily rhythms to the external light/dark (LD) cycle. In fish, the pineal organ acts as a direct photoreceptor, transducing light information into neural and humoral (melatonin) signals. In the present study, we investigate a possible role for the pineal organ and melatonin in the regulation of feeding rhythms of rainbow trout, Oncorhynchus mykiss. We used individual rainbow trout placed in an insulated room at constant temperature (14 degrees C). Fish were self-fed ad rib by means ol self-feeders coupled to a computer that continuously recorded demand-feeding activity. Before and after pinealectomy, the fish were exposed to a LD cycle of 16:8 h and then constant Light (LL) to test the effect of pinealectomy on demand-feeding rhythms. Feeding records revealed that trout fed exclusively during daytime (96% of feeding confined to the light phase), and that removal of the pineal organ did not disrupt this daily feeding profile, with synchronization to the to cycle persisting. Moreover, the appearance of circadian feeding rhythms was not affected by pinealectomy: most of the operated fish free-ran with an average tau longer than 24 h. Plasma melatonin rhythms persisted in the pinealectomized trout, but with small amplitude. These results suggest that the pineal may not be the site of the pacemaker that controls feeding rhythms in trout, although further research is required to study the involvement of other photoperiod-transducing systems and melatonin (of nonpineal origin) in the regulation and expression of circadian rhythms in this species.

Note: Article Sanchez-Vazquez FJ, Univ Murcia, Fac Biol, Dept Physiol & Pharmacol, E-30100 Murcia, SPAIN

Keyword(s): pineal organ; melatonin; circadian rhythms; feeding; rainbow trout; MELATONIN SECRETION; LOCOMOTOR-ACTIVITY; CARASSIUS-AURATUS; ENDOGENOUS CLOCK; ATLANTIC SALMON; BINDING-SITES; ORGAN; GOLDFISH; INVITRO; PLASMA

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