Pineal Melatonin Rhythms in the Lizard Anolis carolinensis: I. Response to Light and Temperature Cycles

Abstract

Both light and temperature can influence the pineal's synthesis of the indoleamine melatonin. An investigation of the effects of light and temperature cycles on the pineal melatonin rhythm (PMR) showed the following: (1) Both daily light cycles and daily temperature cycles could entrain the PMR; melatonin levels peaked during the dark phase of a light-dark cycle or the cool phase of a temperature cycle. (2) The PMR could be entrained by a temperature cycle as low as 2 degrees C in amplitude in lizards held in constant light or constant darkness. (3) The length of the photoperiod or thermoperiod affected the phase, amplitude, or duration of the PMR. (4) When presented together, the effects of light and temperature cycles on the PMR depended on the phase relationship between the light and temperature cycles, as well as on the strength of the entraining stimuli, such as the amplitude of the temperature cycle. (5) Exposure to a constant cold temperature (10 degrees C) eliminated the PMR, yet a rhythm could still be expressed under a 24-hr temperature cycle (32 degrees C/10 degrees C), and the rhythm peaked during the 10 degrees C phase of the cycle. (6) A 6-hr dark pulse presented during the day did not elicit a premature rise in melatonin levels. These studies show how environmental stimuli can control the pineal rhythm of melatonin synthesis and secretion. Previous studies have supported a model in which the lizard's pineal acts as a circadian pacemaker within a multioscillator circadian system, and have implicated melatonin as a hormone by which the pineal may communicate with the rest of the system. The lizard pineal, therefore, may act as a photo- and thermoendocrine transducer translating light and temperature information into an internal cue in the form of the PMR. The PMR, in turn, may control the phase and period of circadian clocks located elsewhere, insuring that the right internal events occur at the right time of day.

Endocrine mechanisms mediating temperature-induced reproductive behavior in red-sided garter snakes (Thamnophis sirtalis parietalis)

“…Thus, photoperiod and temperature interact to influence circadian melatonin rhythms. This relationship has also been observed in the European sea bass (Dicentrarchus labrax), the mudpuppy (Necturus maculosus), the three-toed box turtle (Terrapene carolina triunguis), the marbled gecko (Christinus marmoratus), and the green anole (Anolis carolinensis) (Vivien-Roels et al, 1988;Underwood, 1985a;Rawding and Hutchison, 1992;Tilden and Hutchison, 1993;Moyer et al, 1995;García-Allegue et al, 2001). Thus, circadian melatonin rhythms may transduce low temperature exposure during winter dormancy as well as changing temperature profiles during spring emergence.…”

Tracking the seasons: the internal calendars of vertebrates

“…9 h at 208C, approx. 15 h at 328C in constant dim light) entrain the daily pineal melatonin rhythm, with peak concentrations occurring during the cold phase (Underwood 1985b). In fact, when these lizards are exposed to 'cold days' and 'warm nights' (208C during photophase, 328C during scotophase), the melatonin profile entrains to the temperature cycle with peak values occurring in the light.…”

Immunohistochemical characterization of a parapinopsin-containing photoreceptor cell involved in the ultraviolet/green discrimination in the pineal organ of the river lamprey Lethenteron japonicum

“…The pineal organ is widely accepted as a synthesizer and secretor of melatonin (Falcon et al, 1989;Gern and Greenhouse, 1988;Samejima et al, 2000;Samejima et al, 1997;Underwood, 1985). In addition to the secretory response, the pineal photoreceptor transduces a light signal to an electrical response, which is transmitted to the brain via pineal ganglion cells (Dodt, 1973;Dodt and Heerd, 1962;Morita, 1969).…”