Pinealectomy shortens resynchronisation times of house sparrow (Passer domesticus) circadian rhythms

Abstract

In many birds periodic melatonin secretion by the pineal organ is essential for the high-amplitude self-sustained output of the circadian pacemaker, and thus for the persistence of rhythmicity in 24 h oscillations controlled by it. The elimination of the pineal melatonin rhythm, or a reduction of its amplitude, renders the circadian pacemaker a less self-sustained, often highly damped, oscillatory system. A reduction in the degree of self-sustainment of a rhythm should not only increase its range of entrainment but also shorten the resynchronization times following phase-shifts of the zeitgeber. This hypothesis has not yet been directly tested. We therefore carried out the present study in which house sparrows (Passer domesticus) were subjected to both 6-h advance and 6-h delay phase-shifts of the light-dark cycle before and after the pinealectomy, and the rhythms in locomotion and feeding were recorded. The results indicate that following the delay, but not the advance, phase shift, resynchronization times were significantly shorter after pinealectomy. The dependence of resynchronization times on the presence or absence of the pineal organ is not only of theoretical interest but might also be of functional significance in the natural life of birds. A reduction or elimination of the amplitude of the melatonin secretion rhythm by the pineal organ might be responsible for faster adjustment to changes in zeitgeber conditions in nature.

The Bird Circadian Clock: Insights from a Computational Model

“…In some conditions, the uncoupled oscillator resynchronizes in the same direction as the LD phase shift (orthodromic re-entrainment), whereas the coupled oscillators resynchronize in the opposite direction (antidromic re-entrainment). This faster resynchronization in pinealectomized birds was reported in experimental studies by Hau and Gwinner (1994) and, more recently, by Kumar and Gwinner (2005).…”

“…On the one hand, the rhythm of the locomotor activity in pinealectomized birds can be entrained by a periodic, exogenous administration of melatonin of different periods (Gwinner and Benzinger, 1978; Heigl and Gwinner, 1995). On the other hand, experiments in which the LD cycle is delayed by 6 h have shown that pinealectomized birds resynchronize faster to the LD cycle (Hau and Gwinner, 1995; Kumar and Gwinner, 2005).…”

Daytime light intensity affects seasonal timing via changes in the nocturnal melatonin levels

“…We do not know the exact reason for this but may speculate on the possibilities. Perhaps, a greater responsiveness of the circadian system of which the melatonin secretion is a significant component (Kumar 2001;Kumar and Gwinner 2005) to transition from dim to bright day provides a starting signal for the reinitiation of gonadal growth during the "dry season" so that stonechats are ready to breed when the next rainy season sets in (Dittami and Gwinner 1985;Gwinner and Scheuerlein 1998).…”

Diurnal Rhythm of Plasma Melatonin Concentration in the Domestic Turkey and Its Regulation by Light and Endogenous Oscillators

“…The daily and seasonal changes in the photoperiod duration are the most important factors controlling melatonin (MLT) secretion by the pineal gland. Day-night rhythmic MLT secretion regulates in birds, among others, the diurnal rhythm of locomotor activity and feed intake [1][2][3][4]; body weight [2]; reproductive system functions [2,[5][6][7][8]; immune system activity [9][10][11][12]; seasonal singing, migration, and spatial orientation during flight [8,13]; thermal homeostasis [14][15][16]; and energy metabolism [1,17]. MLT is also an important component of the antioxidative defense system [18].…”