Pineal regulation of circadian rhythms of 2-deoxy[14C]glucose uptake and 2[125I]iodomelatonin binding in the visual system of the house sparrow,Passer domesticus

Abstract

Abstract. The pineal gland and its hormone melatonin are crucial for the generation of circadian rhythms in several species of passerine birds. The sites and mechanisms by which they influence avian behavior are therefore of particular interest. Recent research employing several brain imaging techniques has indicated that the sites of melatonin action within the avian brain are widespread within the 4 major visual pathways. In this study, we have investigated whether the avian homologue of the mammalian suprachiasmatic nucleus, the visual suprachiasmatic nucleus (vSCN), and other visually sensitive structures express circadian rhythms of 2-deoxy[lac]glucose (2DG) uptake and 21125I]iodomelatonin (IMEL) binding in house sparrows, Passer domesticus, under constant environmental conditions in the presence or absence of the pineal gland. The results indicate that 2DG uptake in the vSCN is oscillatory in sham-operated sparrows but damps to arrhythmicity in pinealectomized birds, suggesting this structure contains a damped circadian oscillator independent of pineal input. We have also asked whether IMEL binding is rhythmic under these conditions in the same brains. These results indicate IMEL binding is rhythmic in several structures in the circadian, tectofugal, thalamofugal visual pathways and that pinealectomy increases the level of IMEL binding 2-4 fold suggesting that IMEL binding is down regulated by endogenous melatonin. However, the circadian rhythm of this binding is only gradually abolished, suggesting it too is regulated by a non-pineal circadian clock. These data are discussed in the context of the behavioral neurobiology of avian circadian systems and the neuroendocrine loop model.

Sleep–wake regulation and hypocretin–melatonin interaction in zebrafish

“…Furthermore, in the absence of HCRT signaling, the downstream melatonin pathway and/or circuit could be up-regulated to compensate for the decrease of melatonin production, thus explaining the hypersensitivity to melatonin of hcrtrϪ/Ϫ fish. Such a regulatory loop has been previously reported in mammals and birds where melatonin receptor numbers increased after pinealectomy (24). Moreover, interestingly, HCRT fiber and hcrtr mRNA distributions (Fig.…”

“…In contrast, hcrtrϪ/Ϫ and wild-type siblings showed no differences upon exposure to the other hypnotics (Fig. S3), demonstrating a specific hypersensitivity to melatonin and suggesting, in this mutant, an up-regulation of the actors downstream of melatonin, which might reflect a reduction of endogenous melatonin signaling (24).…”

Daily melatonin administration synchronizes circadian patterns of brain metabolism and behavior in pinealectomized house sparrows,Passer domesticus

“…This idea is supported further by the fact that pinealectomized house sparrows can entrain to skeleton photoperiods and choose an appropriate phase with the remnants of their circadian systems (Takahashi and Menaker 1982a). Recently, we have asked whether the circadian rhythm of 2DG uptake within the vSCN (Cassone 1988) and of IMEL binding within the visual system are abolished by pinealectomy (Lu and Cassone 1993). The data indicated that both 2DG uptake within the vSCN and IMEL binding in the vSCN and several other retinorecipient and integrative visual structures are expressed rhythmically in DD for at least 10 circadian cycles in intact sparrows.…”

“…First, specific, high affinity receptor binding as revealed by in vitro binding of the melatonin agonist 2-[125I]iodomelatonin (IMEL) and autoradiography is present in the retinorecipent and integrative structures of the circadian (vSCN), tectofugal (TeO, Rt E), thalamofugal (GLv, DL, LA) and accessory optic (EM, EW, OM) visual pathways in many species of birds Stehle 1990;Kelm and Cassone 1990;Siuciak et al 1991;Brooks and Cassone 1992;Cozzi et al 1993) including the house sparrow (Cassone and Brooks 1991). This binding is rhythmic with the highest binding during late subjective day and early subjective night Lu and Cassone 1993). Second, uptake of the metabolic marker 2-deoxy[laC]glucose (2DG) is inhibited by administration of 10 gg/kg exogenous melatonin in circadian and visual structures exhibiting specific IMEL binding but not in structures devoid of binding (Cassone and Brooks 1991).…”

Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

“…The exact location of the avian homologue to the mammalian SCN has proven difficult to identify (Dawson, King, Bentley, & Ball, 2001). Some experiments have implicated the medial SCN as the hypothalamic region for the avian circadian oscillator (Simpson & Follett, 1981;Yoshimura, Yasuo, Suzuki, Makino, Yokota, & Ebihara, 2001) whereas other studies point to the more lateral, visual SCN (Lu & Cassone, 1993). Ball & Balthazart (2003) asserted that recent work examining clock gene expression (Yasuo, Watanabe, Okabayashi, Ebihara, & Yoshimura, 2003) demonstrates definitively that the medial hypothalamus is the site of photoperiodic time measurement in birds.…”