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Developmental changes in calbindin-D28k and calretinin expression in the mouse suprachiasmatic nucleus
Masayuki Ikeda1, Charles N Allen
1Department of Molecular Behavioural Biology, Osaka Bioscience Institute, 6-2-4 Furuedai, Suita, 565-0874 Osaka, Japan. msikeda@obi.or.jp
Insights
Circadian rhythms mature with retinal input. Calbindin-D28k decreases in the suprachiasmatic nucleus (SCN) as the retinohypothalamic tract forms, while calretinin increases independently.
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- The suprachiasmatic nucleus (SCN) is the mammalian circadian pacemaker.
- Retinohypothalamic tract (RHT) projections are crucial for circadian rhythm establishment.
- Mechanisms of SCN maturation and RHT influence are not fully understood.
Purpose of the Study:
- To investigate developmental changes in calbindin-D28k and calretinin expression in the mouse hypothalamus.
- To determine the role of RHT input in these developmental changes.
Main Methods:
- Immunohistochemical analysis of calbindin-D28k and calretinin in mouse hypothalamus at different postnatal ages.
- Organotypic slice cultures of SCN from neonatal mice were used to assess RHT-independent development.
Main Results:
- Calbindin-D28k immunoreactivity decreased in the SCN during postnatal development, coinciding with RHT maturation.
- Calretinin immunoreactivity increased in the SCN, paralleling calbindin-D28k reduction.
- SCN slices cultured without RHT input showed reduced calbindin-D28k and calretinin expression, indicating RHT dependence for normal development.
Conclusions:
- Developmental reduction of calbindin-D28k in the SCN is linked to RHT formation.
- Developmental increase of calretinin in the SCN is independent of RHT connections.
- These calcium-binding proteins play distinct roles in SCN maturation and circadian rhythm development.
Abstract:
The hypothalamic suprachiasmatic nucleus, the primary circadian pacemaker in mammals, and the retinohypothalamic tract, the retinal afferent fibres to the suprachiasmatic nucleus, both mature during early postnatal life. The establishment of circadian rhythms is thought to depend on input from the retina, but the mechanism remains unknown. Here we examined developmental changes in the expression of the Ca2+-binding proteins calbindin-D28k and calretinin in the mouse hypothalamus. Robust calbindin-D28k immunoreactivity was observed in the dorsomedial suprachiasmatic nucleus and the supraoptic nucleus in neonatal mice (postnatal day 3). The calbindin-D28k immunoreactivity decreased significantly in the suprachiasmatic nucleus but not in the supraoptic nucleus during postnatal days 9-15, when retinohypothalamic tract projections to the suprachiasmatic nucleus are completed. Calretinin immunoreactivity was low in the neonatal suprachiasmatic nucleus and increased with development in the ventrolateral suprachiasmatic nucleus, in parallel with the developmental reduction of calbindin-D28k immunoreactivity observed in the dorsomedial suprachiasmatic nucleus. Developmentally stable calretinin immunoreactivity was also observed in retinohypothalamic tract fibres. Organotypic slice cultures of the suprachiasmatic nucleus were prepared from postnatal day 3 mice to examine the effect of the absence of retinohypothalamic tract inputs on developmental changes in calbindin-D28k and calretinin expression. After 12 days in vitro, the cultured suprachiasmatic nucleus slices exhibited dense calbindin-D28k immunoreactivity similar to neonatal mice, and calretinin immunoreactivity in the ventrolateral suprachiasmatic nucleus similar to young adult mice. These results demonstrate a developmental reduction in calbindin-D28k expression that paralleled retinohypothalamic tract formation and a developmental increase in calretinin expression that is independent of retinohypothalamic tract connections to suprachiasmatic nucleus neurons.