Adaptation under constant light or dark: a challenge to the pineal

Area of Science:

• Chronobiology
• Endocrinology
• Molecular Biology

Background:

• The pineal gland regulates circadian rhythms through melatonin production, influenced by the light-dark cycle.
• Disruptions to these rhythms can impact physiological processes and overall health.

Purpose of the Study:

• To investigate the effects of prolonged constant light (LL) and constant darkness (DD) on rat pineal gland physiology.
• To analyze changes in gene transcription related to circadian rhythmicity and mitochondrial function under LL and DD conditions.

Main Methods:

• Rats were exposed to LL, DD, or a light-dark (LD) cycle from P21 to P90.
• Monitored voluntary activity patterns, serum melatonin levels, and gene transcription of clock genes, melatonin synthesis enzymes, and adrenergic receptors.
• Utilized Principal Component Analysis (PCA) to analyze gene expression patterns.

Main Results:

• Both LL and DD altered activity patterns and disrupted diurnal rhythms of melatonin and related gene expression.
• LL attenuated core clock gene expression, while DD shifted their expression peaks.
• LL exposure increased mitochondrial biogenesis, mitophagy, and ATP production, alongside elevated corticosterone.
• DD exposure led to decreased ATP levels.

Conclusions:

• Long-term LL exposure presents greater challenges to pineal gland function than DD.
• A strong association exists between the circadian clock and mitochondrial function, as indicated by gene expression clustering.
• Elevated corticosterone in LL suggests significant chronobiological stress, impacting pineal physiology.