Pineal melatonin rhythms in the lizard Anolis carolinensis: II. Photoreceptive inputs

Area of Science:

• Chronobiology
• Neuroendocrinology
• Sensory Physiology

Background:

• The pineal organ in Anolis carolinensis is a key transducer of photoperiodic information.
• Melatonin synthesis and secretion by the pineal gland may regulate peripheral circadian clocks.
• Understanding light's pathway to the pineal gland is crucial for deciphering circadian regulation.

Purpose of the Study:

• To investigate the routes through which light affects the pineal melatonin rhythm (PMR) in Anolis carolinensis.
• To determine the relative roles of the parietal eye, lateral eyes, and direct pineal photoreception in regulating the PMR.

Main Methods:

• Surgical removal of the parietal eye and/or lateral eyes in Anolis carolinensis.
• Exposure of lizards to controlled light-dark (LD) cycles and temperature variations.
• Assessment of PMR under different experimental conditions, including blinded and light-blocking paradigms.
• Evaluation of re-entrainment rates to phase-shifted LD cycles.

Main Results:

• Removal of the parietal eye did not alter the PMR under either constant or cycling temperature conditions.
• Ablation of both parietal and lateral eyes did not affect the PMR under a standard LD cycle.
• Blinded anoles re-entrained to LD cycle shifts as effectively as sighted anoles.
• Blocking light penetration to the brain, while leaving eyes exposed, impaired re-entrainment to LD cycle shifts.

Conclusions:

• Light directly influences the pineal melatonin rhythm in Anolis carolinensis.
• The parietal eye and lateral eyes play minimal to no role in mediating light's effect on the PMR.
• Findings support the hypothesis of direct photoreception within the pineal gland, consistent with known functional photoreceptors.