Light-induced decrease of serotonin N-acetyltransferase activity and melatonin in the chicken pineal gland and...

Area of Science:

• Chronobiology
• Neuroendocrinology
• Biochemistry

Background:

• Serotonin N-acetyltransferase (NAT) is a key enzyme in melatonin synthesis.
• Light exposure, particularly at night, is known to regulate NAT activity in the pineal gland and retina.

Purpose of the Study:

• To investigate the kinetics and mechanisms of light-induced NAT inactivation in chickens.
• To determine the role of the eyes and nervous system in this response.
• To elucidate the intracellular signaling pathways involved.

Main Methods:

• Measurement of NAT activity in pineal gland and retinal tissues of chickens under various light conditions.
• Organ culture of pineal glands to assess direct light sensitivity.
• Pharmacological manipulation of intracellular cyclic nucleotide levels.

Main Results:

• Light exposure at night caused a 4-5 fold decrease in NAT activity with a half-life of 10 minutes.
• Light-induced inactivation continued in the dark, followed by partial recovery.
• Blinding reduced light-induced inactivation, while superior cervical ganglion removal had an intermediate effect.
• The pineal gland demonstrated light sensitivity in organ culture, with decreased NAT activity and melatonin release.
• Drugs elevating cyclic nucleotides blocked light-induced NAT inactivation, while high potassium or EGTA did not.

Conclusions:

• The eyes play a crucial role in mediating the pineal gland's response to light.
• Light-induced NAT inactivation is a rapid process involving the central nervous system and is modulated by cyclic nucleotide signaling pathways.
• The pineal gland is intrinsically photosensitive, and its melatonin production is directly regulated by light.