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Light-induced decrease of serotonin N-acetyltransferase activity and melatonin in the chicken pineal gland and retina
Abstract:
In the pineal gland and retina of chickens, light exposure at night when serotonin N-acetyltransferase (NAT) activity levels are high causes a 4--5-fold decrease in NAT activity. The t1/2 of NAT inactivation is 10 min and the kinetics of inactivation are similar in the pineal gland and retina. A brief pulse of light can initiate the process of NAT inactivation which continues in the dark for 30 min before a partial recovery of NAT activity occurs. In blinded chicks, there is less inactivation of pineal NAT by light than in intact chicks, indicating that the eyes are involved in the pineal's response to light. In chicks that have had their superior cervical ganglia removed inactivation of pineal NAT by light is intermediate between that of intact and blind chicks, indicating that ganglionectomy does not completely mimic the effects of blinding. The pineal gland itself is light-sensitive in culture. Light causes a 4--5-fold decrease in NAT activity in static organ culture, and inhibits melatonin release in flow-through organ culture. Drugs that increase cyclic nucleotide levels in cells (cholera toxin, RO 20-1724, monobutyryl cyclic AMP, monobutyryl cyclic GMP) block the NAT decrease by light, whereas high potassium or EGTA do not block this light-induced NAT inactivation.
Insights
Light exposure at night rapidly decreases serotonin N-acetyltransferase (NAT) activity in chickens. This light-induced NAT inactivation is mediated by the eyes and involves cyclic nucleotides.
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.