Light-induced changes in frog pineal gland N-acetyltransferase activity

Area of Science:

• * Chronobiology
• * Neuroendocrinology
• * Comparative Physiology

Background:

• * The pineal gland plays a crucial role in regulating circadian rhythms and seasonal cycles in vertebrates.
• * N-acetyltransferase (NAT) is a key enzyme in melatonin synthesis, a hormone heavily influenced by light exposure.
• * Understanding light's impact on pineal gland function is vital for comprehending biological timekeeping.

Purpose of the Study:

• * To investigate the effect of nocturnal light exposure on N-acetyltransferase (NAT) activity in the pineal gland of frogs (Rana tigrina) of different ages.
• * To determine if this light-induced inhibition of NAT activity is mediated by the eyes and if it is age-dependent.
• * To explore the role of beta-adrenoceptors in this light-mediated pathway.

Main Methods:

• * Assay of N-acetyltransferase (NAT) activity using high-pressure liquid chromatography with 2-aminofluorene and p-aminobenzoic acid substrates.
• * Exposure of frogs of different ages to controlled light/dark cycles, including brief nocturnal light pulses.
• * Inclusion of bilaterally enucleated frogs and pretreatment with isoproterenol (a beta-adrenoceptor agonist) to assess pathway mediation.

Main Results:

• * Nocturnal light exposure inhibited pineal gland NAT activity in 1-month-old frogs, but not in 6-month-old frogs.
• * The light-induced inhibition was prevented in bilaterally enucleated frogs, indicating retinal mediation.
• * Isoproterenol pretreatment blocked the light-induced inhibition, suggesting a role for beta-adrenoceptors.
• * NAT activity was significantly higher (4-5 fold) in 1-month-old frogs compared to 6-month-old frogs.

Conclusions:

• * A retino-pineal gland pathway mediates light-induced changes in pineal gland NAT activity in young frogs (1-month-old).
• * This pathway is functional in young frogs but appears to be absent or non-functional in older frogs (6-month-old).
• * The findings highlight the age-dependent nature of light's influence on pineal gland function in Rana tigrina.