Rat pineal arylalkylamine-N-acetyltransferase: cyclic AMP inducibility of its gene depends on prior entrained photoperiod

Mar 30, 2004Brain research. Molecular brain research

Light cycle history affects how rat pineal gland gene responds to cAMP

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Abstract

The nocturnal rise in AA-NAT enzyme activity in rats is influenced by the length of daylight exposure.

AA-NAT expression is significantly enhanced during darkness due to adrenergic stimulation from the suprachiasmatic nucleus.
The timing of AA-NAT induction varies with photoperiods, being quicker in longer light periods and slower in shorter ones.
cAMP levels are associated with the strength of AA-NAT response, showing a strong response under long photoperiods and a weak response under short photoperiods.
Full adjustment of cAMP inducibility of the AA-NAT gene requires at least seven cycles of photoperiod exposure.
Increased PKA activity correlates with enhanced cAMP-dependent AA-NAT inducibility, varying with different light/dark cycles.

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The nocturnal biosynthesis of melatonin in the rat pineal depends on strongly enhanced expression of the enzyme N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87]. AA-NAT transcription is stimulated during darkness by adrenergic inputs to the pineal from the suprachiasmatic nucleus (SCN). Nocturnal activation of the AA-NAT promotor following stimulation of pinealocyte adrenoceptors involves cAMP-dependent stimulation of protein kinase A (PKA). The nocturnal rise in AA-NAT depends on the lighting conditions. As compared with light/dark (LD) 12:12, the delay between dark onset and the nocturnal rise in AA-NAT is shortened under long photoperiods and prolonged under short photoperiods. Here, we report that the rapidity of nocturnal AA-NAT induction depends on cAMP inducibility of the gene. Accordingly, cAMP produces a strong AA-NAT response in pineals obtained from rats housed under long photoperiods and a weak AA-NAT response under short photoperiods. Changes in AA-NAT inducibility are fully developed not earlier than after seven cycles. This observation suggests that long-term changes in the photoperiod are necessary to achieve full adjustment of cAMP inducibility of the gene. A direct relationship was found between cAMP-dependent AA-NAT inducibility and the pineal protein kinase A (PKA) activity. As compared to LD 12:12, PKA activity was increased under LD 20:4 and attenuated under LD 4:20. On the basis of the present findings, we suggest that the photoperiod determines the effectiveness of nocturnal AA-NAT induction by long-term modulation of the intrapineal pathway that transmits the cAMP signal to the AA-NAT gene.

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Rat pineal arylalkylamine-N-acetyltransferase: cyclic AMP inducibility of its gene depends on prior entrained photoperiod

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