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Serotonin N‐acetyltransferase activity in chicken retina: In vivo effects of phosphodiesterase inhibitors, forskolin, and drugs affecting dopamine receptors
Author(s) -
Zawilska Jolanta B.,
Kazula Arkadiusz,
Zurawska Ewa,
Nowak Jerzy Z.
Publication year - 1991
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1991.tb00466.x
Subject(s) - medicine , endocrinology , forskolin , dopamine , quinpirole , dopamine receptor , dopaminergic , biology , chemistry , stimulation
A role of D 2 ‐dopaminergic neurotransmission in the regulation of melatonin biosynthesis in retina was studied in vivo in chickens. The nighttime rise in serotonin N‐acetyltransferase (NAT)—the penultimate and key regulatory melatonin‐synthesizing enzyme—was potently inhibited by both acute light exposure and agonists of dopamine D 2 ‐receptor (quinpirole, bromocriptine, and apomorphine). Spiroperidol, a selective dopamine D 2 ‐receptor blocker, increased the enzyme activity in light‐exposed chickens, but had no effect in animals kept in darkness. Inhibitors of cyclic nucleotide phosphodiesterase, aminophylline, and 3‐isobutyl‐l‐methylxanthine given peripherally, along with a direct adenylate cyclase activator forskolin injected directly into the eye, mimicked the action of darkness, and markedly enhanced the retinal NAT activity when administered to animals maintained in an illuminated environment. Dopamine D 2 ‐receptor agonists had no effect on aminophylline‐stimulated enzyme activity, whereas spiroperidol enhanced it. Forskolin‐driven NAT activity was suppressed by quinpirole. Spiroperidol and aminophylline given alone at different times of day under light conditions stimulated NAT activity, and their effects were mainly additive when given in combination. SCH 23390, a selective D 1 ‐dopamine receptor antagonist, did not affect the rise in NAT activity of chicken retina produced by either darkness or by aminophylline. The results provide further evidence that dopamine, acting via D 2 ‐receptors, mediates the inhibitory effects of light on the cyclic AMP‐dependent dark‐evoked induction of NAT activity in chicken retina.