Influence of melatonin on the development of functional nicotinic acetylcholine receptors in cultured chick retinal cells

Abstract

The influence of melatonin on the developmental pattern of functional nicotinic acetylcholine receptors was investigated in embryonic 8-day-old chick retinal cells in culture. The functional response to acetylcholine was measured in cultured retina cells by microphysiometry. The maximal functional response to acetylcholine increased 2.7 times between the 4th and 5th day in vitro (DIV4, DIV5), while the Bmax value for [ 125 I]-α-bungarotoxin was reduced. Despite the presence of α8-like immunoreactivity at DIV4, functional responses mediated by α-bungarotoxin-sensitive nicotinic acetylcholine receptors were observed only at DIV5. Mecamylamine (100 µM) was essentially without effect at DIV4 and DIV5, while dihydro-ß-erythroidine (10-100 µM) blocked the response to acetylcholine (3.0 nM-2.0 µM) only at DIV4, with no effect at DIV5. Inhibition of melatonin receptors with the antagonist luzindole, or melatonin synthesis by stimulation of D4 dopamine receptors blocked the appearance of the α-bungarotoxin-sensitive response at DIV5. Therefore, α-bungarotoxin-sensitive receptors were expressed in retinal cells as early as at DIV4, but they reacted to acetylcholine only after DIV5. The development of an α-bungarotoxin-sensitive response is dependent on the production of melatonin by the retinal culture. Melatonin, which is produced in a tonic manner by this culture, and is a key hormone in the temporal organization of vertebrates, also potentiates responses mediated by α-bungarotoxin-sensitive receptors in rat vas deferens and cerebellum. This common pattern of action on different cell models that express α-bungarotoxin-sensitive receptors probably reflects a more general mechanism of regulation of these receptors. Correspondence

Melatonin inhibitory effect on cAMP accumulation in the chick retina development

“…The mRNA of the immature MT 1 receptor already was showed in undifferentiated 2 days neural stem cells in culture (Niles et al, 2004). The blockage by luzindole of the α‐bungarotoxin acetylcholine receptor appearing occurred only in completely differentiated cells cultivated for at least 5 days (Sampaio et al, 2005). The absence of the luzindole effect also was shown occurring in Chinese hamster ovary cells expressing MT 1 melatonin receptor (Witt‐Enderby and Dubocovich, 1996).…”

“…The mRNA of the Mel 1a , Mel 1b and Mel 1c were located throughout the cellular layers, comprising the photoreceptors layer, the inner nuclear layer and the ganglion cell layer (Natesan and Cassone, 2002). These receptors can be pharmacologically identified in the retina and other tissues by luzindole ( N ‐acetyl‐2‐benziltryptamine), an antagonist/inverse agonist of the melatonin receptors (Dubocovich et al, 2003; Sampaio et al, 2005), and 4‐P‐PDOT (4‐phenyl‐2‐propionamidotetralin), a competitive antagonist capable of differing MT 2 from other melatonin receptors (Markowska et al, 2004).…”

An unexpected effect of 5‐MCA‐NAT in chick retinal development

“…At the embryonic days studied, the melatonin inhibitory effect is not blocked via the melatonin receptor unselective antagonist luzindole (Sampaio, 2008). The same absence of luzindole antagonist activity is observed in melatonin modulator effect on α‐bungarotoxin‐sensitive nicotinic acetylcholine receptors expression in partly differentiated retinal cells cultures (Sampaio et al, 2005). This finding is interesting because the classical luzindole antagonist effect is well known on both melatonin inhibition of the cAMP levels and α‐bungarotoxin‐sensitive nicotinic acetylcholine receptors appearing in differentiated retinal neurons in culture (Iuvone and Gan, 1994; Sampaio et al, 2005).…”

“…The same absence of luzindole antagonist activity is observed in melatonin modulator effect on α‐bungarotoxin‐sensitive nicotinic acetylcholine receptors expression in partly differentiated retinal cells cultures (Sampaio et al, 2005). This finding is interesting because the classical luzindole antagonist effect is well known on both melatonin inhibition of the cAMP levels and α‐bungarotoxin‐sensitive nicotinic acetylcholine receptors appearing in differentiated retinal neurons in culture (Iuvone and Gan, 1994; Sampaio et al, 2005). With this paper, we show that 5‐MCA‐NAT induces increase in cAMP levels in chick retinas, beginning in the precocious stages of neurodevelopment and that luzindole blocks this effect.…”

Melatonin and the time window for the expression of the α8 nicotinic acetylcholine receptor in the membrane of chick retinal cells in culture

“…We have previously shown that melatonin modulates α7 nAChR in fibers of rat skeletal muscle in culture (Almeida‐Paula et al, 2005), in rat sympathetic nerve terminals (Carneiro et al, 1991; Markus et al, 1996; Zago and Markus, 1999) and in rat cerebellar slices (Markus et al, 2003). Melatonin also modulates functional α8 nAChR appearing in the development of chick retinal cells in culture (Sampaio et al, 2005).…”