Suppression of melatonin biosynthesis in the chicken pineal gland by retinally perceived light – involvement of D1‐dopamine receptors

Abstract

In this study the role of retinal dopamine (DA) receptors in the light-induced suppression of melatonin biosynthesis in the chicken pineal gland was examined. Exposure of dark-adapted chickens to low intensity light (4 lux) at night significantly decreased the activity of serotonin N-acetyltransferase (AA-NAT; the penultimate and key regulatory enzyme in melatonin production) and melatonin content in the pineal gland. This suppressive action of light was blocked by intraocular (i.oc.) administration of SCH 23390 (a selective antagonist of D1-DA receptors), but was not affected by sulpiride (a selective antagonist of D2-DA receptors). Injection of DA (i.oc.) to dark-adapted chickens significantly decreased pineal AA-NAT activity and melatonin content in a dose- and time-dependent manner. The action of DA was mimicked by selective agonists of D1-DA receptors, SKF 38393 and SKF 81297, and non-hydrolyzable analogs of cyclic AMP (cAMP), dibutyryl-cAMP and 8-bromo-cAMP. However, i.oc. administration of quinpirole, a selective agonist of D2-DA receptors, did not modify pineal AA-NAT activity. In contrast, quinpirole potently decreased nocturnal AA-NAT activity in the retina. Systemic administration of SCH 23390 to chickens blocked the i.oc. DA-evoked decline in nighttime pineal AA-NAT activity, whereas sulpiride was ineffective. These findings indicate that light activation of retinal dopaminergic neurotransmission, with concomitant stimulation of D1-DA receptors positively coupled to the cAMP generating system, plays an important role in a cascade of events regulating pineal activity.

Spermatogenesis in the turkey (Meleagris gallopavo): Quantitative approach in immature and adult males subjected to various photoperiods

“…In turkeys, plasma concentrations of LH and testosterone are dependent on age and photoperiod [38]. In chickens, the pathways through which a photoperiodic signal stimulates LH secretion in the pituitary may involve local pineal-driven mechanisms associated with mechanisms originating in the retina [39]. More information is needed to better understand the mechanisms involved in the perception, transmission and transduction of the photoperiodic signal in the initiation and maintenance of testes in photosensitive birds.…”

Melatonin, hormone of darkness and more – occurrence, control mechanisms, actions and bioactive metabolites

“…While melatonin in the mammalian pineal is largely regulated by norepinephrine of sympathetic origin, retinal melatonin biosynthesis is stimulated via GABA A and, partially, GABA B receptors [13]. The light-dependent decrease of retinal melatonin is caused by dopamine via D 1 or D 4 receptors [18]. Differences in metabolism exist, too, because retinal melatonin is largely degraded by deacetylation to 5-methoxytryptamine (5-MT) [12,19], a compound which can be further converted to 5-methoxytryptophol (5-ML) or 5-methoxyindoleacetic acid (5-MIAA) [8,10,20].…”

Diurnal Profiles of Melatonin Synthesis-Related Indoles, Catecholamines and Their Metabolites in the Duck Pineal Organ

“…Moreover, these cells possess an endogenous oscillator that generates a rhythm of MLT synthesis [11,13]. In addition, the pineal activity in birds, similar to mammals, is also controlled by light acting on the retina and by the circadian clock in the suprachiasmatic nucleus [14,15]. The integrated signals from the retina and from the hypothalamus are transmitted to the pineal organ via the sympathetic innervation [16].…”