Responsiveness of Pineal N‐Acetyltransferase and Melatonin in the Cotton Rat Exposed to Either Artificial or Natural Light at Night

Abstract

In three separate experiments, the effect of acute exposure to either artificial or natural light during darkness of pineal N-acetyltransferase (NAT) activity and melatonin content was studied in the cotton rat (Sigmodon hispidus). The exposure of animals to an artificial-light irradiance of 160,000 microW/cm2 during darkness for either 1 s, 5 s, or 30 min was followed by a precipitous decline in pineal NAT activity and melatonin content when measured at either 15 or 30 min after light onset. When cotton rats were acutely exposed to light at night for 5 s, irradiances of either 3.2, 32, 320, and 3,200 did not suppress either pineal NAT or melatonin 30 min later; however, if the 5-s exposure had an irradiance of either 32,000 or 160,000 microW/cm2, the pineal enzyme activity and indole content were depressed. Moonlight, which had a maximal irradiance of 0.32 microW/cm2, was unable to suppress pineal NAT activity and melatonin content even when the animals were exposed to the moonlight for 30 min. The treatment of cotton rats with either norepinephrine or its agonist, isoproterenol, before their exposure to light at night retarded slightly the suppressive effect of light on the pineal constituents measured. Also, these drug treatments suppressed the pre-exposure levels of both NAT activity and melatonin content in the cotton rat pineal gland.

Constant illumination reduces circulating melatonin and impairs immune function in the cricketTeleogryllus commodus

“…Our findings support the key prediction that constant illumination is correlated with a reduction in circulating melatonin concentrations, adding to the growing body of literature exploring the negative effect of light exposure on melatonin synthesis ( Lewy et al, 1980 ; Brainard et al, 1982 ; Nurnberger et al, 1985 ; Moore & Siopes, 2000 ; Vera et al, 2005 ; Firth, Belan & Kennaway, 2006 ; Figueiro et al, 2011 ; Moore & Menaker, 2011 ). It should be noted that, to allow a direct comparison of baseline measures, we measured melatonin concentrations during the light period for both regimens.…”

“…Further, while invertebrates lack an adaptive immune system, their innate immune system is highly effective and has cellular recognition and defensive pathways that are analogous with vertebrates (for a comprehensive coverage of the discipline see, Beckage, 2008 ). It is predicted that the potential for melatonin to act either directly or indirectly as a regulator of physiological processes or as an antioxidant will be compromised by constant light exposure, as nocturnal melatonin production is suppressed by light ( Nurnberger et al, 1985 ; Pauley, 2004 ). Evidence suggests that even low levels of light (<1 lux) at night supress circulating melatonin concentrations ( Arendt & Ravault, 1988 ; Dominoni et al, 2013 ).…”

A direct influence of moonlight intensity on changes in melatonin production by cultured pineal glands of the golden rabbitfish, Siganus guttatus

“…The involvement of natural light at night on melatonin levels is reported for some vertebrates [37, 41–44]. No changes in the circulating levels and pineal content of melatonin were observed in Wistar rat [43] and cotton rat [41], respectively. On the contrary, pineal melatonin content in Syrian hamsters was suppressed after exposure to full moonlight [37].…”

Seasonal Reproduction in Vertebrates: Melatonin Synthesis, Binding, and Functionality Using Tinbergen’s Four Questions

“…Moonlight suppressed pineal melatonin production in Syrian hamsters [ 157 ]. However, moonlight appears to have no effect on pineal AANAT activity and melatonin content in the cotton rat ( Sigmodon hispidus ) [ 158 ], reminding us that moonlight will not show conserved effects across species or individuals. The effects of moonlight in fish might be more conserved since the pineal itself is photoreceptive in this order.…”