Artificial Light at Night Increases Recruitment of New Neurons and Differentially Affects Various Brain Regions in Female Zebra Finches

Abstract

Despite growing evidence that demonstrate adverse effects of artificial light at night (ALAN) on many species, relatively little is known regarding its effects on brain plasticity in birds. We recently showed that although ALAN increases cell proliferation in brains of birds, neuronal densities in two brain regions decreased, indicating neuronal death, which might be due to mortality of newly produced neurons or of existing ones. Therefore, in the present study we studied the effect of long-term ALAN on the recruitment of newborn neurons into their target regions in the brain. Accordingly, we exposed zebra finches (Taeniopygia guttata) to 5 lux ALAN, and analysed new neuronal recruitment and total neuronal densities in several brain regions. We found that ALAN increased neuronal recruitment, possibly as a compensatory response to ALAN-induced neuronal death, and/or due to increased nocturnal locomotor activity caused by sleep disruption. Moreover, ALAN also had a differential temporal effect on neuronal densities, because hippocampus was more sensitive to ALAN and its neuronal densities were more affected than in other brain regions. Nocturnal melatonin levels under ALAN were significantly lower compared to controls, indicating that very low ALAN intensities suppress melatonin not only in nocturnal, but also in diurnal species.

Evidence That Artificial Light at Night Induces Structure-Specific Changes in Brain Plasticity in a Diurnal Bird

“…Therefore, in that study we also recorded neuronal densities in several forebrain regions, and found that despite the increased proliferation, total neuronal densities decreased in some regions, suggesting net neuronal death. In a later study [7], in which we exposed female zebra finches to a longer ALAN exposure (six weeks), we recorded NR in these brain regions and found that ALAN increased recruitment compared to controls, possibly as a compensatory response to ALAN-induced neuronal death, and/or due to increased nocturnal locomotor activity caused by sleep disruption. In addition, the decrease in total neuronal densities, which we observed in some brain regions under short-term ALAN exposure [6], was not found under the longer exposure [7], indicating a temporal effect of ALAN.…”

“…Our study consisted of two experiments, a cell proliferation (CP) experiment, which included three groups with six male birds per group (Figure 1A), and a neuronal recruitment experiment (NR), which included two groups with eight male birds per group (Figure 1B). All of the following experimental conditions and procedures were identical to those in our previous studies with females [6,7]. Zebra finches were hatched and reared in our outdoors breeding colonies, at the I. Meier Segals Garden for Zoological Research at Tel-Aviv University, Israel.…”

“…Four blood samples were taken from each bird (Figure 1): at midday on day one of week three of acclimation, at midday on day one of week three of the ALAN period; and two at midnight, three days after each of the midday samples, to allow enough time for the birds to recover between bleedings. Blood collection at midnight was performed as described in [7]. Plasma MEL concentrations were measured by direct radioimmunoassay [37], which has been validated for zebra finches [38].…”

“…This protocol enabled labelling of new neurons within several brain regions (see below). Histology and immunohistochemistry for the NR experiment were performed as described in [7,41]. This staining protocol yielded neurons that were stained fluorescent green (with anti-Huc/HuD), and nuclei of new neurons that were stained fluorescent red (with anti-BrdU) (Figure 3).…”

“…It has vast biological impacts on many species, and is also associated with several health problems in humans [1,2]. For example, ALAN has been shown to induce earlier reproductive maturity [3,4], compromise immune homeostasis [5], and decrease melatonin (MEL) production [6,7]. Nevertheless, little is known regarding the effects of ALAN on brain plasticity processes such as cell proliferation (CP) and new neuronal recruitment (NR), and most of the existing studies have been conducted on nocturnal mammals, e.g., [8][9][10][11].…”