Illuminated night alters hippocampal gene expressions and induces depressive‐like responses in diurnal corvids

Abstract

Artificial light at night induces circadian disruptions and causes cognitive impairment and mood disorders; yet very little is known about the neural and molecular correlates of these effects in diurnal animals. We manipulated the night environment and examined cellular and molecular changes in hippocampus, the brain region involved in cognition and mood, of Indian house crows (Corvus splendens) exposed to 12 hr light (150 lux): 12 hr darkness (0 lux). Diurnal corvids are an ideal model species with cognitive abilities at par with mammals. Dim light (6 lux) at night (dLAN) altered daily activity:rest pattern, reduced sleep, and induced depressive-like responses (decreased eating and self-grooming, self-mutilation, and reduced novel object exploration); return to an absolute dark night reversed these negative effects. dLAN suppressed nocturnal melatonin levels; however, diurnal corticosterone levels were unaffected. Concomitant reduction of immunoreactivity for DCX and BDNF suggested dLAN-induced suppression of hippocampal neurogenesis and compromised neuronal health. dLAN also negatively influenced hippocampal expression of genes associated with depressive-like responses (bdnf, il-1β, tnfr1, nr4a2), but not of those associated with neuronal plasticity (egr1, creb, syngap, syn2, grin2a, grin2b), cellular oxidative stress (gst, sod3, cat1) and neuronal death (caspase2, caspase3, foxo3). Furthermore, we envisaged the role of BDNF and showed epigenetic modification of bdnf gene by decreased histone H3 acetylation and increased hdac4 expression under dLAN. These results demonstrate transcriptional and epigenetic bases of dLAN-induced negative effects in diurnal crows, and provide insights into the risks of exposure to illuminated nights to animals including humans in an urban setting.

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

“…In the HC, which is involved in the processing of spatial information [ 19 , 20 ], the significant increase in the number of new neurons that were recruited under ALAN is contrary to the decrease that was found in Indian house crows [ 3 ]. However, these crows were acclimated, after being caught from the wild, only for a single week, shorter than the recommended three weeks to ensure thermogenic [ 36 ] and physiological [ 37 ] acclimation in birds.…”

“…Despite a growing number of studies that demonstrate adverse effects of artificial light at night (ALAN) on the behaviour and physiology of many species (e.g., reviewed in [ 1 , 2 ]), still, in birds relatively little is known regarding its effects on brain plasticity. The few existing studies report a decrease in the numbers of newly formed neurons in the hippocampus (HC) of Indian house crows ( Corvus splendens ) [ 3 ], and a decrease in soma size of neurons in the HC and the lateral caudal nidopallium (NCL) in this species, suggesting reduced neuronal plasticity [ 4 ]. We have also studied the effect of ALAN on neuronal plasticity in another diurnal species, zebra finches ( Taeniopygia guttata ), which have excellent visual abilities [ 5 ] and their physiology, reproduction and survival are greatly affected by circadian and circannual rhythms [ 6 , 7 ].…”

Sleep in unnatural times: illuminated night negatively affects sleep and associated hypothalamic gene expressions in diurnal zebra finches

“…The evidence, largely accumulated from nocturnal rodents, suggests that artificial light at night (LAN) impacts a wide range of biological functions including sleep [1][2][3]. Similar LAN-induced negative effects have been found on daily cycles of the activity-rest and melatonin secretion, and on metabolism, reproduction, depression and cognitive performance in several songbirds including Indian weaver birds, Ploceus phillipinus [4]; blackbirds, Turdus merula [5]; great tits, Parus major [6][7][8]; Indian house crows, Corvus splendens [9]; zebra finches, Taeniopygia guttata [10,11] and tree sparrows, Passer montanus [12]. In particular, female great tits were awake for a greater portion of the night inside the nest-box when it was dimly illuminated [6].…”

Testing for parallel genomic and epigenomic footprints of adaptation to urban life in a passerine bird

“…Reaction to novel objects and novel food is known as one of the main factors determining the capacity of a species to thrive in an urban environment (41). The DCX gene is related to neuronal plasticity (56) and experimental approaches revealed that artificial light at night induces an overexpression of this gene linked to a change in behaviour and expression of depressive-like behaviour in crows (57). Finally, the CHRNA1 gene is associated with aggressive behaviour in chicken (58), and higher aggressiveness is commonly observed and hypothesized as adaptive in urban bird populations (59).…”