Night melatonin levels affect cognition in diurnal animals: Molecular insights from a corvid exposed to an illuminated night environment

• Published in: Environmental pollution (1987) 2022-09, Vol.308, p.119618-119618, Article 119618
• Main Authors: Buniyaadi, Amaan, Prabhat, Abhilash, Bhardwaj, Sanjay Kumar, Kumar, Vinod
• Format: Article
• Language: English
• Subjects: Cognition; Corvid; Innovative problem-solving; Learning; Melatonin; Memory
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2022.119618

This study investigated the role of nocturnal melatonin secretion in the cognitive performance of diurnal animals. An initial experiment measured the cognitive performance in Indian house crows treated for 11 days with 12 h light at 1.426 W/m2 (∼150 lux) coupled with 12 h of 0.058 W/m2 (∼6-lux) dim light at night (dLAN) or with absolute darkness (0 lux dark night, LD). dLAN treatment significantly decreased midnight melatonin levels and negatively impacted cognitive performance. Subsequently, the role of exogenous melatonin (50 μg; administered intraperitoneally half an hour before the night began) was assessed on the regulation of cognitive performance in two separate experimental cohorts of crows kept under dLAN; LD controls received vehicle. Exogenous melatonin restored its mid-night levels under dLAN at par with those under LD controls, and improved the cognitive performance, as measured in the innovative problem-solving, and spatial and pattern learning-memory efficiency tests in dLAN-treated crows. There were concurrent molecular changes in the cognition-associated brain areas, namely the hippocampus, nidopallium caudolaterale and midbrain. In particular, the expression levels of genes involved in neurogenesis and synaptic plasticity (bdnf, dcx, egr1, creb), and dopamine synthesis and signalling (th, drd1, drd2, darpp32, taar1) were restored to LD control levels in crows treated with illuminated nights and received melatonin. These results demonstrate that the maintenance of nocturnal melatonin levels is crucial for an optimal higher-order brain function in diurnal animals in the face of an environmental threat, such as light pollution. [Display omitted] •The first study on restorative effects of melatonin in cognition of a diurnal species.•Reduced melatonin causes a decline in problem-solving and learning/memory efficiency.•Reduced melatonin lowers the neurogenesis and dopamine regulatory gene expressions.•Exogenous melatonin at night onset alleviates behavioural and molecular deficits.•Night melatonin levels are crucial for optimal cognitive and brain health.