Behavioral, Biochemical, and In Silico Evidence for Extraction-Dependent Neuroprotective Effects of Citrus limon Leaf Essential Oils in Scopolamine-Challenged Zebrafish

Abstract

<b>Background/Objectives:</b><i>Citrus limon</i> leaf essential oil (EO) is traditionally used for its calming and cognitive-enhancing properties. Although the chemical composition of <i>C. limon</i> leaf essential oils (EOs) obtained by means of hydrodistillation (HD) and solvent-free microwave extraction (SFME) has been previously characterized, the influence of the extraction method on their neuroprotective efficacy and dose-response effects remains insufficiently explored. In the present study, EOs obtained by means of HD (CEH) and SFME (CEM) were compared for their behavioral, biochemical, and <i>in silico</i> neuroprotective effects against scopolamine (SCOP)-induced cognitive and anxiety-like impairments in adult zebrafish. <b>Methods:</b> Adult Tübingen zebrafish were exposed to CEH or CEM via immersion at 10, 100, and 150 µL/L for 19 days prior to SCOP challenge (100 µM). Cognitive performance was evaluated using the Y-maze and novel object recognition (NOR) tests, while anxiety-like behavior was assessed using the novel tank test (NTT) and novel approach test (NAT). Brain acetylcholinesterase (AChE) activity and oxidative stress markers were quantified. Molecular docking analyses were conducted to investigate interactions between major EO constituents and AChE and monoamine oxidase A (MAO A). <b>Results:</b> Both CEH and CEM significantly attenuated SCOP-induced memory deficits, improved spontaneous alternation and NOR discrimination, and reduced anxiety-like behaviors. These effects were associated with AChE inhibition and restoration of redox balance. Notably, CEM generally exhibited stronger neurobehavioral and biochemical effects at comparable doses. <i>In silico</i> analyses supported these findings, revealing favorable binding affinities of key EO constituents toward cholinergic and monoaminergic targets. <b>Conclusions:</b> This study demonstrates that the extraction method influences the neuroprotective efficacy of <i>C. limon</i> leaf EOs. While both CEH and CEM exert antioxidant and cholinergic modulatory effects, CEM shows enhanced neuroprotective potential in a zebrafish model of SCOP-induced cognitive impairment, supporting the relevance of extraction-dependent biological profiling in EO-based neurotherapeutic research.