Multilevel Neurotoxicity of Venlafaxine in Zebrafish: Behavioral Impairment, Biomolecular Dysregulation, and Brain Tissue Damage

Venlafaxine, a widely used medication for managing major psychiatric disorders, has garnered attention not only because of its favorable influence on public health, but also because of its potential environmental impact. This medication, which functions as a selective serotonin and norepinephrine reuptake inhibitor, has been discovered in various aquatic matrices, including municipal water, surface and groundwater samples, sediment, freshwater, and wastewater effluent. Although several studies have identified its presence, there is a scarcity of data concerning its harmful effects on aquatic organisms that are not intended targets. The aim of this study was to examine the mechanism that causes toxicity, resulting in brain damage in the bioindicator species Danio rerio when exposed to venlafaxine (VFX) over a prolonged period. Consequently, adult zebrafish were subjected to concentrations of 500, 1000, and 1500 ng/L, which were deemed environmentally relevant, over a period of 28 days. To achieve this objective, we performed various behavioral assessments including the Novel Tank Test (NTT) and Light and Dark Test (LDT), evaluated oxidative damage, assessed acetylcholinesterase (AChE) enzyme activity, expression of genes related to the apoptotic response and antioxidant activity and conducted histopathological examinations of the cerebellar region of the brain. The results of this study indicated that venlafaxine induces variations in anxiety-related symptoms. This was achieved by enhancing the oxidative stress response, as demonstrated by an average seven-fold increase in malondialdehyde (MDA), hydroperoxides content, and carbonyl protein levels, along with a four-fold increase in the antioxidant activities of catalase and superoxide dismutase. Furthermore, the compound significantly decreased AChE activity by up to 60% and facilitated a three-fold increase in apoptotic signaling through the p53, bax, and casp-3 genes, as well as the factors nrf1 and nrf2, which regulate the antioxidant response while maintaining nearly basal levels of the anti-apoptotic gene bcl2. Histopathological changes including vacuolization, gliosis, inflammatory infiltrates, necrosis, and distortion of the overall architecture of the cerebellar region were also observed. These findings underscore the ecological relevance of pharmaceutical contaminants in aquatic systems and highlight the vulnerability of non-target species to long-term exposure at environmentally realistic concentrations.