Cinnamic acid (CA), a natural aromatic carboxylic acid, is an organic acid isolated from cinnamon bark, and is characterized by its white crystals, low-intensity honey-like sweet flavor, low water solubility, and solubility in all organic solvents. It is also found in various plants like cinnamon, basil oil, sycamore, fruits, and vegetables, which is extensively used in medicine, perfumes, polymers, cosmetics, antiseptic agent, and agriculture [1]. It has been demonstrated to have the ability to suppress systemic inflammation, boost immune function in mice exposed to endotoxins, and protect against cisplatin-induced nephrotoxicity [2].

Toxicologists have begun to pay attention to low-toxicity compounds CA, mainly because of their molecular structure similarities with toxic molecules such as styrene. Previous studies have evaluated the toxicity of CA and shown that CA is not genotoxic, phototoxic/photoallergenic and no safety concerns for CA for skin sensitization [3]. Besides, CA analogues was reported have cardiotoxic and an increase in LDH was observed in H9C2 cells treated with it [4]. Ethanolic extract of Petiveria alliacea L. rich in phenolic compounds such as CA induce mutagenicity mediated by oxidative lesions in Saccharomyces cerevisiae CD138(ogg1) strain [5]. A study on faba bean showed that CA decreased the resistance of tissue structure and promoted the occurrence of wilt. However, toxicity studies of CA are still limited and lack strong in vivo experimental evidence, especially for toxicity to the nervous system.

With its rapid embryonic development and a genome that is 86 % similar to human drug targets, zebrafish have become a widely used in vivo model for toxicity testing. Developmental toxicity testing in zebrafish can be conducted by directly exposing the developing organisms to exogenous substances over several days. Following hatching, automated motor behavior assays can be employed to evaluate swimming behavior in response to various stimuli, serving as a functional neurodevelopmental outcome [6]. In addition, the transparency of zebrafish larvae and transgenic lines [such as Tg (lyz: DsRed), Tg (mpeg1: EGFP) and Tg (elavl3: EGFP)] exhibiting cell- and tissue-specific expression of fluorescent proteins make it easy to visualize neurodevelopmental processes and neural activity in zebrafish larvae[7,8]. Therefore, zebrafish are commonly used to study the development of the nervous system and elucidate the mechanisms of neurodevelopmental disorders.

Based on the in vivo imaging and neurofunctional analysis platform of zebrafish model, this study indicated that CA exposure affected the early neurodevelopment and autonomic behavior in zebrafish larvae, and systematically explored its toxic mechanism by using network toxicology, molecular docking and in vivo experiments.