Most neurodegenerative diseases are currently incurable, with large social and economic impacts. Recently, there has been renewed interest in investigating natural products in the modern drug discovery paradigm as novel, bioactive small molecules. Moreover, the discovery of potential therapies for neurological disorders is challenging and involves developing optimized animal models for drug screening. In contemporary biomedicine, the growing need to develop experimental models to obtain a detailed understanding of malady conditions and to portray pioneering treatments has resulted in the application of zebrafish to close the gap between in vitro and in vivo assays. Zebrafish in pharmacogenetics and neuropharmacology are rapidly becoming a widely used organism. Brain function, dysfunction, genetic, and pharmacological modulation considerations are enhanced by both larval and adult zebrafish. Bioassay-guided identification of natural products using zebrafish presents as an attractive strategy for generating new lead compounds. Here, we see evidence that the zebrafish’s central nervous system is suitable for modeling human neurological disease and we review and evaluate natural product research using zebrafish as a vertebrate model platform to systematically identify bioactive natural products. Finally, we review recently developed zebrafish models of neurological disorders that have the potential to be applied in this field of research.

Background: Conus amadis is a carnivorous snail found abundantly in coastal waters of India. Despite its abundance in southern coastal waters of India and the fact that most of the conotoxin act in neuronal system, research work on Conus amadis venom was not much focused. So we have made a brief study on the venom complex of Conus amadis to identify the library of novel conotoxins and to screen the natural venom for neurological function. Objective: De novo sequencing of novel conopeptides from the venom cocktail of Conus amadis and to screen its natural venom for the presence of biological activities in zebrafish model. Methods: Proteome based MALDI-TOF and LC-MS-MS analysis for identification of novel conotoxins and subsequent sequencing. Due to the complex disulfide rich nature of the venom peptides, the study also involves global chemical modification experiments of the venom extract to unambiguously determine the sequence of novel conotoxins. Biological function analysis of natural venom was tested in zebrafish model to ascertain anti-epileptic properties. Results: In this study, we have identified 19 novel conotoxins containing 1, 2 & 3 disulfides, belonging to different classes. Among them, 2 novel contryphans, 3 T-superfamily conotoxins, 2 A-superfamily conotoxins and 2 Mini M-Superfamily conotoxins were sequenced to its amino acid level from the fragmented spectrum of singly and doubly charged parent ions using de novo sequencing strategies. ama1054, a contryphan peptide toxin, possesses post translationally modified bromo tryptophan at its seventh position. Except ama1251, all the sequenced peptide toxins possess modified C-terminal amidation. Crude venom exhibited anticonvulsant properties in pentylenetetrazole-induced seizure in zebrafish larvae, which suggested anti-epileptic property of the venom cocktail. Acetylcholinesterase activity was also identified in the venom complex. Conclusion: Based on the preliminary evidence, if this study is extended further through bioassay guided purification, could possibly yield peptide toxins with anticonvulsant and other neurologically active molecules.

A potential delivery system has to be fabricated for crossing the blood-brain barrier (BBB) to reach the brain fluid for effective delivery of drugs for any neurological disorders. The present study is aimed for the delivery of donepezil through functionalized PNIPAM nanogel by overcoming the BBB using zebrafish model. We had synthesized the poly N-isopropyl acrylamide nanogels with 20 nm size for sustained drug release. The entrapment of donepezil in the nanogel was quantified as 87.5% by HPLC and its sustained drug release pattern was achieved at 37 8C using Janus green dye release assay. Acetylcholineesterase inhibition assay for the donepezil conjugated nanogel (DCN) has confirmed thermoresponsive drug release by obtaining the donepezil peak at 9.3 min retention time in HPLC. Swim behavior and heart beat rates were found to be biocompatible for the functionalized nanogel DCN in zebrafish. Histological analysis revealed increased pial surface in anterior telenchepalon region of zebrafish brain for the DCN administered fishes. DCN treated embryos exhibited minor developmental deformities above 5 mg/ml and thus confirmed its minimal toxicity and its therapeutic efficiency. This study may shed light on the development of neurospecific nanogel for targeted and sustained drug release to brain by crossing the blood-brain barrier.

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