This is a difficult and complicated scenario. However, you could simplify the situation by deciding upon the research question you are trying to answer. You then employ the appropriate tools to answer your research question or to test your research hypothesis.

First, note that there is a difference between a neurotoxin and a neurotoxicant. A neurotoxin is a substance produced by a living organism, such as tetrodotoxin produced by the puffer fish. A neurotoxicant is a synthetic substance such as the nerve agent sarin.

You need to decide what type of acute neurotoxicity you are interested in producing and whether or not the toxicity is reversible.

Finally, note that a neuronal cell line is not really neuronal, given that cell lines consist of transformed cells that can divide. Neurons (except for neuronal stem cells) are post-mitotic cells. In addition, neurotoxicity seldom is expressed within individual cells; it depends upon interactions among and between cells.

Depend on research question!  Glutamate brief exposure, any mitochondrial transport chain blocker e.g. sodium Cyanide or sodium azide exposure results immediate acute toxicity and excitotoxicity.

Botulinum toxin type C (BoNT/C) should do the job well. Unlike any other NT, this strain of BoNTs is known to be deadly to neurons in cultures when in relative excess. SV    

The chemotherapy drugs e.g. oxaliplatin, Cytosine Arabinocide at concentrations of 20 microgram/ml are toxic to sensory neurons causing neurite degeneration and neuronal death apparent after 24 - 48 hours.