The term neurotoxic is used to describe a substance, condition or state that damages the nervous system and / or brain, usually by killing neurons.
The name implies the role of a neurotoxin although the term 'neurotoxic' may be used more loosely to describe states that are known to cause physical brain damage but where no obvious neurotoxin has been identified.
The term is generally used to describe a condition or substance that has been shown to result in observable physical damage. The presence of neurocognitive deficits alone is not usually considered sufficient evidence of neurotoxicity, as many subtances exist which may impair neurocognitive performance without resulting in the death of neurons. This may be due to the direct action of the substance, with the impairment and neurocognitive deficits being temporary, and resolving when the substance is metabolised from the body. In some cases the level or exposure-time may be critical, with some substances only becoming neurotoxic in certain doses or time periods.
The reliability of assessing the full spectrum of neurotoxic potential for a test substance is directly related to the extent to which the detection and evaluation of neurotoxicity is explicitly included as a specific, defined objective of routine toxicity testing.
Under the previous guidelines for toxicity testing of proposed food ingredients the identification of neurotoxic effects was based on information derived from a general pathological evaluation of a few sections of neuronal tissue and an unstructured casual observation of test animals in their cages for overt signs of toxicity.
Since neurotoxicity screening is intended to be a routine part of both general and reproductive toxicity studies, the specific composition of the screen and the endpoints to be recorded should be consistent with the particular focus of the study and, specifically, be appropriate for the age (and species) of the animals to be tested.
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