The return of the dark neuron. A histological artifact complicating contemporary neurotoxicologic evaluation.

A common histological artifact of brain is the presence of contracted, intensely stained neurons. Such cells are termed dark neurons, and can be produced by post-mortem manipulation or trauma in brain tissue. In a number of recently published experimental neurotoxicology reports cells of this nature are interpreted as representing dying or degenerating neurons, thus assigning inappropriate neurotoxic potential to the compounds administered. The latter are the commonly used drugs and pesticides DEET (N,N-diethyl m-toluamide), malathion, permethrin and pyridostigmine bromide. In this paper I review the nature and genesis of the dark neuron, critically discuss the neuropathologic validity of indicated studies and make a plea for increased awareness of this common artifact.