Differing non-additive alterations in different parts of the nervous system of the rat

Synergistic loss of auditory sensitivity has been observed after combined exposure to xylene and n-hexane, and to toluene and n-hexane. After these combined exposures, antagonisms were seen in the auditory pathway, visual pathway, peripheral nerve and testes. Synergistic interaction in one part of the nervous system and antagonistic interaction in another part has also been seen after combined exposure to toluene and dichloromethane. Two conclusions can be drawn from these observations: (1) an antagonism seen in one part of the nervous system after exposure to a specific combination of chemicals does not exclude the possibility of a synergism in other parts; and (2) both synergism and antagonism can occur within the same neurosensory organ after identical combined exposure. The observed, presumably cochlear, loss of auditory sensitivity after exposure to xylene and n-hexane was synergistic, while antagonism was found in the auditory pathway. These observations suggest that extrapolation of the combined effect in one part of the nervous system to another part, even within the same organ system, can be unreliable.