The use of an unbaited tunnel maze in neurotoxicology: I. Trimethyltin-induced brain lesions.

In our laboratory we use an unbaited 6-arm radial tunnel maze (6-arm RTM) to assess working and reference memory in the course of neurotoxicity studies. The 6-arm RTM is believed to measure parameters comparable to those assessed in radial-arm mazes, but without the need of food deprivation and rewarding of animals. This is especially useful in the course of neurotoxicity studies as interferences of e.g. food deprivation with drug pharmacokinetics can be avoided. Since the 6-arm RTM is less evaluated than conventional mazes the aim of this study was to further confirm mean error score as measure of 'working memory', left-right discrimination within each radial arm (expressed as percent "blind-alley" visits) as measure of 'reference memory', and number of arm entries/min as a measure of motor activity. Therefore, hippocampal lesions were induced by injecting animals with the neurotoxicant trimethyltin (TMT). TMT at a dose of 5 mg/kg slightly lesioned hippocampal CA3 pyramidal cells in 3 of 8 animals, but did not affect behavioral measures in the 6-arm RTM. In all surviving animals treated with 7 or 9 mg/kg TMT moderate to marked loss of CA3 pyramidal cells was observed, while in 4 of these 7 rats CA4 pyramidal cells were also affected. Other brain lesions were not observed. TMT-induced brain lesions led to increased mean error score and number of arm visits during the retention phase and after changing maze configuration, whereas percent "blind-alley" visits were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)