The use of an unbaited radial maze in neurotoxicology: II. Sensory inputs, general malaise and locomotor activity.

An unbaited 6-arm radial tunnel maze (6-arm RTM) is used in our laboratory to screen for working- and reference memory deficits in rats in the course of neurotoxicological studies. In the 6-arm RTM animals are minimally stressed, and do not need food reward as a reinforcer. Maze behavior is assessed using mean error score of arm repetitions as a measure of 'working memory', left-right discrimination within each arm (expressed as percent "blind-alley" visits) as a measure of 'reference memory' and trial time (time to complete 12 arm entries) as a measure of locomotor activity. As shown for other mazes sensory deficits may affect spatial orientation. Sensory dysfunction are likely to be induced by neurotoxic compounds, while at toxic doses reduced locomotor activity is a common finding. When using the 6-arm RTM in the course of neurotoxicity studies to assess cognitive functions such potentially confounding effects have to be excluded to allow the conclusion of a cognitive impairment. The aim of the following experiments was to assess if visual, vibrissal or olfactory dysfunction, or hypoactivity may affect memory parameters in the 6-arm RTM. Loss of visual, olfactory or vibrissal input alone did not affect any of the maze parameters. Combined loss of visual and vibrissal or olfactory inputs increased mean error score. Loss of olfaction prolonged trial time under both lighting conditions. Acrylamide- and vitamin B6-induced sensorymotor dysfunctions and hypoactivity did not affect mean error score or percent blind-alley visits in the 6-arm RTM. Similarly, gastrointestinal distress and hypoactivity induced by lithium chloride injections did not affect parameters of working or reference memory. Results indicate that in the 6-arm RTM (1) olfactory, visual and, to a minor extent, vibrissal input contribute to the sensory information necessary for spatial orientation and (2) reduced locomotor activity secondary to impaired sensorymotor abilities or drug-induced illness do not influence working or reference memory parameter.