Validation of an improved nose-only exposure system for rodents

Several types and modifications of nose-only inhalation chambers for exposing rodents are described. The improvement of this 'flow-past' -like nose-only exposure system is that it is modular, i.e. it can be used for acute studies with a maximum of 20 rodents (one segment) or for chronic inhalation studies with 100 (or more) rodents per chamber with five (or more) segments. Another goal was to design a nose-only exposure system that provides maximal computer support and automatization, as well as robust aerosol collection conditions. The evaluation of the five-segment chamber, charged with 98 rats, revealed that a flow rate of 0.75 l air min-1 or approximately 2.5 times the rat minute ventilation volume per exposure port is sufficient to provide homogeneous temporal and spatial exposure conditions. Also, the aerosol size distribution was constant throughout the chamber. Experimental data suggest that computer-controlled sampling of the test atmosphere up to ca. 6 l air min-1 did not alter the flow dynamics of the exposure system. The nose-only inhalation chamber developed is suitable for short-term and long-term inhalation toxicity studies using small laboratory rodents with minimal consumption of test compound.