An olfactometric cage suitable for short duration stimulations of unrestrained small animals

An olfactometric cage was constructed in order to perform experiments on olfactory perception in unrestrained rats. Olfactory stimuli were measured with a flame ionization detector (FID). A cylindrical cage was divided into 2 compartments, an upper expansion chamber (B) and a lower stimulation chamber (A) with a perforated metal plate. Before entering B, the odours were diluted with purified air in a mixing chamber. The odorized air was then delivered to a small chamber on top of the cage and distributed by a thin slit surrounding B. A homogeneous distribution of holes in the metal plate provided a laminar flow characterized by a parabolic front. This flow was suitable for long duration exposures of animals of odours. However, for short stimulations (10 sec), variations of amplitude and delay were observed in the horizontal plane of the olfactometric cage. To flatten this parabolic front a new distribution of holes was calculated. A partially turbulent air flow was obtained in A. creating some fluctuations in the time-course of stimulations. However, the amplitude and the delay of the signals were reasonably constant in all parts of the cage floor. It is possible to use this apparatus for other purposes than those originally intended, e.g. behavioural studies.