APOPO innovates the olfactometer for rapid sample screening

APOPO is also researching a variety of scent detection configurations and olfactometers for optimizing sample evaluation by the rats.

Initial efforts focused on developing a fully automated explosive vapour delivery system attached to a Skinner box, with a typical two-lever press protocol. This was in co-operation with the Canadian lab "Jenel TVD". However, limitations in the variability and quantification of automated scent presentation through a central sniffing hole led to APOPO investigating alternative setups.

This resulted in the initial development of the Line Cage, which is still in use for REST and TB sample evaluation. The cage has a stainless steel floor with a linear array of sniffing holes, through which the scent samples are exposed. The samples are presented in a cassette, containing all samples for one run, thus avoiding individual handling of the scent samples. Upon correct indication on a sample, the rat receives a "click" followed by a food reward delivered at one of the cage ends, before resuming its search from the point of indication. Using this system a detection rat can evaluate approximately 100 scent samples in 15 minutes.

An alternative design consists of a wall-attached, stainless steel tunnel punctuated with number of sniffing holes. The samples are individually placed under each hole and un-covered as the rat approaches. This system needs two sample changers continuously inserting and opening samples ahead of the rat as it progresses. Upon the correct indication of a sample, the trainer delivers the food reinforcer just after the location of the indicated sample.

A recent development is an automated, circular setup that is designed to provide distinct individual sample presentations without a spatial bias. The increased separation of the samples ensures that no cross-contamination of scent can occur between them. The sniffing holes include optical sensors that register a rat's indication, through the breaking of a light-beam for a preset duration. This automatically triggers an electronic clicker and the delivery of a food reinforcer.

Further development of the line cage is underway to automatically register the rats' response and deliver the food reinforcement, in an effort to remove the human factor and improve the standardization of the training protocol.

Frequent analyses of the functional characteristics of each of the designs is essential, as this aids in the further improvement and standardization of APOPO's evaluation and training setup.