Background

Drosophila melanogaster is a useful model for studying drugs of abuse, namely nicotine, cocaine, alcohol, and methamphetamines (Bainton et al., 2000; Velazquez-Ulloa, 2017; Morris et al., 2018; Chvilicek et al., 2020; Baker et al., 2021; Park et al., 2021), as well as substances with therapeutic potential as cannabis (Gómez et al., 2019). Moreover, this model organism has been utilized for studies of toxins (Broderick et al., 2006) and atmospheric pollutants (Wilson et al., 2005). This analysis involves physiological responses (Wilson et al., 2005; Gómez et al., 2019; Santalla et al., 2021), modulation of behavior (Bainton et al., 2000; Rigo et al., 2021), subcellular mechanisms (Petruccelli et al., 2018; Shohat-Ophir et al., 2012), and the relevance of genetic mutations (Sanchez-Díaz et al., 2015; Petruccelli et al., 2018; Rigo et al., 2021). Substances have been administrated orally as supplemented food, including through methods as the CApillary FEeder (CAFE) Assay (Sanchez-Díaz et al., 2015; Baker et al., 2021), or volatilized by use of specific devices (McClung and Hirsh, 1998; Filošević et al., 2018).

One of the main reasons for choosing the passive inhalation route relates to the drawback of oral administration of substances with bad taste, as a fly is not prone to eat drugs with bad taste (Pandey and Nichols, 2011). Advantageously, the inhalation pathway allows the delivery of drugs in a short period of time. The delivery of substances via inhalation increases the availability of the drug and the rate of absorption throughout the cuticle, evading the digestive tract. This way of administration also allows treating a large number of individuals simultaneously, instead of using injection procedures that require one-by-one application. Taking advantage of the demonstrated usefulness of D. melanogaster in modeling various human diseases, this route of administration is suitable for administrating drugs that humans typically consume by the inhalation route, like cannabis. Additionally, D. melanogaster is usually used to test air contaminants by means of this administration route. Different devices designed to provide substances to D. melanogaster include commercial components, are usually expensive, or have a complex design that hampers easy disassembly, transportation, and reassembly (Linde et al., 2014; Tatum-Gibbs et al., 2015).

In a recent publication, we assessed the effect of nicotine on the cardiac performance of Drosophila melanogaster. We found that chronic treatment of adult wild-type flies with vaporized nicotine increased heart rate and altered cardiac contraction/relaxation dynamics (Santalla et al., 2021). Experiments from our laboratory have shown that vaporized cannabis extract also modified heart activity. We observed that a short treatment with cannabis (vaporization of cannabis extract) increased the propensity to cardiac arrhythmias, while a prolonged cannabis dosage enhanced cardiac contractility (Gómez et al., 2019). Herein, we describe the method used for administrating smoke or vaporized substances to Drosophila melanogaster using an easy to mount and low-cost custom device. The protocol allows to simultaneously expose several flies to the substance, thereby saving time and reagents. Although our previously published articles describe the effects of tobacco smoke and vaporized cannabis on D. melanogaster cardiac performance, herein, we are emphasizing the assembly of the device, its maintenance, and the procedure for administrating substances. The experimental amenability of the fruit fly model provides key insights into physiopathological responses to test substances and the subcellular mechanisms involved, many of them conserved between taxa. Noteworthy, the fruit fly is an excellent model for educational purposes. By combining the feasibility of Drosophila and the portability of our small device, simple assays might be conducted for research and education purposes.