Background

Chronic pain represents a substantial burden on society. Patients with this malady often suffer and experience a reduced quality of life (Campbell and Meyer, 2006; Pfau et al., 2012). Importantly, available treatment options are ineffective for the majority of chronic pain patients (Turk et al., 2011); however, an understanding of the basic underlying biology will lead to effective therapeutics (Grosser et al., 2017).

Extensive modelling of chronic pain has been performed in rodents (Costigan et al., 2009); however, these systems are expensive, the genetics of evaluating mouse pain responses are slow, and inducing chronic pain in a significant numbers of animals is required, which can have ethical implications. In contrast, Drosophila are inexpensive to maintain, quick to raise, and have an extensive molecular toolbox that allows rapid genetic manipulation.

Much work has been done to define the underlying nociceptive machinery required for invertebrate “pain” perception (Tracey et al., 2003; Kang et al., 2010; Neely et al., 2010 and 2011; Hamoudi et al., 2018). These systems are primarily dependent on investigating nociception reflexes in the transient larval stage (Babcock et al., 2009 and 2011; Turner et al., 2016; Patel and Cox, 2017; Lopez-Bellido and Galko, 2020) or thermal avoidance assays in adult flies. The first adult Drosophila avoidance assay described involved a sealed tube, noxiously heated, and a light source at one end, which flies were prevented from reaching because of a noxious heat barrier (Manev and Dimitrijevic, 2004). An alternate acute heat nociception system relied on floating a sealed “heat” chamber on hot water, where one surface of the chamber was then rapidly heated to 46°C, while the other reached 31°C during a 4-min trial. Flies with intact heat nociception avoided the hot surface, whereas flies that could not sense heat, or those that had heat-related motor issues or other confounding phenotypes, would fail to avoid the hot surface and rapidly become incapacitated (Neely et al., 2010).

While these assays are useful for assessing a loss of acute heat nociception, they are ineffective for evaluating sensitisation of nociceptive pathways. Here, we present an adaptation of our previously described method (Khuong et al., 2019) for analysis of acute thermal nociception responses, which allows for individualised assessment of both allodynia and hyperalgesia following injury.