Impact of plastic sipper devices on alcohol self-administration in rodents: Limitations for long-term access paradigms

Open source devices are becoming widely used in behavioral neuroscience. Despite their advantages in cost effectiveness, modularity, and customization, measurements obtained using newly developed devices may not always recapitulate measurements from existing and validated equipment, potentially due to the materials used in manufacture. In this study, we evaluated a commonly used open-source optical lickometer that delivers fluid via a Hydropac® plastic valve in a multi-site intermittent access two-bottle choice (IA2BC) paradigm for alcohol consumption. Mice were tested with both traditional metal sippers and plastic sippers equipped with Hydropac® valves to assess differences in alcohol intake, preference, and total fluid consumption. Our findings revealed that mice displayed reduced intake and preference for alcohol (10-20% v/v) delivered via the Hydropac® containing plastic sippers. Notably, the effect was observed at both testing sites, suggesting a generalizable phenomenon. The decreased intake was also specific to alcohol, as water, quinine, and sucrose consumption were unaffected by sipper type. To investigate the underlying cause of the reduced alcohol consumption, we pre-incubated Hydropac® valves in 20% alcohol and found that the pre-treated alcohol reduced intake even when delivered via metal sippers. This suggests that prolonged interaction between alcohol and the components of the Hydropac® valves alter the fluid, likely by generating unpalatable contaminants. These results highlight a limitation of using plastic sippers in long-term alcohol self-administration studies. While these devices may remain suitable for limited access paradigms their use in extended access protocols may compromise data integrity. Our study underscores the need for rigorous validation of open-source hardware in each research project.