Use of subcutaneous transponders to monitor body temperature in laboratory rats.

Implantable radiofrequency transponders may be adequate for the characterization of hazardous chemicals targeting body temperature control in experimental animals when colonic probes and automated monitoring systems based on intraperitoneal transmitters are not available, installable or applicable for any reason. In this work, we summarize a series of experiments showing the implantation protocol and utility of rice-grain size transponders to monitor subcutaneous temperature (T) after exposure to pharmacological or toxicological treatments targeting body temperature control in laboratory rats. In addition, to explore the responsiveness of this thermometric system, the influence of physiological activity on T readings was examined by monitoring T after a motor exercise in a RotaRod system. Moreover, we characterized the effects of acute oral administration of the pyrethroid insecticide permethrin (PRM) in corn oil (1 mL/kg) on T. PRM has been previously reported to cause dose-related increases in core temperature after administering oral doses ≥75 mg/kg, with peak effects at 2-4 h in adult rats. We monitored T at 30 min intervals over a 4 h period after exposure to PRM (40-160 mg/kg). PRM caused a moderate increase in T starting at ~3.5 h. Overall, T assays showed minimal animal stress (if any) and rapid animal recovery from transponder implantation, simplicity to collect data, convenient testing room space requirements, and a competitive global cost per animal examined. However, various experimental factors may greatly influence the variability within and between individuals, some of which can be controlled by carefully setting up experimental conditions.