A pharmacological validation of radiotelemetry in conscious, freely moving rats

Two reference substances were used in the present study. d-Amphetamine is a direct catecholamine-releasing agent which has a marked stimulant effect upon locomotor activity at low to moderate doses and induces stereotypy at higher doses. (+/-)8-Hydroxy-2-(di-n-propylamino)-tetraline [(+/-)8-OH-DPAT] is a selective 5-HT1A receptor agonist which produces a well-defined behavioral syndrome and a dose-dependent hypothermia. The first aim of this study was to validate that the d-amphetamine-induced activity monitored by telemetry correlated to that concomitantly measured in automated cages and complement these measures with an ethologically based direct observational technique. d-Amphetamine (2.5 and 5.0 micromol/kg s.c.) stimulated locomotion as assessed with radiotelemetry, in automatic cages and by observation. Accompanying these behavioral effects was a concurrent increase (assessed by radiotelemetry) in heart rate but not in blood pressure. The second part of this study examined the pharmacological effects of (+/-)8-OH-DPAT (0.09-6.1 micromol/kg s.c.) on behavior (observation and activity) and temperature and on the cardiovascular system. (+/-)8-OH-DPAT induced the classical serotonergic syndrome of lower lip retraction, forepaw treading, and flattened body posture (observation), and this was accompanied by a concomitant hypothermia (radiotelemetry). (+/-)8-OH-DPAT also induced a dose-dependent and significant decrease in heart rate for 50 min of the 1-h long observation period. This was not accompanied by an increase in blood pressure in spite of the increased activity as seen with all three methods. These results show that radiotelemetry can be used as a tool to measure activity, core temperature, and the cardiovascular parameters in animals that are less stressed than those that are restrained for similar more invasive measurements, and that this technique can be used in combination with others to produce a more complete ethogram of the animal's responses to pharmacological challenges.