Measurements of body temperature, heart rate and activity by radiotelemetry have been previously described for laboratory animals as an efficient, reliable, less labor-intensive and more cost-effective means of acquiring data than other measurement techniques which involve animal restraint. One limiting feature however of many telemetric systems is the necessity for battery powered telemetric implants limiting the length of a given study to the life of the implanted battery. We describe the use of a commercially available telemetry and data acquisition system to record heart rate, body temperature and activity of freely moving rats with transmitters that operate without batteries. The system uses PDT-4000HR E-mitters (Mini Mitter Co., USA) to acquire animal temperature, heart rate and activity data. E-mitters obtain power from a radiofrequency field produced by an ER-4000 energizer/receiver so that implanted transponders can collect data on temperature, heart rate and gross motor activity for the lifetime of the animal. ER-4000 energizers/receivers are designed to be placed below the implanted animal's cage. Data output from receivers is managed by an integrated Windows PC based data acquisition system, Vital View, which is capable of monitoring 32 individually housed subjects implanted with E-mitters. Open field behavior is measured with an automatic video tracking system (EthoVision, Noldus Information Technology).

Adult male Sprague Dawley rats (230-250 g) were used as experimental subjects. Weight gain, food intake and home cage activity showed a progressive recovery following intraperitoneal E-mitter implantation surgery with subcutaneous biopotential lead placement, returning to pre-surgery levels 5-7 days following the procedure. Animals with implanted E-mitters performed similarly to un-operated controls in an open field test including the distance moved, mean velocity, rearing and grooming (frequency and duration). Two weeks following surgery daily telemetric recording was started. Diurnal rhythms for all parameters (low during light period 08:00-20:00 h) and high during the dark period 20:00-08:00 h) were established in rats with E-mitters implanted. Pharmacological validation of this system using apomorphine, a non-selective dopamine agonist that has well-documented effects on locomotor activity, core body temperature and heart rate upon acute administration will also be described. We have recently documented the effects of apomorphine using non-telemetric methods [1] so that comparisons can be made between assessment of the response to apomorphine using both telemetric and non-telemetric methods. In conclusion, PDT-4000HR E-mitters with VitalView data acquisition offer a battery-free, valid and reliable means to monitor body temperature, activity and heart rate in freely behaving unrestrained laboratory rats.

Supported by the Higher Education Authority of Ireland.

References

1. Harkin, A.; Kelly, J.P.; Frawley, J.; O'Donnell, J.M.; Leonard, B.E. (2000). Test conditions influence the response to a drug challenge in rodents. Pharmacology, Biochemistry & Behavior, 65, 389-398.

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