AGE-DEPENDING EFFECTS OF NARCOSIS AND TRANSMITTER IMPLANTATION ON CIRCADIAN BODY-TEMPERATURE AND ACTIVITY RHYTHMS IN MICE

The effects of narcosis and of telemetry transmitter implantation on c ore temperature and locomotor activity were investigated in female lab oratory mice of various age (3, 15 and 52 weeks old). Following surger y a transient hypothermia was observed. The body temperatures measured 30 min after beginning of narcosis were lower in juvenile and in pres enile mice (29.6 degrees +/-0.8 degrees C resp. 30.0 degrees +/-0.2 de grees C) than in adult animals (31.9 degrees +/-0.3 degrees C). The fo llowing temperature increase was fastest in juvenile mice. Normal body temperature was reached after 6h 20' already. Adult and presenile mic e needed 8h 30' resp. 7h 30'. The temperature increase seemed to be in dependent from activity behaviour of the animals. No substantial diffe rences could be obtained whether the transmitters had room or body tem perature before implantation and whether the animals were warmed after surgery by an infrared bulb or not. Probably, the temperature increas e depended mainly on the elimination rate of the drug. Normal circadia n core temperature and activity rhythms reappeared on average within 5 -6 days in juvenile mice and a little faster in adult (4-5 days) as we ll as in presenile ones (3-4 days). However, interindividual differenc es in recovery time were more pronounced than age-dependent variations . Circadian core temperature and activity patterns were quite similar in all three age classes investigated. Ontogenetic differences concern , besides changes in daily mean values, mainly a temperature amplitude increasing with age, as well as a high percentage of ultradian compon ents in the activity pattern of juvenile mice compared to older ones. Telemetry systems are widely used for long-term measurements of core t emperature in laboratory animals (Clement et al., 1989; Refinetti and Menaker, 1992). In our investigations of ontogenetic changes of the ci rcadian temperature and activity rhythms in mice we used an integrated telemetry and data acquisition system (Dataquest, Data Sciences Inc., USA), It comprises implantable wireless transmitters, telemetry recei vers, a consolidation matrix and a data acquisition system. The aim of a preliminary study was to analyse the effects of narcosis and transm itter implantation. The time required to recover normal values of body temperature and of locomotor activity as well as normal circadian rhy thms was determined, considering also ontogenetic variations.