Changes in heart rate and body temperature during passive avoidance behavior in rats

Abstract

Heart rate, core temperature and gross locomotor activity during passive avoidance behavior in rats were recorded by a telemetry system connected to a computer data acquisition program. Passive avoidance latency and approach to the dark compartment were evaluated. Rats were assigned to five different groups, i.e., the shock groups that received different intensities of footshock (0.15, 0.25 and 1.0 mA, respectively, for 3 sec), a no footshock control group and a group that had no access to the dark compartment (i.e., no dark compartment control group). Retention tests were carried out 24 and 120 hr after the learning trial. Rats exposed to footshock showed a decrease in heart rate during the first 10 sec of the observation period in both retention tests. An average bradycardia was found in the lowest shock intensity group (0.15 mA) at both the 24- and 120-hr retention test whereas the other two groups (0.25 and 1.0 mA) showed a gradual increase in heart rate. This increase was more pronounced the longer the rats stayed on the platform. Similarly, a gradual rise in core temperature was observed in these rats as well as in the no dark compartment control group. The number of approaches to the dark compartment was significantly depressed in the group exposed to 1.0 mA footshock intensity. Gross locomotor activity was reduced in animals that exhibited maximum avoidance latency. Exposure of rats to the above-described behavioral paradigms induced autonomic activation resulting in changes in heart rate and temperature. These changes were not caused by gross locomotor activity and may thus be related to the various behavioral states. Differential activation of the sympathetic and parasympathetic components of the automatic nervous system in rats under different behavioral conditions are discussed.