Stress-induced fever after postischemic rectal temperature measurements in the gerbil

Postischemic temperature, which modulates brain injury, is commonly determined via a rectal temperature (T-rec) probe. This procedure causes a stress-induced fever (SIF) in rodents that may aggravate injury or diminish the efficacy of a neuroprotectant. We continually measured core temperature (T-core) via an implanted telemetry probe and made 16 T-rec measurements over 4 days in sham and ischemic gerbils (5 min bilateral carotid artery occlusion). Controls did not have T-rec sampled, but T-core was measured. Rectal temperature measurements predicted T-core in sham and ischemic gerbils. The T-rec measurements caused a SIF (1degreesC peak) in shams that did not habituate, whereas the SIF was initially absent and then increased over days in ischemic gerbils. Ischemic groups had similar CA1 injury (similar to32% remaining), presumably because T-rec measurements only resulted in a significant SIF starting on day 2 postischemia, when cell death is less sensitive to hyperthermia. Caution is warranted with T-rec measurements, since the resultant SIF occurs to different extents in normal and ischemic rodents. Furthermore, the SIF could vary according to many other factors, such as the type and severity of insult, the time and frequency of measurement, and drug treatment. Accordingly, postischemic T-rec measurements should be replaced with telemetry probes.