Improved method for optical fiber temperature probe implantation in brains of free-moving rats

The localized monitoring of brain temperature is crucial to the understanding of the mechanisms underlying brain hyperthermia, such as that caused by stimulant drugs. Many animal studies investigating brain hyperthermia have utilized thermocouple electrodes for temperature measurement, however optical fiber sensors have proven to be an attractive alternative to conventional measurement techniques. Despite their advantages, optical fiber sensors in their current form have struggled to find effective use in studies involving free-moving animals.

We have developed an improved optical fiber temperature probe and implantation method suitable for sensing in free-moving animals. By altering the structure of the probe, conventional guide cannulae can be used for stereotaxic implantation thus increasing ease-of-use and probe durability.

The new probe structure was easily implanted and extremely durable both pre-experimentation and during sampling in vivo. Probe re-usability also allowed for increased experimental workflow. Rats administered MDMA showed pathological increases in brain temperature.

Thermocouples commonly used for temperature measurement in deep brain structures lack the advantages offered by optical fiber sensors. Unlike our improved design, previous optical fiber temperature probes were unable to be removed from the brains of rats without removing the dental cement affixing it to the skull. This made the probe susceptible to breakage and often resulted in the complete loss of the animal from the experiment.

Our fiber temperature probe and revised implantation technique can be easily employed in brain thermorecording using advantageous optical fiber sensors suitable for use in awake free-moving animals.