Online Journal Club for February 2009
Our new format includes only relevant articles. If you have articles that you believe should be included in the online journal club, send them to me before the 20th of the month. Not much this month because of the holiday’s and revamping the jclub format; next month's journal club will be more substantial. This month’s journal club was written up by Joe Wider.
*1. Brain temperature measurement and regulation in
awake and freely moving rodents. DeBow and Colbourne et al. Methods 30 (2003) 167-171
Introduction: It is widely accepted that hypothermia is therapeutic in ischemic injuries. To accurately study the processes of ischemic injury in animals, temperatures must be precisely measured and controlled. Apparent variance between brain temperature and core temperature lead DeBow et al. to develop methods to monitor the two using telemetry probes. In addition, they discuss methods to automatically measure and regulate temperature in the conscious rodent.
Methods: Telemetry probes are first implanted into the abdomen, under inhalation anesthesia through a small abdominal incision. To access a specific area of the brain, a guide cannula should be stereotaxically inserted through the skull and secured to the skull with screws and dental cement.
- In gerbils and mice, it is found to be effective to glue the telemetry device to a plastic nut.
The device can then be screwed onto the cannula.
- In rats, the probe is cemented to a plastic cylinder, the probe is inserted into the cannula and cemented to the skull.
To measure and control temperature, readings from a telemetry device are collected every 30s by DataSciences ART software. During the 30s between readings, the program will activate infrared lamps or a fan and fine water mist to regulate temperature.
Results: Temperature measurements recorded at the same time in the same animal showed a variance between the brain and core. They also showed a correlation. Temperature measurements collected every 30s, coupled with automated temperature regulation setup can maintain target temperature within .5 °C, in rodents.
Introduction: General hypothermia is used as therapy for ischemia injury in the brain and heart. Several drawbacks to general hypothermia lead Clark and Colbourne et al. to develop a method to induce localized hypothermia in the brain. Also investigated, are the effects of localized brain ischemia on hemodynamics over a 24-hour period.
Methods: A metal coil is surgically inserted under the Temporalis muscle and pressed against the skull. Cold water is passed through the coil, cooling it. In all experiments, animals were euthanized promptly after the experiment and histology confirmed accurate probe placement.
Experiment 1 investigated the ability to produce focal hypothermia in the anesthetized rat. The cooling coil
was surgically implanted against the skull. Three thermocouple probes were placed into the brain
stereotaxically to measure the temperature in the ipsilateral striatum and cortex, and the
contralateral striatum. Along with the three locations in the brain,
core temperature was measured rectally. After baseline temperatures were
recorded, cold water was passed through the coil for an hour and stopped.
Temperature measurements were made every 5 minutes during cooling and for 10
minutes of re-warming.
Experiment 2 investigated the ability to produce focal hypothermia in the conscious rat. Telemetry probes
were implanted into the abdomen to record core temperature. A guide cannula was steriotaxically
secured to the skull to assist in telemetry probe placement in the ipsilateral striatum. A protective
cylinder was cemented to the skull to ensure the security of the probe as well as the cooling coil.
Silicon tubing was attached to the cooling coil and to a swivel arm mounted on top of the cage.
Animals recovered for 2 days, after which brain telemetry probes were implanted. Due to
telemetry interference, simultaneous measurements can not be made.
Striatum temperature baseline was measured for 24-hours, while core probe was
off. During a 24-hour cooling period, striatum temperature was recorded every
30s while the core probe was off. Every 4-hours the core probe was activated
and temperatures measured.
Experiment 3 investigated the effects of focal hypothermia on mean arterial blood pressure (MABP) and
heart rate (HR). A telemetry probe was implanted in the abdomen. This probe included a
thermocouple probe for core temperature as well as two leads and a catheter. The two leads
tunneled under the skin to measure HR while the catheter was secured in the descending aorta to
monitor MABP. Animals were also instrumented with a cooling coil and a cannula. Cooling was initiated for one day. During this time core temperature, HR and MABP were recorded. Every 4 hours, the core telemetry device was turned off to measure striatum temperature.
Results: It is shown that a metal coil, pressed against the skull and flushed with cold water can quickly cause localized hypothermia in the brain in anesthetized and conscious rats. It is also demonstrated that local hypothermia does not necessarily cause any significant changes in heart rate and mean arterial blood pressure, when compared to baseline. Retrospective analysis shows a decrease in tissue temperature associated with an increase in cold water flow through the coil.
Discussion: Considering the effects of body temperature in the development of ischemic injury, accurate measurement and precise regulation is of importance at the bench and the bedside. These papers present ideas for monitoring and controlling temperature systemically and locally that may help to guide future endeavors, in one way or another.