Targeted brain hypothermia has the potential to prevent cerebral ischemia injury during open heart and neck surgeries or after traumatic head injury. In this study, in vivo experiments were performed to test the performance of a newly developed cooling device in an inexpensive animal model. Rat brain hypothermia was induced by inserting an interstitial cooling device in the rat neck muscle and placing the device on the common carotid artery to cool the arterial blood supplied to the brain. Coolant was circulating inside the cooling device to achieve either mild or moderate temperature reductions at the surface of the device. Temperatures were measured inside the rat brain tissue, as well as on the head skin surface. For the mild cooling (cooling device surface temperature was 18.7 +/- 4.5 degrees C), the temperature reductions were 2.2 +/- 0.6 degrees C, 2.1 +/- 0.6 degrees C, 1.9 +/-0.6 degrees C and 1.6 +/- 0.9 degrees C at sites of brain-5 mm, brain-2 mm, skull, and scalp, respectively. After the surface temperature was further decreased to 12.8 +/- 2.8 degrees C (moderate cooling), the temperature reduction in the head increased more than 85% to 3.7 +/-3.2 degrees C, 3.7 +/- 3.0 degrees C, 3.3 +/- 2.5 degrees C and 2.5 +/-1.0 degrees C, respectively. The experimental data were also used to validate a previously developed theoretical model for humans. Experimentally measured geometrical and physiological parameters of the rat neck and brain were substituted into the scaled-down theoretical model to simulate the temperature distribution in the rat neck and brain. The theoretically predicted brain temperatures showed a good agreement with the experiment data. We believe that this study is the first step in developing a reliable cooling device to achieve fast cooling and to control rewarming in future clinical studies and to benefit a large patient population. (C) 2008 Elsevier Ltd. All rights reserved.