Effects of environmental temperature on physiological function of the brain of the rats suffered hypoxic-ischemic brain insult during neonatal period.

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In order to investigate the effect of brain cooling of the neonate suffered hypoxic-ischemic brain-damage, we performed experiments using animal model. Under the inspired anesthesia, we ligated left common carotid artery of the 7-day-old rat neonate, and exposed them to the hypoxic air (oxygen 8%). After the hypoxic exposure, we divided the rat neonates to three groups. The first group (hypothermia group) was kept in a room of low environmental temperature for 24 hr, which led the rats to the hypothermia (30 degree). The second group (normothermia group) was kept in a room of normal temperature for 24 hr, which kept the rat body temperature in normothermia. The third group was a control, which had a sham operation. After rearing for three months, we performed auditory brainstem response (ABR) for three groups. ABR was successfully recorded in all the rats under light anesthesia. The interpeak latency of III and V peaks of the normothermia group was significantly elongated than those of the hypothermia and control group. The ratio of the amplitude of V peak versus I peak of the normothermia group was also significantly small than those of the other groups. The inferior colliculus of the normothermia group was significantly atrophic than those of the other groups by using light microscope and imaging-data processing software. These findings indicate that high environmental temperature for the neonate rats after the hypoxic-ischemic insult caused more damages in rat midbrain function than low environmental temperature does. We also performed preliminary investigation on the function of neuronal circuit using optic recording, and found that optic recording using low perfusion temperature might be a useful investigation tools for the study of damaged brain function of suffered neonate animal models.