Abstract
The ambient temperature (Ta) of the delivery room has been under discussion because high Ta is suspected to relate to neonatal encephalopathy, but not so well clarified. We investigated the effect of Ta on the learning ability of an adult rat model after neonatal hypoxic-ischemic (HI) insult. Under inspired anesthesia, the left carotid artery of a 7-day-old rat was ligated, and followed by a hypoxic insult made by delivering 8% oxygen at 40 °C for 15 min. The rats were returned to their mother for 1 hr, and then placed in a box of one of three Ta of 40 °C (n=7; high Ta group, HG), 38 °C (n=7; normal Ta group, NG) and 33 °C (n=7; low Ta group, LG). A sham group (n=5; SG) was also established. Three months after the operation, the learning ability of the rats was assessed using a step-down passive avoidance test. On the first day of the measurement, the rat was placed on an insulated rubber platform of 5 cm in diameter on a metal floor. Once the rat stepped onto the metal floor, the rat experienced discomfort via an electrical foot shock. The interval of the rat moving from the rubber to the metal floor was measured for five successive days. The test was performed once a day. On the last day, SG, LG, NG and HG rats stayed on the rubber floor for 600, 585, 40 and 20 sec, respectively. This result indicates that higher Ta after HI insult may result in restricted learning ability after growth. [J Physiol Sci. 2007;57 Suppl:S191]
