Effects of glutamine pretreatment on learning and memory in heat-exposed rats

BACKGROUND: Glutamine (Gln) pretreatment can protect neural cells from injuries due to heat, ischemia, hypoxia, endotoxemia, and inflammatory factors.OBJECTIVE: To observe the effects of Gln pretreatment on learning and memory, survival time, and rectal temperature in heat-exposed rats.DESIGN, TIME AND SETTING: The present randomized grouping, neurobehavioral experiment was performed at the Laboratory of Department of Pharmacology, Basic School of Medicine, Wuhan University between March and September 2007.MATERIALS: Twenty-four healthy, Wistar rats were included in this study. SPX-160B biochemistry incubator (Shanghai Experimental Equipment Co., Ltd., China), probe electronic thermometer (11000 type, Maikepai Science and Technology Co., Ltd., China), Y-type maze box used in conjunction with MG-2 maze stimulator (Zhangjiagang Biomedical Instrument Factory, China), L-Gin (Batch No. 061218, 5 g/bottle, prepared into 10% aqueous solution, Amresco Company, USA) were used.METHODS: Twenty-four rats were randomly and evenly divided into 3 groups: heat-exposed, Gln low-lose, and Gln high-dose. Following learning and memory testing with the Y-maze, rats in the heat-exposed group were subjected to heat injury (40.5-41.5℃) in a biochemistry incubator. Rectal temperature was measured every 5 minutes. Thirty-five minutes after heat exposure, rats were removed and placed in the Y-type maze to test learning and memory again. Subsequently, the rats were returned to the same environment of thermal stimulation until they died. Rat survival time was recorded. Subsequent to learning and memory testing, rats in the Gln low-dose and high-dose groups received an i.p. injection of Gln (0.4 g/kg and 0.8 g/kg, respectively), and were exposed to heat injury. The remaining experimental procedures remained the same as for the heat-exposed group.MAIN OUTCOME MEASURES: Rat learning and memory, rectal temperature, and survival time in heat exposure environment.RESULTS: (1) In the Y-maze experiment, the frequency for the heat-exposed group rats to move 15 successive times through the maze without any mistakes was 13 times greater prior to heat exposure. Thirty-five minutes after heat exposure, rat learning and memory were significantly decreased, i.e., frequency was 9/15 correct trials (P 0.05). (2) The heat-exposed group required 14 minutes to reach the rectal temperature of 39.5℃. After 2 hours of Gln pretreatment, the Gln low-dose and high-dose groups needed 18 and 20 minutes, respectively (P < 0.05).="" (3)="" following="" 2="" hours="" of="" gln="" pretreatment,="" the="" survival="" time="" of="" the="" gln="" low-dose="" and="" high-dose="" groups="" was="" 66="" and="" 69="" minutes,="" which="" was="" prolonged="" by="" 18.2%="" (p="">< 0.05)="" and="" 21.7%="" (p="">< 0.01),="" respectively,="" compared="" with="" the="" heat-exposed="" group="" (54="" minutes).conclusion:="" a="" 2-hour="" gln="" pretreatment="" can="" noticeably="" improve="" learning="" and="" memory,="" delay="" ascending="" speed="" of="" body="" temperature,="" and="" prolong="" survival="" time="" in="" heat-exposed="" rats="" in="" a="" dose-dependent="" manner.="">