Effects of hypothermia during propofol anesthesia on learning and memory ability and hippocampal apoptosis in...

At present, the harm of hypothermia to the central nervous system has received a great attention from scholars. The present study aimed to investigate the effects of hypothermia on learning and memory abilities and hippocampal apoptosis in neonatal rats and the role of p-ERK and p-CREB in anesthesia.

In this study, 60 Sprague Dawley newborn rats (age 7-day-old) were randomly divided into 3 groups (n = 20), including Control Group (Group C), Anesthesia Group (Group A), and Anesthesia Hypothermia Group (Group AH). Group C was intraperitoneally injected with 0.1 ml saline, and rectal temperature was maintained in the range of 38-39 °C; Group A was intraperitoneally injected with 25 mg/kg of propofol (0.1 ml), the 1/2 initial dose was added per each period of 20 min, anesthesia was maintained for 2 h, and rectal temperature was kept in the range of 38-39 °C. The anesthesia mode and duration of Group AH were as same as Group A, room temperature was set to 23 °C, which caused body's temperature naturally dropped down. After the anesthesia recovered, each group randomly involved five rats for analyzing by Western blot to detect the expression level of p-ERK and p-CREB, and other five rates were also analyzed by flow cytometry assay to detect hippocampal apoptosis rate. The remaining 10 rats in each group were kept up to 30 days for conducting the Morris water maze test, five rats were tested for detecting the expression level of p-ERK and p-CREB, as well as hippocampal apoptosis rate in each group.

Compared with Group C and Group A, the rectal temperature of Group AH was decreased significantly (P < 0.05); At the age of 7 days, compared with Group C and Group A, apoptosis rate of hippocampal tissue in Group AH was increased (P < 0.05), the expression level of p-ERK and p-CREB proteins in Group AH was significantly reduced (P < 0.05), and there were no significant differences between Group C and Group A. At the age of 36 days, there were no significant differences in the results of behavioral test, apoptotic rates, and expression level of the proteins.

Our findings suggest that hypothermia during anesthesia can increase the apoptosis rate in the hippocampus of neonatal rats, whose mechanism may be related to the downward adjustment of p-ERK and p-CREB. However, it has no obvious influence on the long-term learning and memory abilities.