Objective To observe the pyramidal neurons in the hippocampal CA1 area varying with time after heat stroke in rats. Meth-ods Sprague-Dawley rats were divided into sham group (n=5) and heat stroke group (n=14), and the heat stroke group was divided into 7-day subgroup and 21-day subgroup (n=7 at each group) after heat stroke. Heat stroke group was established model of heat stroke. The brain tissues of rats were observed with Nissl staining to count the living pyramidal neurons in hippocampal CA1 area. Results The number of living pyramidal neurons in hippocampal CA1 area decreased in the heat stroke group (F=11.80, P<0.01), and decreased more in the 21-day subgroup than in the 7-day subgroup (P<0.05). Conclusion Pyramidal neurons in hippocampal CA1 area decrease with time after heat stroke, which may be associated with the learning and memory impairment.

Objective To compare the spatial learning and memory function of heat stroke rats in different periods, to explore the long-term impairment. Methods 42 Sprague-Dawley rats were randomly divided into heat stroke 7 days group (HS7, n=21), heat stroke 21 days group (HS21, n=21), and another 18 rats were performed femoral artery intubation as surgery control group (sham, n=18). They were tested with Morris water maze 7 days and 21 days after modeling respectively for 5 days. The escaping latency, the frequency of crossing the platform area and the duration in the target quadrant were recorded. Results Compared with the sham group, the escaping latency prolonged in HS7 group in all the time (P<0.05), and 4th and 5th days in HS21 group (P<0.05). Compared with HS7 group, the escaping latency short-ened in HS21 group on the 3rd, 4th and 5th days (P<0.05). The duration in the target quadrant shortened in HS7 group compared with the sham group (P<0.05), and prolonged in HS21 group compared with HS7 group (P<0.05). The frequency of crossing the platform decreased both in HS7 group and HS21 group compared with the sham group (P<0.05), and no difference was found between the later 2 groups (P>0.05). Conclusion The impairment of spatial learning and memory is the most seriously 7 days after heat stroke in rats, and it may remain for long time.