Changes in hippocampal histamine receptors in rats after treatment with Trimeresurus albolabris venom

BACKGROUND: It has been demonstrated that histamine and its receptors in the hippocampus play an important role in memory and/or learning behaviors. OBJECTIVE: To investigate the expression levels of the histamine receptor gene and protein in the hippocampi of rats prior to and after administration of Trimeresurus albolabris venom using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot techniques. DESIGN, TIME AND SETTING: A controlled observation based on cellular protein level was performed in the College of Life Sciences, Chongqing Normal University between March 2005 and April 2007. MATERIALS: Eighty adult male Sprague-Dawley rats were provided by the Laboratory Animal Center of the Third Military Medical University of Chinese PLA. The lyophilized powder of Trimeresurus albolabris venom was collected from Jin-Hu-Shan in Chongqing, China. METHODS: Twenty rats were randomly and evenly divided into an experimental group and a control group. The experimental group was subcutaneously injected with 0.65 mg/mL Trimeresurus albolabris venom, 0.5 mL for each rat. The control group was subcutaneously injected with an equal amount of 0.9% physiological saline. Prior to and after injection, rats from these two groups were placed in the Morris Water Maze for recording of path length and escape latency. The remaining 60 rats were randomly allocated to another experimental group (n = 50) and another control group (n = 10). Rats were correspondingly injected as described above. At different time points (0.1, 0.5, 1, 2, and 3 hours after injection), rats were decapitated and bilateral hippocampal tissues were dissociated (approximately 100 mg for each sample). Then, the acquired hippocampal tissue was immediately preserved at –70 °C for subsequent experiments. MAIN OUTCOME MEASURES: (1) The levels of histamine receptor (including H1R, H2R, and H3R) mRNA and protein in the hippocampi of rats were measured prior to and after injection of Trimeresurus albolabris venom using RT-PCR and Western Blot techniques. (2) Escape latency (namely, time to reach a platform) and path length were examined by Morris Water Maze testing. RESULTS: All 80 rats were included in the final analysis. In the experimental group, the level of mRNA for H3R receptor in rat hippocampi was just slightly changed, but the level of H3R receptor protein was significantly down-regulated compared with that in the control group (P < 0.05). Both mRNA and protein levels for H1R receptor were initially downregulated and then recovered to normal levels. Expression of H2R receptor mRNA was initially upregulated, then downregulated, and finally restored to the control level. The level of H2R receptor protein showed a tendency for downregulation. In the Morris Water Maze testing, escape latency and path length were significantly longer in the experimental group than in the control group (P < 0.05). CONCLUSION: Within three hours of injection with Trimeresurus albolabris venom, mRNA and protein levels of most histamine receptors in rat hippocampi were downregulated. Such changes possibly contribute to an impairment of memory and/or learning behaviors in rats following injection of Trimeresurus albolabris venom.