Protective effects of gastrodia elata on aluminium-chloride-induced learning impairments and alterations of amino acid neurotransmitter release in adult rats

Purpose: High brain levels of aluminum (Al) can be neurotoxic and cause learning and memory deficits. Gastrodia elata (GE) is a Chinese herb widely used for improving mental function in traditional Chinese medicine. We measured changes in Al-induced neurotransmitter alteration and performance on a learning and memory task to elucidate the mechanism of Al toxicity and to assess whether these alterations could be attenuated by GE. Methods: Thirty-six adult, male rats were randomly divided into six groups. Four Al-exposed groups were given aluminum chloride at 5 mg/kg/day or 10 mg/kg/day (i.p.) for two months, with two of these groups (one for each dose of Al) receiving GE (0.4 g/kg, via oral intubation, with the GE powder mixed in the drinking water) while the other two groups received vehicle. A GE control group was given injections of saline plus GE and a saline control group was given injections of saline and with 3 injection days and one day off. A step-down test was used to measure learning and memory ability. Al concentrations in the neocortex were assayed with a graphite furnace atomic absorption spectrophotometer. Amino acid neurotransmitter levels in the neocortex were determined by high performance liquid chromatogram-fluorescence. Results: Al-exposed rats showed impaired learning and memory ability as indicated by shorter step down latency and more retention errors. Cortical concentrations (mean +/- SEM) of Al were: 56.22 +/- 34.10 ng/g (wet weight) in the Saline control group; 172.87 +/- 111.06 in the 5 mg/kg/dayAl group; 289.15 +/- 102.55 in the 10mg Al group; 74.98 +/- 19.00 in the GE control group; 232.55 +/- 35.74 in 5 mg Al+ GE group; and 291.35 +/- 98.38 in 10 mg Al+ GE group respectively. Al exposure produced a significant increase in cortical GABA levels. Gastrodia elata reduced learning and memory deficits without affecting brain Al levels. Conclusions: Rats exposed to AlCl3 suffer from deficits in learning and memory, accompanied by increases in GABA levels in the neocortex. Gastrodia elata is effective in improving memory functions and normalizing GABA levels.