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 10 mg 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 AlCl $_{3}$ 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.