Glutamic acid
Glutamate is also a neurotransmitter (see below), which makes it one of the most abundant molecules in the brain. Malignant brain tumors known as glioma or glioblastoma exploit this phenomenon by using glutamate as an energy source, especially when these tumors become more dependent on glutamate due to mutations in the gene "IDH1".
Neurotoxin
Mercury is capable of inducing CNS damage by migrating into the brain by crossing the BBB. Mercury exists in a number of different compounds, though methylmercury (MeHg), dimethylmercury and diethylmercury are the only significantly neurotoxic forms. Diethylmercury and dimethylmercury are considered some of the most potent neurotoxins ever discovered. MeHg is usually acquired through consumption of seafood, as it tends to concentrate in organisms high on the food chain. It is known that the mercuric ion inhibits amino acid (AA) and glutamate (Glu) transport, potentially leading to excitotoxic effects.