BDNF and insomnia: Although few clinical studies have investigated the effect of acupuncture on brain neurotransmitter levels, it has been shown that acupuncture reduced serum norepinephrine levels and increased serum levels of glutamate, 5-HT, and BDNF in insomnia patients, suggesting that serum BDNF has been implicated in the sedative effect of acupuncture [60, 61].