Pentetrazol drug molecule. Computer model of Pentetrazol (PTZ), a potential drug candidate for Down's syndrome, formally used as a circulatory and respiratory stimulant under the trade name Metrazol. In February 2007 it was found that PTZ substantially improved learning and memory in mice with Down's syndrome symptoms. PTZ is a GABA antagonist, meaning it binds to receptor neurons and hence blocks the action of GABA, an inhibitory neurotransmitter. It is thought that people with Down's syndrome have too much GABA-related inhibition, making it difficult for them to process information and learn effectively. Atoms are colour-coded: nitrogen (yellow), carbon (pink) and hydrogen (white).