When neurotransmitters like dopamine and norepinephrine are produced in the presynaptic neuron, they enter a space called the synaptic cleft, which may be considered the space involving neurons. The $ce H+ $ ions can achieve 1 electron then produce a covalent bond with each other, building $ce H2 $ molecules. https://2-fahcl12223.blogolize.com/details-fiction-and-2-fa-hcl-68720856