Your question on neurotransmitters is excellent but I'm not sure that we really
know all the answers. Neurotransmitters do many things to alter signal transduc
tion in neurons, by affecting ion channels, intracellular processes such as pho
sphorylation and probably affect the ability of the neurons to connect and form
functional synapses. Affects are both short-term and long-term.
A good reference (cheaper then Kandel and easier to read) is The Biochemi
cal Basis of Neuropharmacology by Cooper, Bloom and Roth. There is a new editio
n out recently. It is probably available at your library as well.
Brown University, Box G RW