> What about Nitrogen-oxides ?
> I've read that it might be one way to give a 'feedback' across synapses.......
Yes as someone else has pointed out, NO is a putative (or more than
putative by now) messenger across synpases, both in the 'normal'
forward direction and maybe as a retrograde messenger similiar to
arachidonate. (NO is not a second messenger though - nit picking I
know) The arachidonic acid pathways and nitric oxide systems may
actually be linked. The catalytic cycle of cyclooxygenases and the
lipoxygenases (which use arachidonic acid as substrate) involves free
radical intermediates with which it has been shown NO can interact,
effectively consuming NO. These studies were in monocytic cell lines
but it may be a synaptic mechanism in vivo.