Is a strong candidate to act as a retrograde messenger from the dendrite to the terminal button. nitrous oxide nitric oxide norepinephrine glutamate nmda

I believe the answer is: Nitric oxide
Nitric oxide could be synthesized on demand, because it is considered to be membrane permeant that cannot be stored. Calcium influx through The N-methyl-D-aspartate receptor activates nitric oxide synthase (NOS), which synthesizes Nitric oxide from L-arginine which allow it  to act as a retrograde messenger from the dendrite to the terminal button.