Volume transmission in the spinal dorsal horn: role of neuropeptides in spinal nociceptive – Jurgen Sandkuhler (p.39)

It was long believed that information exchange between neurones would take place at synapses only, where the presynaptic nerve terminal stores transmitter substances in vesicles and comes into close contact (within a few nanometres) with the postsynaptic membrane of the effector cell where there is a high density of specific membrane receptors for the particular neurotransmitter(s).