Cerebral cortex: VIP containing neurons (rat, immunohistochemical staining)
These neurons have two main dendrites running in opposite directions. The pre synaptic endings of their axons appear as dense dots but the axons themselves are invisible. The structure of the nerve endings can be studied only with electron microscope, but larger pre synaptic nerve endings can be noticed also with light microscope (the term "synapse" was generated at the end of the last century, although the clear-cut evidence for its existence was provided only by the electron microscope).
VIP - vasoactive intestinal peptide, was originally described in a certain type of entero-endocrine cells of the small intestine. Later it was also identified in the brain as a neurotransmitter or a modulator.
From the research files of Dr. Ferenc Hajós and Dr. Katalin Gallatz.