Journal of Neuroscience, Vol 3, 1437-1449, Copyright © 1983 by Society for Neuroscience
The peptidergic organization of the cat periaqueductal gray. II. The distribution of immunoreactive substance P and vasoactive intestinal polypeptide
MS Moss and AI Basbaum
Despite the important contribution of the midbrain periaqueductal gray
(PAG) to endogenous pain suppression systems, little is known about the
neuroanatomical basis of its functional organization. In a previous study
of the distribution of the endogenous opiate leucine-enkephalin (ENK) in
the PAG (Moss, M. S., E. J. Glazer, and A. I. Basbaum (1983) J. Neurosci.
3: 603-616), we found that immunoreactive ENK-containing neurons and
terminals are clustered in discrete populations. In this study we have
extended our analysis of the neurochemical organization of the PAG by using
immunocytochemistry to map the distribution of two non-opiate peptides that
produce potent analgesia when administered at central gray levels:
substance P (Sub P) and vasoactive intestinal polypeptide (VIP).
Immunoreactive Sub P neurons and terminal fields are clustered in discrete
populations throughout the PAG. The distribution pattern of these
populations changes at different rostral-caudal levels of the PAG. For
example, there is a ventral-to-dorsal shift in the location of Sub P-like
immunoreactivity from the caudal to the rostral PAG. Few immunoreactive Sub
P neurons are found in the nucleus raphe dorsalis although moderately dense
terminal field staining is present. The staining pattern of immunoreactive
VIP is totally different from that of Sub P. Regardless of the
rostral-caudal level examined, VIP- containing neurons are found tightly
clustered in the subependymal neuropil of the ventromedial PAG. Only a few
immunoreactive VIP- containing neurons are found in the ventral PAG or
nucleus raphe dorsalis. The striking differences between the distribution
of Sub P- and VIP-like immunoreactivity in the PAG indicates that the
neural circuitry underlying pain suppression by Sub P and VIP may also
differ.