Journal of Neuroscience, Vol 8, 1206-1224, Copyright © 1988 by Society for Neuroscience
A study of tachykinin-immunoreactive neurons in monkey cerebral cortex
EG Jones, J DeFelipe, SH Hendry and JE Maggio
Department of Anatomy and Neurobiology, University of California, Irvine 92717.
Immunocytochemical methods were used to localize tachykinin-like
immunoreactivity within neurons of the monkey cerebral cortex. Three
primary antibodies were used: polyclonal antisera raised against fragments
of substance P and substance K that excluded the carboxyl termini of these
peptides, and a monoclonal antibody that recognized the carboxyl terminus
of the tachykinin family. Each antibody stained 2 populations of cortical
nonpyramidal neurons: (1) A small number of large, intensely stained cells
that give rise to long, coarsely beaded processes; (2) a relatively large
number of small, lightly stained cells that are embedded in dense plexuses
of stained punctate profiles. The large, dark cells are present in a
superficial band that includes layers II and III, and in a deep band that
includes layer VI and the subjacent white matter. The smaller, pale cells
are present in the middle layers of cortex (layers IV and/or V).
Colocalization studies indicate that virtually all the small
tachykinin-immunoreactive neurons also display GABA immunoreactivity. The
larger cells are not GABA- positive, but display both somatostatin-like and
neuropeptide Y-like immunoreactivity. The immunocytochemically stained
beaded processes and punctate profiles from plexuses that vary in density
and laminar distribution among different areas of monkey cortex. The
coarsely beaded processes form a basic quadrilaminar pattern, with
relatively dense plexuses in layers I and VI and in 2 middle layers,
usually III and V. However, this pattern varies considerably from area to
area. Electron microscopically, the large cells contain a rich collection
of cytoplasmic organelles, particularly Golgi complex, while the small
cells contain relatively few organelles. Both types of cells, including
large neurons in the white matter, receive symmetric and asymmetric
synaptic contacts on their somata and proximal dendrites. The numbers of
these axosomatic contacts are low. Virtually all synaptic contacts formed
by immunoreactive terminals possess symmetric membrane thickenings. In 2
areas examined in detail (areas 2 and 4), pyramidal cell somata and
dendrites are the major targets of the immunoreactive synaptic terminals.