Journal of Neuroscience, Vol 4, 2497-2517, Copyright © 1984 by Society for Neuroscience
Morphology, distribution, and synaptic relations of somatostatin- and neuropeptide Y-immunoreactive neurons in rat and monkey neocortex
SH Hendry, EG Jones and PC Emson
Neurons in the monkey and rat cerebral cortex immunoreactive for
somatostatin tetradecapeptide (SRIF) and for neuropeptide Y (NPY) were
examined in the light and electron microscope. Neurons immunoreactive for
either peptide are found in all areas of monkey cortex examined as well as
throughout the rat cerebral cortex and in the subcortical white matter of
both species. In monkey and rat cortex, SRIF-positive neurons are
morphologically very similar to NPY-positive neurons. Of the total
population of SRIF-positive and NPY-positive neurons in sensory-motor and
parietal cortex of monkeys, a minimum of 24% was immunoreactive for both
peptides. Most cell bodies are small (8 to 10 micron in diameter) and are
present through the depth of the cortex but are densest in layers II-III,
in layer VI, and in the subjacent white matter. From the cell bodies
several processes commonly emerge, branch two or three times, become
beaded, and extend for long distances through the cortex. The fields formed
by these processes vary from cell to cell; therefore, the usual
morphological terms bipolar, multipolar, and so on do not adequately
characterize the full population of neurons. Virtually every cell, however,
has at least one long vertically oriented process, and most processes of
white matter cells ascent into the cortex. No processes could be positively
identified with the light microscope as axons. The processes of the
peptide-positive neurons form dense plexuses in the cortex. In each area of
monkey cortex, SRIF-positive and NPY-positive processes form a superficial
plexus in layers I and II and a deep plexus in layer VI. These plexuses
vary in density from area to area. All appear to arise from cortical or
white matter cells rather than from extrinsic afferents. In some areas such
as SI and areas 5 and 7, the superficial plexus extends deeply into layers
III and IV; and in area 17, two very prominent middle plexuses occur in
layers IIIB through IVB and in the upper one-third of layer V; these are
separated by layer IVC, a major zone of thalamic terminations, which
contains very few SRIF- or NPY-positive processes. The density of the
plexuses is greater for NPY-positive processes than for SRIF-positive
processes in all areas. In the rat, the plexuses do not display a strict
laminar organization but generally are densest in the supragranular layers
(I to III) and decline steadily in the deeper layers.(ABSTRACT TRUNCATED AT
400 WORDS)
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