Journal of Neuroscience, Vol 13, 4316-4338, Copyright © 1993 by Society for Neuroscience
Autoradiographic localization of serotonin receptor subtypes in cat visual cortex: transient regional, laminar, and columnar distributions during postnatal development
RH Dyck and MS Cynader
Department of Ophthalmology, University of British Columbia, Vancouver, Canada.
Postnatal changes in the distribution of 5-HT receptor subtypes in the
visual cortex of cats were assessed both qualitatively and quantitatively
using in vitro autoradiographic methods. The 5-HT 1A, 1C, 2, and 3 receptor
subtypes and the 5-HT uptake (5-HTUp) site were visualized with
3H-8-hydroxy-2(di-n-propyl-amino)tetralin, 3H- mesulergine,
(2,5-dimethoxy-4-125I-iodophenyl)-2-aminopropane, 3H- BRL43694, and
3H-cyanoimipramine, respectively. Although specific labeling of 5-HT3
receptors was not detected in the cat visual cortex at any age, each of the
remaining 5-HT receptor subtypes exhibited unique temporal, regional, and
laminar patterns of expression in visual cortical areas 17, 18, and 19 and
lateral suprasylvian cortex (LS). 5- HT1A receptors were the earliest to
demonstrate visual cortex-specific changes in expression. They exhibited
peak levels of expression in all visual cortical areas, predominantly in
supra- and infragranular layers, between postnatal day 10 (PD10) and PD30.
Their levels in all areas declined progressively with increasing age.
5-HT1c receptors demonstrated their highest levels of expression in the
deeper half of layer IV, but only in area 17, between PD40 and PD75. The
most striking feature of their distribution throughout this period was
that, in layer IV and extending into layer III, the 5-HT1c receptors were
concentrated in columns that were 400 microns wide and had a
center-to-center spacing of about 900 microns. This transient pattern of
expression was not present beyond PD90. 5-HT2 receptors were most densely
expressed in layer IV between PD40 and PD120, but they displayed a
distinctly different distribution pattern. The densest binding of 5-HT2
receptors was limited to the upper half of layer IV and found in areas 17,
18, and LS. The distribution of layer 5-HT2 receptors along the dense band
in layer IV of area 17 was discontinuous, exhibiting patches that were
found in the same vertical columns as were the 5-HT1c receptors.
Intermediate binding levels for the 5-HT2 receptors were found through
layers I-III, the remainder of layer IV, and the subcortical white matter.
The levels of 5-HT uptake sites increased gradually to reach adult levels
by PD40, but with a distribution pattern that was basically homogeneous,
both across cortical regions and across laminae.(ABSTRACT TRUNCATED AT 400
WORDS)
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