Journal of Neuroscience, Vol 9, 3803-3815, Copyright © 1989 by Society for Neuroscience
Quantified distribution of the noradrenaline innervation in the hippocampus of adult rat
S Oleskevich, L Descarries and JC Lacaille
(Department de physiologie), Faculte de medecine, Universite de Montreal, Quebec, Canada.
A recently developed radioautographic technique, based on the uptake
labeling of monoamine terminals (axonal varicosities) in vitro, was used to
quantify the noradrenaline (NA) innervation in adult rat hippocampus. After
incubation of brain slices with 1 microM 3H-NA, the NA varicosities were
visualized as small aggregates of silver grains, in light microscope
radioautographs prepared at 3 equidistant horizontal levels across the
ventral 2/3 of the hippocampus. Using a computer-assisted image analyzer,
counts were obtained from the subiculum (SUB), 3 sectors of Ammon's horn
(CA1, CA3-a, CA3-b) and 3 sectors of the dentate gyrus (DG-medial blade,
crest, and lateral blade), every lamina being sampled in each region. After
a double correction for duration of radioautographic exposure and section
thickness, and following measurement of varicosity diameter in electron
microscope radioautographs, it was possible to express these results in
number of terminals per volumetric unit of tissue. It was thus found that
the overall density of hippocampal NA innervation averages 2.1 million
varicosities/mm3 of tissue, a value almost twice as high as that in
cerebral cortex. This innervation is 20% denser ventrally than dorsally and
is heterogeneous both in terms of regional and laminar distribution. SUB
and DG are more strongly innervated than Ammon's horn, wherein CA1 has the
lowest overall density. In SUB and CA1, there is a clear predilection of NA
varicosities for the stratum moleculare. In CA3, there is a narrow band of
even stronger innervation in the stratum radiatum, near the apical border
of the stratum pyramidale, contrasting with a 3 times lower density in this
cell layer and the stratum oriens. In DG, the NA innervation is again the
weakest in the cell body layer (granule) and exhibits an almost 3-fold
greater density in the polymorph layer, the highest of all hippocampus.
These figures allow for numerous correlations with other quantitative
parameters-- cytological, biochemical, and pharmacological--of NA function
in the hippocampus. They also provide a strong basis for elucidating, at a
cellular level, the action of NA in this part of the brain.
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