Coerulear projections to the lateral diencephalon in the rat. An anatomical study using wheat-germ agglutinin conjugated to HRP

Abstract

The orthograde axonal transport of wheat-germ agglutinin conjugated to horseradish peroxidase has been used to define the projections of the locus coeruleus toward the lateral thalamic nuclei in the rat. These projections had been overlooked in studies using neuroanatomical tract tracing techniques, despite the demonstration of the presence of norepinephrine in the lateral thalamus using histofluorescence and immunocytochemical techniques. Results obtained confirm the presence of a rather dense network of coeruleo-thalamic afferents. Terminal fibers appear thin and contorted, which could explain previous negative results. These anatomical data underline the possible role of the locus coeruleus in the modulation of the various sensory systems at the thalamic level.