[Distribution of norepinephrine-containing neurons projecting to the parietal associative cortex and spinal cord in the cat locus coeruleus].

The distribution of neurons projecting to the parietal associative cortex and spinal cord in the locus coeruleus (LC) of the cat was examined by the retrograde transport of the horseradish peroxidase (HRP) and catecholamine histofluorescence technique. It was demonstrated that neurons projecting to the parietal cortex were localized predominantly in the dorsal LC and the most dense labeling was observed at the coronal section corresponding to frontal plane P-1. Neurons projecting to the spinal cord were concentrated in the ventral LC and the largest quantity of labeled neurons was found in the frontal plane P-3. Microinjections of HRP into the parietal cortex and spinal cord also caused intense retrograde labeling of neurons in the reticular formations of mesencephalon, pons varolii and medulla oblongata. Coeruleo-cortical and coeruleo-spinal projection neurons formed in the LC two partially overlapping cellular populations which could not be differentiated according to morphologic characteristics of their cells. It was concluded that the parietal associative cortex of cat as well as spinal cord had direct afferent inputs both from the LC and from the reticular formation.