Resumen de Neurochemical organization of projections from nuclei of the pontomesencephalic tegmentum to the retrosplenial granular cortex of the rat
Retrograde labelling was combined with immunohistochemistry to localize neurons containing serotonin, dopamine-?-hydroxylase, choline acetyltransferase, glutamate, leu-enkephalin, neurotensin, and substance P-like immunoreactivity in the projections from nuclei of the mesencephalic tegmentum to the retrosplenial granular cortex in the rat. Injections of horseradish peroxidase conjugated to subunit B of cholera toxin (CT-HRP) into the retrosplenial granular cortex resulted in large numbers of CT-HRP-labelled neurons in the dorsal raphe nucleus and in the locus coeruleus, whereas small numbers were found in the median raphe nucleus. In addition, following injections into the retrosplenial cortex which also involved the adjacent anterior cingulate cortex, small numbers of CT-HRP-labelled neurons were found in the laterodorsal tegmental nucleus. In the dorsal and median raphe nuclei, most of the CT-HRP-labelled neurons (80-85% in the dorsal and 90-95% in the median raphe nuclei) were immunoreactive for serotonin and small numbers (1 to 4-5 per section) of retrogradely labelled neurons were immunoreactive for glutamate, neurotensin, leu-enkephalin or substance P. In the locus coeruleus, 90-95% of the CT-HRP labelled neurons were immunoreactive for dopamine-?-hydroxylase, whereas a few neurons (1-3 per section) also displayed neurotensin - and substance P - immunoreactivity. In the laterodorsal tegmental nucleus, most of the CT-HRP-labelled neurons contained choline acetyltransferase and small numbers were immunoreactive for substance P. These results suggest that serotonergic and noradrenergic fibres represent the main ascending projections from the mesencephalic tegmentum to the retrosplenial granular cortex.
