Presence of 5-HT-positive neurons in the medial nuclei of the solitary tract.

The main serotoninergic groups have been described in the midbrain raphe; in the region of the solitary tract, serotonin (5-HT) has been localized in varicose processes and terminals. This study shows the presence of serotoninergic neurons located in the medial nuclei of the solitary tract of intracisternally injected rats, and describe the mapping, the morphological and morphometrical characteristics of these neurons in young and old rats. In old rats the number of these neurons is approximately double the amount detected in young rats. The suggestions on the functional meaning of these findings are discussed.