LIGHT-MICROSCOPIC EVIDENCE OF SEROTONINERGIC PROJECTIONS TO OLIVOCOCHLEAR NEURONS IN THE BUSH-BABY (OTOLEMUR GARNETTII)

Double-label techniques were used to concomitantly label olivocochlear neurons and serotoninergic fibers in the bush baby (Otolemur garnettii) brainstem. Light-microscopic examination (using a 100 X plan apochromatic oil-immersion objective) of the sections revealed that serotonin-positive varicosities (presumptive terminal endings) contacted somata and dendrites of neurons belonging to both the lateral and medial olivocochlear neurons near the superior olivary nuclei. These results provide direct evidence that the olivocochlear system (a specific auditory brainstem pathway) receives input from the serotoninergic system (a diffuse reticular brainstem network).