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 garnetti i) brainstem. Light-microscopic examination (using a 100 X plan apochr omatic oil-immersion objective) of the sections revealed that serotoni n-positive varicosities (presumptive terminal endings) contacted somat a and dendrites of neurons belonging to both the lateral and medial ol ivocochlear neurons near the superior olivary nuclei. These results pr ovide direct evidence that the olivocochlear system (a specific audito ry brainstem pathway) receives input from the serotoninergic system (a diffuse reticular brainstem network).