SEROTONINERGIC INNERVATION OF STAPEDIAL AND TENSOR TYMPANI MOTONEURONS

Retrograde tracing and neurotransmitter immunohistochemistry were comb ined to determine whether serotonin neurons innervated stapedial and t ensor tympani motoneurons. With high-power light microscopy, putative axe-somatic and axe-dendritic contacts were observed between serotonin -positive endings and both stapedial and tensor tympani motoneurons, i ndicating that serotonin neurons terminate on brainstem motoneurons in nervating the middle-ear muscles. With this connection, the serotonin system may directly modulate middle-ear muscle activity. (C) 1998 Else vier Science B.V.