CERVICAL PRIMARY AFFERENT INPUT TO VESTIBULOSPINAL NEURONS PROJECTINGTO THE CERVICAL DORSAL HORN - AN ANTEROGRADE AND RETROGRADE TRACING STUDY IN THE CAT

Vestibulospinal neurons in the caudal half of the medial and descendin g vestibular nuclei terminate in the cervical spinal cord, not only in the ventral horn and intermediate zone but also in the dorsal horn. T he purpose of the present study was to examine whether the areas conta ining these vestibulospinal neurons are reached by cervical primary af ferents. In one group of experiments, wheat germ agglutinin-horseradis h peroxidase conjugate and horseradish peroxidase were pressure inject ed into spinal ganglia C-2-C-8 and revealed anterogradely labeled fibe rs and boutons in the caudal part (caudal to the dorsal cochlear nucle us) of the ipsilateral medial and descending vestibular nuclei. This p rojection was verified in experiments in which wheat germ agglutinin-h orseradish peroxidase conjugate was microiontophoretically injected in to the caudal half of either the medial or the descending vestibular n uclei and revealed retrogradely labeled cells only in ipsilateral spin al ganglia C-2-C-7, with a maximum of cells in C-3 In another group of experiments, after microiontophoretic injections of Phaseolus vulgari s leucoagglutinin or Biocytin into either the medial or the descending vestibular nuclei, anterogradely labeled fibers and boutons were pres ent in the cervical spinal cord, mainly bilaterally in the dorsal horn (laminae I-VI) but also, to a lesser extent, in the ventral horn and intermediate zone. The existence of a loop that relays cervical primar y afferent information to vestibulospinal neurons projecting to the ce rvical spinal cord, in particular the dorsal horn, may have implicatio ns for vestibular control over local information processing in the cer vical dorsal horn. (C) 1995 Wiley-Liss, Inc.