Differences in mossy and climbing afferent sources between flocculus and ventral and dorsal paraflocculus in the rat

Sources of mossy and climbing fiber inputs to the flocculus (FL), ventral p araflocculus (VP) and/or dorsal paraflocculus (DP) were identified in the v estibular ganglion, medulla oblongata and pens of 19 Wistar rats after 26 l ocal injections of horseradish peroxidase, wheatgerm agglutinin-conjugated horseradish peroxidase, fast blue or diamidino yellow into the FL, VP and/o r DP. There were large differences in the sources of mossy fibers to the FL and VP/DP. Labeled neurons after injections into the FL were observed main ly in the ipsilateral vestibular ganglion, bilaterally in the vestibular an d prepositus hypoglossal nuclei, and in the caudal part of the nucleus reti cularis tegmenti pontis. Labeled neurons were rarely observed in the pontin e nuclei after localized injections into the FL. By contrast, after injecti ons into the VP and/or DP, numerous labeled neurons were observed in the po ntine nuclei with a contralatetral predominance and in the rostral part of the nucleus reticularis tegmenti pontis bilaterally, but not in the vestibu lar nuclei in either side. Sources of climbing fibers to the FL and paraflo cculus were completely contralateral to the injection side. After injection into the FL, labeled neurons were observed in the caudal dorsal cap and ve ntrolateral outgrowth of the inferior olivary nucleus. After injections int o the VP, labeled neurons were observed mainly in the rostral dorsal cap, v entral medial accessory olivary nucleus (MAO) and caudal half of the ventra l leaf of the principal olivary nucleus. After injections into the DP, labe led neurons were observed in the ventral MAO and caudal half of the ventral leaf of the principal olivary nucleus. These differences in the sources of mossy and climbing fiber inputs may suggest functional differences between the FL and VP/DP The present results are consistent with our previous obse rvations in monkey that the FL and VP/DP exhibit quite different mossy fibe r input organizations.