The objective of this investigation was to study the anatomical characteristics of efferent vestibular neurons within the brainstem of the chinchilla. Retrograde labeling of brainstem neurons projecting to the inner ear labyrinth was accomplished by adminstering solution of 30% horseradish peroxidase(HPR) into the labyrinths total of 15 chinchillas. Neurons containing HRP were found in the following regions of the chinchilla brainstem : lateral and medial to the genu of facial nerve, in a region analogous to the caudal pontine reticular nucleus(CPR). The most numerous labeled neurons of any group were found in the lateral portion of group e, where frequency of labeled neurons ranged 27-137 and 52-199 for ipsi- and contralateral areas, respectively. The new group of efferent neurons was found in dorsomedial region of the facial genu in chinchilla. The labeled neurons found in both ipsi and contralateral regions of group e and CPR confirmed to three basic morphologies. These included spherical, ovoid and polymorphic. The most frequently occurring cell morphology in all groups was spherical, which had diameters ranging between 6 and 27μm.
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