MORPHOLOGY OF SINGLE AFFERENTS OF THE SACCULAR MACULA IN CATS

The morphology of single saccular afferents was studied by the intrace llular horseradish peroxidase (HRP) method. Four neurons were sufficie ntly stained to allow reconstruction of their axonal arborizations. Th e main axon of these neurons bifurcated into an ascending and a descen ding branch at the level of the lateral nucleus. The ascending branche s of two axons gave off collaterals with boutons in the caudal part of the superior nucleus, while the other two ascending branches lacked s uch terminations. By contrast, characteristics of the descending axona l arborization patterns of all the four neurons were substantially the same. The descending branches coursed caudally through the lateral pa rt of the descending nucleus, and gave off up to 14 collaterals with b outons that extended throughout this nucleus. These collaterals also r eached the ventral part of the lateral nucleus, the lateral border of the medial nucleus, and group f. A few axon collaterals ramified even outside the border of the vestibular nuclei into the spinal trigeminal nucleus and the reticular formation surrounding it. Axon collaterals from the stem axon also terminated in the interstitial nucleus of the vestibular nerve. There was a noticeable absence of any projection to the y group. (C) 1998 Elsevier Science Ireland Ltd.