Nature of optokinetic response and zonal organization of climbing fiber afferents in the vestibulocerebellum of the pigmented rabbit. II. The nodulus.

In pigmented rabbits anesthetized with N2O (70%) and halothane (2-4%), Purkinje cells were extracellularly recorded in the nodulus. Large field (60 degrees x 60 degrees) optokinetic stimulation (OKS) with constant velocity was delivered to either the ipsi- or contralateral eye, and the direction and velocity selectivities of complex spike responses were examined. To ipsilateral OKS (n = 181), the preferred direction was forward (F, n = 72), upward (U, n = 38) or downward (D, n = 10), while the remaining cells (n = 61) showed no response (N). To contralateral OKS (n = 117), the preferred direction was backward (B, n = 22), upward (U, n = 7) or downward (D, n = 22), while the rest (n = 66) showed N. Cells tested with both eyes (n = 95) fell into 8 categories based on the preferred direction to ipsi- and contralateral OKS: (1) ipsi-F and contra-B (F/B type, n = 20), (2) ipsi-F but contra-N (F/N type, n = 12), (3) ipsi-U and contra-D (U/D type, n = 15), (4) ipsi-U but contra-N (U/N type, n = 13), (5) ipsi-N but contra-D (N/D type, n = 1), (6) ipsi-D but contra-N (D/N type, n = 5), (7) ipsi-N but contra-U (N/U type, n = 6), and (8) N to both eyes (N/N type, n = 23). The optimum velocity was in the range 0.1-2.0 degrees/s for all cells responsive to OKS. In the ventral lamella, four medio-laterally aligned zones were demonstrated. In the most medial zone (0-0.5 mm from the midline), the majority of cells showed ipsi-N or contra-N responses. In the second zone (0.5-1.5 mm), most cells preferred ipsi-F or contra-B directions. In the third zone (1.5-2.5 mm), most cells preferred ipsi-U or contra-D directions. In the most lateral zone (2.5-3.5 mm), most cells preferred ipsi-F or contra-B directions. In the dorsal lamella, a longitudinal zone characterized with cells preferring ipsi-U or contra-D directions was found about 1.5-2.5 mm from the midline. This zone seemed to be the continuation of the third zone in the ventral lamella. Cells preferring ipsi-D or contra-U directions were scattered in the medial half of both the dorsal and ventral lamellae.(ABSTRACT TRUNCATED AT 400 WORDS)