THE OLIVOCEREBELLAR PROJECTION IN NORMAL (+ +), HETEROZYGOUS WEAVER (WV/+), AND HOMOZYGOUS WEAVER (WV/WV) MUTANT MICE - COMPARISON OF TERMINAL PATTERN AND TOPOGRAPHIC ORGANIZATION/

Olivocerebellar organization and topography were analyzed in adult nor mal (+/+), heterozygous weaver (wv/+), and homozygous weaver (wv/wv) m utant mice. The two genotypes (wv/+ and wv/wv) of the weaver mutant pr esent a gradation of abnormal cerebellar morphology. Purkinje cell (PC ) ectopia ranges from mild (wv/+) to moderate (wv/wv), and regional PC loss is also graded in the two types. To determine olivocerebellar or ganization and topography, tritiated amino acids were placed into diff erent regions of the inferior olivary complex (10) in normal, heterozy gous, and homozygous weaver mice. Despite some PC loss and ectopia, ol ivocerebellar fiber (OCF) terminals in both homozygous and heterozygou s weaver mice have an orthogonal distribution and topography similar t o that seen in normal mice. Differences in OCF termination, such as an increased density of OCF terminal label in the lower portion of the m olecular layer, the PC, and granule cell layers, are seen in homozygou s weaver mice. In some heterozygous weaver and normal cases, multiple injections labeling most IO cells on one side of the IO resulted in co ntinuous OCF terminal labeling in many regions of the contralateral ce rebellar cortex, suggesting that all PCs receive OCF input. Retrograde analysis involving injections of horseradish peroxidase conjugated to wheat germ agglutinin into different mediolateral cerebellar regions in homozygous weaver mice further demonstrates a generally normal oliv ocerebellar topography.