Innervation of motoneurons based on dendritic orientation.

1. The distribution of terminals from vestibulospinal (VS) axons on the dendritic trees of neck motoneurons was determined by combining the anterograde transport of Phaseolus Vulgaris Leucoagglutinin (PHA-L) with intracellular staining techniques and three-dimensional reconstruction methods. 2. Contacts between VS axon terminals and dendrites were arranged in a nonuniform pattern that depended on the orientation (i.e., rostro-caudal vs. dorsolateral) of the dendrites. 3. This innervation pattern satisfies a critical structural condition necessary for selective nonlinear interactions between pairs of simultaneously active inputs to motoneurons.