Extensive dendritic arborizations of rat SPON neurons

The rat superior paraolivary nucleus (SPON) is a prominent cell group in the superior olivary complex (SOC). The SOC functions in several aspects of hearing, including sound source localization, coding spectral and temporal features of sounds and descending modulation of the cochlea. Neurons in the rat SPON appear to function mainly in coding sound offsets through GABAergic projections to the midbrain and thalamus. SPON neurons have multipolar dendritic arbors, and several qualitative studies have identified dendritic branches extending beyond the nucleus and into the nearby ventral nucleus of the trapezoid body (VNTB). The purpose of this study was to gauge the predominance of SPON dendrites extending into the VNTB, determine if other SOC nuclei receive such dendrites and perform a quantitative analysis of SPON dendritic arbors. A combination of immunohistochemistry and Golgi impregnations revealed that rat SPON neurons send dendrites in all directions, and the majority of neurons have dendrites that extend into the VNTB and frequently into the dorsal ribbon of the SOC (dSOC). Additionally, there were regional differences in SPON dendrites, including orientation angle, arbor shape and which SOC nuclei were reached, which may impact response properties and dynamic range. The function of SPON dendrites extending into adjacent nuclei is unclear but may involve sampling of descending input from the inferior colliculus and auditory cortex.