The cytoarchitecture of the nucleus angularis of the barn owl (Tyto alba)

Abstract

The cochlear nucleus angularis (NA) of the barn owl (Tyto alba) was analyzed using Golgi, Nissl, and tract tracing techniques. NA forms a column of cells in the dorsolateral brainstem that partly overlaps with, and is rostral and lateral to, the cochlear nucleus magnocellularis (NM). Highest best frequencies are mapped in lateral NA (NAl), intermediate in medial NA (NAm), and lowest in the foot region (NAf). Cell density followed the tonotopic axis and decreased with decreasing best frequency. NA contained four major cell classes: planar, radiate, vertical, and stubby. Planar and radiate classes were further subdivided into bipolar and multipolar types according to their number of primary dendrites. Planar neurons were confined to an isofrequency band, whereas radiate neurons had dendrites that could extend across an isofrequency band. Vertical cells had long dendrites oriented perpendicularly to isofrequency bands. Stubby cells were the most numerous and were confined to an isofrequency band because of their short dendrites. Neurons in each of these four classes projected to the inferior colliculus and dorsal nucleus of the lateral lemniscus.

Heterogeneous Calretinin Expression in the Avian Cochlear Nucleus Angularis

“…Timing and intensity cues are processed in separate ascending pathways beginning with the cochlear nuclei Konishi 1978a, 1978b;Konishi et al 1985Konishi et al , 1988Moiseff and Konishi 1983;Sullivan and Konishi 1984;Takahashi et al 1984). The avian cochlear nuclei, NM and NA, receive information from the auditory nerve (Boord and Rasmussen 1963;Carr and Boudreau 1991;Häusler et al 1999;Krützfeldt et al 2010b;Parks and Rubel 1978;Puelles et al 2007;Soares and Carr 2001). NM specializes in encoding fine timing cues and projects to the binaural nucleus responsible for computing ITD, NL (Carr and Konishi 1990;Fukui et al 2006;Hackett et al 1982;Koyano et al 1996;Nishino et al 2008;Raman et al 1994;Reyes et al 1994;Smith 1981;Trussell 1999;Zhang and Trussell 1994).…”

“…The two anatomically distinct cochlear nuclei, nucleus magnocellularis (NM) and nucleus angularis (NA), each receive information from the auditory nerve and specialize for encoding timing information (NM) and intensity, or sound level, information (NA) for the computation of sound location (Boord 1968;Carr and Boudreau 1991;Parks and Rubel 1978;Puelles et al 2007;Reyes et al 1994;Sullivan and Konishi 1984;Trussell 1999). Nucleus angularis is highly heterogeneous in terms of neuronal morphology, acoustic response types in vivo and intrinsic physiology in vitro, and has multiple ascending projections, suggesting that it performs multiple functions Fukui and Ohmori 2003;Häusler et al 1999;Krützfeldt et al 2010a;MacLeod and Carr 2007;Sachs and Sinnott 1978;Sato et al 2010;Soares and Carr 2001;Soares et al 2002;Wang and Karten 2010;Warchol and Dallos 1990). The present study was undertaken to better define the molecular characterization of neurons in NA.…”

“…Over development, the immunolabeling also became progressively less intense in the neuropil and more intense in the cell body. Previous studies used single antibody approaches and were performed prior to characterization of the different cell types in NA based on morphological analysis Soares and Carr 2001). Therefore, the question of whether CR labeling was ubiquitous among the neuronal cell types in NA was not investigated, although the immunolabel intensity of the immunoreactivity was noted as heterogeneous.…”

Primary innervation of the avian and mammalian cochlear nucleus

“…The cell types in NA represent a heterogeneous mixture that has been defined as bipolar or multipolar cells on the basis of size and dendritic characteristics [69,188]. Planar and stubby cells have dendrites restricted within isofrequency planes, whereas radiate cells and bipolar (or vertical) cells extend their dendrites across the isofrequency planes (Fig.…”

Beyond timing in the auditory brainstem: intensity coding in the avian cochlear nucleus angularis

“…Both cochlear nuclei are monaural, and project to binaural targets which compare inputs from the two ears (Manley et al, 1988;Takahashi and Konishi, 1988). While NM neurons are similar to the mammalian cochlear nucleus bushy cells, NA is a heterogeneous nucleus with many properties similar to non-bushy cell components of the mammalian cochlear nucleus (CN) Köppl and Carr, 2003;Oertel, 1999;Soares and Carr, 2001;Soares et al, 2002). This heterogeneity (described below) coupled with the extreme specialization of one pathway for timing cues beginning with NM, suggests that NA is largely responsible for encoding non-localization aspects of sound in addition to its role in the ILD pathway.…”