Divergent projections of physiologically characterized rat ventral cochlear nucleus neurons as shown by intra-axonal injection of horseradish peroxidase

Abstract

An attempt was made to correlate electrophysiological and morphological characteristics of rat ventral cochlear nucleus neurons. Their axonal course and their soma morphology were investigated using the intra-axonal horseradish peroxidase method. Prior to labeling, neurons were characterized by recording their response patterns to acoustic stimulation with pure tones. Three types of cells were found: Category I (37 neurons) exhibited "primarylike" responses and a spontaneous firing rate below 10 spikes/s. Category II (21 neurons) showed "on" responses and little spontaneous activity. Category III (9 neurons) had "primarylike" responses like neurons in category I. However, the spontaneous activity rate of these neurons was significantly higher (mean: 95 spikes/s). Among the response categories, the morphological characteristics differed in some prominent aspects. Within each category, however, the morphological properties were rather similar. All neurons in category I were globular/bushy cells located in the area of the entrance of the cochlear nerve. The axon of each cell coursed along the ventral acoustic stria and consistently innervated the lateral superior olive ipsilaterally, and the nucleus of the trapezoid body and the nucleus of the lateral lemniscus contralaterally. Some neurons also projected to periolivary nuclei ipsilaterally and contralaterally. Neurons in category II were located in the posteroventral cochlear nucleus and were presumably multipolar/stellate cells. Their axons coursed via the intermediate acoustic stria and innervated mainly contralateral periolivary regions as well as the contralateral nucleus of the lateral lemniscus. Ipsilaterally, the lateral superior olive and the superior periolivary nucleus were innervated by some of the category II neurons. Somata types of neurons in category III could not be identified morphologically, but somata were located in caudal parts of the posteroventral cochlear nucleus that correspond to the octopus cell area. Their axons coursed via the intermediate acoustic stria and innervated periolivary regions and the contralateral nucleus of the lateral lemniscus. Thus, their axonal distribution differed only slightly from neurons in category II. These data confirm and extend previous findings regarding the efferent connections of ventral cochlear neurons. They emphasize the complexity of the axonal projection patterns of single cochlear nucleus cells. Since two types of response patterns and three types of axonal projection patterns have been observed, there remains an ambiguous relation between response pattern and axonal projection site.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurons in the cochlear nuclei controlling the tensor tympani muscle in the rat: A study using pseudorabies virus

“…The presence of those labeled cells were especially significant in the dorsal VCN at survival times for which labeling was also consistently observed in the PO and the MNTB of both SOC. Prior investigations showed that multipolar-type (i.e., marginal and planar) and bushytype of cells in the VCN projected to the PO group and the contralateral MNTB (e.g., Friauf and Ostwald, 1988;see Cant and Benson, 2003;see Malmierca, 2003). On the other hand, cells in the PO and MNTB were shown to control the TT motoneuronal pool bilaterally (e.g., Borg, 1973;Rouiller et al, 1986).…”

Similar Intracellular Ca2+Requirements for Inactivation and Facilitation of Voltage-Gated Ca2+Channels in a Glutamatergic Mammalian Nerve Terminal

“…Auditory brainstem circuits discharge at high rates during sound stimulation and show varying levels of spontaneous AP firing even in the complete absence of sound (Friauf and Ostwald, 1988;Taberner and Liberman, 2005;Tolnai et al, 2008;Sonntag et al, 2009). Within the MNTB of adult rats, spontaneous discharge rates vary between zero and 133 Hz (mean 29 Hz, Tolnai et al, 2008).…”

“…Such elevations of the global volume average [Ca 2ϩ ] i are easily achieved during repetitive AP firing, especially at higher frequencies when individual APevoked [Ca 2ϩ ] i transients start to summate. Since auditory circuits discharge at high rates during sound stimulation and show varying levels of spontaneous AP firing even in the complete absence of sound (Friauf and Ostwald, 1988;Taberner and Liberman, 2005;Tolnai et al, 2008;Sonntag et al, 2009), presynaptic VGCCs at the calyx of Held and presumably also in other auditory terminals predominantly expressing Ca V 2.1 channels will be subject to strong Ca 2ϩ -dependent regulation.…”

Onset Neurones in the Anteroventral Cochlear Nucleus Project to the Dorsal Cochlear Nucleus

“…A previous study in rat (Friauf and Ostwald 1988) indicated that onset responding cells (''presumably stellate'') in the ventral cochlear nucleus projected to various superior olive and periolivary sites as well as to the contralateral lateral lemniscus. We found no evidence of such ramifications, even in the axon that was traced to the contralateral cochlear nucleus.…”