Anatomical aspects of the superior olivary complex

Abstract

The cytology of the superior olivary complex was studied in nissl stained sections of eight human brainstems, including adult, infant and fetus, and in the brains of ten juvenile rhesus monkeys. The most prominent components of the superior olivary complex of primates were specifically investigated, i.e. the medial (SOM) and lateral (SOL) superior olivary nuclei. Cell counts of these segments were done in human brainstems. The adult SOM was comprised of an average of 11,428 (7,850--15,010) perikarya; the SOL contained an average of 3,923 (2,890--5,400) neurons. These findings indicate that the SOL contains as many cells as reported in other primates, and is not reduced. The SOL appears somewhat inconspicuous in the human because it is organized into as many as six clusters of cells rather than forming one well circumscribed configuration as in the monkey and cat. The total cell population of the SOM together with the SOL was approximately the same on each side of individual brains. If one segment was larger on one side than the opposite side, the other segment was correspondingly reduced to maintain the relative symmetry. This suggests that a single mechanism controls the cell complement of at least two segments of the superior olivary complex.

Characterization of the rhesus monkey superior olivary complex by calcium binding proteins and synaptophysin

“…In agreement with other primate studies (Moskowitz, 1969;Moore & Moore, 1971;Strominger & Hurwitz, 1976;Moore, 1987), in our study the rhesus monkey MSO was the most prominent nucleus within SOC.…”

“…Perikarya of MSO are commonly spindle or triangular shaped in rhesus monkeys (present study) as well as in humans (Strominger & Hurwitz, 1976;Strominger, 1978), and are similar to neuronal types found in cats (Schwartz, 1977;Kiss & Majorossy, 1983), mices and gerbils (Schwartz, 1992). We found the principal neurons of the rhesus monkey MSO to be smaller (Table 1) than those of the gerbil, which have a soma size of 14.5 × 25.5 µ m (Bazwinsky, 1998).…”

Organization of the human superior olivary complex

“…As seen in Figure 2, the human LSO is a small oval or bilobed nucleus with dendrites confined to the body of the nucleus. Cell counts of the human lateral olivary nucleus show a total of 2,500 -4,000 cells (Moore and Moore, 1971;Strominger and Hurwitz, 1976), which is smaller than the LSO in the cat and similar in absolute size to the nucleus in rodents and insectivores.…”

“…This low-frequency bias may account for the fact that the MSO is a major component of the SOC of all primates, including man. With 10,000 -11,000 cells (Moore and Moore, 1971;Strominger and Hurwitz, 1976), the human MSO is almost twice as large as that of the cat. The size of the human MSO reflects a steady increase across primates (Moore and Moore, 1971), from prosimians (2,500 -2,700 cells) to ceboid and cercopithecoid monkeys (4,500 -5,500 cells) to apes (7,000 cells).…”

The emerging framework of mammalian auditory hindbrain development

“…Furthermore, two cell types were described based on location, morphology and immunoreactivity against non-phosphorylated neurofilament protein and neuronal nitric oxide synthetase, which lack counterparts in non-primates (Baizer et al 2014). Within the SOC, the human MSO appears as a very prominent nucleus, while the LSO is rather small (Kulesza 2007;Moore 1987;Strominger and Hurwitz 1976). Compared to other mammals, the human MNTB seems to be reduced and was even questioned to exist (Moore 2000;Hilbig et al 2009;Bazwinsky et al 2003).…”