Volumes of cochlear nucleus regions in rodents

Abstract

The cochlear nucleus receives all the coded information about sound from the cochlea and is the source of auditory information for the rest of the central auditory system. As such, it is a critical auditory nucleus. The sizes of the cochlear nucleus as a whole and its three major subdivisions – anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), and dorsal cochlear nucleus (DCN) - have been measured in a large number of mammals, but measurements of its subregions at a more detailed level for a variety of species have not previously been made. Size measurements are reported here for the summed granular regions, DCN layers, AVCN, PVCN, and interstitial nucleus in 15 different rodent species, as well as a lagomorph, carnivore, and small primate. This further refinement of measurements is important because the granular regions and superficial layers of the DCN appear to have some different functions than the other cochlear nucleus regions. Except for DCN layers in the mountain beaver, all regions were clearly identifiable in all the animals studied. Relative regional size differences among most of the rodents, and even the 3 non-rodents, were not large and did not show a consistent relation to their wide range of lifestyles and hearing parameters. However, the mountain beaver, and to a lesser extent the pocket gopher, two rodents that live in tunnel systems, had relative sizes of summed granular regions and DCN molecular layer distinctly larger than those of the other mammals. Among all the mammals studied, there was a high correlation between the size per body weight of summed granular regions and that of the DCN molecular layer, consistent with other evidence for a close relationship between granule cells and superficial DCN neurons.

Brain atlas of the African mole‐ratFukomys anselli

“…(mountain beaver) of the total cochlear nucleus volume (cat: 35%; Osen, 1969). Godfrey et al (2016) interpreted these features of the DCN as possible adaptations facilitating the integration of somatosensory and auditory stimuli in the underground habitat which is in line with the interpretation of the dorsal cochlear nucleus in mammals, generally (see also Malmierca, 2015). The granule cells of the DCN receive direct input from many sources including the trigeminal somatosensory system and this information is likely processed in the molecular layer (Young & Davis, 2002).…”

“…While being less laminated than in the rat, the DCN of the Ansell's mole‐rat is characterized by a thickened molecular layer (DCMo, plate 940, Figure ) and an enlarged granular layer (GrC, plate 920). A prominent DCN has also been reported for the tunnel‐dwelling mountain beaver ( Aplodontia rufa ) and the subterranean pocket gopher (Godfrey et al, ). In these species, the DCN amounts to more than 60% (pocket gopher) or almost 90% (mountain beaver) of the total cochlear nucleus volume (cat: 35%; Osen, ).…”

“…These layers in the Ansell's mole‐rat might fulfill a similar function which is likely related to the somatosensory system but unrelated to pinna movements and sound localization. Godfrey et al () were puzzled by the fact that the naked‐mole rat DCN did not show the “hypertrophic” features seen in other tunnel‐dwelling rodents like the mountain beaver or the pocket gopher but resembled more the DCN of epigeic species. It did not show thickened molecular and granular layers and the relative size of the naked mole‐rat DCN was similar to the DCN of the cat.…”

“…for the tunnel-dwelling mountain beaver (Aplodontia rufa) and the (Continues) (Continues) (Godfrey et al, 2016). In these species, the DCN amounts to more than 60% (pocket gopher) or almost 90%…”

Connexin36 expression in the cochlear nucleus complex of the echolocating bat, Eptesicus fuscus

“…We also used data from Carter et al (2004) to estimate the volume of the bat CN. Results showed that the bat CN exhibits substantial hypertrophy (total volume 1.15 mm 3 ), compared to the total volume of the mouse CN at 0.6 mm 3 (Muniak et al 2013, Godfrey et al 2016). Surprisingly, a larger percent area of the mouse CN compared to the bat’s expressed Cx36.…”