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Brain, Behavior and Evolution (1)
Hearing Research (1)
The Journal of Comparative Neurology (1)
CARR, CATHERINE E. (2)
Carr, Catherine E. (1)
Kubke, M. Fabiana (1)
Massoglia, Dino P. (1)
TANG, YE-ZHONG (1)
Year of Publication
Timing Is Everything: Organization of Timing Circuits in Auditory and Electrical Sensory Systems
The Journal of Comparative Neurology
Bigger Brains or Bigger Nuclei? Regulating the Size of Auditory Structures in Birds
Kubke, M. Fabiana
Massoglia, Dino P.
Brain, Behavior and Evolution
Increases in the size of the neuronal structures that mediate specific behaviors are believed to be related to enhanced computational performance. It is not clear, however, what developmental and evolutionary mechanisms mediate these changes, nor whether an increase in the size of a given neuronal population is a general mechanism to achieve enhanced computational ability. We addressed the issue of size by analyzing the variation in the relative number of cells of auditory structures in auditory specialists and generalists. We show that bird species with different auditory specializations exhibit variation in the relative size of their hindbrain auditory nuclei. In the barn owl, an auditory specialist, the hind-brain auditory nuclei involved in the computation of sound location show hyperplasia. This hyperplasia was also found in songbirds, but not in non-auditory specialists. The hyperplasia of auditory nuclei was also not seen in birds with large body weight suggesting that the total number of cells is selected for in auditory specialists. In barn owls, differences observed in the relative size of the auditory nuclei might be attributed to modifications in neurogenesis and cell death. Thus, hyperplasia of circuits used for auditory computation accompanies auditory specialization in different orders of birds.
Evolution; Auditory; Neuronal computation; Birds; Allometry
Development of N-Methyl-D-Aspartate Receptor Subunits in Avian Auditory Brainstem
N-methyl-D-aspartate (NMDA) receptor subunit-specific probes were used to characterize developmental changes in the distribution of excitatory amino acid receptors in the chicken’s auditory brainstem nuclei. Although NR1 subunit expression does not change greatly during the development of the cochlear nuclei in the chicken (Tang and Carr  Hear. Res 191:79–89), there are significant developmental changes in NR2 subunit expression. We used in situ hybridization against NR1, NR2A, NR2B, NR2C, and NR2D to compare NR1 and NR2 expression during development. All five NMDA subunits were expressed in the auditory brainstem before embryonic day (E) 10, when electrical activity and synaptic responses appear in the nucleus magnocellularis (NM) and the nucleus laminaris (NL). At this time, the dominant form of the receptor appeared to contain NR1 and NR2B. NR2A appeared to replace NR2B by E14, a time that coincides with synaptic refinement and evoked auditory responses. NR2C did not change greatly during auditory development, whereas NR2D increased from E10 and remained at fairly high levels into adulthood. Thus changes in NMDA NR2 receptor subunits may contribute to the development of auditory brainstem responses in the chick.
cochlear nucleus; magnocellularis; laminaris; angularis; tonotopic gradient
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