Age-related neurochemical changes in the rhesus macaque cochlear nucleus

• Published in: Journal of comparative neurology (1911) Vol. 522; no. 7; pp. 1527 - 1541
• Main Authors: Gray, Daniel T., Engle, James R., Recanzone, Gregg H.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.05.2014; Wiley Subscription Services, Inc
• Subjects: ABR; aging; Aging - pathology; Aging - physiology; Animals; brainstem; Cell Count; Cochlear Nucleus - pathology; Cochlear Nucleus - physiology; Evoked Potentials, Auditory, Brain Stem - physiology; Female; Gene Expression - physiology; geriatric; Hair Cells, Auditory, Outer - pathology; Hair Cells, Auditory, Outer - physiology; Immunohistochemistry; Macaca; Macaca mulatta; Male; monkey; NADPH Dehydrogenase - metabolism; NADPH-diaphorase; Neurons - pathology; Neurons - physiology; parvalbumin; Parvalbumins - metabolism; Regression Analysis; ABR; monkey; NADPH-diaphorase; parvalbumin; brainstem; aging; geriatric
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23479

ABSTRACT Neurochemical changes in the expression of various proteins within the central auditory system have been associated with natural aging. These changes may compensate in part for the loss of auditory sensitivity arising from two phenomena of the aging auditory system: cochlear histopathologies and increased excitability of central auditory neurons. Recent studies in the macaque monkey have revealed age‐related changes in the density of nicotinamide adenine dinucleotide phosphate (NADPH)‐diaphorase (NADPHd) and parvalbumin (PV)‐positive cells within the inferior colliculus and superior olivary complex. The cochlear nucleus (CN), which is the first central auditory nucleus, remains unstudied. Since the CN participates in the generation of the auditory brainstem response (ABR) and receives direct innervation from the cochlea, it serves as an ideal nucleus to compare the relationship between these neurochemical changes and the physiological and peripheral changes of the aging auditory system. We used stereological sampling to calculate the densities of NADPHd and PV reactive neurons within the three subdivisions of the CN in middle‐aged and aged rhesus macaques. Regression analyses of these values with ABR properties and cochlear histopathologies revealed relationships between these cell types and the changing characteristics of the aging auditory system. Our results indicate that NADPHd expression does change with age in a specific subdivision of the CN, but PV does not. Conversely, PV expression correlated with ABR amplitudes and outer hair cell loss in the cochlea, but NADPHd did not. These results indicate that NADPHd and PV may take part in distinct compensatory efforts of the aging auditory system. J. Comp. Neurol. 522:1527–1541, 2014. © 2013 Wiley Periodicals, Inc. In the macaque auditory system, the superior olive and inferior colliculus show age‐related increases in the expression of parvalbumin and NADPH‐diaphorase. The cochlear nucleus remains unstudied in this animal model, therefore the purpose of this study was to determine if these chemical changes are also present at this level.