Abstract
Subcortical auditory structures in the macaque auditory system increase their densities of neurons expressing the calcium binding protein parvalbumin (PV) with age. However, it is unknown whether these increases occur in the thalamic division of the auditory system, the medial geniculate nucleus (MGN). Furthermore, it is also unclear whether these age-related changes are specific to the macaque auditory system or are generalized to other sensory systems. To address these questions, the PV immunoreactivity of the medial and lateral geniculate nuclei (LGN) from seven rhesus macaques ranging in age from 15 to 35 was assessed. Densities of PV expressing neurons in the three subdivisions of the MGN and the six layers of the LGN were calculated separately using unbiased stereological sampling techniques. We found that the ventral and magnocellular subdivisions of the MGN and all six layers of the LGN increased their expressions of PV with age, although increases in the MGN were greater in magnitude than in the LGN. Together, these results suggest that the MGN shows age-related increases in PV expression as is seen throughout the macaque ascending auditory system, and that the analogous region of the visual system shows smaller increases. We conclude that, while there are some similarities between sensory systems, the age-related neurochemical changes seen throughout the macaque auditory system cannot be fully generalized to other sensory systems.
Highlights
Parvalbumin (PV) immunoreactivity is a well-established neurochemical marker of subsets of neurons in several sensory systems of the mammalian brain (Demeulemeester et al, 1989; Celio, 1990; Hof et al, 1999; Jones, 2003; Dávid et al, 2007)
To understand the age-related changes in PV expression within the medial geniculate nucleus (MGN) and lateral geniculate nuclei (LGN), serial sections from seven rhesus macaques ranging in age from 15 to 35 years were prepared (Table 1)
AGE-RELATED DIFFERENCES IN PV IMMUNOREACTIVITY IN THE CENTRAL AUDITORY SYSTEM The primary objective of this study was to determine whether the macaque MGN increases its PV expression with age as seen in the superior olivary complex (SOC) (Gray et al, 2013a), and inferior colliculus (IC)
Summary
Parvalbumin (PV) immunoreactivity is a well-established neurochemical marker of subsets of neurons in several sensory systems of the mammalian brain (Demeulemeester et al, 1989; Celio, 1990; Hof et al, 1999; Jones, 2003; Dávid et al, 2007). PV and other calcium binding proteins have calcium-buffering capacities, and several types of cortical interneurons are classified by their chemical signatures to these molecules (Carder et al, 1996). Intracellular calcium affects numerous calcium dependent biochemical pathways, most of which alter the physiological environment of the cell. These calcium-buffering proteins indirectly regulate intracellular processes through their control of free calcium levels (Yáñez et al, 2012). A coarse sense of changes in the intracellular environment and signaling capabilities of neurons can be attained by using histological markers for calcium binding proteins as chemical probes, and noting changes in their expression under different conditions, in this case natural aging
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