Age-related changes in brain RNA of noise stressed mice

Correlative data were obtained on RNA levels of cerebrocortical neurons, adrenal fasciculate cell RNA content and serum corticosterone levels in 10, 40 and 100 week old male C57BL/6J mice immediately following a 30 interval of continuous noise stimulation (100 dB re 2 x 10(-5) N/m2, 0.35-20 kHz) and at 1 hr and 4 hr recovery intervals. Quantification of cellular RNA levels entailed use of scanning-integrating microdensitometry of azure B stained tissue sections. Hormonal analyses were done by radioimmunoassay. Noise stimulation induced a mild to moderate adrenocortical activation and a moderate elevation of serum corticosterone levels in all age groups. Noise exposure also resulted in an increase in the RNA content of cerebrocortical neurons. However, maximal neuronal RNA levels proved to be considerably lower (32-36%) in 100 week old mice as compared to both 10 and 40 week old mice during the post-exposure intervals. The overall data support the existence of a lower neuronal capacity for sensory induced RNA synthesis in 100 week old mice. The data also suggest that age dependent differences in neuronal responsiveness are not directly related to the extent of adrenal RNA activation or to a lower availability of circulating glucocorticoids.