Aging effects on monoamines in rat medial vestibular and cochlear nuclei

• Published in: Hearing research 1996-10, Vol.100 (1), p.150-156
• Main Authors: Cransac, Hervé, Peyrin, Liliane, Cottet-Emard, Jean-Marie, Farhat, Faten, Pequignot, Jean-Marc, Reber, Annie
• Format: Article
• Language: English
• Subjects: 3,4-Dihydroxyphenylacetic Acid - analysis; 3,4-Dihydroxyphenylacetic Acid - metabolism; Aging; Aging - pathology; Animals; Anterior Hypothalamic Nucleus - cytology; Anterior Hypothalamic Nucleus - metabolism; Auditory Threshold - physiology; Chromatography, High Pressure Liquid; Cochlear nucleus; Cochlear Nucleus - cytology; Cochlear Nucleus - metabolism; Dopamine - analysis; Dopamine - metabolism; Dorsomedial Hypothalamic Nucleus - cytology; Dorsomedial Hypothalamic Nucleus - metabolism; Female; Hydroxyindoleacetic Acid - analysis; Hydroxyindoleacetic Acid - metabolism; Locus Coeruleus - cytology; Locus Coeruleus - metabolism; Medial vestibular nucleus; Methoxyhydroxyphenylglycol - analysis; Methoxyhydroxyphenylglycol - metabolism; Monoamine; Neurochemistry; Neurons - cytology; Norepinephrine - analysis; Norepinephrine - metabolism; Raphe Nuclei - cytology; Raphe Nuclei - metabolism; Rat; Rats; Serotonin - analysis; Serotonin - metabolism; Ventromedial Hypothalamic Nucleus - cytology; Ventromedial Hypothalamic Nucleus - metabolism
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/0378-5955(96)00116-5

Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and their metabolites — 3-methoxy,4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) — were determined using HPLC in medial vestibular nucleus (MVN), anteroventral cochlear nucleus (AVCN), dorsal+posteroventral cochlear nucleus (DCN+PVCN), locus coeruleus (LC) and raphe dorsalis of Dark Agouti-Hanovre (DA-HAN) rats aged 4, 21 and 24 months. In older rats, the main noradrenergic changes were a decrease of NA content with an increase of the MHPG/NA ratio in MVN and a selective NA increase in AVCN. 5-HT and 5-HIAA levels were increased in all the brainstem nuclei except raphe dorsalis. DA and DOPAC remained unchanged. These data show that noradrenergic neurons in sensory nuclei are differently affected by aging whereas serotonergic activation occurs in most of them possibly as a compensatory response to dysfunction of sensory input and processing. The increase of NA stores in the AVCN of aged rats is in line with the elevated auditory brainstem threshold reported in old rats and could improve the signal-to-noise ratio. Noradrenergic neurons in the MVN seem to be more sensitive to age effect than cochlear nuclei; however, even if neuronal loss occurs, NA synthesis and/or metabolism increase to ensure normal or increased noradrenergic activity.