Brief and repeated noise exposure produces different morphological and biochemical effects in noradrenaline and adrenaline cells of adrenal medulla

Abstract

Exposure to stressful stimuli is known to activate the peripheral sympathetic nervous system and the adrenal gland. In this study, we evaluated the effects of single or repeated bouts of exposure to a readily measurable stressful stimulus (loud noise) on the catecholamine content and ultrastructure of the rat adrenal medulla. In particular, we measured tissue levels of dopamine, noradrenaline, adrenaline and metabolites. In parallel studies, we evaluated the fine ultrastructure of catecholamine cells, including a detailed study of catecholamine granules and a morphometric analysis of adrenaline and noradrenaline medullary cells. Animals were exposed either to a single (6 h) session of loud (100 dBA) noise, or to this noise stimulus repeated every day for 21 consecutive days. There was a marked correlation between biochemical indexes of catecholamine activity and the ultrastructural morphometry of specific catecholamine granules. Exposure to loud noise for 6 h induced a parallel increase in dopamine, noradrenaline, adrenaline and their metabolites, a polarization and an increased numerical density of noradrenaline and adrenaline granules in the cells. After repeated noise exposure, noradrenaline levels were significantly higher than in controls, and adrenaline decreased significantly. In addition, adrenaline cells also exhibited ultrastructural alterations consisting of wide homogeneous cytoplasmic areas and large, pale vesicles.

Fig. 1

Effects of noise exposure on CA content in the adrenal medulla. (A) Dopamine (DA); (B) noradrenaline (NA); (C) vanilmandelic acid (VMA); (D) methoxyhydroxyphenylethylglycole (MOPEG); (E) adrenaline (A) levels in the adrenal medulla in baseline conditions (□) or following noise exposure (▪). Brief noise exposure consisted of a single session (6 h) of loud (100 dBA) noise, while prolonged noise exposure consisted of consecutive sessions repeated for 21 days. Values are given in nmol/mg of medullary protein. Each group was composed of 10 rats and data represent the mean ± SEM of each group. Comparisons between groups were carried out by using anova with Sheffè's post-hoc analysis. P< 0.05 compared with baseline levels.

Fig. 2

Noradrenaline cells after noise exposure. (A) After brief noise exposure, a NA cell shows areas of empty cytoplasm (*) (×12 000), alternating with areas of densely packed granules (B, ×9500). After repeated noise exposure, granules increase homogeneously within the cytoplasm (C, ×10 000). N = nucleus.

Fig. 3

Adrenaline cells after repeated noise exposure. (A) (×13 600) The cytoplasm of an A cell shows scattered granules (arrows) alternated with big vacuoles at low (B, ×7000) and high (C, ×14 500) magnification. Arrowheads indicate the zone between two vacuoles. N = nucleus.