Sound stimulation and its effects on the pituitary-adrenocortical function and brain catecholamines in rats

The purpose of the present study was to investigate in rats, the effects of sound stimulation upon both the pituitary-adrenal activity (evaluated by the levels of serum corticosterone (B)) and brain dopamine (DA) and noradrenaline (NA). Serum B in rats placed inside the experimental chamber without any sound stimulation was increased and brain DA decreased. For this reason, prior to any sound application, animals were kept in the experimental chamber for 115--120 min, when values had returned to basal levels. The results obtained on the effects of sound frequencies between 500 and 4,000 cps indicated a greater response in the rat pituitary-adrenal system to the lowest frequency (500 cps) we studied. Adrenal cortex hyperactivity occurred in the initial stage of daily repeated 500 cps sound stimulation. During extended periods of daily exposure, the activity of the pituitary-adrenal axis gradually diminished. Changes in the pituitary-adrenal activity, induced by sound stimulation, are closely related to changes in brain NA. The results obtained suggest that at least some of the effects of sound stimulation might be mediated by brain noradrenergic pathways and agree with the hypothesis concerning the existence of a central noradrenergic nervous component which could participate in the control of ACTH secretion.