Stress-reactive response of the gerbil pineal gland: concretion genesis.

The reaction of pinealocytes and glia cells to an acute immobilization stress and their poststress recovery was studied in gerbils. Pinealocytes responded to immobilization with an increased peptidergic activity and formation of new concretions, whereas glia cells with an increased growth of interstitial concretions. The occurrence of degenerating pinealocytes indicated deleterious actions of immobilization stress on functionally stimulated cells. The pyroantimonate method to detect Ca2+ demonstrated enlarged crystalline profiles (Ca2+ crystallization into hydroxyapatite) in functionally stimulated pinealocytes and the accumulation of Ca2+ in the interstitial concretion. The pinealocyte concretions did not show the Ca2+ accumulation. The pineal gland poststress recovery was manifested by a reduced functionally stimulated pinealocyte activity and a protracted increase in glia cell activity. It is suggested that the physiological relevance of the crystallization of Ca2+ into hydroxyapatite is to maintain a noradrenalin-stimulated Ca2+ influx at an optimal level during attentuated pinealocyte turnover. The interstitial concretions may lower the extracellular Ca2+ concentrations and thereby stimulate pinealocytes and restrict an increased Ca2+ influx.