Effect of endorphin exposure at weaning on the endorphin and serotonin content of white blood cells and mast cells in adult rat

Hormonal imprinting takes place perinatally at the first encounter between the developing receptor and its target hormone, resulting in the accomplishment of normal receptor development. In the presence of an excess of target hormone or the absence of it, or an excess of related molecules which can be bound by the receptor, faulty imprinting develops with life-long consequences. In previous experiments neonatal endorphin exposure caused a decrease in endorphin and serotonin content of peritoneal mast cells of adult animals. In the present experiment 25-day-old (weaned) female rats received 2 mug endorphin, and the endorphin as well as serotonin content of adult mast cells and white blood cells was studied by flow cytometry and confocal microscopy. Peritoneal lymphocytes and blood monocytes contained significantly (p < 0.01) less endorphin and peritoneal mast cells less serotonin (p < 0.07, i.e. of questionable significance) than the untreated control. The results bring attention to the possibility of durable imprinting of differentiating cells later in life and to the durable (possibly life-long) effect of an endorphin excess (perhaps caused by injury) manifested in the change of endorphin and serotonin content of immune cells. Copyright (C) 2004 John Wiley Sons, Ltd.