EFFECT OF ISOLATION STRESS ON BRAIN MAST-CELLS AND BRAIN HISTAMINE LEVELS IN RATS

The effects of the chronic social stress of isolation on changes in br ain mast cells (MC), the hypothalamic histamine content and the activi ty of the hypothalamic-pituitary adrenal (HPA) axis were investigated in rats. Social stress of isolation markedly reduced the total number of brain mast cells, most significantly by 90% in the first day. The e xtent of MC degranulation, 36-67%, in stressed rats did not significan tly differ from that in control animals, 45-58%. Isolation stress subs tantially, though not significantly, increased the hypothalamic histam ine content. The serum corticosterone levels in isolated rats did not significantly differ from the control levels. These results indicate t hat social stress of isolation considerably diminishes the number of b rain MC and suggest that histamine which might be liberated from these cells does not significantly influence the HPA activity.