Single and repeated air blast stress and brain histamine.

Exposure of rats to air blasts for 1, 5 and 15 min resulted in a significant increase in plasma corticosterone level and in the hypothalamic histamine concentration. Midbrain histamine content was increased after 1 and 5 min of exposure but cortical histamine increased following 1 min of exposure only. Stress of longer duration (30 mins did not significantly affect histamine concentration in any of the three brain regions investigated, although plasma corticosterone level remained very significantly (14.5-fold) elevated. Repeated exposure of rats to air blasts of 15 min duration resulted in a significant elevation of hypothalamic histamine concentration while midbrain and cortical histamine was not significantly altered. Plasma corticosterone level was again very significantly (10-fold) increased. Present results suggest the involvement of brain histamine in the response to stress.