We examined the effects of restraint stress on α 1 adrenoceptor mRNA expression in the rat brain using reverse transcriptase-polymerase chain reaction (RT-PCR). After rats had been restrained for 10, 30, 60, 120 or 240 min, the hypothalamus and midbrain were removed immediately and α 1 adrenoceptor mRNA levels in these regions were determined by RT-PCR. Blood samples were also collected for simultaneous measurement of serum adrenocorticotropic hormone (ACTH) and corticosterone. Restraint stress resulted in a variety of changes in the hypothalamus and midbrain. In the hypothalamus, 30 and 60 min of stress resulted in a significant fall in the level of α 1 adrenoceptor mRNA relative to the control. This was associated with a rise in serum ACTH and corticosterone. In the midbrain, significant elevation of α 1 adrenoceptor mRNA was noted after 60, 120 and 240 min of restraint stress. Our findings indicated that the influence of restraint stress on α 1 adrenoceptor mRNA level in the hypothalamus is different to that of the midbrain region in rats.