It has been recognized that the stress-related peptides are involved in anxiety states.
Angiotensin II receptor blockade by systemic administration of the AT(1) receptor
antagonists has been proposed as a new treatment possibility for anxiety disorders.
For better understanding of the related mechanisms, in this study we evaluated effects
of bilateral intraamygdaloid injections of 2 (LOS 2) and 4 (LOS 4) μg of losartan
(LOS), a selective AT(1) receptor antagonist, on the behavior of the not stressed
and acutely stressed rats in an elevated "plus" maze. Under non-stress conditions,
LOS 4 increased time spent in the open arms (p < 0.01), number of extreme open arm
arrivals (p < 0.05), time per entry (p < 0.01), and the number of total arm entries
(p < 0.05) showing thus considerable anxiolytic activity. The open arm extreme arrivals
were increased by LOS 4 in both not stressed (p < 0.05) and stressed (p < 0.05) rats.
When no stressed and stressed LOS 4 animals were compared, time per entry and the
number of closed arm entries (p < 0.05, both) were decreased in the latter group.
Moreover, the LOS 4 stressed rats had significantly increased open/closed arm quotient
(p < 0.05) as compared to the both control and LOS 4 non-stress group (p < 0.05, both).
These findings suggest that the AT(1) receptor blockade in amygdala is important for
the anxiolytic action of LOS (and probably other AT(1) receptor blockers) under both
non-stress and stress conditions.