Influence of nitric oxide agents in the rat amygdala on anxiogenic-like effect induced by histamine

Both histamine and nitric oxide (NO) may play a role in anxiety-like behavior. Within the brain, the amygdala is an important area involved in processing emotional responses such as anxiety. The aim of the present study was to assess whether the NO system in the basolateral amygdala (BLA) influences histamine-induced anxiety-like behavior in rats.

Male Wistar rats weighing 200-220g were used. Bilateral cannulae were implanted in the BLA place for microinjections of drugs and the elevated plus maze apparatus has been used to test parameters (%OAT, %OAE, locomotor activity) of anxiety-like behavior.

Intra-BLA administration of histamine (2.5 and 5μg/rat) decreased %OAT [P<0.001]. Histamine (5μg/rat) also reduced %OAE [P<0.05] but not locomotor activity. The results obtained may indicate an anxiolytic response for histamine. Furthermore, bilateral intra-BLA microinjections of different doses of l-arginine (l-arg), an NO precursor (0.5 and 1μg/rat) increased %OAT [P<0.01], %OAE [P<0.01] and locomotor activity [P<0.001] while NG-nitro-l-arg methylester (l-NAME), a potent inhibitor of NO-synthase (NOS; 0.025, 0.05 and 0.1μg/rat) decreased %OAT [P<0.05] and locomotor activity [P<0.001] but not %OAE. The combination of l-arg (0.5μg/rat) with histamine increased %OAE [P<0.001] but had no effect on %OAT and locomotor activity. Finally, the combination of l-NAME (0.025μg/rat) with histamine decreased %OAT [P<0.001] and locomotor activity [P<0.05] but increased %OAE.

The results indicate a modulatory role for NO in BLA in the anxiogenic response of histamine in rats.