Behavioral effects of intra-amygdala injections of GABA and 5-HT acting drugs in the elevated plus-maze.

The effect of drugs bilaterally injected into the basolateral/medial nuclei of the amygdala on the behavior of male Wistar rats (300-330 g) in the elevated plus-maze was measured. The benzodiazepine agonist midazolam (MDZ, 20 and 40 nmol, 0.2 microliters; N = 8-14) significantly increased open-arm exploration (% open-arm entries: control = 20.27 +/- 3.71; 40 nmol MDZ = 42.63 +/- 7.16), having thus an anxiolytic effect. On the contrary, the non-selective 5-HT2 antagonist ketanserin (KET, 1 and 10 nmol, 0.2 microliters; N = 8-11) had an anxiogenic effect (% open-arm entries: control = 35.61 +/- 6.41; 10 nmol KET = 18.65 +/- 3.89). The 5-HT1A full agonist 8-OH-DPAT (2, 4, and 8 nmol, 0.2 microliters; N = 9-12) did not significantly change rat behavior in the plus-maze. While the present anxiolytic effect of midazolam agrees with results reported by others using punished behavior, the effect of the serotonergic drugs does not. Therefore, the effect of 5-HT acting drugs injected into the amygdala may be determined by the type of experimental model of anxiety used.