Some behavioral effects of microinjections of noradrenaline and serotonin into the amygdaloid body of the rat brain

The effects of microinjections of noradrenaline (NA) and serotonin (5HT) into the basomedial part of the amygdaloid body (BM AB) on various forms of behavior were studied in rats. NA as well as 5HT administered to the BM AB had dose-related and general inhibitory influence on the rats' behavior in the open field test. The reactivity of rats to pain (tail compression) was attenuated by 5HT injections. The effect of NA in this test was less clear, though some inhibitory tendency was also present. Pretrial injections of NA (40 micrograms) and 5HT (40 micrograms) significantly impaired the retention of a passive avoidance reaction. NA injections also produced some disinhibitory effects on shock-suppressed drinking in the conflict test. The effects of intra-amygdalar administration of NA and 5HT on open field behavior were potentiated by pretreatment of rats with nialamide, a monoaminooxidase inhibitor. The results are discussed in terms of an involvement of the amydalar NA and 5HT in the regulation of animal behavior.