Analysis of monoaminergic mechanisms of the dorsal hippocampus producing the conditioned avoidance reaction in rats

The local microinjection of dopamine (DA), noradrenalin (NA), and serotonin (5-HT) into the dorsal hippocampus of rats in doses of 5 μg did not affect muscle tone or spontaneous motor activity but lengthened the latent period of the conditioned avoidance reflex. The inhibition of the reflex by DA took place through receptors of neurons sensitive to haloperiodol only. The effect of NA was abolished by α-adrenolytics. Perphenazine did not change the inhibitory effect of all the bioamines on the conditioned defensive reflex, but if given before NA the latter significantly stimulated the motor activity of the rats. After melipramine, DA inhibited the avoidance reaction more strongly and stimulated the spontaneous motor activity, whereas microinjection of NA under the same conditions was followed by inhibition of the animals' motor activity.