Effects of Administration of Serotonin 5-HT 1A Receptor Ligands into the Amygdala on the Behavior of Rats with Different Manifestations of Conditioned Reflex Fear

The neurotransmitter mechanisms underlying the individual/group characteristics of behavior in animals were studied by comparing the effects of modulation of serotoninergic transmission in the amygdala in rats with different manifestations of conditioned reflex fear (high- and low-freezing rats). Administration of a 5-HT_1A receptor agonist (8-OH-DPAT, 0.3 μg/0.5 μl) into the basolateral amygdala before testing of a previously acquired classical defensive reflex decreased freezing time in response to sound in low-freezing animals and weakened the signs of conditioned reflex fear in response to the signal. Administration of the receptor antagonist (WAY-100635, 0.2 μg/0.5 μl) decreased freezing time during exploration of context and in response to sound in all rats, which probably occurred as a result of increases in motor activity and the occurrence of a panic-like state. Administration of both the agonist and antagonist before extinction sessions accelerated extinction of the reflex in high-freezing rats, though the mechanisms of the effects of different ligands were different. Administration of receptor antagonist before retraining prevented acquisition of conditioned reflex freezing in all rats. 5-HT_1A receptors in the amygdala play a major role not only in the manifestations and repeat acquisition, but also the extinction of conditioned reflex fear. High-freezing rats, as compared with low-freezing animals, were more sensitive to administration of 5-HT₁ receptor ligands into the amygdala in relation to extinction and repeat acquisition.

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