[Effects of intra-amygdala injection of GABA(A)-receptor agonist and antagonist on respiratory and cardiac components of conditioned fear in rabbits].

ABSTRACT

The role of GABAergic system of amygdala in vegetative and behavioral manifestations of conditioned fear was studied in groups of active and passive rabbits, selected upon testing in open field and light-dark chamber. During training, the light (4 s) was paired with electrodermal stimulation of hind limbs(1 s, 10 Hz). Conditioned fear was judged by heartbeats and respiratory rates before and in the process of conditioned and unconditioned stimuli presentation. Solutions of GABA(A)-receptor agonist (muscimol, 0.1 µg/µL) or antagonist (bicuculline methbromide, 0.5 µg/µL) were applied to the right or left basal nucleus of amygdala after conditioning. Muscimol injection evoked more powerful vegetative changes in passive rabbits than in the active ones; respiratory deceleration during freezing in response to conditioned stimuli was eliminated and the reaction to electrodermal stimulation was reduced or altered. Activation of the left amygdala by bicuculline resulted in the increased probability of active locomotor reactions in active rabbits, activation of the right amygdale, on the contrary, increased probability of freezing. The results evidence the non-equivalence of amygdalar GABAergic system in active and passive animals.