Electrophysiological characteristics of depressive states in rats with passive strategies of adaptive behavior.

The behavior of rats in a T-maze was used to select individuals with a passive strategy of adaptive behavior from a population of Wistar rats. These animals were subjected to water immersion and olfactory cortex slices were prepared from the brain 10 days later and used for recording of evoked focal potentials and the effects of tetanic stimulation. Postsynaptic potentials, of both the AMPA and NMDA types, were initially of decreased amplitude in passive rats. After unavoidable stress, the suppression of excitatory potentials increased and there was a simultaneous increase in the amplitude of inhibitory GABAB-ergic mechanisms. Addition of corticoliberin (10(-10) M) to the incubation medium led to reversible blockade of synaptic transmission. Tetanic stimulation of slices from stressed rats led to the development of posttetanic depression in 84% of cases and to post-tetanic potentiation in 12%; this is evidence for profound changes in synaptic transmission. Thus, activation of corticoliberinergic mechanisms in cortical structures does not promote recovery from depressive states in rats with the passive behavioral strategy induced by unavoidable stress.