LATENT INHIBITION IN CONDITIONED EMOTIONAL RESPONSE - C-FOS IMMUNOLABELING EVIDENCE FOR BRAIN-AREAS INVOLVED IN THE RAT

Latent inhibition refers to the fact that the formation of a condition ed association between a conditioned and an unconditioned stimulus is delayed by prior exposure to the conditioned stimulus. Latent inhibiti on is often investigated in the context of the conditioned emotional r esponse, in which a tone serves as the conditioned and a footshock as the unconditioned stimulus. Such a paradigm was used for the present e xperiments in which some rats had been pre-exposed to the tone. Two ho urs after a subsequent exposure to the tone, c-fos immunocytochemistry was used to map activated brain areas. The density of immunoreactive neurones was measured in brain areas involved in audition, fear, stres s and memory. For the basic conditioning group, pre-exposure to the to ne decreased the density of labelled cells in the auditory system, are as involved in fear and stress and a number of Limbic areas, namely th e amygdala, the Ammon's horn of the hippocampus and the entorhinal cor tex. In contrast, the density increased in three limbic areas: the den tate gyrus, the subiculum and the nucleus accumbens. Taken together, t hese data suggest that latent inhibition corresponds to alterations of sensory processing which renders difficult to state about the alterat ion of the transfers of the sensory information to structures involved in the control of emotional responses. As some brain areas show a spe cific increase of activity in cases of latent inhibition, further stud ies will investigate how the latter brain areas contribute to the othe r cell density alterations reported in this study and to the latent in hibition phenomenon itself.