Involvement of cerebral cortical structures in the classical conditioning of eyelid responses in rabbits

The classical conditioning of the eyelid motor system in alert behaving rab bits has been used to study the expression of Fos in the hippocampus, and i n the occipital, parietal, piriform and temporal cortices, Animals were cla ssically conditioned with both delay and trace conditioning paradigms. As c onditioned stimulus, both short and long (20 and 100 ms) tones (600 Hz, 90 dB) or short. weak (20 ms, 1 kg/cm(2)) air puffs were used. The uncondition ed stimulus was always a long, strong (100 ms, 3 kg/cm(2)) air puff that st arted 250-270 ms after the onset of the conditioned stimulus. The expressio n of Fos was significantly increased after both delayed and trace condition ing in the hippocampus, and in the parietal and piriform cortices contralat eral to the unconditioned stimulus presentation side, compared with equival ent ipsilateral structures in conditioned animals, or with Fos production i n the same contralateral structures in pseudo-conditioned and control anima ls. Fos expression in some cortical sites was specific to tone versus air p uff stimuli when used as conditioned stimulus. Thus, Fos expression was sig nificantly increased in the contralateral temporal lobe when tones were use d as conditioned stimulus, for both delayed and trace conditioning paradigm s, but not when animals were conditioned to short, weak air puffs. The present results indicate a specific Fos activation in several cerebral cortical structures during associative eyelid conditioning. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.