Abstract

Kainic acid (KA) was used to investigate the effects of lesion of the hippocampal CA3 cell field on blocking and latent inhibition in Experiment 1 and 3. In experiment 2, 6-0HDA was used to study the effects of norepinephrine (NE) depletion of hippocampal cell field on blocking. Subjects were 80 albino rats_ In Experiment 1 and 2, blocking paradigm was used. Subjects were allocated into hippocampal or Sham-operated group,. each of which was again divided into experimental or control group. Subjects in experimental group of both sham-operated and hippocampal rats were classically conditioned to a tone in stage 1. Subjects in control group were yoked to the animals in the experimental group and were simply put in the test chamber. In stage 2, compound CS (tone + light) was presented to all subjects and blocking was measured by the suppression ratio of licking during light presentation. In Experiment 3, latent inhibition paradigm was used. Subjects in this experiment were allocated into hippocampal or sham-operated group, each of which was again divided into pre-exposure or control group. In pre-exposure stage, subjects in pre-exposure group received 30 tone-alone presentations without being followed by shock. Subjects in the control group were simply put in the test chamber. In acquisition stage. tone was paired with shock for all subjects. In test stage, lone was presented and latent inhibition was measured. Results of Experiment 1 showed that the lesion of hippocampal CA3 field with KA severely attenuated blocking. Experiment 2 indicated that NE depletion of the hippocampal CA3 field with 6-0HDA attenuated blocking as well. And results of Experiment 3 showed that the lesion of hoppocampal CA3 fieid with KA did not affect latent inhibition. These results suggest that hippocampal CA3 field is involved in blocking, that NE is important neurotransmitter substance in this area Hppocampal CA3 field was not found to be involved in latent inhibition.