Abstract
We chose the conditioned taste aversion (CTA) paradigm, a model of emotional learning, in order to examine the effect of modification of gravitational force on acquisition and retention of emotional learning and memory. We used centrifugal machine for rodents to add the gravitational force and 3D clinostat to cancel the gravitational force. The centrifugation of 1G or low gravitational environment was applied between 0.1% sodium saccharin as a conditioned stimulus (CS) and an i.p. injection of 0.15 M LiCl as an unconditioned stimulus (US). Under the 1G condition, both acquisition and retention was suppressed. When 1G condition was employed instead of LiCl as US, the CTA was established, indicating that the malaise induced by 1G cancelled that by LiCl. Although low gravitational condition did not serve as US, it suppressed both acquisition and retention. Furthermore, after CTA acquisition with low gravitation, expression of an immediately early gene, c-Fos was greatly suppressed in the external lateral subnucleus of parabrachial nucleus and in several midline-intralaminar thalamic nuclei, which strongly appeared under control condition. These results suggest that low gravitational force prevents CTA memory formation through suppression of association process between CS and US in medial thalamic pathway to limbic system as well as gustatory pathways of brain stem. [Jpn J Physiol 54 Suppl:S205 (2004)]
