Abstract
We have already reported that both acquisition and retention of the conditioned taste aversion memory (CTAM) were markedly suppressed in C57BL/6 male mice when the gravity disturbance 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) using 3D clinostat to cancel the gravitational force. However, gravitational disturbance applied before CS never affected the acquisition and retention of CTAM. Muscarinic acetylcholine receptor (mAChR) have been reported to contribute to discrimination process of novel tastants from familiar ones. Therefore, we employed knockout mice for two subtypes (M1 and M3) of mAChR to examine contribution of mAChR to gravitational modulation of acquision mechanism of conditioned taste aversion memory. Both acquisition and retention of CTAM were suppressed in M1 knockout mice (M1KO) with the gravitational disturbance, whereas in double knockout mice of M1 and M3 (M1/M3KO), the CTAM was not affected. These results suggest that the gravitational disturbance prevents CTAM formation through suppression of association process between CS and US, and M3 receptors play more important role for mice to accept gravitational disturbance rather than discrimination among taste qualities. [J Physiol Sci. 2008;58 Suppl:S92]
