ABSTRACT-Effect of mosapride, a benzamide, on the motor activity associated with the release of endogenous acetylcholine (ACh) from enteric neurons was examined in the ileum of anesthetized dogs using an in vivo microdialysis method and compared with the effect of 5-hydroxytryptamine (5-HT). Intraarterial administration of 5-HT accelerated intestinal motor activity and increased the concentration of dialysate ACh, and the responses were inhibited by SB204070, a specific 5-HT 4 -receptor antagonist, but were apparently not affected by methiothepin, ketanserin and granisetron. Intraarterial administration of mosapride, a prokinetic benzamide, accelerated intestinal motor activity and the concentration of dialysate ACh increased. The effects of mosapride were antagonized by SB204070. Specific

Abstract. Characterization of the g-aminobutyric acid (GABA) B receptor involved in the motility of dog small intestine was analyzed by application of the microdialysis method to the small intestine of the whole body of the dog. The reverse transcription-polymerase chain reaction (RT-PCR) was used. Intraarterial administration of muscimol induced acceleration of motility associated with acetylcholine (ACh) release, these responses being antagonized by bicuculline. Intraarterial administration of baclofen induced inhibition of motility associated with ACh release, these responses being antagonized by CGP62349. GABA induced inhibition of motility associated with decrease in ACh release. CGP62349 alone induced acceleration of motility associated with increase in ACh release. RT-PCR revealed the presence of mRNAs for both subunits of GABA B receptor, GABA B1 and GABA B2 , in the dog small intestine, although GABA B1 subunits were 6 isoforms of GABA B1 (GABA B1(a) -GABA B1(g) ), except GABA B1(d) . Thus, the GABA B receptor located at cholinergic neurons as a heterodimer with subunits of GABA B1 and GABA B2 in the dog small intestine operates predominantly relative to the GABA A receptor in physiological motility.

Abstract. Characterization of the GABA B receptor in the human colon was performed by the reverse transcription-polymerase chain reaction (RT-PCR). mRNAs for both subunits of the GABA B receptor, GABA B1 and GABA B2 , were detected in the human colon. The GABA B1(e) isoform was detected in the human colon, but not in the brain, and the other isoforms, except GABA B1(d) , were detected in both tissues. Thus, the GABA B receptor may be present as a heterodimer with subunits of GABA B1 and GABA B2 in the human colon.

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