ABSTRACT
MASAHIRO NEMOTOl, TORU ENDO2, MASARU MINAMI2 andHIDEYASAITO1* 1 Department of Basic Sciences, Japanese Red Cross Hokkaido College of Nursing, 664-1 Akebono, Kitami, Hokkaido 090-0011, Japan
2 Department of Pharmacology, Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido 061-0293, Japan
Abstract-The abdominal vagus is the major nerve involved in the detection of emetic stimuli. Although afferent vagus nerves are considered to have polymodal properties, depolarization of the vagus nerve is mainly mediated by 5-HT in emesis. We studied direct drug effects on rat abdominal vagus nerve using the grease-gap technique. In this study, we also investigated reactions to various emetic stimuli such as dopamine (DA), prostaglandins (PGs) and digitalis. The abdominal vagus nerves rapidly depolarize with potassium chloride application, rapidly declining towards basal levels by the end of the application. Concentration-related depolarization evoked by DA (1 x 10~8 M to 1 x 10 - 4 M) showed a pattern, in contrast to potassium, where depolarization occurred approximately 30 s later. PGEi and PGE2 showed a maximum response to concentration of 1 x 10 - 5 M and 1 x 10 - 4 M, respectively. The concentration-related curves of PGEj are similar in PGE2, in that 1 nM elicited depolarization. Ouabain (1 x 10~9 M to 1 x 10~4 M) induced concentration-dependent depolarization responses on the isolated abdominal vagus nerve. The application of 100 /ZM ouabain induced prolonged depolarization. We confirmed that the peripheral role of the vagus nerve may be involved in the appearance of emesis caused by DA, PGs and digitalis. The grease gap technique of the isolated abdominal vagus nerve is a useful technique for screening the emetic agents.
