Chem. Senses 25: 739-746,
2000
© Oxford University Press 2000
Diazepam-binding Inhibitor-like Activity in Rat Cerebrospinal Fluid after Stimulation by an Aversive Quinine Taste
Laboratory of Nutrition Chemistry, Division of Applied Life Science, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, 1 Laboratory of Behavioral Physiology, Graduate School of Human Sciences, Osaka University, Osaka 565-0871 and 2 Laboratory of Physics, Kyoto Prefectural University of Medicine, Kyoto 603-8334, Japan
Correspondence to be sent to: Kazumitsu Hanai, Biosensing Laboratory, Department of Physics, Kyoto Prefectural University of Medicine, Nishitakatsukasa-cho 13, Taishogun, Kita-ku, Kyoto 603-8334, Japan. e-mail hanai{at}koto.kpu-m.ac.jp
Cerebrospinal fluid (CSF) taken from rats after stimulation by an aversive quinine taste (hereafter called quinine CSF) administered into the fourth ventricle of mice suppressed their intake of 5% sucrose solution. We examined the effects of CSF on glutathione-induced tentacle ball formation (TBF) of hydra to determine the change in CSF components associated with aversive taste stimuli. The suppressive activity of quinine CSF on TBF in the presence of 3 µM S-methyl-glutathione (GSM) was markedly lower than that of CSF obtained from control rats (control CSF). Pronase-treated quinine CSF had suppressive activity similar to that of control CSF. The active principle passed through an ultrafiltration membrane, with a molecular weight cut-off of 30 kDa, but not through one with a cut-off of 3 kDa. A peptide fragment of diazepam-binding inhibitor (DBI) nullified the suppression of TBF at 3 µM GSM by control CSF. The nullifying activity of quinine CSF was not observed after treatment with a benzodiazepine receptor preparation that was able to bind DBI. When flumazenil, a benzodiazepine receptor antagonist, was given to mice, the suppression of the intake of 5% sucrose solution by quinine CSF was partially reversed. It is suggested that quinine CSF contains a DBI-like substance.