Diazepam-binding inhibitor-like activity in rat cerebrospinal fluid after stimulation by an aversive quinine taste

Cerebrospinal fluid (CSF) taken from rats after stimulation by an aversive quinine taste (hereafter called quinine CSF) administered into the fourth v entricle of mice suppressed their intake of 5% sucrose solution. We examine d the effects of CSF on glutathione-induced tentacle ball formation (TBF) o f hydra to determine the change in CSF components associated with aversive taste stimuli. The suppressive activity of quinine CSF on TBF in the presen ce of 3 muM S-methyl-glutathione (GSM) was markedly lower than that of CSF obtained from control rats (control CSF). Pronase-treated quinine CSF had s uppressive activity similar to that of control CSF: The active principle pa ssed through an ultrafiltration membrane, with a molecular weight cut-off o f 30 kDa, but not through one with a cut-off of 3 kDa. A peptide fragment o f diazepam-binding inhibitor (DBI) nullified the suppression of TBF at 3 mu M GSM by control CSF. The nullifying activity of quinine CSF was not observ ed after treatment with a benzodiazepine receptor preparation that was able to bind DBI. When flumazenil, a benzodiazepine receptor antagonist, was gi ven to mice, the suppression of the intake of 5% sucrose solution by quinin e CSF was partially reversed. It is suggested that quinine CSF contains a D BI-like substance.