Behavioral tolerance to one effect of the serotonergic agonist TFMPP

1. In mice isolated for one week and observed in pairs with non-isolated mice under a reversed beaker, the serotonergic agonist: 1-3-(trifluoromethyl)phenylpiperazine (TFMPP) increased the number of escape attempts. 2. A partial tolerance to this effect has been observed in mice which were tested a first time after administration of TFMPP one week sooner. 3. An analysis of this form of tolerance was carried out by changing successively and separately each of the events concomitant of this tolerance. 4. The results show that this tolerance is not a pharmacocinetic or a pharmacodynamic one. Observation of the tolerance required the performance of the first test in a drug state. The more likely explanation is that this tolerance results from a conditioned opponent response.