1 The aim of the present study was to test the effects of DAU 6215 (endo-N-(8-methyl-8-azabicyclo-[3.2.1]-octo-3-yl)-2,3-dihydro-2-oxo-lH-benzimidazole-1-carboxamide hydrochloride), a newly synthesized, selective aminophosphonovaleric acid (APV; 501M) and 6,7-dinitroquinoxaline-2,3-dione (DNQX; 25 tiM), and were elicited by the selective 5-HT3 agonist, 2-methyl-5-HT (2-Me-5-HT, 50 pM).5 The increase in frequency of s.p.s.ps induced by 5-HT was significantly antagonized by DAU 6215 in 70% of the cases, whereas the 5-HT3 antagonist always suppressed the effect of 2-Me-5-HT, at concentrations as low as 60 nM. 6 The antagonistic effect of DAU 6215 was also tested on the 5-HT3-mediated block of induction of long-term potentiation (LTP), elicited by a primed burst (PB) stimulation. Extracellular recordings showed that low concentrations (60 nM) of DAU 6215 suppressed the inhibitory action of 5-HT on PB-induced LTP, without affecting the 5-HTlA-induced reduction in the amplitude of the population spike. 7 These results provide evidence that DAU 6215 is an effective antagonist of the 5-HT3-mediated responses in the central nervous system and may offer a cellular correlate for the pharmacological effects of DAU 6215 as an anxiolytic and cognition enhancer.