Neuroscience Lel/ers, 81 (1987) 209-214 Elsevier Scientific Publishers Ireland Ltd. NSL04874 209 Complex synaptic responses of entorhinal cortical cells in the rat to subicular stimulation in vitro: demonstration of an NMDA receptor-mediated component Roland S.G. Jones Departl1lelll oj Pharmacology. John Curtin School oj Medical Research. Australian National Unhersity. Canberra. A.C.T. (Australia) (Received 4 June 1987; Revised version received and accepted 22 June 1987) Key words: Medial entorhinal cortex; Subiculum; Synaptic response; N-Methyl-D-aspartate receptor; Rat Intracellular recordings from neurones in the medial entorhinal cortex of the rat in vitro showed that the lowest threshold response to stimulation in the subiculum was a long latency, prolonged depolariza- tion, which in extracellular records corresponded to a late, negative DC shift. These responses were reduced or abolished by 2-aminophosphonovalerate suggesting mediation via activation of amino acid receptors of the' N-methyl-D-aspartate' -type. Anatomical studies in the rat and guinea pig show a pronounced fibre projection from the subiculum to the deep layers of the entorhinal cortex [5, 10], and electrophys- iological studies in vivo have demonstrated excitation of entorhinal cells following subicular stimulation [3, 14]. Recent work has suggested that this subicular-entorhinal pathway may be maintained intact in a slice preparation from the rat brain. Paroxys- mal DC shifts, which resemble ictal epileptic activity, can be recorded extracellularly in slices of rat entorhinal cortex following depletion of extracellular magnesium ([Mg2+]o) [11, 15]. These events invariably occur spontaneously, but practically iden- tical events can be evoked by stimulation in the subiculum when the latter area re- mains as an integral part of the slice. Both spontaneous and evoked events occurring in Mg2+ -free medium can be blocked by 2-aminophosphonovalerate (2-AP5) [11, 15] indicating that amino acid receptors of the N-methyl-D-aspartate (NMDA) type may be involved in the gener- ation of this activity. While these epileptic-like events can be recorded readily in all Correspondence: R.S.G. Jones, Department of Pharmacology, John Curtis School of Medical Research, Australian National University, Canberra, A.C.T. 2601, Australia. 0304-3940/87/S 03.50 © 1987 Elsevier Scientific Publishers Ireland Ltd.